Development and Evaluation of Conservation Tillage for Squash in Western
Oregon
by
Brandon M. Reich
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Bachelor of Science
Presented June 10, 1996
Commencement December 1996
ABSTRACT
Squash varieties of Golden Delicious and Squash Hybrid NK 530 were
grown in disk-till, strip-till, and no-till conservation tillage systems following a cover
crop of'Monida' oats (Avena sativa L.) and common vetch (Vicia sativa L.). Tillage
systems were evaluated for effects on squash emergence and yield, weed density
and biomass, and the time it took to hand hoe the growing area.
Squash
emergence was similar among treatments and squash yield was similar between
strip-till and disk-till systems.
However, propane flaming appeared to increase
squash emergence in strip-till treatments and reduce emergence in no-till
treatments. Weed abundance was lower in strip-till and no-till treatments where a
cover crop mulch remained on the soil surface than in disk-till treatments where
the soil was less covered. Weed biomass in no-till treatments, where a cover crop
mulch lay on the surface, was reduced for up to six weeks after squash planting.
However, once the mulch broke down, weeds became abundant and no-till plots
were abandoned one month prior to harvest because of concerns over
contamination of weed seeds into the soil. This one year study suggests that
squash grown in a strip-till conservation tillage system with a cover crop has
adequate weed control and equivalent yields with a disk-till system and that
squash grown in a no-till system has similar emergence and inadequate weed
control at this amount of mulch.
TABLE OF CONTENTS
Page
INTRODUCTION ........................................................................................................1
Benefits and Challenges .................................................................................2
Vegetable Crop Establishment and Yields .....................................................6
Objectives of this Research ............................................................................7
MATERIALS AND METHODS ...................................................................................8
Cover Crop Management and Soil Preparation ..............................................9
Planting ........................................................................................................... 9
Weed Management .......................................................................................10
Squash Harvest ..............................................................................................10
Sampling ........................................................................................................10
Data Analysis .................................................................................................11
RESULTS AND DISCUSSION .................................................................................12
CONCLUSIONS ........................................................................................................14
BIBLIOGRAPHY .......................................................................................................16
LIST OF FIGURES
Page
Figure
1
Percent squash emergence by treatment ...................................................20
2
Weed abundance in-rows ...........................................................................21
3
Between-row weed abundance (by species) .............................................. 22
4
In-row weed abundance (by species) ......................................................... 23
LIST OF TABLES
Table
Page
1
Effects of tillage treatment on weed abundance and biomass ................ 24
2
Effects of tillage on the time it took to hoe the squash growing area ...... 25
INTRODUCTION
World wide, 8.5 million ha of agricultural land are lost to erosion every year
(Oregonian, 1996).
A 1982 National Resources Inventory estimated that
croplands in the United States lose to erosion an average of 16.4 Mg/ha at a cost,
estimated by the Conservation Foundation, of $2.2 billion (Brady, 1990). Growers
and researchers in Oregon have developed soil erosion management plans in the
past and continue to develop management strategies, including whole-farm
strategies and management practices for vegetables. One of the most common
and widely developed practices developed to reduce soil erosion is conservation
tillage.
Conservation tillage has been defined as any set of soil management
practices that leaves at least 30% of the available residue on the surface (Dickey
et al., 1992; Pierce, 1985; Reeder, 1992). Originally, researchers thought that this
was a minimum amount of residue that would protect the soil from erosion. Tillage
systems that meet the 30% criteria include: disk-till, strip-till, ridge-till, and no-till
systems.
As researchers, growers, and others began evaluating other factors
contributing to erosion (such as soil compaction) the definition changed.
Conservation tillage systems are defined now by the unique sets of benefits and
challenges these systems share in common (Cook and Robertson, 1979; Dickey,
1992; Reeder, 1992). Conservation tillage systems are generally associated with
increased water holding capacity of the soil, improved soil structure, reduced soil
2
erosion, increased amounts of organic matter, and greater densities of soil
arthropods. However, a number of challenges toward adoption of conservation
tillage systems have been identified. Cook and Robertson (1979) identified that
conservation tillage systems must be created specific to an area's soil types,
weather patterns, and equipment availability. A survey in Tillage for the Times
identified growers' major concerns about the adoption of conservation tillage
practices: 48% of growers were concerned about inadequate weed control, 21%
identified yield reductions as a major concern, and 15% expressed concerns about
managing excessive crop residue. Similarly, Nowak (1983) argues that growers'
concerns are the major obstacle to adoption.
Benefits and Challenges
Conservation tillage systems usually include a cover crop that is planted the
fall before spring planting of the main crop. Frequently used cover crops include
cereal grains, legumes, and cereal/legume mixtures. Often it is not harvested and,
instead, is allowed to remain on the surface as a mulch or partially incorporated
into the soil.
Growing a cover crop and allowing it to remain on the surface as a mulch
increases the water available to the main crop. The mulch acts as a barrier to
water evaporating from the soil (Blevins, 1983; Koskinen and McWhorten, 1986).
The mulch also reduces the severity of runoff events. For example, Jones et al.
(1969) measured the amount of water leaving areas of soil with and without a
3
mulch as a percent of the precipitation.
He determined that 27% of the
precipitation onto soil without a mulch became runoff water, while only 5% of the
rainfall onto soil with a mulch became runoff water. Finally, improved soil structure
increases the amount of water in the soil. The mulch influences soil compaction
by protecting the soil from the impact of rainfall that can lead to compaction
(Triplett et al., 1968). Under a mulch, soil is often found with a greater number of
micropores, small airspaces that hold most of the soil's water (Froud-Williams et
al., 1981). Blevins et al. (1971) grew corn in conventional tillage and no tillage
systems and found soil moisture higher in the no tillage system, with effects most
profound in the top 0-8 cm of soil. Jones et al. (1969) determined the soil moisture
increased under a mulch to 30 cm compared to soil without a mulch. Conserving
moisture in the soil for the main crop can be a major factor in increasing yields,
especially in areas where crops are not irrigated (Triplett et al., 1968).
Conservation tillage practices also reduce soil erosion.
Koskinen and
McWhorten (1986) determined that applying as little as one ton of wheat straw
reduces soil losses to water runoff to nearly zero. They attributed this reduction in
soil loss to (1) the mulch reducing the severity of rainfall impact, thus improving
water infiltration; and (2) the mulch slowing water runoff and retaining soil particles
from the water. They observed this benefits of a mulch on reduced soil erosion at
rates as little as 0.7 Mg/ha and 1.4 Mg/ha (1/4 tons/ac and 1/2 tons/ac). Even at
the lowest mulch rate of 0.7 Mg/ha, they observed a 75% reduction in soil loss
compared to the soil loss on soil without a mulch.
4
Increased amounts of organic matter are also associated with conservation
tillage systems. Blevins et al. (1983) determined that in corn grown in different
tillage systems for ten years, there was twice as much organic matter in the first 5
cm of the no-till treatment compared with the conventional tillage treatment.
Haines and Uren (1990) similarly found more organic matter near the surface of
direct drilled systems than conventionally cultivated systems.
Koskinen and
McWhorten (1986) attribute increases of organic matter in reduced tillage systems
to both the addition of plant biomass and to organic matter not being lost through
erosion. Plant material can be introduced in conservation tillage systems through
incorporating or disking the cover crop or crop stubble.
Increased amounts organic matter, improved soil structure, and reduced
soil disturbance creates beneficial habitat for microorganisms, bacteria, and
earthworms. Haines and Uren (1990) found greater earthworm densities, more
than twice as many in the top 10 cm, in direct drill systems compared to
conventionally cultivated systems. However, the high moisture content of soils in
conservation tillage systems, along with high amounts of organic matter levels,
may create anaerobic conditions where bacteria can cause denitrification (Blevins,
1983; Doran, 1980). This effect may be, however, offset by nitrogen contribution
from incorporated legume cover crops.
When cover crops are incorporated into the soil, they break down in the
soil, can contribute nutrients, including nitrogen, to growing main crops.
By
comparing the yields of corn grown with fertilizer and cover crops, Mitchell and
Teel (1977) estimated the nitrogen contribution of the incorporated cover crop to
5
the main crop. They estimated that a cover crop of oats or rye contributes 55 kg
N/ha to corn in a no-till system; a cover crop of hairy vetch or crimson clover
contributes 112 kg N/ha; and a combination of grain and legume contributes 180
kg N/ha. Similarly, Wagger (1989) estimated the nitrogen contribution to corn in a
no-till system of a rye cover crop at 25 kg N/ha and a legume cover crop of
crimson clover and hairy vetch at an average of 40-45 kg N/ha. He estimated that
36% of the nitrogen in the crimson clover and 30% of the nitrogen in the hairy
vetch cover crop was returned to the corn crop. Nova (1995) estimated that cover
crops of legume and mixtures of legumes and grains contributed 90 kg N/ha
equivalent to broccoli in a disk-till system.
Conservation tillage systems reduce weed abundance in a number of ways:
through allelopathic cover crops, through shading weed seeds under a mulch, and
through non-disturbance of weed seeds in soil.
Research has identified
allelopathic chemicals from cover crops that inhibit germination of seeds, thus
reducing weed densities (Putnam et at., 1983).
Mohler and Calloway (1992)
identified reduced weed seed disturbance in the soil as the reason that lower
densities of weeds were found in no-till treatments than in conventional tillage
treatments. They also identified the presence of a mulch on the soil surface as a
factor further reducing weed densities. Studies have shown that a mulch reduces
weed germination by reducing sunlight infiltration through the mulch and by
physically blocking seedling emergence (Teasdale et al., 1991; Teasdale, 1993).
They determined that soil covered with a much on 42% of its surface will have
lower weed density.
6
However, because seeds are not disturbed and stimulated to germinate, the
seeds remain in the soil (Forcella and Lindstrom, 1988; Froud-Williams et al.,
1983).
On the other hand, high water content of soils in conservation tillage
systems with a mulch, have been found to stimulate weed seeds (Buhler and
Mester, 1991).
A number of researchers have identified the weed species
composition in conservation tillage systems, especially no-till systems and systems
with a mulch, to shift from summer annuals and broadleaves to winter annuals and
perennials (Blackshaw et al., 1994; Buhler et al., 1994; Cussan, 1975; Mohler and
Calloway, 1992; Teasdale et al., 1991; Wrucke and Arnold, 1985). Shifts toward
winter annuals may occur because winter annuals grow better than summer
annuals in the cooler, moister soils often found in conservation tillage systems,
especially under a mulch. Also, winter annuals may be able to better compete in
low light conditions under a mulch. Shifts towards perennials may occur because
of reduced cultivation that would control perennials. A number of researchers
have identified the need for herbicides in conservation tillage systems, especially
no tillage systems, to control weeds (Cussan, 1985; Koskinen and McWhorten,
1986; Triplett and VanDoren, 1974).
Vegetable Crop Establishment and Yield
The main factors affecting crop establishment in conservation tillage
systems, especially no-till systems, are increased water content and reduced
temperatures in the soil under a mulch (Knavel et al., 1977; Weston, 1990). Large
seed size and rapid germination are two factors that may predict success of crop
7
establishment (Weston, 1990). Lima beans and squash have been established
successfully in no-till systems (Beste, 1973; Mullins et al., 1980; NeSmith et al,
1994). Some studies have found that cucumber (Knavel et al., 1977) and snap
beans (Mullens et al., 1988) establish poorly. However, most studies have found
that tomatoes, peppers, cucumber and snap beans establish as well or better in
no-till systems than in conventional tillage systems (Beste, 1973; Knavel et al.,
1977; Morse and Seward, 1986; Mullins et al., 1980; NeSmith et al, 1994; Weston
et al., 1990).
Vegetable crops with good stands grown in a no-till system that includes a
pre-plant or a pre-emergence herbicide, generally have as good or better yields
than conventional tillage systems (Abdul-Baki, 1993; Bellinder et al., 1984;
Bennett, 1975; Beste et al, 1973; Loy et al., 1987; Masiunas et al., 1995; Morse
and Seward, 1986; Mullins et al., 1980; NeSmith et al., 1994; Skarphol et al.,
1987). Wilhoit et al. (1990) determined that cabbage grown in a strip-till system
had greater yields than no-till or conventionally tilled systems. Some researchers
identified poor weed control as the main factor contributing to reduced yields in no-
till systems, even when an herbicide was used (Knavel et al., 1977; Knavel and
Herron, 1981; Loy et al., 1987; Mullins et al., 1988).
Objectives of This Research
The following research project was conducted to assess effects, if any, of
disk-, strip-, and no-till systems on squash production in western Oregon. The
8
effects of tillage systems on squash stand and yield, weed density and biomass,
and hoeing times were evaluated.
MATERIALS AND METHODS
A cover crop of 'Monida' oats (Avena sativa L.) at 56 kg/ha and common
vetch (Vicia sativa L.) at 50 kg/ha was seeded on 24 October 1994 in a 0.4 ha plot
at the Oregon State University Vegetable Research Farm, near Corvallis, Oregon.
Seed was drilled in 15 cm row spacing using a Nordsten® grain drill. 'Monida' oats
was chosen because of apparent weed suppression qualities reported by Nova
(1995). Common vetch was selected for the mixture because it is a nitrogen-fixing
legume and was expected to contribute nitrogen to the squash.
A split-plot, randomized complete block experiment was established in the
spring of 1995, with three tillage systems, disk-till, strip-till, and no-till. Treatments
plot size was 12 m by 15 m and four rows of squash were planted in each plot on
1.5 m centers.
Each main treatment tillage plot of four rows of squash was divided into:
two squash rows with weed control (flaming, cultivating, and hoeing) and two
squash rows with no weed control. Each two row weed control subplot measured
6 m by 15 m. Between blocks, in 7 m strips, buckwheat was seeded at 56 kg/ha to
maintain soil cover and to suppress weeds during the growing season.
9
Cover Crop Management and Soil Preparation
In the disk-till treatments, the cover crop was flailed on 17 May 1995. On
18 May 1995 plots were disked twice and field harrowed twice with a Lely Roterra®
power harrow.
Five days before planting (1 June 1995) plots were again field
harrowed once.
In the strip-till treatments, 56 cm wide strips in the cover crop were mowed
using a rotary lawn mower on 28 April 1995. Two weeks before planting (21 May
1995) mowed strips were tilled three times at an 8 cm depth with a rototiller. Plots
were tilled again one week before planting (1 June 1995) using a tractor-mounted
rotovator. Three days after planting (9 June 1995) cover crop regrowth was killed
with glyphosate at 3.6 kg a.i./ha.
In the no-till treatments, the cover crop was killed with glyphosate at 3.6 kg
a.i./ha one month before planting (3 May 1995). No additional soil preparation
occurred.
Planting
A mixture of Golden Delicious and Hybrid NK 530 Squash (50:50 by
volume) was planted 6 June 1995 at 6 seeds/row m on 1.5 m centers. A modified
no-till "slot planter" was used to plant all plots and liquid fertilizer was banded at the
time of planting at the rates of 56 kg/ha (N) and 191 kg/ha (P). Additional nitrogen
fertilizer (70 kg/ha) was surface applied five weeks after planting (14 July 1995).
10
Weed Management
The squash rows in the weed control plots were flamed ten days after
squash planting (but prior to squash emergence) with a propane hand torch
delivering 2 kg/cm2 (30 p.s.i.) of propane and the operator walking approximately 5
km/hr.
Disk-till and strip-till treatments were cultivated five weeks after planting
with a tractor mounted sweep cultivator. Strip-till treatments were only cultivated in
the mowed strips. Disk-till and strip-till treatments were hand-hoed on 13 July, 23
July and 8 August 1995. The time it took to hand hoe each of the 29 m2 squash
growing areas was timed with a stop watch and averaged over treatments
Squash Harvest
A harvest area of 29 m2 in the weed control subplots, were hand harvested
on 10 and 11 October 1995. Entire plots were weighed on truck scales accurate to
9 kg. No-till treatments were flailed on 14 August 1995 to minimize weed seed
production and contamination of the research plots and, therefore, were not
harvested.
Sampling
Cover crop biomass was estimated by collecting and sorting all above
ground material in four 0.25 m2 quadrats in each plot (3 May 1995). Oats, vetch,
and weeds were sorted and placed in paper bags. Samples were dried at 49 °C
for 83 hrs and dry weights determined. The percent cover of the soil by cover crop
was estimated by recording the presence of residue at 30 cm intervals along a
11
diagonal across the middle of each plot. Percent soil cover was estimated in the
disk-till plots on 19 June 1995 and in the strip-till and no-till plots on 12 July 1995.
Squash seedlings was estimated for each tillage treatment plot one month
(4 July 1995) after planting and compared to the number of seeds planted to
estimate percent seedling emergence.
Rows that had been flamed for weed
control were compared with rows that were not flamed to estimate any effects of
flaming on squash emergence
Four weeks after planting (5 July 1995) weed density was estimated in all
treatment plots.
Within each treatment, two 0.25 m2 quadrat samples were
randomly taken between rows of squash, from inside the rows of squash in weed
control subplots, and from inside the rows of squash in the no-weed control
subplots. Weeds were identified and counted. Rows that had been flamed for
weed control were compared with rows that were not flamed to evaluate any
effects of flaming on weed density. One week later (12 July 1995), samples from
four 0.25 m2 quadrats were taken from the rows of squash in weed control
subplots were clipped and dried at 67 °C until dry and dry weight determined.
Data Analysis
All weed abundance data were square root transformed for analysis and
means LSD separated. Other data not transformed and means LSD separated.
I
considered p-values up to p = .21 significant enough to report because I was
willing to risk a Type II error in order to separate differences between means that
are large enough to be significant to growers, but not scientifically significant.
12
RESULTS AND DISCUSSION
Cover crop biomass was, on 3 May 1995, was: 'Monida' oats, 2,355 kg/ha;
common vetch, 2,341 kg/ha; and weeds, 283 kg/ha. Weeds were less than 6% of
the total biomass. The cover crop was approximately 60 cm high at this time.
Prior to planting, percent soil covered by cover crop residue was: disk-till, 63%;
strip-till, 95%; no-till, 89%. Cover crop growth occurs rapidly in the spring and
because the no-till treatments were killed early, they had less biomass covering the
soil at planting time. This difference was evident at approximately six weeks after
planting when the cover crop cover began to decay, whereas the cover crop on the
strip-till treatments still remained intact.
Pre-emergence flaming caused an apparent increase in squash emergence
in strip-till treatments (p = .04) and an apparent decrease in no-till treatments (p =
.15) (Figure 1). This was an unanticipated effect and further research is needed to
determine whether flaming squash rows affects emergence differently among
tillage treatments. There was no significant difference in wet weight harvest yields
between treatments:
disk-till, 28 tons/ac; strip-till, 31 tons/ac.
Both yields are
comparable to typical commercial squash yields in western Oregon.
Both no-till and strip-till treatments, with the mulch residue on the soil
surface, had fewer weeds between squash rows than the disk-till treatment (p =
.11) (Table 1). Weed density between rows was greater in the disk-till treatments
than in strip-till and no-till treatments for the four most abundant weed species
13
sampled: common groundsel (Senecio vulgaris L.), common purslane (Portulaca
oleracea L.), hairy nightshade (Solanum sarrachoides Sendtner), and redroot
pigweed (Amaranthus retroflexus L.) (Figure 3). No hairy nightshade was found in
either strip-till or no-till treatments; no common purslane was found in strip-till
treatments; and no redroot pigweed was found in no-till treatments.
Within squash rows, there was a significant interaction between treatment
and weed control effects (p = .01). Strip-till plots had fewer weeds (p = .06) when
flamed than when non-flamed (Figure 2). When strip-till treatments were tilled, the
soil was wet and tillage was difficult; the soil formed large clods that were not
consistent with other treatments.
Perhaps, because the soil was open and
exposed, weed seedlings were exposed to the flaming and weed densities were
lower in flamed strip-till than in non-flamed strip-till treatments. Further research
may determine whether this interaction is a result of the disk-till treatment
responding differently to flaming than other treatments. Within rows, weed density
by species responded differently depending on whether the rows were flamed
(Figure 4).
Common groundsel and common purslane responded similarly to
tillage and flaming treatments.
Hairy nightshade was generally unaffected by
tillage or flaming treatments, expect in no-till treatments where flaming increased
seeding abundance.
Redroot pigweed had low abundance in all tillage and
flaming treatments.
Dry weight biomass of weeds in-row at six weeks after planting differed
among treatments (p = .09).
Less biomass was found in the no-till treatment,
which had a mulch residue around the rows of squash (Table 1). This result is
14
consistent with Mohler (1991) who found a reduction of weed biomass with a rye
cover crop.
Strip-till treatments required less time to hoe (140 person hours/ha) than the
disk-till treatments (199 person hours/ha) (p = .21). Because different teams hoed
different treatments at different dates,
it
is difficult to accurately attribute
differences in hoeing times to tillage treatments. However, a difference of nearly
50 people hours/ha is an important economic difference and it is demonstrated
throughout the season (Table 2).
CONCLUSIONS
Tillage did not have an effect on emergence of squash seedlings; however,
flaming did effect emergence in strip-till and no-till treatments. The tillage system
did not affect crop yields; yields of both disk-till and strip-till were similar to and
consistent with growers' yields of squash in western Oregon.
The mulch residue in the strip-till and no-till treatments reduced weed
density for approximately four weeks compared with the disk-till.
The mulch
residue in the no-till treatment reduced weed biomass, compared to disk-till and
strip-till treatments for approximately six weeks. This time period for weed control
is consistent with the research of Putnam et al (1983) who recorded adequate
weed control under a mulch for four to six weeks. Further research is needed to
evaluate the effects of flaming within different tillage treatments on weed density.
15
Results of this one year study indicate that a grower could expect weed
control from a mulch residue for four to six weeks and expect yields from both the
strip-till and disk-till system to be consistent with commercial squash yields in
western Oregon.
16
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Pumpkin emergence
flame
no-flame
a
70
b
40
disk-till
strip-till
no-till
tillage treatment
Figure 1. Percent squash emergence by treatment, sampled 4 July 1995. Data
analyzed as percent of squash seeds planted and means LSD seperated.
Letters above bars indicate significant differences between means (within a tillage
treatment): disk-till flame v no flame, p =.55; strip-till flame v no flame, p =.04;
no-till flame v no flame, p =.15.
Weed abundance in-rows
300
a
flame
250
® no-flame
200
150
b
b
a
100
50
0
disk-till
strip-till
no-till
tillage treatment
Figure 2. Weed abundance in-rows, two samples, four replicates per mean,
sampled 5 July 1995. Data square root transformed and means LSD seperated.
Letters above bars indicate significant differences between means (within a tillage
treatment): disk-till flame v no flame, p =.01; strip till flame v no flame, p =.01;
no-till flame v no flame, p =.03.
22
Total weed densities between rows
40
purslane
35
® niteshade
o pigweed
30
® groundsel
25
zero counts
20
15
10
5
0
disk-till
strip-till
no-till
tillage treatment
Figure 3. Between-row weed abundance (by species), two samples, four
replicates, sampled 5 July 1995.
2
Pigweed
Pursiane
20
20
flame
b
18
flame
® no-flame
D = .16
N 16
E
® no-flame
E15
014
m
CL
CL
0> 12
c
010
m
0
I-
8
d
.0
E6
c
4
b
2
0
0
disk-till
strip-till
no-till
20
no-till
strip-till
disk-till
tillage treatment
tillage treatment
Groundsel
Nightshade
60
flame
flame
® no-flame
50
a
40
no-flame
15
p=.14
10
p=.02
30
20
5
10
0
disk-till
strip-till
tillage treatment
no-till
disk-till
strip-till
tillage treatment
no-till
Figure 4. In-row weed abundance (by species), two samples, four replicates,
sampled 5 July 1995. Data square root transformed and means LSD seperated.
Letters above bars indicate significant differences between means (within a tillage
treatment).
24
Table 1. Effects of tillage and weed control treatments on weed abundance (two
samples, four replicates, sampled 5 July 1995) and biomass (four samples, four
replicates, sampled 12 July 1995). Data square root transformed and means LSD
seperated.
weed abundance
weed dry
between rows
biomass in-rows
(number/m2)
(g/m2)
disk-till
232 a
104 a
strip-till
19 b
128 a
no-till
30 b
19 b
p-value
0.11
0.09
Tillage treatment
25
Table 2. Effect of tillage on the time it took to hoe the 37 m2 squash growing area
(sampling dates listed). Means LSD separated.
time to hoe (people hours/ha)
July 13
July 23
August 8
Season average
disk-till
31 a
100 a
67
199 a
strip-till
14 b
54 b
72
140 b
p-value
0.15
0.06
0.90
0.21
Tillage treatment