AN ABSTRACT OF THE THESIS OF
Timothy John O'Brien for the degree of Master of Science in Horticulture presented on
September 12, 1997. Title: Integration of Conservation Tillage and Cover Crops in
Broccoli Production Systems of the Pacific Northwest.
Abstract approved:
^.,
I
_
John M. Luna
Field and greenhouse experiments were conducted in 1996 and 1997 to evaluate
the effects of integrating conservation tillage and cover cropping on broccoli production
as well as agroecological parameters.
A field experiment was conducted during 1996-97 at the Oregon State University
Horticulture Research farm near Corvallis, OR. The specific objectives of the research
project were: To evaluate the effects of the integration and management of cover crops
and strip-tillage on: 1) broccoli yield, 2) weed populations, and 3) relative abundance of
earthworms. The experimental design was a split-split-plot in randomized complete
blocks with 3 replications. Two tillage types (strip and conventional) constituted the main
effects; two cover crops comprised the sub-effects. Time of cover crop suppression (early
or late glyphosate) constituted the second sub-effect within the cover crop treatments.
Strip-till plots had significantly lower total weed density than conventional till plots.
'Dacold' rye and vetch plots in combination with early glyphosate and strip-tillage had
the highest broccoli yield.
An on-farm research experiment was conducted during the summer of 1996 at
Crestview Farms, Inc. near Molalla, OR. to compare strip-till and conventional tillage on
broccoli yield. After the fall sown (1995) cover crop mixture 'Steptoe' barley / common
vetch was chemically suppressed in the spring, two tillage regimes consisting of: striptillage and disc/harrow tillage were evaluated for their impact on broccoli yield, relative
earthworm abundance, and relative Carabidae and Staphylinidae beetle abundance. The
experimental design was a randomized complete block with three replications. No
significant differences were detected for broccoli yields between the two tillage regimes,
nor were statistical differences detected for Carabidae beetle relative abundance under
the different tillage regimes. The carabid sampling period was only two weeks thus not
allowing for justifiable conclusions to be drawn. Significantly higher densities of
earthworms were detected in the strip-till plots on the first sample date but no earthworms
were found on the second sampling date.
A field experiment was conducted during 1996-97 in a cherry (Prunus avium)
orchard at the Botany and Plant Pathology Research Farm near Corvallis, OR. The
objective of this research was: 1) To evaluate the effectiveness of formalin, xylene, and
ground cooking mustard in estimating relative abundance of the earthworm, Lumbricus
terrestris, and 2) To evaluate the effectiveness of the three expulsion materials at three
different times of the year. The mustard treatment extracted statistically similar numbers
of L. terrestris as the formalin treatment in the fall and winter experiments but fewer
worms in the spring experiment. The xylene treatment extracted significanlty fewer L.
terrestris than formalin and mustard in all three sample dates.
Three greenhouse studies were conducted in 1996 and 1997 to evaluate the effects
of two agricultural by-products (meadowfoam meal and hydrolyzed com gluten) and a
cover crop 'Monida' oat (Avena sativa) on the biomass accumulation of broccoli
{Brassica oleraceae var. italica (direct seeded and transplanted), sweet com {Zea mais),
barnyardgrass {Echinichloa crus-gali), and pigweed {Amaranthus retrqflexus). The
addition of meadowfoam meal to sterile greenhouse potting mix significantly reduced
broccoli biomass (direct seed by 34% and transplanted by 50%) when compared to
controls. Hydrolyzed com gluten significantly reduced sweet com biomass by 46% when
compared to controls..'Monica' oat reduced the biomass of both weeds as well as broccoli
(direct seeded). Results suggest that hydrolyzed com gluten and meadowfoam meal
inhibit the biomass accumulation of barnyardgrass and pigweed.
Cop^ight by Timothy J. O'Brien
September 12, 1997
All rights reserved
Integration of Conservation Tillage and Cover Crops in Broccoli Production Systems of
the Pacific Northwest
by
Timothy John O'Brien
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
Completed September 12, 1997
Commencement June 1998
Master of Science thesis of Timothy John O'Brien presented on September 12. 1997
APPROVED:
Maio/PmfessorS/enresentine Horticulture
Head of Department cxijHorticulture
\
Dean of Gradoate School
I understand that my thesis will become part of the permanent collection of Oregon State
University libraries. My signature below authorizes release of my thesis to any reader
upon request.
y
1oth^%MO'Brien, Author
ACKNOWLEDGMENTS
First and foremost, I would like to thank my parents, John and Chris O'Brien for
sacrificing all that they have so that I may have the chance to pursue my dreams. Thanks
to my sister, Kelly and brother-in-law, Mike who helped to keep my Mom at ease in New
Jersey while her baby boy was out on yet another adventurous trip on the rivers and in the
mountains of the Pacific Northwest. Thanks to my uncle, Kevin O'Brien, for teaching me
to "seize the day" and for our alpine adventures together. My whole family is a source of
infinite support and laughter.
Sincere appreciation is extended to my major professor. Dr. John Luna, for not
only technically advising me and financially supporting me through a successful master's
degree program but for being a friend and father figure while I was studying in Oregon. I
would like to thank his family, Sue, Michael and Jesse for making me feel at home when
I first moved to Oregon. Brandon Reich, Joey Ratliff, Segundo Nova all deserve thanks
for their friendship when I first showed up at OSU.
I would also like to extend thanks to my graduate committee members: Drs. Carol
Mallory-Smith and Delbert Hemphill for their expert advice and support throughout my
program of study. Dan McGrath and Ed Peachey deserve special thanks for their
willingness to spontaneously consult with me on the problems I faced in the field.
Gratitude is extended to Randy Hopson, Gary Horton, Scott Robbins, and Matt Compton
who provided their expertise in conducting fieldwork in my field experiments.
I could not have accomplished everything I did in the short time I studied at
Oregon State University if it wasn't for the help of our Agroecology Research Team:
Mary Staben, Micaela Colley, and Kate Christensen. I would like to thank the following
people for their friendship throughout my time at OSU: Roberto Valverde, Patrik
Schonenberger and Stefan Seiter. Jeb Hopper deserves special thanks for making my last
year at OSU the funniest and most enjoyable I could imagine.
Finally, I wish to express my deepest gratitude to Liz Harrison for being the best
friend anyone could ask for. She always knows just what to say and would listen for
hours if that's what it took. Her husband Dean was most patient with us as we tended to
talk "shop" quite a bit. I thank him for that. Most of all, I need to thank Caroline Nichols
for her love and companionship for the past years. She unconditionally supported me
with all of my endeavors and taught me to enjoy life in its simplest ways.
Table of Contents
Page
Chapter 1. AReview of the Literature
1
Introduction
1
Conservation Tillage
2
Cover Crops
3
Integration of Conservation Tillage and Cover Crops
3
Effects of Integrating Conservation Tillage and Cover Crops on
Agroecosystems
4
Integrated Vegetable Production Systems
13
References
15
Chapter 2. Integration of Cover Crops and Strip-tillage in Broccoli, Brassica oleracea
var. italica Production Systems of the Pacific Northwest
25
Abstract
25
Introduction
27
Experiment 1: OSU Vegetable Research Farm, 1996-97
29
Materials and Methods
Data Collection
Results and Discussion
Weed Density
Experiment 2: On-Farm Research at Crestview Farms 1995-96
Materials and Methods
Data Collection
Results and Discussion
29
31
33
41
53
53
54
56
Table of Contents (Continued)
Results and Discussion
69
References
72
Chapter 4. Effects of Organic Soil Amendments on Broccoli, Brassica oleracea var.
italica. Com Zea mais, and Weed Growth
73
Abstract
73
Introduction
73
Materials and Methods
75
Results and Discussion
77
References
82
Chapter 5. Conclusions
83
Bibliography
86
List of Figures
Figure
2.1
2.2
2.3
Page
Effect of tillage and cover crops on the relative abundance of the
earthworm: Lumbricus terrestris
48
Effects of strip and conventional tillage on daily soil temperature
fluctuations in a broccoli production system(May 29 to June 23, 1997)
50
Effects of strip and conventional tillage on daily soil temperature
fluctuations in a broccoli production system(June 24 to July 26, 1997)
51
List of Tables
Table
2.1
Page
Total dry matter accumulation of cover crop polycultures, April 2, 1997
(Strip-tillage plots)
34
Total dry matter accumulation of cover crop polycultures, April 18, 1997
(Conventional tillage plots)
34
Total dry matter accumulation of cover crop polycultures, May 2, 1997
(Early glyphosate)
34
2.4
Effect of tillage and cover crops on soil nitrate content within the top 15 cm
37
2.5
Effect of tillage, cover crops, and cover crop kill date on broccoli yield
40
2.6
Tillage and cover crop effects on weed density, sampled 23 June 1997
43
2.7
Effects of tillage on broccoli head diameter, dry weight biomass, and total
yield. Crestview Farm, 1996
57
Effects of tillage on arthropod and earthworm (Lumbricus terrestris)
activity and abundance: Crestview Farm, 1996
59
Estimation of relative abundance of the earthworm: L. terrestris in a 'Black'
Republican' cherry orchard using three different chemical materials
71
2.2
2.3
2.8
3.1
4.1
Mean dry weight biomass of barnyardgrass (Echinichloa cruss-gali), redroot
pigweed (Amaranthus retrqflexus), sweet com (Zea mais), or broccoli
(Brassica oleraceae var. italica) (direct seed and transplanted) grown for
four weeks in sterile potting mix amended with either meadowfoam
(Limanthes alba) meal, hydrolyzed com gluten, or finely ground oat
(var='Monida') residue
78
Integration of Conservation Tillage and Cover Crops
in Vegetable Production Systems of the Pacific Northwest
Chapter 1
A Review of the Literature
Introduction
Conservation tillage is defined by the Soil Science Society of America (1978) as
"any tillage sequence which reduces loss of soil or water relative to conventional tillage."
A more recent operational definition of conservation tillage used by the Natural Resource
Conservation Service states that conservation tillage is "any tillage system that leaves
greater than 30 percent residue remaining on the soil surface after planting" (Galloway et
al., 1981). This operational definition encompasses the breadth of conservation tillage
options available to growers by including such systems as chisel plow, strip-till, ridge-till,
stubble-mulch-till, and no-till. The use of a particular conservation tillage system depends
on site-specific soil and climatic conditions, crop growth requirements, weed
management options and individual preferences by growers.
The use of conservation tillage practices has increased due to both economic and
environmental concerns. Increases in energy costs have created a desire for practices that
conserve fuel and labor (Frye and Phillips, 1981). Since conservation tillage systems
utilize shallow tillage or direct seeding, residues remain on or near the soil surface,
conserving water and reducing erosion (Hoyt et al., 1994). Other factors leading to
increased use of conservation tillage are improved herbicide and planting technologies
(Staniforth and Wiese, 1985), and decreased need for specialized equipment (Phatak,
1992).
Conservation Tillage
Reviews of the advantages and disadvantages of conservation tillage have been
provided by Blevins et al. (1977) and Doran (1987). Specific benefits associated with
conservation tillage practices in the Midwest are increased control of soil erosion
(Coolman and Hoyt, 1993) and increased soil water and nutrient conservation (Munawar
et al., 1990). Blevins et al. (1983) reported improved soil organic matter content under
no-till. Haines and Uren (1990) and Koskinen and McWhorten (1986) report enhanced
microbial activity and higher earthworm populations under conservation tillage.
Reduction of fuel and labor costs has been a major economic factor in the adoption of
conservation tillage systems (Sprague, 1986).
Conservation tillage is not without problems. Weed control is frequently cited as
the limiting factor in adoption of conservation tillage (Koskinen and McWhorten, 1986).
Specific detrimental aspects of conservation tillage include lower soil temperatures in the
spring and potential overwintering of pests on surface residues (Hoyt and Konsler, 1988).
However, Buhler and Daniel (1988) report that no-till did not effect com (Zea mays L.)
establishment. Another obstacle for conservation tillage systems to overcome, as pointed
out by Nowak (1983), is the increased complexity of decision-making required. Nowak
reports that the number, timing, and sequence of management decisions are much more
critical than with conventional tillage. For example, chemical and nutrient incorporation
while maintaining surface residues and selection of seeds that are suited to the altered
microclimate are just two extra decisions required under conservation tillage.
Cover Crops
Cover crops are defined as crops that are grown not for immediate economic gain
through harvest but for their abilities to protect and improve soil quality rather than direct
economic gain (Lai et al., 1991). Reviews of the advantages of utilizing cover crops have
been provided by Luna, 1993; Shennan, 1992; andBugg, 1992. Specific benefits include:
increased soil fertility (Doran and Smith, 1991; Nova, 1995), decreased soil
erosion(Meisinger et. al., 1991), increased nitrogen scavenging (Jackson et al., 1993),
suppression of weeds (physically or chemically) (Barnes and Putnam, 1983), suppression
of symphylan (Scutigerella immmaculata) (Datta, 1996), suppression of
nematodes(Ingham 1993), increased habitat for beneficial insects (Clark et. al. 1993), and
decreased off-farm energy usage (Ess et al., 1994).
Utilization of cover crops can also produce deleterious effects, including: delay of
planting time associated with excess soil moisture (tuna, 1993), increased nitrogen
immobilization (Wyland et al., 1995), increased insect pest and weed incidence (Bug",
1991; Nova, 1995), and increased production costs (Allison and Ott, 1987).
Integration of Conservation Tillage and Cover Crops
Integrating the practices of conservation tillage and cover cropping can enhance
or inhibit the overall productivity of an agroecosytem (Hoyt, 1984; Wilhoit et al., 1990).
The presence of cover crop residues in minimally tilled environments can help to reduce
negative environmental impacts like erosion and runoff while maintaining economically
viable yields by improving soil physical properties (Rickerl and Smolik, 1990),
enhancing nutrient cycling (Karlen and Doran, 1991), diversifying soil biota (Doran,
1980), and decreasing pest abundance (House and Alzugaray, 1989; Smeda and Putnam,
1988). Frye and Blevins (1989) concluded that using a legume winter cover crop as a
mulch and as a partial supply of nitrogen for no-till com was agronomically and
economically feasible.
Vegetable producing river valleys of the Pacific Northwest that are prone to
erosion and groundwater contamination as a result of intensive management practices and
intensive rainfall during the winter could be potentially improved by adopting production
strategies that integrate cover crops and conservation tillage. Many Oregon vegetable
growers have expressed an increased interest in the integration of cover crops and
conservation tillage as approaches to improving profitability, reducing fertilizer,
pesticide, and fuel inputs, improving soil and environmental quality.
Effects of Integrating Cover Crops and Conservation Tillage on Agroecosystems
Soil Physical Properties. Tillage and residue affect soil properties in numerous
ways and are reviewed by Blevins et al. (1983). Under no-tillage, higher soil moisture is
observed when compared with conventional (moldboard plow/disk) tillage. The presence
of plant residue lessens evaporation early in the growing season. This retained moisture
could help to minimize yield loss by enabling plant survival through short periods of
drought during the growing season but can also delay planting dates and early crop
growth by limiting field access and lowering soil temperatures. Excessive soil water
conditions can accelerate nitrogen loss from denitrification. The presence of cover crop
residue and minimally disturbed soil contribute to increased water infiltration and
percolation by reducing the impact of raindrops and increasing soil aggregate stability
and macroporosity. According to Blevins et al. (1983), organic matter content of no-till
soil was twice as high in the plow layer of the soil profile when compared to conventional
tillage. Conclusions drawn by Blevins et al. (1983) are in accordance with other reviews
conducted by Coolman and Hoyt, 1993, and Heilman et al., 1992.
Effects on Nutrient Cycling. One of the major impacts that the integration of
conservation tillage and cover crops have on soil nutrient cycling is their effects on soil
nitrogen. These integrated systems have the potential to sign)ficantly reduce nitrate
leaching. In a Kentucky study (McCracken et al., 1994), losses with ammonium fertilizer
and no cover crop were equivalent to 37.3 kg N/ha~i but with a rye (Secale cereale L.)
cover crop and a stubble mulch conservation tillage they were equivalent to l.S kg
N/ha~t These authors concluded that rye was more effective at nitrate scavenging than
hairy vetch (Vicia villosa). According to Luna and McGrath (1996), results of on-farm
cover crop trials in Oregon show soil nitrate concentrations sign)ficantly reduced under
both barley (Hordeum vulgare, c.v.= "Belford") and rye (Secale cereale, c.v.= 'Common')
cover crops when compared to non-cover cropped fallow control plots. These authors
report increases in soil nitrate levels in hairy vetch (Vicia villosa) cover cropped plots.
They hypothesize increased nitrogen contributions to the soil from the vetch and
increased area of soil macropores from enhanced earthworm populations as possible
explanations to this leakage of nitrogen in the system.
Cover crops are traditionally suppressed before or at planting of the cash crop.
The timing of this suppression can have different effects as pointed out by a North
Carolina study (Wagger, 1989). Legume cover crops desiccated later (2 weeks later than
controls) had sign)ficantly higher biomass and total nitrogen content but decomposed
slower than cover crops desiccated early (2 weeks earlier than controls). Although late
desiccated cover crops had a higher nitrogen content this advantage seemed to be offset
by soil immobilization and a slower release of nitrogen for plant uptake.
Legume cover crops are characterized by their ability to fix nitrogen through a
symbiotic relationship with Rhizobia bacteria living in root nodules. Examples of
leguminous cover crops include: hairy vetch, Austrian peas (Pisum sativum spp. arvense
L.), and crimson clover (Trifolium incarnatum L). According to Hoyt and Hargrove
(1986), legumes provide aufficient biomass to reduce erosion, accumulate more than 150
kg N/ha of organic nitrogen, and supply up to 100 kg N/ha for the subsequent cash crop.
Effects on Arthropods. Conservation tillage can play a major role in maintaining
the populations of predatory ground arthropods (Weiss et al., 1990; Barney and Pass,
1986; Fan et al., 1993). In a North Carolina study, House et al., 1989 monitored
populations of several arthropod species in no-till and conventionally tilled
agroecosystems. Conclusions drawn by the authors state that no-till plots harbored more
beneficial arthropod species, had a higher diversity of soil arthropod species, and
promoted a more trophically balanced soil arthropod community. Stinner and House
(1990) provide an excellent review of tillage and residue effects of arthropods and other
invertebrates in conservation tillage agriculture.
The major approach to maintaining and enhancing populations of predatory
ground arthropods (of which Carabidae is a key family) is to modify the habitat to favor
their immigration and tenure (Gross, 1987; Russel 1989; Culliney and Pimentel, 1986;
House and All, 1981). Some types of habitat mod)fication include pesticide applications,
tillage, crop rotation, and the presence or absence of a mulch. Effects from habitat
modification range from providing shelter for arthropods (Riechert and Bishop 1990) to
altering the microclimate in favor of arthropods (Honek, 1988). Clark et al., 1993, studied
habitat preferences of carabids in a reduced till com experiment in Virginia. They
demonstrated that carabid populations were higher in plots that contained surface rye
residue than plots that were fallow. Similar trends were observed on other predatory
arthropods collected such as species of Staphylinidae. Rivard (1966) provides an
insightful discussion on the influence of vegetation management on predaceous ground
arthropods. He demonstrates the differences in predatory ground arthropod abundance
under varying intensities of chemical and mechanical habitat management.
Pitfall traps are most commonly used for sampling ground dwelling arthropods
such as Carabidae, Staphlynidae, and Arachnida (Stinner and House 1990). Pitfall
trapping is useful in determining species presence and activity but is a poor method for
estimating abundance (Franke et al. 1988). Pitfall trapping can be influenced by
temperature and moisture (Honek, 1988), material used for the construction of the trap,
and the type of preservative used (Wagge 1975). Halsall and Wratten (1988) found that
time of day influenced the numbers of carabids trapped in their study in England. Spence
and Niemela (1994), provide an in-depth discussion on the biases of pitfall trapping.
Effects on Earthworms. Earthworms are receiving increased attention for their
role in maintaining soil health and enhancing nutrient cycling. Their feeding and
burrowing activities incorporate organic residues into soils (Mackay and Kladivko, 1985;
Kretschmar and Ladd, 1993), accelerating decomposition and humus formation
(Kladivko et al., 1986). Earthworm burrows help to improve water infiltration (Zachmann
and Linden, 1989), gas exchange (Mackay and Kladivko, 1985), and overall nutrient
cycling (Edwards and Lofty, 1972). Lee (1985), provides a thorough review of
earthworm ecology as related to soil and land use.
Tillage is one of the most detrimental agricultural practices to earthworms. In
general, the more intense and frequent the tillage operation, the lower the population of
earthworm (Edwards, 1983; Barnes and Ellis, 1979). Tillage destroys macropores formed
by earthworms that are vital to water infiltration and gas exchange (Kladivko and
Timmenga, 1990; Doran and Werner, 1990). Bugg (1994) provides a thorough review of
the benefits of earthworms and tillage effects associated with them.
Crop residues and cover crop mulches help to enhance earthworm populations by
providing a food source (Edwards and Lofty 1979), conserving soil moisture (Edwards
and Lofty, 1982), and providing a cooler and/or insulative microenvironment (Grant,
1955). Kretschmar and Ladd (1993), report that although cover crops provide favorable
earthworm habitat, ultimately the earthworms feed on the cover crop, enhancing the
building of soil organic matter.
Werner and Dindal (1989) report different community dynamics of earthworms in
low-input and conventional agroecoystems. The researchers demonstrated a higher
earthworm density and biomass in plots managed organically with green manures added
when compared to plots managed with moldboard plow based tillage and synthetic
chemical inputs. However, they did report that spring tillage inhibited earthworm activity
in all tillage treatments.
In a Swiss experiment, Wyss and Glasstetter (1992) report that strip rotary tillage
caused a decrease in earthworm abundance due to soil compaction. However, the winter
catch crop they planted aided to offset that phenomenon by enhancing their food supply
and hence their biomass. The researchers report a shift from endogeic species (horizontal
burrowers) to anecique species (vertical burrowers). According to Laing et al., (1986),
the earthworm Lumbricus terrestris is an excellent biological control organism for the
spotted teniform leafminer (Phyllonorycter blancardella). The leafminer overwinters in
the leaf litter of apple (Malus spp.) orchards and the burial of the leaves by the worms
proves to be fatal to the insect eggs.
Effects on Other Soil Biota. Haines and Uren (1990) monitored microbial
biomass in a wheat (Triticum aestivum) stubble mulch conservation tillage system. They
found 19~o greater microbial biomass in the conservation tillage system when compared
to conventional tillage. Doran (1980) found populations of bacteria, actinomycetes, and
fimgi increased two to sixfold as a result of mulch left on the soil surface. Counts of
nitrifying and denitrifying bacteria doubled and tripled respectively in plots receiving
surface applications of com (ZeamaisL.) stover. Under controlled conditions, microbial
populations increased two to fivefold under the addition of com stover. According to
Powlson et al. (1987), soil microbial biomass responds quicker to changes in
management practice (i.e. tillage) and may be a better indicator of overall soil organic
matter content changes than traditional laboratory soil analysis.
Effects on Weeds. Herbicides for weed control have been essential for the
success of conservation tillage systems (Regnier and Janke, 1990). However, growing
concerns of groundwater quality and dependence on off-farm resources have provided an
impetus to develop alternatives to herbicides in conservation tillage systems (Worsham,
1991).
10
Tillage directly affects the soil seed bank by disturbing the soil. This disturbance
promotes the germination of viable seed by creating favorable growing conditions.
Conservation tillage systems integrated with cover crops aim to minimize soil
disturbance and subsequent weed seed germination by keeping viable but dormant seed
beneath the soil surface where they lack specific germination requirements (Buhler and
Mester, 1991). This results in a buildup of weed seed in the upper profiles of the soil.
Yenish et al. (1992) found 60% more total weed seed in the top 19 cm of soil in a com
(Zea mays L.) no-till system when compared to moldboard plowing.
Integrating cover crops into conservation tillage systems as weed management
tools have been shown to provide weed control comparable to herbicides (Crutchfield et
al., 1985; Smeda and Putnam, 1988; Teasdale and Mohler, 1992; Purvis et al., 1985;
Johmson et al., 1993). Research in this area has focused on exploiting competitive
characteristics of living cover crop species for water, nutrients, and sunlight and after the
cover crop is killed, the ability of the cover crop to suppress weeds as a mulch (Putnam,
1990; Barker and Bhowmik, 1994; Masiunas et al., 1995; Teasdale, 1993).
Cereal cover crop residues suppress weeds by modifying the light, temperature,
moisture, and chemical environment of germinating seeds (Putnam, 1986 and Teasdale et
al., 1991). Teasdale and Mohler (1992) noted that microclimatic changes caused by
legume cover crops, namely alterations of temperature and light intensity, inhibit weed
seed germination.
Considerable research in the past decade has focused on the allelopathic effects of
cover crops in conservation tillage systems. Allelopathy is defined by Zimdahl (1993) as
a form of plant interference that occurs when one plant, through living or decaying tissue,
11
releases a chemical inhibitor which interferes with the growth of another plant. The use
of allelopathic mulches has been a common research theme in the development of
integrated management strategies (Barnes and Putnam, 1983; Putnam and DeFrank,
1983; Overland, 1966). In Barnes and Putnam's (1983) study of cereal rye (Secale
cereale, c.v.= 'Wheeler' and 'MSU-13') residues, the biomass of three summer annual
weeds (Chenopodium album L., Digitaria sanguinalis L., and Ambrosia artemisiifolia L.)
was sign)ficantly decreased when grown in the presence of rye cover crop residue.
Chemical and physical effects of mulches have been difficult to distinguish in
studies of allelopathy. Barnes and Putnam (1983) attempted to distinguish these effects
by using poplar excelsior wood shavings (an inert material) to mimic physical mulch
effects. Echinochloa crusgalli L. and Amaranthus retrqflexus L. growth was significantly
suppressed under rye residues when compared to the excelsior. In a greenhouse study,
Barnes and Putnam (1986) reported that rye (Secale cereale, c.v.= 'Wheeler') residues in
a simulated no-till environment reduced emergence ofPanicum miliaceum L. by 35%
when compared to a wood shaving control mulch.
Duration of weed suppressiveness provided by decomposing cover crop residue is
an important consideration in developing weed management strategies. In the first year of
a North Carolina study, Hinen and Worsham (1990) reported that rye (Secale cereale)
residues alone provided adequate weed control. In the second year of study, however,
supplemental herbicide applications were required to maintain adequate weed control.
Although decomposing plant residues can negatively impact weeds, negative
impacts on subsequent cash crops have also been reported (Putnam et al., 1983). Barnes
and Putnam (1986), report that rye (Secale cereale, c.v.= 'Wheeler') residues reduced the
12
emergence of lettuce {Lactuca sativa) by 58% when compared to a wood shaving control
mulch. In a recent Oregon study, Nova (1995) noted the possible allelopathic suppression
of broccoli (Brassica oleracea var. italica) by an oat (Avena sativa L., c.v.= 'Monida')
cover crop.
Concerns of ecological weed species shifts due to altered microclimatic
environments and disturbance levels in conservation tillage systems have arisen as seen
in the results of a grower survey conducted by Koskinen and McWhorter (1986). Results
of the survey indicate that large-seeded weeds, such asXanthium strumarium L. and
Abutilon theophrasti Medic, diminished as problem weeds in conservation tillage
systems, but small-seeded annuals, such as Setaria faberi Herrm., Panicum
dichotomiflomm Michx., and Amaranthus retroflexus L., either remained constant or
increased as problem weeds. They also indicate that reduced tillage systems continually
select for perennial weeds with economically limiting infestations arising after two or
three years of continuous reduced tillage.
Derksen et al. (1994) contradict Koskinen and McWhorter in finding that the
selection of conservation tillage systems towards perennial weed species to be
inconsistent over time. They explain that different weed communities receive variable
selection pressures. For example, the timing of the emergence of the different weed
species in relation to each other and the cash crop, tillage intensity, and/or herbicide
application greatly influences weed communities' response to different management
systems.
13
Integrated Vegetable Production Systems
Certain limitations of producing vegetable crops limit the adoption of systems that
utilize cover crops and conservation tillage (Phatak, 1992). A lack of herbicides labeled
for use in vegetable crop production results in hesitance of a grower to amend already
existing practices. Another major problem is the reduced flexibility of planting time of
the summer cash crop (tuna, 1993). The latter is a major problem with growers of the
Maritime Pacific Northwest where cool wet springs often inhibit planting and early
season crop growth. Shennan (1992) provides an in-depth review of these and other
limitations.
There are production methods in use that overcome most limitations posed by
these integrated systems, while maintaining profitable yields. One form of cover crop
management, termed "living mulch", allows the cover crop to provide ground cover year
round with chemical or mechanical suppression of the cover crop taking place during
peak growth periods of the cash crop. Enache and Illnicki (1990) obtained adequate
control ofPanicum dichotomultiflorum L. in a subterranean clover (Trifolium
subterraneum L.) living mulch system. Com yields were comparable to or higher than
those obtained with chemical weed control. Success of this system was attributed to the
compatibility of the clover's life cycle during peak periods of crop growth minimizing
competition with sweet com. Living mulches have been shown to provide insect control
along with weed control in integrated vegetable production systems. Castle and Alteri,
(1994) report that cabbage aphid {Brevicoryne brassicae) abundance was reduced on
14
broccoli grown in living mulches compared to broccoli grown in clean cultivation,
possibly because light reflectance patterns are less attractive to incoming aphids.
In a Virginia study, Morse and Seward (1986) report that a no-till broccoli
{Brassica oleracea var. italica) and cabbage (Brassica oleracea var. capitata) production
system produced yields equal to or greater than conventionally grown broccoli and
cabbage. Crops were transplanted into chemically killed mulches of hairy vetch, Austrian
winter pea, and cereal rye. Results indicated that crops grown in the leguminous mulches
yielded higher and grew more vigorously due to increased nitrogen mineralization,
however all three cover crop species were conducive to broccoli and cabbage growth.
Hoyt (1984) reported that in a North Carolina study tomato (Lycopersicon
esculentum) and broccoli yield response to legume residues in strip till production
systems were consistently greater than conventionally grown plots. Hoyt (1984) notes
that if the summer cash crop is planted late enough for good spring growth of winter
legumes, these residues will also provide soil coverage and ultimately increase the total
amount of nitrogen recycled in the system.
Mohler (1991) reported that the presence of a rye mulch in a no-till sweet com
production system had no detrimental effect on com yield. However, other data shows
that under no-till situations, com yields have increased due to the increased moisture
content of the soil (Jones et al., 1969; Van Dom et al., 1973). Rye residue decreased
weed biomass during both years of the study (Mohler, 1991). The allelopathic effect of
rye on the weeds was consistent with the results reported by Putnam and DeFrank (1983).
15
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25
Chapter 2
Integration of Cover Crops and Strip-tillage in a Broccoli Production System in the
Maritime Pacific Northwest
Abstract
Strip-tillage and fall sown annual cover crops were evaluated in two separate field
experiments for their ability to produce economically competitive broccoli yields as well
as enhance biological resource conservation. The first experiment was conducted during
1996-97 at the OSU Vegetable Research Farm near Corvallis, Ore. 'Monida' oat (Avena
sativa) and 'Dacold' rye (Secale cereale) were fall sown in combination with common
vetch {Vicia sativa), dessicated with either pre-flail glyphosate or flail mowed alone, and
incorporated via either strip or moldboard plow based tillage in a split-split block in
randomized complete block experiment with three replications. Each management tactic
previously described created a unique set of consequences in which few broad
generalizations can be made. Plots under strip-tillage management had significantly
reduced amounts of total weed density and biomass. Plots under strip-tillage
management had significantly higher relative slug abundance and soil temperatures.
'Dacold' rye and vetch plots in combination with pre-flail glyphosate and strip tillage had
the highest broccoli yield. Those plots were determined to have the highest early season
soil nitrate contents but also the highest total weed biomass. Overall, a management
scenario was identified that could provide economically competitive broccoli yields as
well as minimize environmental impact. Future research will focus on strip-tiller
26
modifications for better seedbed preparation along with more precise timing of cover
crop management tactics to manage spring biomass.
A second experiment was conducted during 1995-96 at Crestview Farms near
Mollala, OR. The experimental design was a randomized complete block with 3
replications. After the fall sown (1995) cover crop mixture of 60% (by weight) 'Steptoe'
barley / 40% (by weight) common vetch was chemically suppressed, strip-tillage and
conventional (disc/harrow) tillage were conducted in appropriate areas of field plots in
early spring. Thirty day old broccoli transplants (c.v.='Packman') were commercially
transplanted.
Broccoli performance was evaluated based on: 1) head diameter at 42 days after
planting (DAP), 2) above ground dry weight biomass of broccoli plants at 42 DAP, and
3) broccoli yield. No significant treatment differences between strip and conventional
tillage were detected among the three sets of broccoli performance data. Yield was
reduced in both treatments by approximately 50% due to poor cover crop establishment
(excessive rains), subsequent erosion, and erratic temperature fluctuations during the
spring of 1996.
Biological resource conservation associated with the treatments was evaluated by
monitoring activities of ground dwelling arthropods and earthworms. No significant
treatment differences between strip and conventional tillage were detected in the
arthropod data. The sampling period (2 weeks) was too short to justify any conclusions.
No earthworms were detected in Conventional plots on either of our sampling dates.
Relative earthworm abundance was significantly higher in strip-tilled plots (P=.04). The
27
reduction in tillage associated with the strip-tillage plots demonstrates potential savings
in time, labor, and machinery costs.
Introduction
Conservation tillage systems and cover crops create the potential to alleviate
many of the environmental concerns associated with agricultural practices, while
improving soil productivity and economic profitability. The presence of cover crop
residues in minimally tilled environments can help to improve soil physical properties
(Rickerl and Smolik, 1990), enhance nutrient cycling (Karlen and Doran, 1991), diversify
soil biota (Doran, 1980), and decrease pest abundance (House and Alzugaray, 1989;
Smeda and Putnam, 1988). Frye and Blevins (1989) concluded that using a legume
winter cover crop as a mulch and as a partial supply of nitrogen for no-till com was
agronomically and economically feasible.
Additional benefits associated with the integration of cover crops and
conservation tillage practices include: increased control of soil erosion (Mannering and
Fenster, 1983; Coolman and Hoyt, 1993) and increased soil water and nutrient
retention(Munawar et al., 1990). Blevins et al. (1983) and Froud-Williams et al. (1981)
reported improved soil organic matter content under no-till when compared to organic
matter content in soils under moldboard plow based tillage Haines and Uren (1990) and
Koskinen and McWhorter (1986) report enhanced microbial activity and higher
earthworm populations under conservation tillage. Reduction of fuel and labor costs has
been a major economic factor in the adoption of conservation tillage systems (Sprague,
1986).
28
Although the integration of cover crops and conservation tillage for agronomic
crops has been reported extensively, there has been limited work reported in vegetable
crops. In a Virginia study, Morse and Seward (1986) report that a no-till broccoli
(Brassica oleracea var. italica) and cabbage (Brassica oleracea var. capitata) production
system produced yields equal to or greater than conventionally grown broccoli and
cabbage. Hoyt (1984) reported that in a North Carolina study tomato (Lycopersicon
esculentum) and broccoli response to legume residues in strip-till production systems
were consistently greater than conventionally grown plots. Mohler and Calloway (1992)
reported that the presence of a rye mulch in a no-till sweet com production system had no
detrimental effect on com yield. Abdul-Baki and Teasdale (1993) documented higher
yield in a no-till tomato production system that integrates a hairy vetch cover crop when
compared to a conventional black polyethylene production system.
Vegetable producing areas of the Pacific Northwest that are prone to erosion and
groundwater contamination as a result of intensive management practices and intensive
rainfall during the winter could be potentially improved by adopting production strategies
that integrate cover crops and conservation tillage. Many Oregon vegetable growers have
expressed an increased interest in the integration of cover crops and conservation tillage
as approaches to improving profitability, reducing fertilizer, pesticide, and fuel inputs,
improving soil and environmental quality (J. Luna, personal communication).
The following research project was initiated to evaluate broccoli production
systems integrating winter annual cover crops and strip-tillage. Specific objectives of
these research projects include: To evaluate the cover crop selection and spring
management practices in strip-tillage and conventional systems on: l)broccoli yield, 2)
29
weed population abundance, 3) relative abundance of earthworms and ground dwelling
arthropods. Two experiments were conducted. The first was conducted during 1996-97
at the OSU Vegetable Research Farm near Corvallis, Ore. The second was conducted
during 1995-96 at Crestview Farms, Inc. near Molalla, Ore.
Experiment 1: OSU Vegetable Research Farm, 1996-97
Materials and Methods
A field study was conducted during 1996-97 at the Oregon State University
Department of Horticulture Research Farm near Corvallis, OR. The soil at the site is
classified as a Chehalis silt clay loam. The field was fallow during 1995 and in
strawberry (Fragaria x Ananassa) production in 1994. The experimental design was a
split - split -plot design in randomized complete blocks with 3 replications. Two tillage
types (strip and conventional) constituted the main effects; two cover crop combinations
comprised the sub-effects. Time of cover crop suppression (early glyphosate or no early
glyphosate) constituted the second sub-effect within the cover crop treatments. Each
individual plot measured 4.6 m by 15.2 m.
The two cover crop combinations consisting of either 60% by weight 'Monida'
oat (Avena sativa) I 40% by weight common vetch (Vicia sativa) or 60% by weight
'Dacold' rye (Secale cereale) 140% by weight common vetch were seeded at a rate of
0.12 Mg ha
on 24 September 1996. The vetch seed was inoculated with Rhizobium
leguminosarum at an approximate rate of 4 g/kg of seeds by mixing the Rhizobium with
lightly moistened seed before planting. The cover crops were planted on 15-cm row
spacing using a grain drill.
30
Glyphosate was sprayed in the "early glyphosate" treatment within the strip and
conventional tillage plots with a CO2 backpack sprayer at an active ingredient rate of 3.3
kg a.i. ha
+ 187 L water ha
on 2 April and 18 April 1997 for the strip and
conventional tillage plots respectively. On 7 May 1997 all plots were flail mowed.
Tillage was conducted in conventional and strip-till plots on 12 May 1997. A moldboard
plow followed by one pass of a Lely
Northwest Tillers
®
®
roterra was used for the conventional till plots. A
strip-tiller was modified to till 15-cm wide strip on 0.76 m centers for
the strip-tillage plots.
An application of oxyflourfen and glyphosate herbicides was made on 14 May
1997, to all plots at rates of 0.56 kg ha"1 and 7 L ha
for oxyflourfen and glyphosate
respectively. The sprayer was shut off over a randomly selected 3.04 m section of each
individual plot to allow for a weedy check All plots were broadcast fertilized with a 1515-15 granular fertilizer at a rate of 0.44 Mg ha
-1
®
with a Gandy drop spreader and
followed by irrigation. Broccoli (Brassica oleraceae var. /to//ca)(c.v.='Arcadia') was
transplanted on 16 May 1997, on 0.76-m centers with a 0.38-m in-row spacing between
plants using a mechanical transplanter. Transplants were obtained from Northwest
Transplants, Inc. Mollala, Ore. On 23 May, 1997 chlorpyriphos insecticide was sprayed
in all plots as a prophylactic control of seed com maggot {Delia platurd) and flea beetles
{Phyllotreta cruciferae) at a rate of 0.38 kg a.i. ha + 187 L water ha
On June 18,
1997, all plots were fertilized with liquid ammonium nitrate at a rate of 123.2 kg ha +
187 L water ha
and incorporated via irrigation.
Data Collection
Cover Crop Biomass Cover crop biomass was estimated in all plots by clipping
2
the vegetation in two 0.25-m quadrats per plot, drying them for 48 hours at 43C0 and
weighing the dried biomass. Cover crop biomass was sampled in the "early glyphosate"
treatment within the strip-till plots using the previously described method on 2 April
1997. On 18 April 1997 biomass was sampled in the "early glyphosate" half of each
conventional till plot as described before. On 7 May 1997 all other plots (strip and
conventional tillage)(no pre-flail glyphosate) were sampled for biomass following the
previously described procedures.
Earthworms On 9 May. 1 June, and 2 July 1997 all plots were sampled for
relative earthworms abundance using a mustard expulsion technique (Gunn, 1992). Two
samples were taken in each plot using a metal ring 0.25m deep with a diameter of 0.6m.
The ring was placed on the soil surface and rotated until the bottom edges were firmly
embedded in the soil. Soil was pressed along the bottom outside edge to create a seal.
Any vegetation or debris found in the ring was carefully removed and 1.85 L of mustard
solution (7.2g ground cooking mustard/L water) was poured into each ring. Ten minutes
later another pour of the same volume of mustard solution was made. No other
earthworm species were identified in the field except L. terrestris which were collected
and sorted into one of the following size categories as they emerged: 1) adults, 2) large
juveniles (longer than 10 cm), and 3) small juveniles (less than 10 cm).
Soil Temperature Hobo
©
(Onset Computer Corp., Pocasset, Mass.) soil
temperature recorders were installed on 16 May in paired strip and conventional tillage
32
plots of 'Monida' oat and no pre-flail glyphosate to monitor daily soil temperature
fluctuations. The recorders were placed in the broccoli rows at an approximate depth of
7.6 cm.
Soil Nitrate On 21 May and 18 June 1997, soil nitrate sampling was conducted
by taking a composite of five soil core samples was taken from each individual plot
within the broccoli row to a 15.2 cm depth. Samples were analyzed for nitrate nitrogen
by the Central Analytical Services Soil Testing Laboratory at Oregon State University in
Corvallis, Ore. using an Alpkem
®
RFA300 rapid flow analyzer.
Weed Density Estimates of total weed species density were obtained by counting
2
in a 0.25-m quadrat at two randomly selected locations within the weedy check area of
each plot between the broccoli rows on 23 June 1997. Weeds were separated into
predominant species: pigweed (Amaranthus retroflexus), purslane (Portulaca oleraceae),
lambsquarter (Chenopodium album), and common groundsel (Senecio vulgaris). All
other weeds were grouped into a miscellaneous category.
Broccoli Yield Broccoli heads were harvested on 24 July and 27 July 1997. A
12.2 m long section of the interior four rows of each individual plot was harvested
constituting a total area harvested of 37 m2. Grading protocols utilized by Norpac Foods,
Inc. (Salem, OR), the major broccoli processing cooperative in the Willamette Valley,
were followed. Broccoli heads were separated into three categories: grade 1, grade 2, and
cull. The primary difference between grade 1 and grade 2 broccoli is maturity at harvest,
with grade 1 being the optimum maturity and grade 2 being slightly over-mature. A
commercial broccoli grower typically conducts multiple harvests (2-3 harvests) to
maximize grade 1 broccoli yield. In our research plots, the initial harvest timing was
based on our over-all experiment maturity. Some treatments matured more quickly and
produced a higher proportion of grade 2 heads than other treatments. Norpac, Inc., does
not pay a price differential for the two broccoli grades.
All data were analyzed using GLM and Mixed procedures (SAS, 1990). The data
were interpreted in the following manner as suggested by Ramsey and Schafer (1997): ^
0.01 highly significant difference; ^ 0.05 significant; < 0.15 suggestive but inconclusive.
Results and Discussion
In the following section, the abbreviations MO/CV will be used for the 'Monida'
oat and vetch mixture; DR/CV will be used for the 'Dacold' rye and vetch mixture.
Cover Crop Biomass The cover crop mixtures produced similar quantities of dry
weight biomass in the spring of 1997 however the proportion of common vetch varied
dramatically between the cereal cover crops at all three spring sampling dates (Tables
2.1-2.3).. 'Dacold' rye does not grow as rapidly as 'Monida' oat in the fall and is less
competitive with the vetch. Although cover crop samples were not analyzed for nitrogen
content in this experiment, percent N content from an adjacent cover crop experiment
sampled during this same time period can be used to give imprecise but useful estimates
of total N in the cover crops (Tables 2.1-2.3). Clearly the DR/CV cover crop mixture
with the higher proportion of vetch contained significantly higher quantities of nitrogen
than the MO/CV mixtures at all three sampling dates. Not only was this total N content
higher, but the typically lower carbon to nitrogen (C:N) ratios of vetch compared to
cereals would result in more rapid mineralization of the cover crop N in the soil system.
34
Table 2.1. Total dry matter accumulation of cover crop mixtures, 2 April 1997 (Early
glyphosate, strip-tillage).
Cover crop treatments
Cereal
Biomass
N
(kg ha1)
Content
Legume
Biomass
N
(kg ha'1) Content
Total
Biomass
N
(kg ha'1) Content
'Monida' oat + common vetch
1712
18
469
15
2182
34
'Dacold' rye + common vetch
1076
15
1193
43
2269
59
Table 2.2. Total dry matter accumulation of cover crop mixtures, 18 April 1997 (Early
glyphosate, conventional tillage).
Cover crop treatments
Cereal
Biomass
N
(kg ha1)
Content
Legume
Biomass
N
(kg ha"1) Content
Total
Biomass
N
(kg ha"1) Content
'Monida' oat + common vetch
1907
20
308
10
2215
30
'Dacold' rye + common vetch
741
10
1901
69
2642
80
Table 2.3. Total dry matter accumulation of cover crop mixtures, 7 May 1997 (No preflail glyphosate, strip and conventional tillage).
Cover crop treatments
Cereal
N
Biomass
(kg ha1)
Content
Legume
Biomass
N
(kg ha1) Content
Total
N
Biomass
(kg ha'1) Content
'Monida'oat + common vetch
3041
33
2276
10
5317
43
'Dacold'rye + common vetch
805
11
4178
15
4983
16
35
Soil Nitrate Content The type of cover crop and time of cover crop suppression
were significant factors in the soil nitrate trends of these broccoli production systems at
the early season (21 May) sampling date but not the mid-season sampling date(Early
Season: P= 02 for type of cover crop and P=.01 for time of cover crop suppression; Late
Season: P= 20 for type of cover crop; P=.58 for time of cover crop suppression). Soil
nitrate levels in the early glyphosate treatment were significantly higher than those of the
late glyphosate treatments at the early season sampling date (21 may) (P= 04). but not the
mid-season sampling date 18 June (P=.44). The application of glyphosate accelerated the
degradation process of the cover crop allowing more nitrogen to be mineralized into the
surrounding soil solution. Because of the significant type of cover crop and cover crop
kill date effects in the early season (21 May) strip-tillage treatments, the effects of cover
crops and tillage will be evaluated separately for each kill time.
Soil Nitrate Content (Early glyphosate) There was a significantly higher soil
nitrate content in DR/CV plots under strip-tillage than DR/CV plots under conventional
tillage at the early season sampling date (May 21) (P=.05) but not the mid-season
sampling date (18 June)(P=.37) (Table 2.6). No significant differences were detected
between strip and conventional tillage in MO/CV plots at either sample dates (P=.68 for
early season; P=.15 for mid-season). When comparing soil nitrate contents of plots from
the two different cover crops within the same tillage systems, we found that plots
containing the DR/CV cover crops had significantly higher soil nitrate contents in strip
tillage (P= 04) but not in conventional tillage (P= 58). We expected DR/CV plots to
36
contain higher amounts of soil nitrates due to the higher proportion of vetch biomass
contained in these plots.
Table 2.4. Effect of tillage and cover crops on soil nitrate content within the top 15 cm.
Strip-tilla£e
'Monida' oat + common vetch (MO/CV)
'Dacold' rye + common vetch (DR/CV)
Conventional tillage
'Monida' oat + common vetch (MO/CV)
'Dacold' rye + common vetch (DR/CV)
1
2
3
4
Early glyphosate
21 May'
18 June
3
7.7
2.2
2.5
19.9
5.8
8.3
2.8
2.8
Late glyphosate
21 May
18 June
2.7
2.4
7.2
2.4
4.2
9.5
2.5
3.4
Late glyphosate
Earlv glyphosate
21 May
18 June
21 May
18 June
Pairwise Comparisons
.15
.684
.16
.80
Strip MO/CV vs. Conv MO/CV
.05
.37
.05
.10
Strip DR/CV vs. Conv DR/CV
.04
.38
.005
.93
Strip DR/CV vs. Strip MO/CV
.58
.90
.003
.07
Conv DR/CV vs. Conv MO/CV
Glyphosate was applied on 2 April and 18 April for strip and conventional tillage plots respectively.
Soil nitrate content sampled at time of planting (21 May) and prior to sidedress fertilizer (18 June).
Soil nitrate reported in ppm with an Alpkem® RFA300 rapid flow analyzer by OSU Central Analytical Services Laboratory,
Corvallis, OR.
P-value associated with pairwise comparison based on mixed model ANOVA in SAS.
38
(Tables 2.1-2.3). However, we would also expect that soil nitrate levels be higher in
conventional tillage due to higher rates of microbial respiration and subsequent nitrogen
mineralization.
Soil Nitrate Content (Late glyphosate) In DR/CV plots, conventional tillage
had a significantly higher soil nitrate content than strip-tillage at the early season
sampling date (P= 05) and the late season sampling date (P=. 10). No significant
differences were detected between strip and conventional tillage in MO/CV plots at either
sampling date (P=. 16 and .80 for early season and mid-season respectively). The higher
microbial respiration rates associated with the conventional tillage plots could have
resulted in higher amounts of mineralized nitrate nitrogen. Plots containing the DR/CV
cover crop had consistently higher early season soil nitrate contents regardless of the
tillage type employed (P=.005 and .003 for strip and conventional tillage respectively).
However, in mid-season, this effect was only observed in conventional tillage (P=.07) but
not in strip-tillage (P=.93). We attribute this to the biomass effect associated with
DR/CV plots as previously described.
The phenomenon observed with the biomass of the DR/CV cover crop mixture
resulted in those plots being higher in nitrate nitrogen. Conventional tillage helps to
accelerate the mineralization process by stimulating microbial populations. Cover crop
biomass management proves especially important when dealing with soil nitrate contents.
Considerations must include growth habits of specific cover crop species and when to
suppress the cover crop biomass in accordance with subsequent cash crop planting.
39
Broccoli Yield The time of cover crop suppression was a significant factor in the
yield trends of these broccoli production systems (P=.08). Broccoli yields were
dramatically reduced in the Late glyphosate treatment in the strip-till treatments
(MO/CV, P=.005; DR/CV, P=.010). This kill date effect was not observed in the
conventional tillage treatments. Cover crop regrowth appeared to be a major factor in
reducing yields in the late killed strip-till treatments. When no pre-flail glyphosate was
used we observed higher amounts of cover crop regrowth during the broccoli growing
season which likely competed with the broccoli plants for light, water, and nutrients.
Also, by applying glyphosate prior to flail mowing, the residue had more time to
decompose thus minimizing any immobilization of nitrogen for the subsequent broccoli
crop. Because of the significant cover crop kill date effect in the strip-till treatments, the
effects of cover crops and tillage will be evaluated separately for each kill time.
Broccoli Yield (Early Glyphosate) There was not a significant tillage effect on
broccoli yield within the early cover crop kill date (p=.39)(Table 2.4). However, broccoli
yields were higher in the strip-till DR/CV than in the conventional tillage DR/CV, but
these trends reversed for tillage treatments in the MO/CV cover crops. In the strip-tillage
plots, broccoli yields were significantly higher in the DR/CV plots when compared to
MO/CV plots (P=.04), however this effect was not observed in conventional tillage plots
(P=.68). One possible reason for why yields weren't suppressed by 'Monida' oat in
conventional tillage plots, was that there could be a dilution and increased microbial
degradation of any allelochemicals exuded by 'Monida' oat to non-inhibitive levels.
Broccoli Yield (Late glyphosate) In the strip-tillage plots, broccoli yields were
significantly lower in MO/CV plots when compared to DR/CV plots however this effect
Table 2.5. Effect of tillage, cover crops, and cover crop kill date on broccoli yield.
Strip-tillage
'Monida' oat + common vetch (MO/CV)
'Dacold' rye + common vetch (DR/CV)
Conventional tillage
'Monida' oat + common vetch (MO/CV)
'Dacold' rye + common vetch (DR/CV)
1
2
3
Early glyphosate
Total yield2
9.2
15.8
Late glyphosate
Total yield
1.9
8.8
10.9
12.
11.8
8.6
Early glyphosate
Late glyphosate
Total yield
Total yield
Pairwise Comparisons
3
. .40
.01
Strip MO/CV vs. Conv MO/CV
.29
.83
Strip DR/CV vs. Conv DR/CV
.04
.05
Strip DR/CV vs. Strip MO/CV
.68
.32
Conv DR/CV vs. Conv MO/CV
Glyphosate was applied on 2 April and 18 April for strip and conventional tillage plots respectively.
Broccoli total yield (Mg ha'1) consists of all grade 1 broccoli using Norpac Foods, Inc., Salem, Ore. grading standards.
P-value associated with pairwise comparison based on mixed model analysis of variance in SAS.
o
was not observed in conventional tillage plots (P=.05 and .32 for strip-tillage and
conventional tillage respectively)(Table 2.5). We attribute this effect to the reasons
previously described for this effect in the early glyphosate cover crop treatment. Broccoli
yield was significantly reduced by strip-tillage management when compared to
conventional tillage when the data was compared within the MO/CV cover crop
treatment (P=.01) but not when the data was compared within the 'Dacold' rye cover
crop treatment (P=.83).
Overall, broccoli yielded lowest when grown utilizing strip-tillage and a 'Monida'
oat cover crop residue with no pre-flail glyphosate. The combination of the possible
allelopathic effects of 'Monida' oat as demonstrated by Nova (1996) and the high amount
of cover crop regrowth associated with not applying glyphosate prior to flail mowing the
spring biomass create an unsuitable growth environment for broccoli. Cover crop residue
chemically desiccated early in the spring creates a microenvironment favorable to the
establishment and growth of transplanted broccoli.
Weed Density
Total Weed Density Total weed density was significantly lower in strip tillage
treatment plots when compared to conventional tillage treatment plots (P=.001) however
individual weed species responded differently among the cover crop and tillage
combinations. The time of cover crop suppression was not a significant factor in the total
weed density trends of these broccoli production systems (P= 13) (Data not shown). In
strip-tillage, total weed density was not significantly different in MO/CV plots than
42
DR/CV plots (P=.60)(Table 2.5). The same effect was observed for conventional tillage
as well (P-49).
Table 2.6. Tillage and cover crop effects on weed density, sampled 23 June 1997.
Strip-tillage
'Monida' oat + common vetch (MO/CV)
'Dacold' rye + common vetch (DR/CV)
Conventional tillage
'Monida' oat + common vetch (MO/CV)
'Dacold' rye + common vetch (DR/CV)
Purslane
Groundsel
Lambsquarter
Miscellaneous
Mean Total Number
5.31
0.66
2.3
1.6
0
0
2.3
0
14
18.3
24
20.6
23.3
8
20
35.6
16
4.6
0.6
0.6
9.6
11
69.6
60
.02
.06
1
.05
.17
.68
.09
1
.12
.58
.39
.79
.06
.04
.60
.49
Pairwise Comparisons
.31
08^
Strip MO/CV vs. Conv MO/CV
.46
.06
Strip DR/CV vs. Conv DR/CV
.95
.49
Strip DR/CV vs. Strip MO/CV
.03
.19
Conv DR/CV vs. Conv MO/CV
Density calcluated as number of plants per m .
P-value associated with pairwise comparison based on mixed model
—1—
2
Pigweed
H
""""
ANOVA in SAS.
44
Pigweed Density Pigweed density was not significantly affected by the time of
cover crop suppression (P=.71). Pigweed density was significantly greater in MO/CV
plots than the DR/CV plots within the conventional tillage treatment (P= 03)(Table 2.5).
Pigweed was significantly less dense in strip tillage plots within the MO/CV plots
(P= 08) but not within the DR/CV plots (P=.46). Pigweed density was significantly
effected by the type of cover crop (P=.05). A possible explanation for the observed
pigweed density in the DR/CV plots might be explained by examining the cover crop
biomass data (Tables 2.1-2.3). Although the cover crops had similar amounts of total
biomass, the DR/CV had a much higher proportion of vetch. Vetch has been documented
to have weed suppressing abilities (allelochemically and physically) by Mohler (1991)
and Shilling et al. (1985).
Purslane Density There was no significant effect of cover crop kill date on
purslane density (P=.25). However, purslane density was dramatically lower in strip
tillage plots when compared to conventional tillage plots (P=.009). Strip-tillage plots had
lower purslane density within the DR/CV cover crop mixture (P= 06) but not within the
MO/CV cover crop mixture (P= 3 l)(Table 2.5). No significant differences in purslane
density were detected between the individual cover crops within strip tillage (P=.95) and
conventional tillage (P= 19). The minimization of soil disturbance associated with the
strip-tillage was concluded to be the major cause of lower overall purslane reductions.
This conclusion is supported by Teasdale (1991).
Groundsel Density Common groundsel density was not observed in strip-tillage
plots but was quite prevalent in conventional tillage plots (P=.02 and .06 for comparisons
45
within MO/CV plots and DR/CV plots respectively)(Table 2.5). Groundsel density was
significantly affected by the type of cover crop in conventional tillage with MO/CV plots
having a significantly higher groundsel density than DR/CV plots (P=.05). Groundsel
density was higher in MO/CV plots than DR/CV plots (P= 04). The rationale for this
effect is believed to be the same as previously described for purslane.
Lambsquarter Density Lambsquarter density was not significantly affected by
cover crop type (P=.20) or time of cover crop suppression (P=.48). Lambsquarter density
was significantly higher in strip-tillage than conventional tillage (P= 03). However, in
strip-tillage plots, lambsquarter density was higher in MO/CV plots than DR/CV plots
(P=.09)(Table 2.5). No significant differences were detected between cover crops within
conventional tillage (P=l .00). The lambsquarter density data was excessively variable
thus we are relucant to draw firm conclusions.
Miscellaneous Weed Density No significant differences in miscellaneous weed
density were detected between any of the pairwise comparisons we constructed (Table
2.5). This category contains many different species of weeds which creates variability in
the treatment means and the separation of them difficult.
Overall, the weed density and biomass data indicate that with certain species of
weeds, minimizing tillage is paramount to reduce their populations to tolerable levels.
This effect can be enhanced with the appropriate choice of cover crop to integrate into the
system. The enhancement stems mainly from exploiting the allelopathic properties of
certain cereals as described by Putnam et al. (1983), as well as certain legumes (Teasdale,
1993). The reduction of tillage combined with allelopathic cover crops are two
46
compatible management practices that could provide economically viable levels of weed
control as well as integrate easily into existing broccoli production systems.
Relative Earthworm Abundance The effect of tillage and cover crops on the
relative abundance of the earthworm: Lumbricus terrestris resulted in mixed effects.
Relative earthworm abundance was higher in strip tillage than conventional tillage at the
11 May samplinge date (P=. 13) and 1 June samling date (P=. 12) but not the 2 July
sampling date (P=.80)(Figure 2.1). Strip-tillage conserves earthworms by creating a
refuge for earthworms and providing a food source on the soil surface. We expect to see
the relative abundance of earthworms higher in strip-tillage plots based on the findings by
Lee (1985) and Kretschmar and Ladd (1993). Relative earthworm abundance was not
signficantly effected by the time of cover crop suppression at all three sampling dates
(P=.89, .56, and .19 for 11 May, 1 June, and 2 July respectively). The type of cover crop
did not effect the relative earthworm abundance at the 11 May (P=.82) and 2 July (P=.37)
sampling dates but did have an effect at the 1 June sampling date (P=. 15).
We found no significant differences between any of the pairwise comparisons we
made on the 11 May sampling date. On the second sampling date (1 June), there were
significantly more L. terrestris earthworms in the strip tillage plots under both cover
crops (P= 002 and .08 for MO/CV and DR/CV respectively). There were significantly
more L. terrestris in the MO/CV cover cropped plots in strip-tillage plots (P=.06) but no
significant difference between the cover crops under conventional tillage (P=.88). On the
third sampling date (2 July), we found no significant differences between strip and
conventional tillage in MO/CV plots (P=.63) and in DR/CV plots (P=.28). In strip-
47
tillage, relative abundance of earthworms was higher in DR/CV plots than MO/CV plots
(P= 12) but not in conventional tillage (P=.51).
48
D 'Monida' oat + common vetch
B 'Decolcf rye + common vetch
E
u
a
a.
w
J3
E
3
z
2+
^1
Vs.-
STRIP
CONV
11 May
Pairw Ise C o m parisons
Strip M O/CV vs.Conv M O/CV
Strip DR/CV vs.Conv DR/CV
Strip DR/CV vs. Strip M O/CV
Conv DR/CV vs.Conv M O/CV
1
f
STRIP
CONV
STRIP
1 lune
1 1
M a y
.3 3'
.2 6
.8 6
.7 4
CONV
2 My
1
June
.0 0 2
.0 8
.0 6
.8 8
P-value associated with pairwise comparison based on mixed model ANOVA in SAS.
Figure 5.1. Effect of tillage and cover crops on the relative abundance of
the earthworm: Lumbricus terrestris.
2
J u ly
.6 3
.2 8
.1 2
.5 1
49
Overall, trends indicate that the major factor influencing the relative abundance
of earthworms in this study was tillage. Strip-tillage conserves more earthworms than
conventional tillage. The relative abundance data we collected was much lower overall
than we expected. We believe one possible reason for the results we obtained is that the
vertical burrowing (Anecique) earthworms like L. terrestris are predominantly dormant in
the summer. Soil moisture conditions must be adequate for earthworm activity. The
irrigation of the broccoli crop did not create conditions favorable to earthworm activity.
Another possible reason for overall low relative abundance we obtained is that the effects
of tillage on relative earthworm abundance are not immediately apparent. Effects might
not be apparent until multiple generations of earthworms have inhabited the area, this
could take longer than this study allowed.
Soil Temperature On average, daily high soil temperatures were warmer in
strip-tillage plots than conventional tillage plots (P:=.05)(Figures 2.2 and 2.3). There was
no significant difference between the daily low soil temperatures of strip and
conventional tillage (P=.56) This phenomenon presents itself as counterintuitive when
one looks at the findings of Hoyt (1984) and Hoyt and Konsler (1988). They document
lower soil temperatures in strip-tillage plots due to increased soil moisture and less soil
surface exposed to sunlight. However, most importantly our data shows conventional
tillage plots to have higher soil temperatures during the first half of the broccoli growing
season (P= 14) with the emperature of the strip-tillage plots gradually equaling and
surpassing the conventional tillage plots to become significantly higher by the time of
broccoli harvest (P=.08).
Figure 2.2. Effect of strip and conventional tillage on daily soil temperatures: 19 May to 23
June 1997.
32.0
28.0
O 24.0
Q)
w
3
4-*
ssa>
Q.
E
20.0
16.0
12.0
19-May
23-May
27-May
31-May
4-Jun
8-Jun
12-Jun
16-Jun
20-Jun
Time of Year
o
Figure 2.3. Effect of strip and conventional tillage on daily soil temperatures: 24 June to 26
July 1997.
29.0
■StLow
■StHigh
■ConvLow
•ConvHigh
17.0
15.0
24-Jun
28-Juh
2-Jul
6-Jul
10-Jul
Time of Year
14-Jul
18-Jul
22-Jul
26-Jul
52
Summary and Conclusions This experiment proved most useful in
demonstrating the interactive effects of integrating strip-tillage and cover crops. In
certain scenarios, the two acted synergistically, providing ground cover in the fall,
adequate weed control in the spring, and economically profitable yields in the summer.
Additional benefits derived from their integration were increased soil fertility plus habitat
and refuge for earthworms. However, certain scenarios were observed to be detrimental
to the production of broccoli. These scenarios seemed to be most contingent on the time
of cover crop suppression. Suppressing cover crop with glyphosate prior to flail mowing
minimized cover crop regrowth from flail mowing thus minimizing further competition
of the cover crop with broccoli. 'Monida' oat has been shown to be allelopathic to the
growth and yield of broccoli. Future recommendations for use of this cover crop will
exclude broccoli production systems.
An ideal scenario that could be derived from this experiment would constitute the
following: 1) Sow cover crops in early fall, 2) chemically dessicate with a lethal rate of
herbicide two to three weeks prior to flail mowing in spring, 3) one week later flail mow
cover crop to accelerate the degradation process 4) conduct appropriate tillage, 4) two
weeks later, apply pre-emergent herbicide (oxyflourfen) combined with lethal rate of
glyphosate to kill any emerging weeds and transplant broccoli.
Future research involving the integration of cover crops and strip-tillage will
focus on modifying the strip-tiller to create a more favorable soil environment and
determining precision cover crop biomass management techniques.
53
Experiment 2: On-Farm Research at Crestview Farms, 1995-96
Materials and Methods
A field experiment was conducted at Crestview Farms, Mollala, OR during the
summer of 1996. The soil at the site is a Woodbume silty clay loam with pH varying
from 6.5 to 6.7. The experimental design was a randomized complete block with three
replications. Each individual replication contained an area measuring 0.32 ha. Tillage
treatments of strip and disk/harrow tillage (conventional) constituted the main plots. The
field had been in a corn-broccoli-cauliflower rotation with the 1995's crop being com.
Upon com harvest, the field was field cultivated, disced twice, and rotovated. A cover
crop mixture of 'Steptoe' barley {Hordeum vulgare) and common vetch {Vicia sativa)
was planted at rates of 67.2 kg ha"1 and 33.6 kg ha"1 for barley and vetch respectively
using a 4 m John Deere® grain drill.
During late March, 1996, a strip application of glyphosate was made in the striptillage plots at a rate of 0.9 kg ai ha"1 + 187 L water ha"1. On 6 April 1996, cover crop
suppression occurred by broadcast spraying glyphosate at a rate of 0.9 kg ai ha"1 + 187 L
water ha"1. Strip-till plots were flailed mowed on 28 April 1996 and strip-tilled the
following day. The strip-tillage plots were strip rototilled using a Multivator® strip
rototiller set on 0.9-m centers. This strip-till machine was used in this experiment to
accommodate the 0.9-m row spacing of Crestview Farm. The Northwest Tillers®
machine used in experiment 1 is set up on 0.75-m row spacings. Conventional tillage
plots were tilled over a period of approximately 30 days preceeding broccoli planting,
receiving, 1 pass of the chisel plow followed by 2 passes of the disc and 1 pass of the
rotovator to prepare a suitable transplant bed. The strip-tillage plots required two passes
54
of the rototiller to prepare a suitable transplant bed. An insecticide application of
chlorpyrifos was applied at a rate of 0.04 kg ai ha"1 + 187 L ha"1 to control symphylans
(Scutigerella immaculatd) and cabbage root maggot {Delia brassicae). A mixture of
oxyfluorfen and glyphosate were broadcast sprayed on 29 April 1996 at a rate of 0.56 kg
ai ha"1 + 187 L ha"1 and 0.9 kg ai ha"1 + 187 L ha"1 respectively across all plots using a
tractor-mounted boom sprayer.
On 30 April 1996, 30 day old broccoli (Brassica oleracea var. italica,
c.v.='Packman') plants were mechanically transplanted on 0.9 m centers with a 0.61 m
in-row spacing by the Northwest Transplant Company, Mollala, OR. Transplants
received a band application of 20-20-10 liquid fertilizer at a rate of 90 kg ha'1 at time of
transplanting. After stand establishment, overhead irrigation was provided as needed to
ensure maximum crop growth. On 25 May 1996, an application of carbaryl was applied
at a rate of 2.33 L ha"1 + 187 L ha"1 to control aphids (Myzuspersicae). Cultivation was
conducted on 30 May 1996 using a Buffalo® high residue cultivator in strip-tillage plots
and a field cultivator in conventional tillage plot. An additional broadcast application of
liquid ammonium nitrate (32-0-0) fertilizer was made at a rate of 156 kg/ha. at the time
of cultivation.
Data Collection
Cover crop establishment was extremely poor and erratic due to the record
rainfalls and flooding of the winter of 1996. By 15 April 1996 cover crop biomass was
visually estimated to be between 0 and 2.24 Mg ha"1. On 21 May and 13 June 1996
relative earthworm {Lumhricus terrestris) populations were estimated by using a mustard
expulsion technique .(Gunn 1992). as previously described in Experiment 1.
55
On 12 June 1996, head diameters of broccoli were measured on 60 random plants
per plot. Six plants per plot were cut at the soil surface dried for 72 hours and dry weight
biomass determined.
On 30 May 1996, arthropod pitfall sampling was initiated. A pit was installed
consisting of two plastic cups (180 ml, 9.5 cm rim diameter) one inside the other placed
in a hole in the ground so that the rim of the inside cup was flush with the soil surface.
This allowed the inner cup, which contained the trapped specimens, to be taken out
without damaging the structure of the pit. The inner cup contained a solution of ethylene
glycol as a killing agent and preservative. Plywood rain covers (20 X 15 cm) were
suspended above the pits by inserting 9 cm long nails through the four comers of each
cover to serve as supports. The trapping period lasted for 2 weeks with the traps being
emptied weekly. Samples were sorted in the laboratory and identified.
Broccoli was harvested on 17 June, 21 June, and 24 June 1996. Yield was
determined by estimating the weight of harvest totes based on their volumetric content
and multiplying by the number of totes filled in each plot.
Data analysis was completed by using the General Linear Models (GLM)
procedure of SAS® for analysis of variance (ANOVA) (SAS Institute, 1990). Means
were separated by using the Least Significant Difference (LSD) method.
56
Results and Discussion
Broccoli Growth and Yield No significant differences (a=. 10) were detected
between the treatments for all three sets of broccoli performance data (Table 2.7).
Increased variability of the data was attributed to erratic weather (excessive fall and
winter rains) that caused poor cover crop establishment (< 1.12 Mg ha"1 spring biomass,
visual estimation).
Mean broccoli head diameter was not significantly different between strip and
conventional tillage plots (P=.46). Mean dry weight biomass of broccoli was not
significantly different between strip and conventional tillage (P=.26). Broccoli total yield
was not significantly different between strip and conventional tillage (P=.33). This data is
supported by Hoyt (1984) when he reported no morphological or yield differences
between crops grown in strip-tillage plots when compared to conventional tillage plots in
North Carolina.
Overall, these results prove to be inconclusive when evaluating the effectiveness
of the strip-tillage treatments in maintaining competitive yields with the conventional
tillage treatments. A combination of environmental and cultural factors contributed to
overall yield decline. Erratic temperatures such as cold (70C) temperatures early in the
season followed by excessive hot weather (30oC) just prior to harvest provided
explanation for the observations of bolted plants throughout the fields. The shallow root
system associated with the transplants could have inhibited the early growth of the
transplants (Mansour, personal communication). The possible leaching of fertilizer via
irrigation past the rooting
Table 2.7. Effects of tillage on broccoli head diameter, dry weight biomass, and total yield. Crestview Farm, 1996.
Tillage treatments
Broccoli Head Diameter (cm)
Broccoli dry weight biomass (g)
Broccoli Yield (Mg ha"1)
Strip-tillage
4.11
42.58
3.62
Conventional tillage (Disc/Harrow)
4.52
39.67
3.98
Pairwise Comparison
.461
.26
.33
* Means within a column followed by the same letter do not differ significantly using F-protected LSD, a = . 10.
P-value associated with t-test comparing strip and conventional tillage using SAS.
1
58
zone could have also contributed to the overall inhibition of the productivity of the
system. A combination of these factors has been determined to be the cause of the results
obtained in this study.
The effectiveness of these systems could be demonstrated in terms of savings of
time and labor. The strip-tillage plots were dry enough to plant a day earlier than the
conventional tillage plots. This could prove beneficial for growers when trying to stay on
schedule with cannery planting schedules. Overall, the conventional plots required 4
passes of the disk and field cultivator to create a friable seedbed. The strip-tillage plots
only required 2 passes of the strip tiller. A 50% reduction in the number of passes across
the field and 83% reduction of the total amount of tilled ground could add up to
significant economic savings in time, labor, and fuel..
Biological Resource Conservation There were no significant treatment effects
when evaluating the relative abundance of ground dwelling arthropods (P=.89, .52, and
.19 for Carabidae, Staphylinidae, and Arachnida respectively)(Table 2.8). A longer pitfall
trapping period is necessary in order to make stronger conclusions about the relative
abundance of these arthropods in these broccoli production systems.
Species of Carabidae that were trapped included: Pterostichus melanarius Illiger,
Agonum subsericeum LeConte, Agonum muelleri Herbst, Amora littoralis Mannerheim,
Anisodactylus califomicus Dajaan, Anisodactylus binotatus F., Anisodactylus
sanctaecrucis F., and Clivinafossor L. P. melanarius, an introduced European species,
has been reported to be a major insectivore in agroecoystems (Rivard, 1964). The rest of
Table 2.8 Effects of tillage on arthropod and earthworm (Lumbricus terrestris) acitivity and abundance. Crestview Farm, 1996.
Tillage treatments
Carabidae
(mean no./trap)
Staphylinidae
(mean no./trap)
Arachnida
(mean no./trap)
Lumbricidae {Lumbricus terrestris)
(mean no.An2)
21 May1
13 June
Strip-tillage
0.3
9
6
2
0
Conventional tilalge (Disc/harrow)
0.3
6
3
0
0
Pairwise Comparison
.892
.52
.19
.04
1.00
Relative earthworm abundance was determined in early broccoli growing season
(21 May) and late broccoli growing season (13 June).
2
P-value associated with t-test comparing strip and conventional tillage using SAS
60
the species collected could be classified as opportunistic omnivores. A review by
Sweetman (1958) reported species of carabids that have been reported to cause
agricultural plant damage but none of the species we collected were reported.
Strip-tillage plots had significantly more relative earthworm abundance at the
early season sampling date (21 May) (P= 04) but no worms were detected in strip-tillage
plots on the late-season sampling date (13 June) (P=1.00). No worms were detected
from the conventional tillage treatments on either sampling date. This phenomenon
could be attributed to the excessive tillage required in those plots to create a favorable
seedbed.. These results are in confirmation with other studies monitoring earthworm
populations under differing tillage intensities (Wyss and Glasstetterj 1992; Rovira et al.,
1987). We believe there are three possible reasons for not detecting any earthworms on
our late season sampling date (13 June). First, this second sampling was conducted
toward the end of the growing season under excessively warm conditions. Our
expulsion solution did not thoroughly saturate the dry soil resulting in an ineffective
volume of solution per sample area. The warm weather could have also driven the
worms further down in the soil profile Lee (1985). What could have resulted is that by
the time the irritant solution reached the worms in the lower depths of the soil profile it
had become diluted to an ineffective concentration. Second, cultivation of the row
middles was conducted 2 weeks prior to our second sampling date and the combination of
vertical burrow destruction and the presence of high concentrations of anhydrous
ammonia fertilizer could have deterred earthworm activity in the plots. Third, an
insecticide application of carbaryl, a carbamate, was made two days before cultivation.
61
Carbamates have been documented as highly toxic to earthworms (Tomlin and Gore,
1976).
Conclusions
The results of this study indicate that growers who integrate the practices of cover
cropping and conservation tillage into their farming sytems can expect certain short term
benefits such as reductions in the amount of tillage translating to savings in time, labor,
and machinery costs. Thorough documentation of the effects of conserving soil
organisms in these systems can come only after a longer term study.
62
References
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hairy vetch and subterranean clover mulches. HortScience 28(2):406-408.
Blevins, R.L., M.S. Smith, G.W. Thomas, and W.W. Frye. 1983. Influence of
conservation tillage on soil properties. J. Soil Water Cons. 38:301-305.
Coolman, R.M. and G.D. Hoyt. 1993. The effects of reduced tillage on the soil
environment. HortTechnol. 3:143-145.
Doran, J.W. 1980. Microbial changes associated with residue management with reduced
tillage. Soil Sci. Soc. Amer. J. 44:518-524.
Doran, J.W. and M.S. Smith. 1991. Role of cover crops in nitrogen cycling, p. 85-90
In W.L. Hargrove (ed.) Cover crops for clean water. Soil and Water
Conserv. Soc. Amer. Ankeny, Iowa.
Ess, D.R., D.H. Vaughan, J.M. Luna, and P.G. Sullivan. 1994. Energy and economic
savings from the use of legume cover crops in Virginia com production. Am. J.
Alt. Ag. 9:178-185.
Frye, W.W. and R.L. Blevins. 1989. Economically sustainable crop production with
legume cover crops and conservation tillage. J. Soil Water Cons. 23:57-60.
Haines, P.J. and N.C. Uren. 1990. Effects of conservation tillage farming on soil
microbial biomass, organic matter and earthworm populations, in north-eastern
Victoria. Australian!. ofExper. Agric. 30:365-371.
House, G.J., and M. Alzugaray. 1989. Influence of cover cropping and no-tillage
practices on community composition of soil arthropods in a North Carolina
agroecosystem. Environ. Entomol. 18:302-307.
Hoyt, G.D. 1984. The effect of cover crops on strip-till vegetable and tobacco
production. Soil Sci. Soc. of North Carolina Proc. 27: 10-20.
Hoyt, G.D. and T.R. Konsler. 1988. Soil water and temperature regimes under tillage
and cover crop management of vegetable culture, p. 697-702 In Proc. 11th Intl.
Conf, ISTRO. Edinburgh, Scotland.
Karlen, D.L., and J.W. Doran. 1991. Cover crop management effects on soybean and
com growth and nitrogen dynamics in an on-farm study. Amer. J. of Alt. Ag. 6:
71-82.
Koskinen, W.C. and C.G. McWhorter. 1986. Weed control in conservation tillage. J. Soil
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Kretzschmar, A. and J.N. Ladd. 1993. Decomposition of 14C-labelled plant material in
soil: The influence of substrate location, soil compaction, and earthworm
numbers. Soil Biol. and Biochem. 25:803-809.
Lee, K.E. 1985. Earthworms: their ecology and relationships with soils and land use.
Academic press, New York. 411pp.
Mannering, J.V., and C.R. Fenster. 1983. What is conservation tillage? J. of Soil and
Water Conserv. 38:141-143.
Mohler, C.L. 1991. Effects of tillage and mulch on weed biomass and sweet com yield.
Weed Tech. 5:545-552.
Mohler, C.L and T.R. Calloway. 1992. Effects of tillage and mulch on weed biomass and
sweet com yield. Weed Tech. 5:545-552.
Morse, R.D. and D.L. Seward. 1986. No-Tillage Production of Broccoli and Cabbage.
Appl. Agric. Res. l(2):96-99
Munawar, A, R.L. Blevins, W.W. Frye, and M.R. Saul. 1990. Tillage and cover crop
management for soil water conservation. Agron. J. 82:773-777.
Putnam, A.R., J.DeFrank, and J.P. Barnes. 1983. Exploitation of allelopathy for weed
control in annual and perennial cropping systems. J. Chem. Ecol. 9:1001-1010.
Rickerl, D.H. and J.D. Smolik. 1990. Farming systems' influences on soil properties and
crop yields. J. of Soil and Water Conserv. 27:121-125.
Ramsey, F. L. and D.W. Schafer. 1997. Interpretation of P-values. pgs. 44-45 In: The
Statistical Slueth: A Course in Methods of Data Analysis. Duxberry Press,
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Shilling, D.G., AD. Worsham, and DA Danehower. 1986. Influence of mulch, tillage,
and dephenamid on weed control, yield and quality in no-till fluecured tobacco
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65
Acknowledgements
The authors would like to express their gratitude to Dale Lucht, owner and
operator of Crestview Farms, Mollala, OR. Dale and his entire field crew expended
countless efforts to ensure the success of the field trial. Special thanks to Mary Staben,
Micaela Colley and Kate Christensen of Oregon State University for their help in the data
collection of both field experiments. Caroline Nichols and Hans Wittig helped in carabid
sampling and earthworm harvesting respectively. Special thanks is extended to James
LaBonte of Oregon State University for help in carabid identification.
66
Chapter 3
Evaluation of Three Expulsion Chemicals for Estimating Relative Abundance of the
Earthworm: Lumbricus terrestris (Lumbricidae)
in the Maritime Pacific Northwest
Abstract
Chemical expulsion involves saturating the soil with an irritant solution causing
earthworms to leave their burrows and emerge on the soil surface where they can be
collected. In this study, formalin, xylene and ground cooking mustard were compared for
their efficacy as irritant solutions for the expulsion of Lumbricus terrestris earthworms at
three different times of the year in an unsprayed cherry orchard. The mustard treatment
extracted statistically similar numbers of L. terrestris as the formalin treatment in the fall
and winter experiments but extracted fewer worms in the spring experiment. The xylene
treatment extracted significantly fewer L. terrestris than formalin and mustard in all three
experiments.
Introduction
Earthworms are difficult organisms to quantitatively sample in agroecosystems.
Their abundance can differ greatly over a relatively small amount of area, they respond
quickly to disturbance, and their behavior changes seasonally (i.e. dormancy in summer).
This does not permit scientists to accurately estimate their abundance and biomass. Often
what results is a considerable underestimation of earthworm populations in a given
sample area.
67
There are many different types of sampling methods utilized to estimate
earthworm abundance. Some of these include: hand sorting, washing and sieving,
flotation, heat extraction, electrical extraction, mechanical vibration, and chemical
extraction. Lee (1984) provides an excellent review of the biases associated with these
sampling methods. For the purposes of this paper, only chemical extraction sampling
methods will be discussed.
Chemical extraction (expulsion) involves saturating the soil with an irritant
solution causing earthworms to leave their burrows and emerge on the soil surface where
they can be collected. The most common method used for this is the formalin expulsion
technique as described by Satchell (1971). However, the formalin expulsion technique
has some serious limitations. According to Raw (1959) the formalin expulsion technique
is ineffective at sampling earthworm species that horizontally burrow. Satchell (1969)
showed that the effectiveness of the technique was inversely related to soil temperatures.
The technique relies on the ability of the solution to infiltrate the soil profile and can be a
problem in soils with high moisture and clay contents and sites with dense vegetational
cover as documented by Barnes and Ellis (1979). Finally, but most importantly, formalin
is carcinogenic and is quite toxic to humans and will kill the earthworms unless they are
immediately washed.
There are a number of other substances being used as irritants to earthworms in
these field sampling methods. Some of these include: mercuric chloride (HgCh),
potassium permanganate (KMn04), ground cooking mustard, and mowrah meal.
According to Gunn (1992), ground cooking mustard was equally effective as formalin at
estimating the relative abundance of earthworms. Ground cooking mustard is safe to
68
handle and is relatively inexpensive and accessible. The mustard expulsion technique
used by Gunn (1992) shows promise as an alternative to formalin for sampling relative
abundance of earthworms.
In the Pacific Northwest, xylene is used in an irritant solution to expel earthworms
from the understory of hazelnut orchards to be sold in the fishing bait industry. The
orchard floors are flooded with the xylene solution and emerged earthworms are hand
collected. Xylene is highly volatile and evaporates from the surface of the earthworm
allowing it to live. Xylene might be a useful irritant to use when samples are needed in
the lab for rearing or further experimentation.
The Maritime climate of the Pacific Northwest creates an interesting environment
in which to study earthworms. The cool wet winters of the Willamette Valley of Oregon
create an ideal habitat for earthworms. Specifically, the earthworm Lumbricus terrestris
must be expelled by these irritants as it is the most common and economically important
earthworm of the Willamette Valley.
Our experiment had the following objectives: 1) To evaluate the effectiveness of
formalin, xylene, and ground cooking mustard in estimating relative abundance of the
earthworm: Lumbricus terrestris, and 2) To evaluate time of year on the performance of
the three expulsion materials.
Materials and Methods
A field study was conducted in the fall of 1996 (November 1) and repeated in the
winter (January 28) and spring (April 30) of 1997 at the Oregon State University Botany
and Plant Pathology Farm near Corvallis, OR. The site was a sweet cherry (Prunus
69
avium) orchard (c.v. 'Black Republican'). The soil at the site is classified as aNewberg
sandy loam with a pH varying from 5.8 to 6.0. The experimental design was a
randomized complete block with four replications.
Treatments consisted of the following earthworm expulsion solutions: 1) ground
cooking mustard (7.1g/L water) 2) formalin (1.7mL of 45% formalin/L water), and 3)
xylene (1 mL/L water). The sample area was defined by a metal ring 0.6 m in diameter
and 0.25 m deep. Two samples were taken per tree for a total of 0.56 m2 per tree. The
rings were placed on the soil surface and rotated until the bottom edges were firmly
embedded in the soil. Soil was pressed along the bottom outside edge to create a seal.
Any vegetation or debris found in the ring was carefully removed and 1.85 L of each
solution were poured into each ring. Ten minutes later another pour was made. L.
terrestris were collected and sorted into one of the following categories as they emerged:
1) adults, 2) large juveniles (longer than 10 cm), and 3) small juveniles (less than 10 cm).
Data were analyzed with analysis of variance procedures using the GLM procedures of
SAS.
Results
The mustard treatment extracted statistically similar numbers of L. terrestris as
the formalin treatment in the fall and winter experiments but extracted significantly fewer
worms in the spring experiment (Table 3.1?. The xylene treatment extracted significantly
fewer L. terrestris than formalin and mustard in all three experiments. All three expulsion
techniques expelled the most total worms in the fall experiment. None of the expulsion
solutions seemed to be selective for adults or small juveniles in all three experiments
70
(Data not shown). Data collected during the spring 1997 experiment had the highest mean
coefficient of variation (57.4%, 68.7%, and 88.2% for the fall, winter, and spring
experiments respectively).
Discussion and Conclusions
These results suggest that mustard may be an adequate alternative to formalin
when determining the relative abundance of the earthworm: L. terrestris in the Pacific
Northwest during the fall and winter months, but underestimates populations in the
spring. These results generally support those obtained by Gunn (1992), however, he did
not account for time of year effects. These results demonstrate that the rate of xylene used
in the expulsion technique significantly underestimates populations of L. terrestris and
may be economically limiting the yield of earthworms harvested for the fishing bait
industry in the Pacific Northwest.
71
Table 3.1. Estimation of relative abundance of the earthworm: L. terrestris in a 'Black
Republican' cherry orchard using three different chemical extraction chemicals
(mean number of earthworms per 0.56 m2).
Winter
Spring
Fall
1997
1997
1996
Small
Extraction Adult + Small Total Adult + Small Total Adult +
Lg. Juv.
Juv.
Juv.
Lg. Juv.
Juv.
Technique Lg. Juv.
7a
9.8a
19.8a
4.3a
40.8a 58.8a
10a
Mustard
18a1
±3.77
±3.22
±4.12 ±5.23
±4.26 ±6.21
±2.43
±2.452
20.8b
22.8a
51.3a
12.8a
10a
8.8b
Formalin
17.3a
34a
±5.67
±5.87
±2.31 ±4.46
±4.33
±2.12 ±5.83
±2.12
lib
0.5c
0c
0.8b
1.8b
8.5b
10.3b
0.3b
Xylene
±0.97
±0.00
±4.33 ±0.37
±1.10 ±1.90
±0.23
±2.82
1
Means within the same column followed by the same letter do not significantly differ.
(P^OS, LSD).
Standard Deviation
Note: 3.71 L of each extraction solution was poured over a 0.36 m area.
Total
11.3a
±6.43
29.6b
±8.97
0c
±0.00
72
References
Barnes, B.T. and F.B. Ellis. 1979. Effects of different methods of cultivation and direct
drilling and disposal of straw residues, on populations of earthworms. Soil Sci.
30:669-679.
Gunn, A. 1992. The use of mustard to estimate earthworm populations. Pedobiologia
36:65-67.
Lee, K.E. 1985. Earthworms: Their Ecology and Relationships with Soils and Land Use
(Academic Press) 411 pps.
Raw, F. 1959. Estimating earthworm populations by using formalin. Nature 184:
16611662.
Satchell, J.E. 1969. Methods of sampling earthworm populations. Pedobiologia 9:20-25.
Satchell, J.E. (1971) Earthworms, pp. 107-127. In Methods of Study in Quantitative Soil
Ecology: Population, Production and Energy Flow (J. Phillipson, ed.).
73
Chapter 4
Effects of Meadowfoam Meal {Limanthes alba), Hydrolyzed Corn Gluten, and
'Monida' oat (Avena sativa) on Broccoli {Brassica oleracea var. italica), Corn (Zea
mats), and Weed Growth
Abstract
Three greenhouse studies were conducted in 1996 and 1997 to evaluate the effects
of two agricultural by-products (meadowfoam meal and hydrolyzed com gluten) and
finely ground, dried oat plants (var^Monida') on the biomass accumulation of broccoli
(direct seeded and transplanted), sweet com, bamyardgrass, and pigweed. The addition of
meadowfoam meal to sterile greenhouse potting mix sign)ficantly reduced broccoli
biomass (direct seed by 34% and transplanted by 50%) when compared to controls.
Hydrolyzed com gluten sign)ficantly reduced sweet com biomass by 46% when
compared to controls. 'Monica' oat reduced the biomass of both weeds as well as broccoli
(direct seeded). Results suggest that hydrolyzed com gluten and meadowfoam meal
inhibit the biomass accumulation of bamyardgrass and pigweed.
Introduction
Certain limitations of vegetable cropping systems are resulting in research
exploring alternatives to herbicides (Phatak 1992). The main limitation to these systems
is a lack of herbicides labeled for use in certain vegetable crops. Combined with an
increasing concern for groundwater quality and dependence on off farm inputs, growers
are continually seeking to further integrate their production methods to create
74
environmentally sound and economically profitable vegetable production systems.
Certain natural plant compounds that inhibit growth and development of other plants may
provide a means of overcoming the previously mentioned production limitations.
Meadowfoam (Limnanthes alba) is an oilseed crop grown in the Willamette
Valley of Oregon for use in the manufacturing of cosmetics, lubricants, and plastics.
After processing, the remaining seedmeal is currently being disposed of in landfills.
During preliminary field trials exploring meadowfoam meal as a soil
amendment/fertilizer, observations were made documenting reduced numbers of weeds in
meadowfoam treated plots (Mallory-Smith, personal communication). Vaughn et al.
(1995) isolated and identified 3-methoxyphenyl acetonitrile, a glucosinilate compound, as
a phytotoxin from meadowfoam seedmeal.
Com gluten meal, a byproduct of the wet-milling of com (Zea mats L.), has been
documented to be an effective preemergence herbicide and fertilizer for certain
production systems (Christians 1993). Liu et al. (1994) showed enhanced herbicidal
efficacy by hydrolyzing the com gluten meal. Liu and Christians (1994) isolated 5
dipeptides from com gluten hydrolysate by conducting a petri dish bioassay to test the
root-inhibiting activity. Unruh et al. (1997), documented the exact mode of action of the
5 dipeptides isolated from com gluten meal hydrolysate as growth regulating root
inhibitors. Bingamin and Christians (1995) screened a series of 22 monocotyledonous
and dicotolydenous weeds to document the spectrum of these herbicidal effects.
Nonnecke and Christians (1993) published the first report of the successful use of com
gluten meal for weed control in a strawberry production system.
75
'Monica' oat (Avena sativa L.) is a commonly cultivated cover crop grown in the
Willamette Valley of Oregon. During initial variety screening trials, decreased abundance
of weeds were observed in 'Monica' oat plots when compared to other cultivars (Luna,
unpublished data). Nova (1995) documented a 97% reduction of shepherdspurse
(Capsella bursa-pastoris) biomass and 82% black nightshade {Solarium ptycanthuni)
biomass suppression with slight yield suppression of broccoli (Brassica oleracea var.
italica L.) when using a 'Monida' oat cover crop compared to no cover crop.
Our objectives in conducting this research were to: 1) evaluate the three
previously mentioned materials for their abilities to inhibit the biomass of redroot
pigweed {Amaranthus retroflexus L.) and bamyardgrass {Echinichloa crus-galli L.) and
2) to document their effects on two vegetable crop species, broccoli and com.
Materials and Methods
Three greenhouse studies were conducted during 1996 (spring and fall) and 1997
(winter) at Oregon State University, Corvallis, OR. Three soil amendments with known
or suspected growth inhibiting activity were evaluated for effects on biomass
accumulation of two vegetable crops and two weed species. Broccoli (c.v.= 'Gem') (30
day old transplants and direct seed), com (c.v.= 'Honey n Pearl'), bamyardgrass and
pigweed were seeded or transplanted into 16.2 cm3 pots containing commercially
purchased 2:1:1 (peat:perlite:vermiculite) sterile potting mix. Each pot was planted with
10 seeds each of com, broccoli, bamyardgrass or pigweed or 1 broccoli
transplant. The transplants received 120 ml of a liquid fertilizer (6g/L of 15-30-15) at
time of transplanting and on weekly intervals throughout the studies. All pots were
76
irrigated with capillary mat irrigation. The weed seed was hand collected at the OSU
Vegetable Research Farm near Corvallis, OR in the late summer of 1995. At 2 weeks
after planting, all experimental units (except broccoli transplants) were thinned to 3
plants per pot.
Treatments of organic soil amendments were the following: (1) meadowfoam
meal 8 g/pot (8.96 Mg/ha"1), (2) com gluten hydrolysate 1 g/pot (0.9 Mg/ha'1), and (3)
finely ground (1 cm sieve) cover crop of'Monida' Oat 2 g/pot (2.24 Mg/ha'1). The source
of the meadowfoam meal was from Antler Bros., Inc., Tempe, AZ meadowfoam
processing plant. The hydrolyzed com gluten was purchased at a home/garden store
under the tradename Amaizing Lawn™. The source of the cover crop was a collection
from 1994-95 on-farm research trials that had been dried, ground, and archived at OSU in
Corvallis, OR. An additional treatment of no soil amendment served as a control.
Each amendment treatment was applied in two ways: (1) incorporated into the
potting mix and (2) surface-applied. All treatments were replicated 5 times except for the
transplanted broccoli which had 8 replicates. The experimental design was a randomized
block, factorial design for each crop and weed species in the trial.
Greenhouse conditions consisted of ambient sunlight (Spring 1996) with a
photoperiod of approximately 10 hours. Greenhouse conditions (Fall 1996 and Winter
1997) consisted of supplemental lighting at a photointensity of 6.54 Kj/hr in addition to
ambient sunlight with a photoperiod of approximately 8.5 hours. Temperature was
maintained at approximately 25 j C during all three studies.
At week 4 of the study, dry biomass of weeds, com, and broccoli was determined
by clipping above-ground portions of plants and drying at 50j C for 48 hours. Data were
77
analyzed using the SAS software package (SAS, 1990). Plant biomass data was analyzed
by analysis of variance procedures. Means were separated by using the least mean
squares procedure. The data were interpreted in the following manner as suggested by
Ramsey and Schafer (1997): < 0.01 highly significant difference; < 0.05 significant;
< 0.15 suggestive but inconclusive.
Results and Discussion
Analysis of variance for amendment type and application method of the
individual plant species revealed a lack of statistically significant interaction for most
plant species in most of the three experiments. Visual examination of the plotted data also
indicated a similar lack of application method effect or interaction with amendment type.
Therefore data were pooled across the application method factor but will be discussed
separately where appropriate.
Barnyardgrass Both meadowfoam meal and hydrolyzed com gluten reduced the
biomass of barnyardgrass compared to the control in the first two experiments we
conducted (Table 4.1). However, in experiment 3 meadowfoam meal, com gluten, and
'Monida' oat stimulated the growth of barnyardgrass (P=.04, .0001, and .02 for
meadowfoam, com gluten, and 'Monida' oat respectively). Bingaman and Christians
(1995) reported similar results to experiments 1 and 2 with hydrolyzed com gluten with a
55% reduction of barnyardgrass biomass.
We believe there are two possible reasons for the differing results we obtained
among the experiments. First, the greenhouse lighting system used in this trial was
renovated between conducting experiments 2 and 3, producting a much higher
78
Table 4.1. Mean dry biomass barnyardgrass (Echinichloa cnis-gali), redroot pigweed
(Amaranthus retroflexus), sweet com (Zea mais), or broccoli (Brassica
oleracea var. italica) (direct seed and transplanted) grown for four weeks in
sterile potting mix amended with either meadowfoam meal, hydrolyzed com
gluten, or finely ground oat (var.= 'Monida') residue.
Barnyardgrass
Meadowfoam
Com gluten
'Monida' Oat
Control
Pigweed
Meadowfoam
Com gluten
'Monida' Oat
Control
Sweet Corn
Meadowfoam
Com gluten
'Monida' Oat
Control
Broccoli (direct seed)
Meadowfoam
Com gluten
'Monida' Oat
Control
Broccoli (transplant)
Meadowfoam
Com gluten
'Monida' Oat
Control
Experiment 1
es1 m1
31
58
.004
.01
no
60
26
84
133
.0009
.0001
.14
Experiment 2
8 .07
6 .05
12 .12
24
"3—3"
Experiment 3
83 .04
15 .0001
99 .02
67
33 .67
45 .18
11 .001
36
4
4
63 .04
64 .04
180 .01
120
10 .04
5 .002
11 .06
20
99 .02
190 .04
160 .37
150
14 .0001
37 .14
24 .002
49
55 .0001
23 .01
15 .67
17
31 .001
125 .0001
59 .77
62
17 .01
24 .17
37 .34
39
41 .0006
64 .34
72 1.00
72
P-value associated with comparing treatment mean with the appropriate control mean
using the least squares means procedure (SAS).
Data were not collected due to a lack of pigweed germination.
Data are not included because of excessive variability between application methods
within the control treatment.
79
photointensity in experiment 3 than experiments 1 and 2. This could have caused the
barnyardgrass to outgrow the suppression effect in the time allotted for the experiment.
Second, the control pots of barnyardgrass in experiment 3 were infested with a complex
of saprophytic fungi that, although not plant parasitic, could have caused reductions in
biomass of the control treatments of barnyardgrass.
Pigweed In experiment 1, both meadowfoam meal and com gluten sign)ficantly
reduced pigweed growth, however this effect was not observed in experiment 3 (P=.67
and .18). No data were collected in experiment 2 because pigweed seed did not
germinate. 'Monida' oat significantly reduced pigweed growth in experiment 3, however
effects were influenced by application method in experiment 1. Surface application
significantly reduced pigweed growth (P= 008) compared to the control, but no effect
was detected for the incorporated soil amendment (P=.52). The lack of a com gluten
effect in experiment 3 contradicts results obtained by Bingaman and Christians (1995)
where they report greater than 75% suppression of pigweed growth and root development
with hydrolyzed com gluten.
Sweet Corn Both meadowfoam meal and com gluten sign)ficantly reduced com
growth in both experiments (Table 4.1). 'Monida' oat stimulated com growth in
experiment 1 (P=.01) and suppressed com growth in experiment 2 (P=.06). The
stimulation effect observed in experiment 1 could be the result of a fertilizer effect.
Results from cover crop experiments at Oregon State University have determined
'Monica' oat plant material to contain approximately 0.85% nitrogen (tuna 1997,
unpublished data).
80
Broccoli (direct seeded) As in the previous sweet corn discussion, data obtained
from experiment 2 will not be included in the discussion for direct-seeded broccoli
because of excessive variability associated with the control treatments. Broccoli biomass
was significantly reduced by the addition of meadowfoam meal (P=.02 and .0001 for
experiments 1 and 3 respectively) but a significant stimulation response was observed
with com gluten (P=.04 and .01 for experiments 1 and 3 respectively). The method of
application influenced the effect of com gluten on broccoli growth, with incorporation
causing a significant stimulation of growth (P=.004) whereas there was no effect from
applying the amendment on the surface (P=.95). One possible explanation for the
stimulation of broccoli growth by com gluten may be from a fertilizer effect, since no
effect was observed for surface applied com gluten in experiment 1. Com gluten is 10%
nitrogen by weight (Christians 1993). The addition of'Monica' oat did not effect the
growth of direct seeded broccoli (P= 37 and .67 for experiments 1 and 3 respectively).
Broccoli (transplanted) Meadowfoam meal suppressed broccoli transplant
growth in all three experiments (P= .001, .01, and .0006 for experiments 1, 2, and 3
respectively). Com gluten stimulated broccoli growth in experiment 1 (P=.0001) and no
effect in experiments 2 (P=.17) and 3 (P= 34). "Monida1 oat had no detectable effect on
broccoli transplant growth in all three experiments (P= .77, .34, and 1.00 for experiments
1, 2, and 3 respectively).
In summary, meadowfoam meal appears to be phytotoxic to all the plant species
tested. Com gluten and 'Monida' oat provided mixed results, stimulating plant growth.
We believe these mixed results may be explained by the nitrogen contribution from these
plant materials. The growth-suppressive effects of'Monida' oat agree with data of Nova
81
(1995) who studied the response of weeds and broccoli to the presence of a "Monida1 oat
cover crop residue. He demonstrated a significant reduction in fresh weight yield of
broccoli grown in 'Monida' oat cover cropped plots when compared to yields obtained in
a fallow control plot. In the work reported here, conclusions drawn from experiment 3 on
all amendments must take into account the presence of the confounding variables
mentioned previously (photointensity and fungal infestations). Experimental trends
indicate that incorporating the amendment increased the suppression of the crop or weed
in some instances. By incorporating the amendment more surface area is present for the
roots of the growing plant to intercept it and heighten the allelopathic effect.
Consequently, decisions on whether to incorporate the amendment must be based on
specific site and situation requirements. Since all plants in the studies reported in this
paper were sub-surface (capillary mat) irrigated, further experimentation in the field will
need to examine the effect of overhead irrigation on the effectiveness of these
amendments.
82
References
Bingaman, B.R. andN.E. Christians. 1995. Grreenhouse screening of com gluten mean as
a natural weed control product for broadleaf and grass weeds. HortScience 30:12561259.
Christians, N.E. 1993. The use of com gluten meal as a natural preemergence weed
control in turf. In R.C. Carrow et al. (ed.) Int. Turfgrass Soc. Res. J. 7:284-290.
Christians, N.E. 1993. A natural product for the control of annual weeds. Golf Course
Mgmt. 16:72-76.
Liu, D.L. andN.E. Christians. 1994. Isolation and identification of root-inhibiting
compounds from com gluten hydrosylate. J. Plant Growth Regul. 13:227-230.
Liu, D.L., N.E. Christians, and J.T. Garbutt. 1994. Herbicidal activity of hydrolyzed com
gluten meal on three grass species under controlled environments. J. Plant Growth
Regul., 13:221-226.
Nonnecke, G.R. and N.E. Christians. 1993. Evaluation of com gluten meal as a natural
weed control product in strawberry. ActaHortic. 348:315-320.
Nova, S. 1995. Impact of cover crops on weed abundance and nitrogen contribution in
broccoli, Brassica oleracea var. italica, production systems in the maritime pacific
northwest. M.S. Thesis, Department of Horticulture, Oregon State University,
Corvallis, OR. 97pps.
Phatak, S.C. 1992. An integrated sustainable vegetable production system. HortScience
27:738-741.
Ramsey, F.L. and D.W. Schafer. 1997. Interpretation of P-values. pps44-45 In. The
Statistical Sleuth: A Course in Methods of Data Analysis. Duxberry Press, Boston,
MA.
SAS. 1990. User's Guide: Statistics. SAS Institute Inc. Gary, NC.
Unruh, J.B., N.E. Christians, and H.T. Homer. 1997. Herbicidal effects of the dipeptide
alaninyl-alanine on perennial ryegrass (Lolium perenne L.) seedlings. Crop Sci.
37:208-212.
Vaughn, S.F., R.A. Boydston, and CM. Smith. 1995. Isolation and identification of (3methoxyphenyl) acetonitrile as a phytotoxin from meadowfoam (Limanthes alba)
seedmeal. J. Plant Growth Regul. 13:45-58.
83
Chapter 5
Conclusions
Strip-tillage and fall sown annual cover crops were evaluated in two separate field
experiments for their ability to produce economically competitive broccoli yields as well
as enhance biological resource conservation. The first experiment was conducted during
1996-97 at the OSU Vegetable Research Farm near Corvallis, Ore. 'Monida' oat (Avena
sativd) and 'Dacold' rye (Secale cereale) were fall sown in combination with common
vetch (Vicia sativd), dessicated with either pre-flail glyphosate or flail mowed alone, and
incorporated via either strip or moldboard plow based tillage in a split-split block in
randomized complete block experiment with three replications. Each management tactic
previously described created a unique set of consequences in which few broad
generalizations can be made. Plots under strip-tillage management had significantly
reduced amounts of total weed density and biomass. Plots under strip-tillage
management had significantly higher soil temperatures. 'Dacold' rye and vetch plots in
combination with pre-flail glyphosate and strip tillage had the highest broccoli yield.
Those plots were determined to have the highest early season soil nitrate contents but also
the highest total weed biomass. Overall, a management scenario was identified that
could provide economically competitive broccoli yields as well as minimize
environmental impact. Future research will focus on strip-tiller modifications for better
seedbed preparation along with more precise timing of cover crop management tactics to
manage spring biomass.
84
A second experiment was conducted during 1995-96 at Crestview Farms near
Mollala, OR.. The experimental design was a randomized complete block with 3
replications. After the fall sown (1995) cover crop mixture of 60% (by weight) 'Steptoe'
barley / 40% (by weight) common vetch was chemically suppressed, strip-tillage and
conventional (disc/harrow) tillage were conducted in appropriate areas of field plots in
early spring. Thirty day old broccoli transplants (c.v.='Packman') were commercially
transplanted.
Broccoli performance was evaluated based on: 1) head diameter at 42 days after
planting (DAP), 2) above ground dry weight biomass of broccoli plants at 42 DAP, and
3) broccoli yield. No significant treatment differences between strip and conventional
tillage were detected among the three sets of broccoli performance data. Yield was
reduced in both treatments by approximately 50% due to poor cover crop establishment
(excessive rains), subsequent erosion, and erratic temperature fluctuations during the
spring of 1996.
Biological resource conservation associated with the treatments was evaluated by
monitoring activities of ground dwelling arthropods and earthworms. No significant
treatment differences between strip and conventional tillage were detected in the
arthropod data. The sampling period (2 weeks) was too short to justify any conclusions.
No earthworms were detected in Conventional plots on either of our sampling dates.
Relative earthworm abundance was significantly higher in strip-tilled plots (P=.04). The
reduction in tillage associated with the strip-tillage plots demonstrates potential savings
in time, labor, and machinery costs.
85
Chemical expulsion involves saturating the soil with an irritant solution causing
earthworms to leave their burrows and emerge on the soil surface where they can be
collected. In this study, formalin, xylene and ground cooking mustard were compared for
their efficacy as irritant solutions for the expulsion ofLumbricus terrestris earthworms at
three different times of the year in an unsprayed cherry orchard. The mustard treatment
extracted statistically similar numbers of L. terrestris as the formalin treatment in the fall
and winter experiments but extracted fewer worms in the spring experiment. The xylene
treatment extracted significantly fewer L. terrestris than formalin and mustard in all three
experiments.
Three greenhouse studies were conducted in 1996 and 1997 to evaluate the effects
of two agricultural by-products meadowfoam meal and hydrolyzed com gluten) and
finely ground, dried oat plants (var^'Monida1) on the biomass accumulation of broccoli
(direct seeded and transplanted), sweet com, bamyardgrass, and pigweed. The addition of
meadowfoam meal to sterile greenhouse potting mix significantly reduced broccoli
biomass (direct seed by 34% and transplanted by 50%) when compared to controls.
Hydrolyzed com gluten significantly reduced sweet com biomass by 46% when
compared to controls. 'Monica' oat reduced the biomass of both weeds as well as broccoli
(direct seeded). Results suggest that hydrolyzed com gluten and meadowfoam meal
inhibit the biomass accumulation of bamyardgrass and pigweed.
86
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