Water use efficiency of three green manure legume species as influenced by stand density
by Sharon Lee Pfaff
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in
Agronomy
Montana State University
© Copyright by Sharon Lee Pfaff (1994)
Abstract:
The water use efficiencies of legume green manure species are needed to facilitate green manuring as a
viable alternative to summerfallowing in semiarid environments. The objectives of this study were to
determine the water use efficiency (WUE) of three legume species, Austrian winterpea [Pisum sativum
ssp. arvense (L.) Poir. cv. Melrose], lentil (Lens culinaris Medik cv. Indianhead), and black medic
(Medicago lupulina L. cv. George), in terms of dry matter production, canopy N accumulation and
N2-fixation, and as influenced by stand density. The legumes and barley (Hordeum vulgare L.
Bearpaw) were planted at three seeding rates in a split plot design at Logan, Montana, in 1993 and
1994. Cumulative evapotranspiration (ET), percent canopy closure, canopy biomass accumulation,
canopy N accumulation, and stem length were measured over the two growing seasons. Legume dry
matter production was unusually high in 1993, relative to 1994, due to an unusually cool wet growing
season. Despite this, of the three legumes, Austrian winterpea consistently displayed the highest WUE
in terms of canopy closure, canopy biomass accumulation, canopy N accumulation and N2-fixation,
with comparisons made at each seeding rate. George black medic had similar performance to Austrian
winterpea. Indianhead lentil consistently displayed lowest WUE of the three legume species at all
seeding rates. No clear trends emerged in comparisons within species of the three seeding rates. During
both years, the medium seeding rate (which is the standard recommended rate) often emerged as having
highest WUE. It would appear this seeding rate has the optimum potential when these legume species
are used as green manure. Plant height (stem length) and growth stage have been suggested as practical
tools for farmers to use in estimating ET. In this study, plant height correlated well with cumulative ET
for all three species both years. However, the slopes of the regression lines were quite different each of
the two years. Growth stage was somewhat related to cumulative ET, but the relationship was not as
distinct as plant height. WATER USE EFFICIENCY OF THREE GREEN MANURE LEGUME
SPECIES AS INFLUENCED BY STAND DENSITY
by
Sharon Lee Pfaff
-~7->
A thesis submitted.in partial fulfillment
of the requirements for the degree
of
Master of Science
in
Agronomy
MONTANA STATE UNIVERSITY
Bozeman, Montana
December, 1994
nnv
cp 4-71
ii
APPROVAL
of a thesis submitted by
Sharon Lee Pfaff
This thesis has been read by each member of the thesis
committee and has been found to be satisfactory regarding
content, English usage, format, citations, bibliographic
style, and consistency, and is ready for submission to the
College of Graduate Studies.
Date
airperson, Graduate Committee
<7
Approved for the Major Department
Date
Approved for the College of Graduate Studies
Date
iii
STATEMENT OF PERMISSION TO USE
In presenting this thesis in partial fulfillment of the
requirements
for
a
master's
degree
at
Montana
State
University, I agree that the Library shall make it available
to borrowers under rules of the Library.
' If I have indicated my intention to copyright this thesis
by including a copyright notice page,
only for scholarly purposes,
copying is allowable
consistent with "fair use" as
prescribed in the U.S. Copyright Law.
Requests for permission
for extended quotation from or reproduction of this thesis in
whole or in parts may be granted only by the copyright holder.
Signature
Date
CI^V\AAjD n
W-
4'
iv
ACKNOWLEDGEMENTS
The
author
wishes
to
thank
the
following:
the
Soil
Conservation Service Plant Materials Center at Bridger, MT for
funding this project; the Steve McDonell family for providing
the study site; Jack Martin and Dick Lund for their patience
and guidance with the statistical analysis of this research;
Jon Wraith for providing equipment and always having time to
answer my many questions; Deb Solum for her willing assistance
in planting and maintaining the field plots; and, a special
thanks to my major professor. Dr. Jim Sims, for his friendship
and leadership on this project.
to have worked with him.
It has been a real privilege
V
TABLE OF CONTENTS
List of T a b l e s .............
List of F i g u r e s .......................................
..............................
Abstract
. . . . . . .
Page
vd
vii
xii
1. INTRODUCTION ........................................
I
2. LITERATURE R E V I E W .....................
5
3. METHODS AND MATERIALS
.................
. . . . .
Site D e s c r i p t i o n .................................
Experimental Design
............................
Meteorological Observations
........... . . . .
Soil Moisture C o n t e n t ...............
Soil, Biomass, Plant Height and Canopy
Cover S a m p l i n g ............................
Analyses of Soil and Biomass S a m p l e s .........•.
Estimating Legume !^,-fixation
.................
Statistical Methods
............. . . . . . . .
4. RESULTS AND DISCUSSION ...............
Appraisal of Crop Performance
. . . . . . . . .
Cumulative Evapotranspiration (ET)
. . . .
Percent Canopy Cover
. . ..................
Above Ground Biomass Production ...........
Total Canopy Nitrogen (N) Accumulation
. .
!^,-fixation.................................
Water Use E f f i c i e n c y ............................
In terms of Cumulative ET vs.
Percent Canopy Cover . . . . . . . . .
In terms of Biomass vs. E T ...............
In Terms of Total Canopy N vs. E T .........
In Terms of N2-fixation vs. ET
...........
11
11
11
12
12
13
14
15
15
17
17
18
2.5
33
37
42
49
49
57
60
65
5. APPRAISAL OF METHODS FOR MANAGEMENT
OF GREEN M A N U R E ............................
Plant Height . .....................................
Growth S t a g e ...................
71
71
79
6. SUMMARY AND CONCLUSIONS
. . •......................
91
.....................................
94
A P P E N D I X ..............................................
99
LITERATURE CITED
vi
LJST OF TABLES
Table
Page
1. Stand density in plants/m2 for A W P , IHL
GBM and BAR at three seeding r a t e s .............
18
2. 1993 soil NO3- N 7 P 7 K 7 organic, matter, and
pH at time of p l a n t i n g ................
44
3. 1994 soil NO3- N 7 P 7 K 7 and organic matter
at time of e m e r g e n c e ............................
45
vii
LIST OF FIGURES
Figure
Page
1 . Cumulative ET after emergence in 1993. Comparisons
between A W P z IHLz and GBM at each seeding rate .
19
2. Cumulative ET after emergence in 1994. Comparisons
between A W P z IHL and GBM at each seeding rate
.
20
3. Soil water content after emergence in 1994.
Comparisons between A W P z IHL and GBM
at high seeding r a t e ............................
22
4. Soil water content after emergence in 1994.
Comparisons between A W P z IHL and GBM
at medium seeding rate . . . ....................
23
5. Soil water content after emergence in 1994.
Comparisons between A W P z IHL and GBM
at low seeding r a t e .............
24
6. Canopy cover after emergence in 1993. Comparisons
between A W P z IHL and GBM at each seeding rate
.
26
7. Canopy cover after emergence in 1994. Comparisons
between A W P z IHL and GBM at each seeding rate
.
27
8. Canopy cover after emergence in 1993. Comparisons
between seeding rates for A W P z IHL and GBM . . .
28
9. Canopy cover after emergence in 1994. Comparisons
between seeding rates for A W P z IHL and GBM . . .
29
10. Canopy biomass after emergence in 1993. Comparisons
between A W P z IHL and GBM at each seeding rate
.
31
11. Canopy biomass after emergence in 1994. Comparisons
between A W P z IHL and GBM at each seeding rate
.
32
12. Canopy biomass after emergence in 1993. Comparisons
between seeding rates for A W P z IHL and GBM . . .
34
13. Canopy biomass after emergence in 1994. Comparisons
between seeding rates for A W P z IHL and GBM . . .
35
viii
LIST OF FIGURES-Continued
Figure
Page
14. Canopy nitrogen accumulation after emergence
in 1993. Comparisons between three species at
each seeding r a t e ..............................
38
15. Canopy nitrogen accumulation after emergence .
in 1994. Comparisons between three species at
each seeding r a t e ..............................
39
16. Canopy nitrogen accumulation after emergence
in 1993. Comparisons between seeding rates for
A W P , IHL and G B M ............... -................
40
17. Canopy nitrogen accumulation after emergence
in 1994. Comparisons between seeding rates for
A W P , IHL and G B M ................................
41
18. Total canopy N accumulated after emergence
in 1993 and 1994. Comparisons between A W P ,
IHL, GBM and B A R ................................
43
19. Cumulative E T z biomass and canopy N accumulation
after emergence for barley in 1993 and 1994
. .
46
20. N2-fixation after emergence in 1993. Comparisons
between A W P z IHL and GBM at each seeding rate
.
47
21. N2-fixation after emergence in 1994. Comparisons
between AWP and GBM at each seeding rate . . . .
48
22. Cumulative ET vs. canopy cover regressions
for 1993. Comparisons of A W P z IHL and GBM
at each seeding r a t e ............................
50
23. Cumulative ET vs. canopy cover regressions
for 1994. Comparisons of A W P z IHL and GBM
at each seeding r a t e ............................
51
24. Cumulative ET vs. canopy cover regressions
for 1993. Comparisons between seeding rates
for A W P z IHL and G B M ............................
52
25. Cumulative ET vs. canopy cover regressions
for 1994. Comparisons between seeding rates
for A W P z IHL and G B M ............................
53
ix
LIST OF FIGURES-Continued
Figure
Page
26. Canopy biomass accumulation vs. ET regressions
for 1993. Comparisons of A W P , IHL and GBM at
each seeding r a t e ................. .............
55
27. Canopy biomass accumulation vs. ET regressions
for 1994. Comparisons of AWP,. IHL and GBM at
each seeding rate
. .......................... . .
56
28. Canopy biomass accumulation vs. ET regressions
for 1993. Comparisons between seeding rates
for A W P , IHL and G B M ............................
58
29. Canopy biomass accumulation vs. ET regressions
for 1994. Comparisons between seeding rates
for A W P , IHL and G B M ............................
59
30. Canopy nitrogen accumulation vs. ET regressions
for 1993. Comparisons of A W P , IHL and GBM at
each seeding rate . .............................
61
31. Canopy nitrogen accumulation vs. ET regressions
for 1994. Comparisons of A W P , IHL and GBM at
each seeding rate. . . . . . . .
................
62
32. Canopy nitrogen accumulation vs. ET regressions
for 1993. Comparisons between seeding rates
for A W P , IHL and GBM .............................
63
33. Canopy nitrogen accumulation vs. ET regressions
for 1994. Comparisons between seeding rates
for A W P , IHL and G B M ............................
64
34. N2-fixation vs. cumulative ET in 1993. Comparisons
between A W P , IHL, and GBM at each seeding rate .
66
35. N2-fixation vs. cumulative ET in 1994. Comparisons
between AWP and GBM at each seeding rate . . . .
67
36. N2-fixation vs. cumulative ET in 1993.
Comparisons between seeding rates for
A W P , IHL and G B M ........... ................... ..
68
37. N2-fixation vs. cumulative ET in 1994. Comparisons
between seeding rates for AWP and G B M .........
69
<3
X
LIST OF FIGURES-Gontinued
Figure
Page
38. Cumulative ET v s . plant height regressions in 1993
for A W P , IHL and GBM at each seeding rate
...
72
39. Cumulative ET vs. plant height regressions in 1994
for A W P , IHL and GBM at each seeding rate
...
73
40. Cumulative ET vs. plant height regression for
1993/1994 for A W P , IH L , and GBM at each
seeding rate ................................. ..
.
74
41. Biomass vs. plant height regression for 1993, for
A W P , IHL, and GBM at each seeding r a t e .........
76
42. Biomass vs. plant height regression for 1994, for
A W P , IHL, and GBM at each seeding r a t e .........
77
43. Biomass vs. plant height regressions for 1993/1994
for A W P , IHL, and GBM at each seeding rate . . .
78
44. Canopy N accumulation vs. plant height
regressions for 1993, for A W P , IHL and
GBM at each seeding r a t e ........................
80
45. Canopy N accumulation vs. plant height
regressions for 1994, for A W P , IHL and
GBM at each seeding r a t e ........... .............
81.
46. Canopy N accumulation vs. plant height
regressions for 1993/1994, for A W P , IHL,
and GBM at each seeding r a t e ...................
82
47. Biomass, ET and N accumulation after
emergence for AWP at each seeding rate
in 1993, by growth s t a g e ........................
85
48. Biomass, ET and N accumulation after
emergence for AWP at each.seeding rate
in 1994, by growth s t a g e ........................
86
49. Biomass, ET and N.accumulation after
emergence for IHL at each seeding rate
in 1993, by growth s t a g e ............. ..
87
50. Biomass, ET and N accumulation after
emergence for IHL at each seeding rate
in 1994, by growth s t a g e ........................
88
xi
LIST OF FIGURES-Continued
Figure
Page
51. Biomass, ET and N accumulation after
emergence for GBM at each seeding rate
in 1993, by growth s t a g e .........................
89
52. Biomass, ET and N accumulation after
emergence for GBM at each seeding rate
in 1994, by growth s t a g e ....................
90
53. Cum. pan evaporation and precipitation
for 1993/1994
99
xii
ABSTRACT
The water use efficiencies of legume green manure species
are needed to
facilitate
green manuring
as a viable
alternative to summerfallowing in semiarid environments. The
objectives of this study were to determine the water use
efficiency
(WUE) of three legume species, Austrian winterpea
[Pisum sativum ssp. arvense (L.) Poir= cv. Melrose], lentil
(Lens culinaris Medik cv. Indianhead), and black medic
(Medicago lupulina L= cv. George), in terms of dry matter
production, canopy N accumulation and N2-fixation, and as
influenced by stand density. The legumes and barley (Hordeum
vulgare L. Bearpaw) were planted at three seeding rates in a
split plot design at Logan, Montana, in 1993 and 1994.
Cumulative evapotranspiration (ET), percent canopy closure,
canopy biomass accumulation, canopy N accumulation, and stem
length were measured over the two growing seasons. Legume dry
matter production was unusually high in 1993, relative to
1994, due to an unusually cool wet growing season.
Despite
this, of the three legumes, Austrian winterpea consistently
displayed the highest WUE in terms of c a n o p y closure, canopy
biomass accumulation, canopy N accumulation and N2-fixation,
with comparisons made at each seeding rate.
George black
medic
had
similar
performance
to
Austrian
winterpea.
Indianhead lentil consistently displayed lowest WUE of the
three legume species at all seeding rates.
No clear trends
emerged in comparisons within species of the three seeding
rates.
During both years, the medium seeding rate (which is
the standard recommended rate) often emerged as having highest
WUE.
It would appear this seeding rate has the optimum
potential when these legume species are used as green manure.
Plant height
(stem length) and growth stage have been
suggested as practical tools for farmers to use in estimating
ET.
In this study, plant height correlated well with
cumulative ET for all three species both years. However, the
slopes of the regression lines were quite different each of
the two years.
Growth stage was somewhat related to
cumulative E T , but the relationship was not as distinct as
plant height.
I
Chapter I
INTRODUCTION
Green manure crops have long been recognized by farmers
as a beneficial component of a cropping system.
Green
manuring is one of the oldest practices known to
agriculture, with written records of this practice dating
back 3000 years or more to China (Allison, 1973).
In the
United States and Canada, green manure crops are commonly
grown in higher rainfall, more humid areas, as they have
many beneficial aspects:
They act as a cover crop to
decrease wind and water erosion; maintain soil organic
matter and soil structure; improve soil fertility by adding
nitrogen (in the case of N2-fixing legumes) ; use excess soil
water and thereby reduce leaching of soil nutrients and
surface runoff; and break disease, insect and weed cycles
(Power and Biederbeck, 1991).
In addition to the above,
green manure crops can reduce the formation and growth of
saline seeps in semi-arid environments.
In the semi-arid Northern Great Plains states,
traditional use of green manure crops has often resulted in
negative impacts on the following cash crop (Army & Hide,
1959; Power, 1991).
The climate in this region is
characterized by relatively low humidity and precipitation.
2
with almost one half of the annual precipitation falling as
rain in April, May and Ju n e .
Summer temperatures often
reach a high of 100° F or greater with hot dry winds being
common.
For these reasons, potential evapotranspiration
greatly exceeds growing season precipitation.
Winters are
characterized by extremely cold temperatures, with typically
only a few inches of precipitation in the form of snow
(Power and Biederbeck, 1991).
Small grains are the most
commonly grown dryland crop in this region, with an
alternating fallow year being included.
Not only does
fallow allow, for storage of soil moisture for the subsequent
crop, but it also promotes mineralization and release of
nutrients from soil organic matter and plant residues.
Although these benefits have helped to stabilize crop
yields, in many instances fallowing has proven not to be a
sustainable system (Sims and Slinkard, 1991).
Continued oxidation and mineralization of organic
matter has caused soil fertility to steadily decrease in
soils under the crop-fallow system.
It is estimated that
soils in the Canadian Prairies and U.S. Great Plains have
suffered soil organic matter losses of 40 to 60%, after
being farmed under the crop-fallow system for the past 70 to
80 years (Campbell and Souster, 1982). Additions of chemical
fertilizers under a continuous small grain rotation have
been shown to maintain soil organic matter in the long term
(Campbell et a l ., 1991), however, continuous cropping is not
(
3
always feasible in the semi-arid Great Plains.
Also,
application of chemical fertilizers is becoming more costly,
as the fossil fuels used to manufacture them become more
scarce and expensive.
Fallowing is an extremely inefficient method of soil
water capture and storage.
Results from early studies in
Montana indicated storage efficiency of fallow averaged 21%
(Ford and Krall, 1979).
Results from more recent studies
conducted in Sidney, Montana, indicated an average storage
efficiency of fallow under a stubble-mulch system averaged
31.6% (Tanaka and- A a s e , 1987).
Rapid mineralization of
organic matter also leaves nitrates vulnerable to leaching.
Excess water leaches nitrates and other nutrients below crop
rooting depths., causing potential groundwater contamination.
If excess water is impeded from deep percolation by an
impermeable layer in the soil profile, a saline seep often
results (Sims and Slinkard, 1991).
Legume green manure
crops grown during the fallow period have great potential
for correcting problems associated with fallow, especially
in terms of using excess soil water and maintaining soil
fertility.
However, the challenge lies in managing the
legume in such a way as to provide the optimum amount of
nitrogen and other benefits, without unduly reducing the
amount of water available to the subsequent crop.
The
objectives of this study were to determine the water use
efficiency of three legume species in terms of dry matter
4
production and N2-fixation and as a function of stand
density =
Since Austrian Winterpea IPisum sativum ssp.
arvense (L„) P o i r ] has consistently displayed higher water
use efficiencies than other species (Wright, 1993), it is
postulated that it has the ability to close its canopy more
quickly than some other legume species, thus limiting soil
evaporation.
Therefore, it is hypothesized that changing
the stand density of the legume green manure crop from low
to medium to high will more quickly achieve canopy closure,
hence improve water use efficiency.
5
Chapter 2
LITERATURE REVIEW
Results from early studies in the Northern Great Plains
showed no benefit from using legumes in crop rotations =
This may have been primarily due. to two factors.
First, at
the time.of these early studies, soil organic matter levels
had not yet been greatly depleted, therefore, N
contributions by legumes would not have been as significant
as in a depleted soil (Campbell et a l ., 1991) .
Secondly,
green manure crops were not managed in such a way as to
limit water use, which often depleted stored soil moisture
reserves necessary for the subsequent crop
1959).
(Army
and Hide,
The results of these studies, and the availability
of inexpensive N fertilizer, appeared to discourage further
research of green manure crops for a period of time.
However, the energy crisis of the 1970's helped to renew an
interest in the contributions of legumes to sustainable
cropping systems (Mahler and A u l d , 1989, Sims et a l . 1985,
Koala, 1982).
In recent years, researchers have made great strides
toward incorporating legumes into cropping systems in semiarid environments.
These research efforts have been focused
in three major areas:
species adaptability (which includes
6
water use efficiency), contributions to subsequent crops,
and associated cultural practices =
. Water use
efficiency
is defined as the amount of
biomass produced per a given area for a unit of water
evaporated or transpired (ET) for that area (Tanner and
Sinclair, 1983).
The soil evaporation component of ET is a
purely physical process occurring primarily at the soil
surface.
During the growing season, evaporation from the
soil surface is substantially reduced one to two days after
wetting, and soil moisture below 20 to 30 cm is relatively
safe from soil surface evaporation (Hanks, 1985).
Plant
transpiration is much more complex, being, composed of both
biological and physical processes.
In water-limiting
environments, transpiration is often more critical to total
water use than soil evaporation. Transpiration efficiency
for a given crop is relatively stable if climatic conditions
are normalized for a given location and time of year
(Ritchie, 1983).
In 1958, de Wit (as reported
by
Hanks,
1983) demonstrated a strong correlation between biomass
production and transpiration.
Mathematically, he expressed
this relationship as
Y = mT/ETmax
where Y = total dry matter mass per area, m = a crop
coefficient (a constant related to crop performance of
different crop species and varieties within species), T =
transpiration, and ETmax = total potential evaporation from
7
an open body of water.
In reality, however, it is very
difficult to separate transpiration from soil evaporation in
a field situation.
Water use efficiency based on ET is not
as closely correlated to dry matter production as when based
solely on T.
Cultural practices can substantially alter ET
by changing soil evaporation, weed transpiration, etc.
(Tanner and Sinclair, 1983).
However, ET is relatively easy
to measure in the field and, for the purposes of this
research, will be used as the basis for calculating water
use efficiency.
Producers incorporating legumes into their cropping
system need accurate information to select appropriate
species.
Response to temperature, biomass production, N2-
fixation, and water use efficiency are among the factors
which need to be considered in species selection, along with
seed availability and cost of establishment.
Legumes used
as green manure have been divided into three main groups,
the small-seeded forage legumes, and medium-seeded and
large-seeded grain legumes.
In adaptation trials in
Bozeman, Montana, small-seeded annual forage legumes
performed quite well in biomass production and N2-fixation,
especially several varieties of clover and medic (Sims and
Slinkard, 1991; Wright, 1993).
However, small-seeded
legumes have the disadvantage of needing shallow seedbed
placement.
If the upper surface layer is dry, they will not
establish, and if planted deeper into moist so i l , they often
8
do not emerge, as can the large-seeded grain legumes =
This
is perhaps one reason'why peas, lentils, and snail medic
have emerged as the most adaptable legume species for green
manuring in this region.
In several field trials across a
variety of dryland environments, researchers found that peas
(Pisum sativum L . ) consistently had the highest biomass
production and N production of all legume species tested
(Sims and Slinkard, 1991; Power, 1991; Zachariassen and
Power, 1991; Bremer et a l ., 1988; Auld et a l ., 1982).
Townley-Smith and associates (1993) also found this to be
true, but determined lentils (Lens culinaris Medik) to be
the most desirable green manure species.
Even though
lentils had only intermediate biomass and N production, the
small seed size and low seeding rate made it a much more
economical choice.
Since green manure is not a cash crop,
producers need to minimize inputs into this practice.
Maximum biomass production in a green manure crop is
not always desirable, since legume species that exhibit the
most rapid growth also tend to have the greatest water use
(Zachariassen and Power, 1991).
Researchers in several
locations have found increases in small grain yields
following incorporation of legume residues (Mahler and
Hemamda, 1993; Welty et al., 1988, Koala, 1982) or even
after production of a legume grain crop (Wright, 1990).
However, maximum yields were obtained in winter wheat at
Bozeman, Montana, when Indianhead lentils were terminated
9
after using an intermediate amount of stored soil water
(Sims and Slinkard, 1991).
This research also shows that if
legumes are terminated too early, little benefit from N2fixation may occur.
Kucey (1989) and Wright (1993) found
that it took peas approximately six weeks to begin fixing
substantial amounts of N.
Results from several studies revealed that only 11 to
28% of mature legume residues were mineralized and taken up
by the subsequent cereal crop (Mahler and Hemamda, 1993;
Janzen et a l ., 1990)=
approximately
Bremer and van Kessel (1992) found
40% of lentil green manure was mineralized,
but only 19% was taken up by the subsequent wheat crop. They
surmised that later seeding and incorporation would increase
the amount of N made available to the following crop.
Other cultural practices which may govern the
successful use. of green manure crops include planting date
and plant density.
For maximum seed and biomass production,
Sims and associates (1989) recommend that cool season
legumes should be planted as early as equipment can be taken
into a field.
Warm season legumes should be planted to
avoid the last killing frost.
But, delaying planting too
long substantially decreases legume yields.
Plant density of green manure crops as it relates to
canopy closure and ET has received very little attention
from scientists.
Early researchers studying soil
evaporation hypothesized that earlier canopy closure
10
(narrower rows and greater plant densities) resulted in
greater interception of solar radiation, and a reduction of
soil evaporation (Alessi and Power, 1982).
More recent
research on a variety of crops indicates that this may be
true in regions where the soil surface is kept wet by
precipitation or irrigation.
However, in regions where the
soil surface is typically dry, and plants are dependant on
stored soil moisture reserves, increased leaf surface area
(greater plant densities) has resulted in increased
transpiration and water use (Ritchie and Johnson, 1990).
Increased dry matter production is
usually
the result of
increased planting density; whether this results in higher
water use efficiencies in terms of biomass production is hot
clear.
11
Chapter 3
METHODS AND MATERIALS
Site Description
A site near Logan, Montana (SE 1/4 of the SW 1/4 of
Sec= 35, T2N, R2E) was selected because of its dryland
characteristics, having coarse soils and low average annual
precipitation (10-14 inches)=
Field plots were established
May 11, 1993 and April 21, 1994 on Kalsted sandy loam
(coarse
loamy,
mixed, borollic calciorthids).
This site was
broken out of native rangeland in the fall of 1992 =
The
area for the.1994 experimental plots was planted to barley
in 1993 =
Experimental Desicm
Three legume, species and a non N2-Tixing species,
barley (Hordeum vulgare L= Bearpaw) were planted at a high,
medium and low seeding rate in a split-plot design with four
replications=.
Changing the stand density by varying row
spacings had been considered, however, because of a lack of
available equipment, this was not possible.
stand density was altered by changing plant
the row.
Unit plot size was 6=1 m x 3=1 m=
Therefore,
density
within
12
Before planting, the three legume species, Austrian
winterpea [Pisum sativum ssp. arvense (L=) Poir= cv=
Melrose], lentil (Lens culinaris Medik cv. Indianhead), and
black medic (Medicago lupulina L= cv. George) were
inoculated with the proper Rhizobium strain (Liphatech,
Inc=, Milwaukee, WI)=
Legumes and barley were seeded into
a firm seedbed at the following rates:
Austrian winterpea,
251, 168, and 83 kg/ha;- Indianhead lentil, 119, 79, and 40
kg/ha; George black medic, 34, 22, and 11 kg/ha; barley,
169, 112, and 57 kg/ha.
Row spacing in all plots was
25=4 cm=
*
Meteorological Observations
Precipitation and pan evaporation were collected
weekly, using the system proposed by Sims and Jackson
(1971).
Collection site for weather data was located
approximately 400 m from the study site = Pan evaporation
data reported in this documents was adjusted with a pan
factor of 0.55 (Jenson, 1974).
Soil Moisture Content .
After planting, PVC access tubes were installed with a
hydraulically-driven soil probe near the center of each
plot.
Soil moisture content was determined using a neutron
moisture probe (model no. 503DR Hydroprobe, Campbell Pacific
Nuclear, Pacheco, C A ) =
The probe was calibrated at the site
13
each year, by obtaining soil samples at 0=2 m increments to
a depth of 1=8 m.
Soil moisture content of these samples
was determined gravimetrically and a regression eguation
developed to convert neutron probe readings to volumetric
soil water content=.
Soil moisture content readings were
taken in 0.2 m increments
every
7 to 10 days during the
growing season.
S o i l . Biomass = Plant Height and Canopy Cover Samplincr
Soil samples were obtained to determine initial pH,
organic matter content, NO3-N, phosphorus, and potassium.
Monocalciumphosphate (0-44-0) fertilizer was applied at a
rate of 145 pounds per acre.
Biomass.samples were taken every 7 to 10 d a y s .
Within
each plot, a.I m row-strip was randomly selected and hand
clipped to the soil surface to gather all above ground
biomass.
At the end of the growing season in 1994, when
conditions turned
very
hot and
leaf senescence.
A portion of decaying plant materials
dry,
all species underwent
could not be recovered, therefore recorded biomass levels
dropped.
To adjust for this, biomass and canopy N
accumulation levels are reported as remaining at the point
of peak performance.
Plant height and percent canopy cover were obtained
every 7 to 10 days.
Plant height was determined by
averaging heights (stem lengths) of three randomly selected
14
plants within each plot =
Canopy cover was determined
by
ocular estimations of canopy within I m of the access tube
in each pl o t .
Stand
density
fully emerged=
was also determined once all plants had
Density was estimated by counting plants
within three randomly selected I m row-strips and averaging
the results within each plot.
Analyses of Soil and Biomass Samples
Initial soil samples were weighed and dried at 50°
Celsius in a forced-air oven.
Analysis for pH, NO3-N,
phosphorus, soil organic matter, and potassium, was
conducted by the Montana State University Soil Testing
Laboratory.
An automated cadmium reduction method (American
Public Health Association, 1981) was used to determine NO3-N
concentration =
The Olsen method (Olsen and Sommers, 1982)
was used to determine phosphorus concentration using sodium
bicarbonate as an extractant.
The colorimetric method of
Sims and Haby (1971) was used to determine soil organic
matter content, and an extractable cation method (Knudsen et
al. 1982) was used to determine potassium concentration.
Biomass samples were dried at 50° Celsius in a forcedair oven.
Dry matter samples were weighed, ground and a
sub-sample analyzed for the total Kjeldahl nitrogen content
15
(Bremner and Mulvaney, 1982)
by
Montana State University
Soil Testing Laboratory,
Estimating Lecnme ftt-fIxation
An adjusted, measure of fixation was obtained
by
the
difference method (Henson and Heichel, 1984; LaRue and
Patterson 1981),
Canopy nitrogen of the non-fixing barley
crop was subtracted from the canopy nitrogen content of the
legumes,
The nitrogen in the norilegume was assumed to come
strictly from the soil N p o o l ,
Secondly, it was assumed
that differences between the growth patterns and root
morphology of the nonlegume and legumes were not great
enough to negate using this technique.
Statistical Methods
Data was examined statistically with the MSUSTAT
statistical package.
The analysis of Variance, comparison
of sample means using Student's t , and a general linear
model were used to examine research results.
Comparisons
between regression lines were generated using the general
linear model.
Polynomial constants reported in regression
equations were generated using mregress in MSUSTAT,
A relatively simple logistic equation, y=a/(l+be"cx) ,
with a,b, and c being constants, generally provides a
suitable portrayal of vegetative growth (Milthorpe and
Moorby, 1974),
This equation was used to fit curves to crop
16
performance .data (means of four replications in all cases).
Sigmaplot software (Jandel Scientific, San Rafael, CA) was
used for logistic and polynomial curve fitting operations.
17
Chapter 4
RESULTS AND DISCUSSION
Appraisal of Crop Performance
The 1993 growing season was uncharacteristically cool
and wet, with 27 cm of precipitation falling at the research
site during the data collection period. May 20 to August 18=
In contrast, the 1994 growing season advanced normally, with
ample precipitation falling early, and conditions turning
hot and dry during June and July.
During the 1994 data
collection period. May I to July 31, 12 cm of precipitation
fel l =
(Graphs of 1993. and 1994 pan evaporation and
precipitation can be found in the appendix =)
Stand densities for 1993 and 1994 are reported below
(Table I) for Austrian winterpea (AWP), Indianhead lentil
(IHL), George black medic (GBM) and barley (BAR) at high (H)
medium (M) and low (L) seeding rates =
All species showed a
marked drop in stand density at most seeding rates in 1994 =
This was especially evident in G B M .
Heavy barley residues
(due to excessive moisture in 1993) impeded proper seedplacement of G B M , a small-seeded species, resulting in
initially poor stand establishment across all seeding rates.
This illustrates the advantage of using large-seeded species
18
when it is difficult to maintain proper seeding depth =
It
should be noted, however, that the high GBM stand density in
1994 is quite near the low
stand
density
of 1993, As will be
seen in the following data, GBM was still able to expand its
above ground canopy and remain competitive with the other
two species, despite this disadvantage.
In fact, GBM
performed very similarly relative to the other two legume
species both years, suggesting that GBM can maintain crop
performance with lower stand densities.
Table I, Stand density in plants/m2 for 1993 and 1994 for
A W P , I H L , GBM and BAR at three seeding rates,______
Soecies
AWP
GBM
IHL
BAR
Seed
rate
1993
1994
1993
1994
1993
High
133
124
307
212
385
133
Med,
101
81
207
136 •
226
67
130
78
Low
51
46
87
HO
46
74
51
88
1994 . 1993
177 .
1994
107
Cirmnlatiye Evapotranspiration fETY
Comparisons of cumulative ET between A W P , IHL and GBM
at high, medium and low seeding rates, reveal only minor
differences (Figs = I and 2),
Maximum cumulative ET achieved
was 26 cm in 1993, and 17 cm in 1994, . George black medic
consistently had
years.
slightly
lower ET over time, during both
Cumulative ET was similar for AWP and I HL, with IHL
slightly exceeding AWP in 1993, and AWP being slightly
higher in 1994,
19
Curve F it
- AWP: y=27.0/(l+26.Ble ° 06X ), K =0.9
), R =0.99
IHL- y=29.6/(l+30.9e”°‘06x
~ GBM: y = 27.4/(1+ 26.6e 0"05X ), R =0.99
O A W P-H
S IH L -H
V G B M -H
1993
Curve Fit
-
-
0 .06 *
AWP: y=26.9/(1+28.Be
). R =0.99
I H L y=28.9/(I +33. Ie
), R =0.99
GBM: 7=27.3/(l+31.2e
), R =0.99
O AWP-M
S IH L -M
V GB M -M
Curve F it
AWP: y=27.6/(l+31.6e~° 001 ), R =0.99
IHL: 7=2B.6/(l + 32.2e ~0 06x ^ R = Q GQ
GBM: 7=30.0/(l+28.3e~0'°5X ), R =0.99
O AW P-L
• IH L -L
V G B M -L
0
20
40
60
80
100
Days After Emergence
Fig.
I.
C u m u la tiv e ET a fte r e m erg en ce in 1993. Com parisons
betw een AWP, IHL and GBM a t each seeding ra te .
20
30
25
Curve F it
- A W P : y = 1 7 . 5 / ( 1 + 4 6 . S e ~ 0 0 9 x ), R = 0 . 9 9
IHL: y = 1 6 . 6 / ( l + 3 5 . 2 e ” °'08X ). R = 0 . 9 9
20
” GBM: y ^ l 8 . 7 / ( l + 3 7 . 1 e - 0 '0 7 x ), R = 0 . 9 9
15
10
O A W P-H
• IH L -H
V G B M -H
5
1994
30
Curve F it
25
A W P : y=16.8/(l+40.1e_°'O 9 x ). R =0.99
IHL: y = 17.5/1 l + 2 9 . 3 e ™ 0-071), R =0.99
20
GBM: y = 19.8/(1+35.5e
-0.07x
2
), R =0.99
15
10
O AWP-M
S IH L -M
V GBM -M
5
30
25
-
Curve Fit
-o.oex). R
A W P : y = 17.2/(1+46.Oe
— 0 07y
IHL: y=17.5/(l+29.3e
20
=0.99
2
), R = 0 . 9 9
GBM: y=20.1/(l+30.8e“O06x ). R =0.99
15
10
AW P-L
S IH L -L
V G B M -L
5
0
1C
Days After Emergence
2
C u m u la tiv e ET a fte r e m erg en ce in 1994. Com parisons
betw een AWP1 IHL and GBM a t each seeding ra te .
21
Within species comparisons of A W P , IH L , and GBM
cumulative ET generally did not vary significantly between
high, medium and low seeding rates in 1993 or 1994.
This
similarity between seeding rates has been explained as
follows:
Under the lower seeding rates, there is less leaf
surface area, therefore, less transpiration, and greater
exposure of the soil surface to evaporation.
The opposite
being true for the higher seeding rates (Loomis, 1983).
There were two minor exceptions to this trend.
In
1993, IHL under the low seeding rate used slightly less
water than higher seeding rates =
In 1994, a similar but
still minor separation of curves occurred in AWP=
The 1993 soil profile volume water content data did not
reveal any clear depletion trends because of heavy rainfall
throughout the growing season.
Analysis of 1994 soil profile volume water content data
(Figs. 3, 4 and 5) provide insight into cumulative ET
differences between species.
During days 5 to 42 after
emergence, AWP and IHL clearly had higher depletion of soil
water than G B M .
Interestingly, during this time, GBM
gathered more moisture from the 40 to 80 cm depths than from
the surface 40 cm.
Based on this and biomass data reported
later, it would appear that GBM spent this time in downward
development of its root system, while IHL aggressively
developed above ground canopy, drawing on moisture closer to
the surface to accomplish this.
Indianhead lentil drew more
22
AW P-H
--- D A Y 5
--- D A Y 29
--- D A Y 42
... D A Y 56
D A Y 70
--- D A Y 84
-100
-1 2 0
Depth (cm )
IH L -H
--- D A Y 5
- - D A Y 29
.... d a y 42
...D A Y 56
D A Y 70
— - D A Y 84
— I00
-1 2 0
G B M -H
--- D A Y 5
- - D A Y 29
— - D A Y 42
... D A Y 56
D A Y 70
---D A Y 84
-100
-120
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Volume Water Content
Fig. 3.
Soil w a te r c o n te n t a fte r e m erg en ce in 1994. Com parisons
betw een AWP1 IHL and GBM a t high seeding ra te .
23
AW P-M
\ \
-100
-1 2 0
\
--- D A Y 5
--- D A Y 29
--- D A Y 42
D A Y 56
D A Y 70
--- D A Y 84
Depth (cm )
IH L -M
-100
-1 2 0
DAY 5
- - D A Y 29
D A Y 42
D A Y 56
D A Y 70
D A Y 84
GB M -M
-100
-1 2 0
0.00
---- D A Y 5
--- D A Y 29
... D A Y 42
... D A Y 56
D A Y 70
--- D A Y 84
0.05
0.10
0.15
0.20
0.25
0.30
Volume Water Content
Fig. 4. Soil water content after emergence in 1994. Comparisons
between AWP, IHL and GBM at medium seeding rate.
24
AWP - L
--- D A Y 5
--- D A Y 29
... D A Y 42
... D A Y 56
D A Y 70
--- D A Y 84
-100
-1 2 0
Depth (cm)
IH L -L
--- D A Y 5
- - D A Y 29
D A Y 42
D A Y 56
D A Y 70
■—
D A Y 84
-100
-1 2 0
G B M -L
DAY 5
D A Y 29
D A Y 42
D A Y 56
D A Y 70
- - D A Y 84
-100
-1 2 0
-
Volume Water Content
Fig.
5.
Soil w a te r c o n te n t a fte r em ergence in 1994. Com parisons
betw een AWP, IHL and GBM a t low seeding ra te .
25
water out of the surface 50 or 60 cm than did AWP and GBM=
Austrian winterpea growth apparently involved both downward
root development and canopy growth f thereby drawing water
more uniformly from the surface down to 80 cm.
After day
42, water depletion proceeded rapidly under G B M , until it
was at the same level as the other two species.
In general, more water was drawn from deeper depths
under the higher seeding rates, as compared to the low. It
would also be expected that a higher percentage of depletion
under the low seeding rates in the 0-30 cm depth was
partitioned into surface evaporation rather than
transpiration (Hanks, 1985).'
Percent Canopy Cover
Crop canopy was measured in this study because of its
close relationship to E T .
When the soil surface is wet, as
in 1993, evaporation is a critical component of E T , and the
ability of the crop canopy to shade the soil surface can
influence the amount of water that is partitioned between
evaporation and transpiration.
A heavier canopy will shade
the soil surface, reduce soil surface temperatures, thus
reducing evaporation, and leaving more moisture available
for transpiration.
When the soil surface is dry, as in
1994, evaporation is not as critical, although a heavier
canopy may still reduce transpiration by reducing the amount
of radiant heat coming from the soil surface, increasing
26
Curve F it
- A W P : J= 100.5/(1 +405.5e
), R =0.98
IHL: y=109.1/(l + 139.5e~<
- GBM:: y=97.1/(l+8177.4"
20
. R =0.99
O A W F-H 1993
S IH L -H
V
G B M -H
-
Curve F it
-
), R =0.98
A W P : y=99.5/(l+622.0e
IHL: y = 105.5/(1 +132.4e
- G B M : y=98.0/( 1+ 10004e
: ), R 2=O.98 O
: 2
y/
), R = 0 . 9 9 /
O AWP-M
• IH L -M
Curve F it
- A W P : y=95.3/(l+800.8
), R =0.99
IHL: y = 108.5/(1+377.4©
- GBM: y=97.6/(l + 11751e
D
y#
O AW P-L
# IH L -L
V
G B M -L
Days After Emergence
Fig.
6.
Canopy cover a fte r em ergence in 1993. Com parisons
betw een AWP, IHL and GBM a t each seeding ra te .
27
Curve F it
IHL: y=33.0/(l+61.Se"01
O A W P-H 1994
• IH L -H
V G B M -H
), R =0.94
A W P : y=54.7/(l+240.6e
), R =0.98
G B M : y = 4 2 . 1/(1+ 9 3 6 2 8 e
Curve F it
O AWP-M
• IH L -M
V GBM -M
AWP: y=49.0/(l + 190.0e_!> 15
). R i =0.99
IHL: y=30.7/(l + 113.Se-0 ^
GBM: y=34.5/(l + 16471e-°: ), R =0.99
Curve F it
_ AWP: y=42.7/(l+238.1e
O AW P-L
• IH L -L
V G B M -L
)„ R=0.99
IHL: y=25.3/(1+397.1e~°
0 99
- GBM: y=27.2/(l+4803.4e
---Y7~'f
0
20
40
60
80
Days After Emergence
Fig. 7.
Canopy cover a fte r e m erg en ce in 1994. Com parisons
b etw een AWP, IHL and GBM a t each seeding ra te .
100
28
Curve F it
-
H: y = 100.5/(1+405.5e
), R =0.98
M: y=99.5/(l+622.Oe-'
L: 7=95.3/(l+800.8e °
, R 2 =0.98
,, R 2 =0.99
O A W P - H 1993
S AWP-M
V AWP-L
Curve F it
), R =0.98
H: 7=109.1/(1 + 139.Se
M: 7 = 105.5/(1 +132.4e
L: 7 = 108.5/(1+377.4e~
O IH L -H
• IH L -M
V IH L -L
Curve F it
H: y=97.01/(l + 18177.4e-00 r
M: y=98.0/(l + 10004e-0i‘®1
L: y=97.8/(l + 11751e
), R
=0.99
O G B M -H
• GBM -M
V
G B M -L
Days After Emergence
Fig.
8.
Canopy cover a fte r em erg en ce in 1993. Com parisons
betw een seeding ra te s fo r AWP, IHL and GBM.
29
Curve Fit
H: y=54.7/(l+240.6e
), R =0.94
M: y=49.0/(1+190.Oe
L; y=42.7/(l+238. Ie
), R 8 =0.96
), R — 0.99
O AWP-H 1994
• AWP-M
V AWP-L
Curve Fit
O IHL-H
S IHL-M
v IHL-L
). R =0.98
H: y=33.0/(l + 61.3e
M: 7=30.7/(1 + 113.66
L: 7=25.3/(1+397. Ie-
). R
=0.99
Curve Fit
H: 7=42.l/(l + 9362Be
M: 7=34.5/(l + 16471e
L: y=27.2/(I +4803.4e
O GBM-H
• GBM-M
V GBM-L
), R =0.97
), R =0.99
O
0
20
40
60
O
80
Days After Emergence
Fig. 9. Canopy cover after emergence in 1994. Comparisons
between seeding rates for AWP, IHL and G B M .
100
30
leaf surface temperatures and thus transpiration (Loomis
1983; Ritchie, 1983),
Comparisons of percent canopy cover between species
reveal, during both years and over all seeding rates, canopy
development for AWP and IHL was similar in area but not
pattern, for approximately the first 40 days (Figs. 6 and
7).
After this, AWP clearly was the most aggressive species
in canopy development.
George black medic had much slower canopy closure early
in the growing season, probably using early season
metabolites to develop a deep root system instead.
By day
40, however, GBM underwent rapid canopy closure, quickly
equaling and often exceeding IHL performance.
With adequate moisture in 1993, all species were able
to reach almost 100% canopy closure.
In 1994, percent
canopy ranged from a low of 30% in the low seeding rate of
IHL and G B M , to a high of 60% in AWP at the high seeding
rate.
The geometry of the b a r e , exposed soil varied between
species.
The erect growth of IHL resulted in large, uniform
blocks of exposed soil between ro w s ; whereas the prostrate
and viney growth of AWP and GBM resulted in a mosaic pattern
of shaded and exposed soil.
Comparing seeding rates within species reveal that,
generally, 1993 and 1994 growth curves are graduated down
from high to medium to low seeding rates in all species
31
15000
12500
Curve F it
-
A W P : y = 1605/(1+235.4e
IHL: y = 12682/(1 +136.46”°
I OOOQ
GBM: y = U 2 7 2 / ( l + 1799.5e
), R =0.98
). R =0.99
), R =0.98
7500
5000
2500
O A W P -H 1993
• IH L -H
V G B M -H
Canopy Biomass (k g /h a )
15000
Curve F it
12500
A W P : y=27124/ ( l + 2 2 0 . 4 e ”'
), if =0.98
IHL: y = 14760/(1 + 150.1 e”°
10000
GBM: y = 11 6 7 0 / ( l + 2 6 9 9 e ”D
7500
5000
2500
O AW P-M
• IH L -M
V GB M -M
15000
Curve F it
12500
_ A W P : y = 17979/(1 +277.7e”°
10000
_ G BM: y=7614/( l + 7 0 5 0 . 9 e ”°
IHL: y = 12 8 18/(I+ 198.5e”°’°
7500
5000
2500
Fig. 10.
O A W P-L
• IH L -L
V G B M -L
Days After Emergence
Canopy biom ass a fte r em erg e n c e in 1993. Com parisons
betw een AWP, IHL and GBM a t each seeding ra te .
Canopy Biomass (k g /h a )
32
Days After Emergence
Fig. 11.
Canopy biom ass a fte r e m erg en ce in 1994. Com parisons
betw een AWP1 IHL and GBM a t each seeding ra te .
33
(Figs. 8 and 9).
The exception to this trend occurred in
1993 in AWP and IHL, where high and medium canopy closure
was nearly the same.
Above Ground Biomass Production
Comparisons of biomass production between species
(Figs. 10 and 11) reveal AWP clearly held an advantage over
IHL and G B M .
Although AWP and IHL maintained similar
production during the early part of the growing season, AWP
rapidly began to out-produce IHL at all seeding rates, as
the season progressed.
This trend became evident about day
60 in 1993, the cool, wet year, but expressed itself about
day 40 in 1994, the hot dry year.
As seen here and intimated from water use data
presented earlier, GBM had low early season biomass
production compared to AWP and IHL=
Not until later in the
season, when temperatures increased, did it begin to rapidly
commence canopy development. By days 60 to 70, GBM was at
similar production levels to I H L , but was never able to
reach AWP levels.
In 1993, biomass production levels peaked at
approximately 14,000 kg/ha for A W P , and 8,750 kg/ha for IHL
and G B M , at the medium seeding rate.
In 1994, peak
production occurred at approximately 4,100 kg/ha (29=3% of
1993 production) for AWP at the high seeding rate, and 3,000
kg/ha (34.3% of 1993 production) for IHL and GBM at medium
and high seeding rates respectively.
34
15000
12500
10000
7500
5000
2500
15000
12500
10000
7500
5000
2500
15000
12500
10000
7500
5000
2500
0
(
Days After Emergence
g.
12.
Canopy biom ass a fte r em ergence in 1993. Com parisons
b etw een seeding ra te s fo r AWP, IHL and GBM.
35
15000
12500
Curve F it
-0.1 IX
-
H: y = 4 195.5/(I + 166.4e
), R =1.00
-0.1 lx
M: y=40B5.7/( 1 + 303.7e"
10000
_
L: y=3760.4/( 1+800.6e"
), R =I OO
7500
5000
2500
O A W P -H 1994
S AWP-M
V
AW P-L
Canopy Biomass (k g /h a )
15000
Curve F it
12500 10000
H: y=2731.2/(l+541.4e
M: y=3334.8/(l + 16B.8e
L: y=2973.4/(1 + 838.Be
), R =0.99
), R 8=0.99
7500
5000
2500
O IH L -H
S IH L -M
V
IH L -L
15000
Curve F it
12500
10000
H: y=2756.8/(l + 3466.7e
), R =0.99
M: y=3307.4/(l + 16860e"
L: y=4720.7/(l +1576. le"
). R =0.98
7500
5000
2500
O G B M -H
S GB M -M
V G B M -L
Days After Emergence
Fig.
13.
Canopy biom ass a fte r em ergence in 1994. Com parisons
b etw een seeding ra te s fo r AWP, IHL an d GBM.
36
Seeding rate comparisons within species in 1993 (Figs,
12 and 13) revealed under medium seeding rate,- biomass
production was similar to or even exceeded that of the high
seeding rate, for all three species.
The low seeding rate
production level was only slightly below the other two.
During this excessively cool, wet growing season, AWP had
the greatest distribution between seeding rates, while GBM
appeared to have the least.
The narrowness of the range of
performance between seeding rates in 1993 is somewhat
surprising.
With ample moisture, the high seeding rate
should have been able to maintain superior production.
Apparently, increased competition for light and nutrients
kept production near that of the medium seeding rate.
As
seen in the canopy closure data above, the low seeding rate
was not able to achieve complete canopy closure as rapidly
as the other two rates.
Because the soil surface was often
wet in 1993, more water was likely partitioned to
evaporation under the sparser canopy of the low seeding
rate.
This was one factor which could have held back
production levels at the low seeding rates,
In general, for all species in 19-94, there was very
little difference in biomass production over all seeding
rates.
After day 60, the medium rate production nearly
equaled that of the high rate in A W P , while both medium and
low surpassed that of high in IHL and GBM=
In 1994, a hot
dry year where the soil surface remained relatively dry
37
throughout the growing season, soil evaporation was not as
critical=
Having stored soil moisture reserves later in the
season eventually gave the medium and low rates an advantage
over the high=
In the case of G B M z with its presumed deeper
rooting system, the low rate was even able to surpass the
medium rate at the end of the season.
To generalize, optimum, biomass production occurred at
the medium seeding rate in all species, during an
excessively wet and a relatively dry (normal) growing
season =
Total Canopy Nitrogen fNd Accumulation
Species differences become more apparent with canopy N
comparisons (Figs= 14 and 15)= Both years, AW-P had a
distinct early season advantage over the other two species,
which it maintained for the rest of -the season=
Canopy N
continued to increase in all species at a steady rate in
'1993=
However, in 1994, IHL canopy N quickly leveled off
\
after approximately day 50, while AWP continued to steadily
increase for several more days=
Initially, GBM canopy N
accumulated slowly, but began to rapidly increase about day
40, exceeding'IHL canopy N between day 50 and 60, and
approaching that of AWP by the end of the season=
The
ability of peas to maintain higher canopy N levels than IHL
has been reported in other green manure studies.
In a
recent study in Saskatchewan, which included another variety
of field peas (Pisum sativum L= 'Trapper') and IHL, field
38
Curve F it
), R =0.90
A W P : y=296.4/(l +122.5e
), R =0.98
IHL: y=236.2/(l+88.O e -0
). R =0.98
- GBM: 7=251.1/(1+898.7©
O A W P-H 1993
# IH L -H
V G B M -H
Curve F it
A W P : 7=572.3/(1 + 100.9e'0t
IHL: 7=279.9/(1+ 1081.Oe"0'
0.98
GBM: 7=257.5/(l + 12076e_°
O AW P-M
• IH L -M
V GB M -M
Curve F it
-0 07
A W P : 7=337.3/(1 + 179.5©
- IHL: y=265.2/(l + 1 I S ^ e "0 061
GBM; 7=204.5/(l+9314.7e"° 1
), R =0.99
O A W P-L
• IH L -L
V G B M -L
0
Fig.
14.
20
40
60
80
100
Days After Emergence
Canopy n itro g e n a c c u m u la tio n a fte r em ergence in 1993.
C om parisons betw een th re e species a t each seeding ra te .
39
350
300
250
Curve Fit
A W P : y=83.6/(1+385.7e"0'1Bl ), R 2=0.99
1HL: y=65.0/(l+304.4e~°15x ), R 8= L O O
CBM: y = 7 5 . 9 / ( l + 2 8 3 1.le”0161 ), R 2=0.99
200
150
100
50
O A W P-H 1994
# IH L -H
V
G B M -H
* * i •
0
Curve Fit
350
—0.1lx
300
A W P : y=B5.9/(l + 150.4e”"',1X ), R 2 =0.99
IHL: y=58.6/(1+325.7e~° Ux ), R 2 =0.99
250
GBM: y = 8 0 . 6 / ( l + 5 7 3 8 . 1 e ^ ^ X ). R Z=0-98
200
150
100
50
O AW P-M
S IH L -M
V
GBM -M
0
Curve F it
350
—0.17x
A W P : y=79.9/(1 +1572.7e
300
250
), R
=
1.00
IHL: y=47.B/(l + 1748.4e”C 191 ), R 2= I-OO
GBM: y=74.1/(l+977.Be -0'121 ). R 2 =0.98
200
150
100
50
0
O A W P-L
# IH L -L
V
G B M -L
L-r-V
V-"
60
80
100
Days After Emergence
15
Canopy n itro g e n a c c u m u la tio n a fte r em erg en ce in 1994.
C om parisons betw een th re e species a t each seeding ra te .
40
80
Fig. 16.
100
Days After Emergence
Canopy n itro g e n a c c u m u la tio n a fte r em erg en ce in 1993.
C om parisons betw een seeding ra te s fo r AWP, IHL and GBM.
41
Curve F it
H: y=83.6/( 1+385.7e
), R =0.99
). R =0.99
M: y=85.9/(1+150.4e"
L y=79.9/(1 +1572.7e
O A W P -H 1994
• AW P-M
V AW P-L
Curve F it
c
H: y=55.0/(l+304.4e"
). R =1.00
M: y=58.6/( 1+325.7e"
L: y=47.8/(1+1748.4e
), R =0.99
), R =1.00
150
O IH L -H
S IH L -M
V IH L -L
Curve F it
H: 7=75.9/(1+2831.Ie
). R =0.99
-OlSl ), R =0.98
M: 7=80.6/(1+5738. Ie
L: y=74.1/(l+977.6e"C
), R =0.98
O G B M -H
• GBM -M
V G B M -L
0
20
40
60
80
100
Days After Emergence
Fig.
17.
Canopy n itro g e n a c c u m u la tio n a fte r em erg en ce in 1994.
C om parisons betw een seeding ra te s fo r AWP, IHL and GBM.
42
peas had greater dry matter production and canopy N
accumulation than did IHL (Townley-Smith et a l ., 1993).
Peak N production in 1993 occurred at approximately 320
kg/ha for A W P , 240 kg/ha for GBM and 190 kg/ha for IHL at
the medium seeding rate.
In 1994, peak N production was
only approximately 82 kg/ha for AWP and GBM, and 50 kg/ha
for IHL at the medium seeding r a t e .
Since canopy N and biomass production are so closely
correlated, within species comparisons of seeding rates show
very similar results (Figs = 16 and 17) to biomass data
(Figs. 12 and 13).
During both years, medium seeding rate
canopy N levels equaled and generally exceeded high seeding
rates.
Low seeding rates had lowest canopy N across all
species, even in 1994.
High plant populations apparently
were able to.maintain more canopy N, despite the increasing
biomass production in the low seeding rate plots later in
the season.
In general, maximum canopy N production
occurred with the medium seeding rate in all species.
N-—fixation
Figure 18 illustrates canopy N accumulation by barley
in comparison to the three legume species for 1993 and 1994.
Using the difference method, !^,-fixation iq assumed to be
that part of the legume N accumulation at a given time which
exceeds the N accumulated by barley.
The reader is reminded
that the difference method merely provides an estimate of
N2-fixation by legumes and is not totally accurate =
High
43
1994
1993
350
300
250
O
•
V
T
A W P-H
IH L -H
G B M -H
B A R -H
O
S
V
▼
AW P-M
IH L -M
GB M -M
B A R -M
O
•
V
▼
AW P-L
IH L -L
GBM—L
B A R -L
-
rv A ~
O
•
V
▼
A W P-H
IH L -H
G B M -H
B A R -H
O
•
V
▼
AW P-M
IH L -M
GBM -M
B AR -M
O
•
V
▼
A W P-L
IH L -L
G B M -L
B A R -L
200
150
100
50
350
o
300
-
250
-
-C
o j6
L -
200
>
N
Cl
O 150
C
O
O
100
O
O
50
350
300
250
-
-
200
150
100
50
0
100
Days After Emergence
Days After Emergence
10. T o ta l canopy N a c c u m u la te d a fte r em erg en ce in 1993 and
1994. C om parisons b etw een AWP, IH L1 GBM1 and BAR.
44
levels of NO3-N in the soil are known to inhibit nodulation
and/or !^-fixation by legumes =
A l s o , the level of NO3-N
which inhibits these processes varies from species to
species„
Soils data for 1993 and 1994, are reported in Tables 2
and 3 below.
Having been freshly broke out of sod,- soil
NO3-N was very low at planting in 1993.
Although an effort
was made to maintain these low levels in the 1994 plot area
by planting barley in 1993, NO3-N levels had increased
significantly by 1994=
Mineralization of soil N was no
doubt enhanced by the wet growing season of 1993.
Healthy
pink nodules were observed by day is o n -the three legume
species in 1993, and by day 23 in 1994 , indicating that N 2fixation was taking place.
T h u s , an unknown portion of the
N accumulated by the legumes prior to day 40 to 50 probably
was derived from N2-fixation.
Wright (1993) found that,
although both barley and legumes accumulated N from the soil
N po o l , at the end of the season legumes had taken less N
out of the soil pool than had barley.
This indicated
substantial N2-fixation had occurred.
Table 2.
1993 soil NO3-N, P, .K, organic matter, and pH at
at time of planting.
Depth
NO 3-N
P
K
O.M.
(cm)
(mg/kg)
(mg/kg)
(mg/kg)
(%)
0-15
1.73
5.33
421
1.53
8 =5
15 - 30
0.63
2.47
367
0.97
8.5
30 - 45
0.30
372
0.78
8.7
1-3 ,
pH
45
Table 3 =
1994 soil NO3-N,- P f K and organic matter at time
of emergence.
Depth
NO3- N '
P
K
O.M.
(cm)
(mg/kg)
(mg/kg)
(mg/kg)
(%)
0-15
15.5
11.7
356
1.5
15 - 30
9.9
—
—
30 - 45
4.8
----- —
— ——
—
Differences between 1993 and 1994 barley canopy N (Fig.
19) are a little less dramatic than were the differences for
the legume canopy N accumulation curves =
This is likely due
to earlier seed set and maturity in barley, as compared with
the legumes.
However, had the 1994 soil NO3-N remained at
the same low level as in 1993, 1994 barley canopy N levels
may have been even lower.
In general, in 1993, legume canopy N exceeded that of
barley around day 50 to 60 (Fig. 20), with the earliest
instance around day 50, noted with the AWP medium seeding
rate.
Negative values were considered to be zero.
Differences between legume performance are the same as those
discussed in the previous section on legume canopy N
accumulation.
Peak performance occurred at the medium
seeding rate for all species, where AWP led with
approximately 225 kg/ha, GBM at almost 150 kg/ha and IHL at
100 kg/ha.
46
O B A R -H
9 BAR—M
V B A R -L
1994
Biomass (k g /h a )
15000
12500
O B A R -H
S BAR-M
V B A R -L
1993
10000
7500
5000 1994
2500
O B A R -H
• BAR-M
V B A R -L
1993
1994
Days After Emergence
Fig.
19.
C u m u la tiv e ET1 biom ass and canopy N a c c u m u la tio n
a f t e r e m erg en ce fo r b a rle y in 1993 and 1994.
47
Curve F it
-
A W P : y = 1 18.2/(1 +3.86E9e~° 30J, R S=0.98
IHL: y=46.2/(l + 1.53E9e”0Zte), R 2=O.96
_ G B M : y=92.5/(l+3.16E9e”0'3ta ), R 2=0.97
..-V
O A W P-H 1993
S IH L -H
V
G B M -H
Curve F it
A W P : y=627.8/( I + 1 3 7 1.7e"0
R
IHL: y = 102.5/(1+2.6 9 E 9 e _° 2Bl )> R
G B M : y=138.3/(l+4.06E9e”a3ta)' I
O AW P-M
• IH L -M
V
GB M -M
Curve F it
_ A W P : y=95.1/(l+3.65E9e_° 2
IHL: y = 125.1/(1+1.00E9e"° 2
G B M : y=36.3/(l + 1.25E9e™°'2,
O A W P-L
• IH L -L
V
G B M -L
0
20
40
60
80
Days After Emergence
Fig.
20.
N2- fix a tio n a fte r em ergence in 1993. Com parisons
b etw een AWP, IHL, an d GBM a t each seeding ra te .
100
48
Curve F it
200
AWP: 7=29.5/(1+8.S B E Q e -0
R 2=0.99
GBM: y=20.9/(l+7.35E8e -°"361 ), R 2=0.99
150
100
50
0
O A W P-H 1994
V G B M -H
[
Curve F it
200
AWP: y=18.Q/(l + 7.19E8e-° ^
GBM: y=lB.4/(l+5.59EBe -°'a8
150
100
50
O AW P-M
V GBM -M
— -©
0
200
r© 0)
|©
Curve F it
C3
(y?
®
^
AWP: y=23.2/(l + 1.33E6e -°591 ), R Z=0.99
GBM: y=13.4/(l+6.3BEBe-°'3te), R 2 =O.92
150
100
50
0
O A W P-L
V G B M -L
© --©--©
Days After Emergence
21
N g - fix a tio n a fte r em erg en ce in 1994. C om parison
b etw een AWP and GBM a t each seeding ra te .
49
In 1994,
(Fig= 21) legume canopy N exceeded barley N
between day 40 and 50=
Performance was very similar for all
seeding rates in AWP and G B M f and reached a plateau pf only
25 kg/ha.
Indianhead lentil had very similar performance to
barley, but was never able to exceed barley levels in 1994=
Although there are inherent problems with using the
difference method to calculate N2-fixation, it does give a
graphic illustration of the advantages of using a legume
crop for green manure, rather than one that is not able to
fix nitrogen.
Water Use Efficiency
In Terms of Cumulative ET vs= Percent Canonv Cover
Data shown here and in following water use efficiency
(WUE) comparisons were fit to polynomial equations which
were statistically compared for coincidence.
Regressions
displayed in the following figures which have the same
letter are considered coincident at the p=0.05 level.
In
general, in 1993 (Fig. 22) AWP and GBM had similar WUE=
Indianhead lentil usually had lowest WUE=
One explanation
for this may be that IHL has a more open upright canopy, as
compared to the more dense, prostrate growth habit of AWP
and GBM=
Thus, the IHL canopy allows for greater
evaporation at all seeding rates.
Biederbeck and associates
(1993) came to a similar conclusion in a green manure study
which included black lentil (Lens culinaris Medikus) and a
50
30
‘Curve F it'
A W P : y=-10.5+1.3x-0.02x2+0.00015z3, R 2=.0.94
25
IHL:
y=-17.3+l.gx-0.03x2+0.00019x3 R 2=O.99
GBM:
20
15
y=0.9+0.66x-0.014x2+0.00009x3 R 2=0.96
Paired Compa r i s o n s (p=0.05)
AWP: A
.
------------IHL: B
GBM: A
_ -
-G.. V'
10
O A W P-H
• IH L -H
V
G B M -H
5
30
Curve F it
1993
T
A W P : y = - 5 . 1 + 0 9x-0.002x 2+0.00011x3, R 3==0.87
IHL:
y = - 8 . 9 + 1.3 x -0.02 x 2+0.OOOlSx3, R 2=O.99
25
GBM:
20
y=l.l+0.67x-0.014x2+0.00009xa, R 2=O.98
15
10
P a ir e d C o m p a r is o n s ( p = 0 . 0 5 )
AWP: A
IHL: B
5
GBM:
30
A
O AWP-M
# IH L -M
V
GBM-M
T
Curve F it
A W P : y=-2.8+0.9x-0.02x2+0.00013xa, R 2=.0.97
IHL: y=-3.0-H.lx-0.02x2+0.00014x3, R 2=O.99
25
GBM:
20
y=8.0+0.68x-0.014x2+0.0001x3, R 2=0.98 ,
15
10
Paired C ompar i s o n s (p=0.05) _
AWP: B
IHL C
GBM: A
5
O AW P-L
• IH L -L
V
G B M -L
I
0
(
60
80
100
Canopy Cover (%)
2.
u m u la tiv e ET vs. canopy cover regressions fo r 1993.
om parisons of AWP, IHL and GBM a t each seeding ra te .
12i
51
Line F it
A W P : y=l.l+0.26x, R Z=0.88
IHL:
y=-1.3+0.48x, R Z=0.90
GBM:
y=3.25+0.27x, R 3=O-Sl
o °
P a ir e d C o m p a r is o n s ( p = 0 . 0 5 )
AW P:
IH L :
G BM :
A
B
A
O A W P-H
• IH L -H
V G B M -H
1994
Line F it
AW P:
y = 1 . 2 + 0 . 2 9 x , R2= 0 . 9 3
IH L :
y = 0 . 2 7 + 0 . 4 B x , R 2= 0 .9 3
G BM :
y = 1 . 7 6 + 0 . 3 4 x , R2= O .8 8
Paired C o mparisons (p=0.05)
AWP: A
IHL B
GBM: A
O AWP-M
• IH L -M
V GBM—M
Line F it
AW P:
IH L :
-
GBM :
y = 0 . 6 + 0 . 3 4 x , R2= . 0 .9 7
y = 0 . 6 3 + 0 . 5 7 x , R " = 0 .9 1
y = 2 . 9 4 + 0 . 4 4 x . R2= O .9 1
Paired Compa r i s o n s (p=0.05)
AWP: A
IHL: B
GBM: B
Canopy Cover
Fig.
23.
O AW P-L
• IH L -L
V G B M -L
(% )
C u m u la tiv e ET vs. canopy cover regressions fo r 1994.
C om parisons of AWP, IHL and GBM a t each seeding ra te .
52
30
Curve F it
25
H:
M:
y = — 5.1 + 0.9 x — 0.002xa+0.00011x3, R 2=O.87
20
L
y=-2.8+0.9x-0.02x2+0.00013x3, R 2=.0.97
15
y=-10.5+1.3x-0.02xS+0.00015xa, R 2=.0.94
Paired C ompar i s o n s (p=0.05)
H: A
M: A B
L: B
.--V
10
O A W P-H
# AW P-M
V
A W P-L
5
30
Curve F it
H:
25
1993
y = - 17.3+1.9x-0.03x + 0 . 0 0 0 IOxgl R
=0.99
2
y=-8.9+1.3x-0.02x<1+0.00015x3. R^=O-Og
M:
L:
y=-3.0+l.lx-0.02x3+0.00014x3, R 2=O.99
^
20
15
Paired C o mparisons (p=0.05)
H: A
M: A
L: A
10
O IH L -H
S IH L -M
V IH L -L
5
30
25
'Curve F it 1
H:
y=0.9+0.66x-0.014x2+0.00009x3, R 2=O.96
M: y=l.l+0.67x-0.014^2+0.0000%xa,^ = 0 . 9 8
L: y=2.0+0.6Bx— 0.014x +0.OOOlx . R =0.98
20
Paired Compar i s o n s (p=0.05)
15
H: A
M: A
L: A
10
O G B M -H
S GBM -M
V
G B M -L
5
0
80
100
Canopy Cover (%)
24.
C u m u la tiv e ET vs. can o p y cover regressions fo r 1993.
C om parisons betw een seeding ra te s fo r AWP, IHL and
1:
53
Line F it
H:
y=l.l+0.26x, R Z=0.88
M:
y=1.2+0.29x, R 2=O.93
L:
y=0.6+0.34x, R 2=.0.97
P a ir e d C o m p a r is o n s ( p = 0 . 0 5 )
O A W P-H
• AW P-M
V A W P-L
1994
Line F it
H:
M:
y = — 1.3+0.48x, if=0.90
y=0.27+0.4Bx, R 2=O.93
L:
y=0.63+0.57x, R =0.91
Paired C omparisons (p=0.05)
H: A
M: A
L: B
----- -----
O IH L -H
S IH L -M
V IH L -L
Line F it
H: y=3.25+0.27x, R^=0.81
M: y=1.76+0.34x, ^ = 0 . 8 8
- L: y=2.94+0.44x, R =0.91
Paired Compar i s o n s (p=0.05)
H: A
M: A
L: B
O G B M -H
• GBM-M
V G B M -L
Canopy Cover (%)
Fig.
25.
C u m u la tiv e ET vs. canopy cover regressions fo r 1994.
C om parisons betw een seeding ra te s fo r AWP1 IHL and GBM.
54
feedpea (Pisum sativum L=)=
They measured stem length and
canopy h e i g h t a n d calculated the degree of decumbency =
Their conclusion was that the lentil has an erect growth
habit, while the feedpea has a more prostrate growth habit =
This allowed the feedpea to provide more ground coverf and
thus more soil protection.
During the first 20 days after emergence, GBM appeared
to have lower WUE due to greater evaporation, however, this
quickly changed after GBM commenced canopy growth =
The same trends were true in 1994,
(Fig. 23).
However,
distinctions were not quite as obvious, possibly because
evaporation was not as critical=. Statistically, there was
no advantage between AWP and GBM at high and low seeding
rates, but AWP had higher WUE at low densities =
It was postulated that higher stand densities should
have higher W U E .
In terms of canopy cover, this often
appears to be true for all species between the high and low
seeding rates and often the medium and low rates (Figs. 24
and 25)=
The low seeding rate appeared to have left more
soil exposed and had higher evaporation.
Medium and high seeding rates were often coincident at
the 5% level.
If there was similar evaporation for both
seeding rates, one explanation for this may be that
increased seedling mortality in the high rate caused
population levels to decrease to near those of the medium
rate, hen c e , transpiration was similar.
55
I
I
I
Curve F it
15000
A W P : y=514.7-142.1x+SS.8x2, R*=.0.99
12500
IHL:
y = 1 4 9 . 1-5.7x+12.lxS, R 2=O.99
GBM:
10000
7500
y=-227.1-22.9x+15.0x2, R S=O.90
Paired C o mparisons ^p=0.05)
AWP: A
IHL: C
GBM: B
5000
O A W P-H
S IH L -H
V
G B M -H
2500
1993
0
C urve F it
15000
Biomass (k g /h a )
A W P : y=663.6- 177.2x+26.8x2, R Z= 0 9 8
12500
IHL:
y=218.8-36.6x+13.6x‘', R 2=O.98
GBM:
y=82.5-113.0x+21.3xe, R 8= L O O
10000
P a ir e d C o m p a r is o n s ( p = 0 . 0 5 )
7500
5000
AWP: A
IHL: C
GBM: B
O AWP-M
• IH L -M
V
GBM -M
2500
0
15000
12500
10000
7500
Curve F it
A W P : y=350.3-119.7x+20.3x2, R 2=-0.98
IHL: y=-88.77+27.4x+10.5x2 R 2=O.98
GBM:
y = - 5 1 3 . 2 + 6 2 . 7 x + 1 1.3x , R 2=0.98
Paired C o mparisons (p=0.05)
AWP: B
IHL: C
GBM: A
5000
O AW P-L
• IH L -L
V
G B M -L
2500
0
Cumulative ET (cm )
Fig.
26.
Canopy biom ass a c c u m u la tio n vs. ET regressions fo r 1993.
C om parisons of AWP, IHL an d GBM a t each seeding ra te .
56
I
I
Curve F it
15000
AVP:
IH L :
12500
G BM :
10000
i
O A W P-H
y = 3 9 7 . 1 - 1 5 4 . 8 x + 4 4 . 3 x ‘ - 1 . 4 x S, R * = . 0 .9 0
1994
• IHL-H
y = 1 1 2 6 . O - 5 8 D . 0 x + lO 3 . 7 x 2- 3 . 9 x 3, R3= 0 .9 B
V
G B M -H
y = 5 6 1 . 1 - 3 7 0 . 0 x + 6 9 . 8 x 3- 2 . 4 x 3. R 3= 0 . 9 9
P a ir e d C o m p a r is o n s ( p = 0 . 0 5 )
AVP: A
7500
IH L :
G BM :
B
B
5000
2500
0'
Curve F it
15000
O AWP-M
• IH L -M
V GBM -M
Biomass (k g /h a )
A W P : y=366.8-166.1x+42.2x8-1.2x33, R*- 0 9 9
12500
10000
7500
IHL:
y=424.3-212.9x+45.2x3-1.4x3>R 2=0.98
GBM:
y=52 5 . 4 — 485.6x+110.6x2— 4.6x3, R 3=O.97
Paired C o mparisons (p=0.05)
AWP: A
IHL: C
GBM : B
5000
2500
O AW P-L
• IH L -L
V G B M -L
A W P : y=552.9-364.7x+84.8x®-3.1x3, R 3= O GG
12500
10000
7500
IHL:
GBM:
y=546.2-307.7x+61.2xZ-2.1x3, R 3= O GG
y = — 156.1+28.5x+5.8xZ+0.27x3, R 3=O.92
Paired C o mparisons (p=0.05)
AWP: A
IHL: B
GBM: B
10
15
20
25
30
C um ulative ET (cm )
Fig.
27.
Canopy biom ass a c c u m u la tio n vs. ET regressions fo r 1994.
C om parisons of AWP, IHL and GBM a t each seeding ra te .
57
In Terms of Biomass vs„ ET
Austrian winterpea had highest WUE during both years
(Figs= 26 and 27)=
The only exception to this occurring in
the low seeding rate in 1993, where there was very little
distinction between the three species and GBM eventually led
in efficiency.
In 1993, differences between species did not become
apparent until after approximately 15 cm of water use.
In
1994 , the growth cycle was almost complete by this point and
there appeared to be very little distinction between the
three species =
However, AWP curves were generally not
coincident at the 5% level with GBM and IHL curves =
Biederbeck and Bouman (1994) found similar results
using a feed pea (Pisum sativum L=) and black lentil (Lens
culinaris Medikus) =
The feed pea. used water more
efficiently in. terms of dry matter production than did the
black lentil.
On the other h a n d , Wright (1993) found there
was no significant difference in WUE in terms of biomass
production between A W P , IHL and GBM in a wet year.
However,
in a dry year AWP and IHL had similar W U E , but significantly
greater than GBM=
Within species comparisons between seeding rates (Figs =
28 and 29) reveal no distinctive trends between 1993 and
1994.
In 1993, the medium rate had highest WUE for AWP and
G B M , with IHL showing no difference between rates.
58
Curve F it
15000
12500
H:
y=514.7-142.1x+22.Bx , R =0.99
M:
y=6B3.8-177.2x+26.8xZ, R Z= 0 9 B
L:
y = 3 5 0 . 3 - 119.7x+20.3x*, R*=.0.90
10000
Paired C o mparisons (p=0.05)
7500
H: B
M: A
L: B
5000
O A W P-H
• AW P-M
V AW P-L
2500
Curve F it
15000
H:
mass (k g /h a )
1993
12500
y=149.1-5.7x+12.1x2, R 8= 0.99
M:
y=218.8-36.6x+13.BxZ, R Z=0.98
L:
y = - B 6 . 77+27.4x+10.5xZ, R 2=0.98
10000
Paired C o mparisons (p=0.05)
7500
H: A
M: A
L: A
5000
O IH L -H
• IH L -M
V IH L -L
2500
Curve F it
15000
12500
H:
y=-227.1-22.9x+15.8x8, R Z=0.98
M:
y = B 2 . 5 - 1 1 3 . 0 x + 2 1 . 3 x 2^ R a | 1 . 0 0
L:
y=-513.2+62.7x+11.3x . R =0.98
10000
Paired C o mparisons (p=0.05)
H: B
M: A
L: B
7500
5000
O G B M -H
# GB M -M
V G B M -L
2500
0
5
10
15
20
25
30
C um ulative ET (cm )
Fig.
28.
Canopy biom ass a c c u m u la tio n vs. ET regressions fo r 1993.
C om parisons betw een seeding ra te s fo r AWP1 IHL and GBM.
59
Curve F it
15000
H:
12500
- M:
L:
y = 3 9 7 . 1 - 1 54.8x+44.3x2- 1.4x3, R"=.0.98
y=366.8-166.1z+42.2x2-1.2x3, R 2= 0 9 9
O A W P -H
• AW P-M
V
AW P-L
1994
y=552.9-364.7x+84.8xZ-3.1x3, R 2=O.99
10000
7500
5000
_
Paired C o mparisons (p=0.05)
H: A
M: A
L: A
2500
Curve F it
15000
Biomass (k g /h a )
H:
12500
y = l 128.0— 580.8 x + 103.7x -3.9x , R =0.96
M:
y=424.3-212.9 x +45.2x 2- 1.4x 3,R2=0.98
L:
y=546.2-307.7x+61.2x2-2.1x3, R 2=O.99
O IH L -H
• IH L -M
V
IH L -L
10000
7500
5000
Paired C omparisons (p=0.05)
H: A
M: B
L: A B
2500
Curve F it
15000
12500
H:
y=561.l-370.0x+69.Bx -2.4x , R =0.99
M:
y=525.4-485.6x+110.|>x2-4.6£3, ^f= 0.97
O G B M -H
# GBM-M
V
G B M -L
10000
P a ir e d C o m p a r is o n s ( p = 0 . 0 5 )
7500
5000
2500
Cumulative ET (cm)
Fig.
29.
Canopy biom ass a c c u m u la tio n vs. ET regressions fo r 1994.
C om parisons betw een seeding ra te s fo r AWP, IHL and GBM.
60
After producing the largest gradients between seeding
rates in 1993, no coincidence between rates was detected for
AWP in 1994 =
For IHL, slight differences were detected with
greatest WUE occurring in the high seeding rate and,
surprisingly, lowest occurring in the medium seeding rate.
Only GBM showed any consistency between years, with the
medium seeding rate being detected as having the highest WUE
and the high seeding rate the lowest.
In Terms of Total Canopy H vs. ET
During both 1993 and 1994, AWP clearly had the highest
WUE of the three species (Figs. 30 and 31).
In 1993, GBM
curves were shown to be coincident with AWP curves at the 5%
level.
Indianhead lentil had significantly lower WUE than
the other two species.
In 1994, this trend changed.
Austrian winterpea still
had significantly higher WUE at all three seeding rates,,
whereas the GBM WUE at the high seeding rate was less than
that of A W P , but higher than that of IHL.
At the medium and
low seeding rates, the WUE curves for GBM and IHL. were
coincident at the 5% level.
The detected differences in WUE
noted above were slight in 1994 when compared to those found
in 1993.
In a wet year, Wright (1993) reported the same trend
with AWP and GBM having similar WUE in terms of canopy N ,
and significantly higher than IHL.
However, in a hot dry
61
I
T
Curve F it
A V P : y=-6.5+3.5x+0.3x 2,BR 2=.0.97
IHL:
y=7.4+0.4x+0.2x8, R 8= 0.99
G B M : 3t= - 1 7 . 9 + 3 . 0 x +0. 3 x 8, R Z=0.97
Paired Compa r i s o n s (p=0.05)
AVP: A
IHL: B
GBM: A
O A W P-H
• IH L -H
V G B M -H
tv
1993
r
Curve F it
o
SZ
Ch
-X
A VP:
y=-2.7+3.0x+0.3x8, R 2= 096
IHL:
y=6.0+0.25x+0.26x2, R Z=0.99
OO
G B M : y=-11.6+1.0x+0.4x2, R Z=0.97
Paired Compa r i s o n s (p=0.05)
AVP: A
£
O
C
O
O
IHL:
B
GBM: A
O AWP-M
S IH L -M
V GBM—M
O
350
Curve F it
A V P : y=-0.5+0.7x+0.34x2. R Z=.0.99
IHL:
GBM:
y=-1.6+1.7x+0.2xZ, R 2=0.97
y = - 2 6 . 1+5.3x+0.Sx 21 R 2=0.94
Paired C o mparisons (p=0.05)
AVP: A
IHL: B
GBM: A
O AW P-L
S IH L -L t
V GBM—L
Cumulative ETT (cm )
Fig.
30.
Canopy n itro g e n a c c u m u la tio n vs. ET regressions fo r 1993.
C om parisons of AWP, IHL and GBM a t e a ch seeding ra te .
62
Curve F it
350
O A W P -H
S IH L -H
V GBM—H
A W P : y=44.7-20.3x+3.5x2-0.13x3, R 8=.0.96
300
IHL
y = 19.1-9.8x+2.3xS-0. Ilx3, R 8= O 98
250
- GBM:
200
- Paired C o mparisons (p=0.05)
AWP: A
150
- IHL C
GBM: B
1994
y=30.58— 18.6x+3.3 x 8— 0.1 3x3, R 3=O.98
100
50
0
350
------- T----Curve F it
o
-C
O AWP-M
• IH L -M
V GBM -M
A W P : y=31.07-14.7x+2.8x8-0.11x3, R 2= O Q S
300
Ch
250
-
IHL
y=1.5— 1.7 x + 1. Ix8-O.OSx 31R 2=O. 93
GBM:
y=14.7-14.2x+3.5x8-0.15xS, R 2=0.92
200
Cl
O
C
O
O
Paired C o mparisons (p=0.05)
AWP: A
EL : B
GBM: B
150
100
50
O AW P-L
• IH L -L
V G B M -L
A W P : y=11.35-8.2x+2.6x”-0.12x3^ R Z=0.97
300
I H L y = — 2 .1— 0.26x+0.9x2-0.046x39 R 2=0.94
GBM: y=15.0— 10.3x+1.9x -0.069X , R = 0 7 9
250
200
150
-
Paired C o mparisons (p=0.05)
I-
AWP: A
E L
B
GBM: B
100
50
V
Oi
0
5
10
15
20
25
30
Cum ulative ET (cm )
Fig.
31.
Canopy n itro g e n a c c u m u la tio n vs. ET regressions fo r 1994.
C om parisons of AWP, IHL and GBM a t each seeding ra te .
63
Curve F it
H:
y = — 6.5+3.5x+0.3x‘, R*=.0.97
M:
y=-2.7+3.0x+0.3x2, R 2= 0 9 6
L:
y=-0.5+0.7x+0.34xZ, R 8=.0.99
Paired Compa r i s o n s (p=0.05)
H: A B
M: A
k
B
O A W P-H
• AW P-M
V A W P-L
1993
Curve F it
H:
M:
L:
y = 7 .4 + 0 .4 x + 0 .2 x , R = 0 .9 9
y=6.0+0.25x+0.26xZ, R 2= O GG
y=-1.6+1.7x+0.2x8, R 8=0.97
P a ir e d C o m p a r is o n s ( p = 0 . 0 5 )
M: A
k
A
O IH L -H
• IH L -M
V IH L -L
Curve F it
H:
y=-17.g+3.0x+0.3x2, R 3=O-G?
M: y=-11.6+1.0x+0.4^8, I^=0.97
L: y=-26.1+5.3x+0.2x , R =0.94
P a ir e d C o m p a r is o n s ( p = 0 . 0 5 )
O G B M -H
• GBM-M
V G B M -L
0
5
10
15
20
25
30
C um ulative ET (cm )
Fig.
32.
Canopy n itro g e n a c c u m u la tio n vs. ET regressions fo r 1993.
C om parisons betw een seeding ra te s fo r AWP, IHL and GBM.
64
Curve F it
H:
M:
- L:
y=44.7-20.3x+3.5x2-0.13x3, R 2=.0.96
y=31.07-14.7x+2.8 x 2-0.1 lx3, R 2= O O S
O A W P -H
• AW P-M
V
A W P-L
1994
y = U . 3 5 - 8 . 2 x + 2 . 6 x 2-0.12x3, R 2=O-O?
Paired C o mparisons (p=0.05)
H: B
M: B
L: A
Curve F it
H:
y=19.1-9.8x+2.3x -O.llx , R =0.98
M:
y=1.5-1.7x+l.lx2-0.05x3,RZ=0.93
L:
O IH L -H
S IH L -M
V
IH L -L
y=-2.1-O.20x+O.9x2-O.O46x3, R 2=O.94
Paired C o mparisons (p=0.05)
H: A
M: B
L: B
Curve F it
H:
y=30.58-18.6x+3.3x -0.13x , R =0.98
M: y=14.7-14.2x+3.6^-0. ISx8s R 2=0.92
L: y=15.0-10.3x+1.9x -0.069x , R = 0 7 9
O G B M -H
• GBM-M
V
G B M -L
P a ir e d C o m p a r is o n s ( p = 0 . 0 5 )
H: A
M: A
L: A
Cumulative ET (cm )
Fig.
33.
C anopy n itro g e n a c c u m u la tio n vs. ET regressions fo r 1994.
C om parisons betw een seeding ra te s fo r AWP1 IHL and GBM.
65
year, IHL and A W P ’had highest WUE with GBM being
significantly lower.
Comparisons between seeding rates within species (Figs,
32 and 33) does not conclusively confirm the theory that
higher stand densities will have higher WUE=
In 1993, only
AWP showed any differences between seeding rates.
The
medium seeding rate led in WUE over the low rate.
With
ample moisture in 1993, competition for light and nutrients
in the high rate may have resulted in smaller individual
plants.
This is consistent with the WUE in terms of biomass
accumulation shown in Fig, 28,
Though this trend was not
detected statistically in the other two species, it would
appear that their curves were beginning to separate in this
same fashion by the end of the season.
In 1994., there was even less variation between species.
For A W P , the low rate was detected as having the highest
WUE,
In a dry year, this would be expected since
evaporation is not as critical as are stored moisture
reserves.
This trend does not appear to carry through to
the other two species.
In the case of I H L , the high rate
was not coincident with the other two rates, while there was
no difference detected between fates in G B M .
Tn tPgvrmK of U-,-fixation vs. Cumulative ET
Comparisons between species (Figs. 34 and 35) reveal
that in 1993, AWP and GBM had almost identical WUE at all
66
I
I
Curve F it
200
I
I
r
A W P : y=23.71-7.88x+0.48x3, R 3=0.92
IHL:
y=11.72-3.4x+0.17x , R 8=0.69
GBM: y=16.55-5.76x+0.36x2, R 2=O.90
150
Paired C o mparisons (p=0.05)
100
50
0
200
150
100
50
0
200
AWP:
IHL:
y=20.57-5.89x+0.29x , R =0.73
y=2.B8-0.73x+0.03x2, R 2=0.43
GBM:
y=5.90-2.17x+0.15xe, R 2=O.91
150
Paired C o mparisons (p=0.05)
100
AWP:
A
IHL:
B
50
0
I
34
Cumulative ET (cm )
N g - fix a tio n vs. c u m u la tiv e ET in 1993. Com parisons
b etw een AWP, IH L1 and GBM a t each seeding ra te .
67
Curve F it
A W P : y = -6.43+1.14x+0.07|2, p 2=0.93
GBM: y=0.42-O.B0x+O.13x , R =0.93
P a ir e d C o m p a r is o n s ( p = 0 . 0 5 )
AWP:
GBM:
A
B
O A W P -H 1994
G B M -H
V
Curve F it
GBM:
y=1.36-1.08x+0.14x , R =0.96
Paired C o mparisons (p=0.05)
AVfP:
GBM:
A
A
O AW P-M
rS? GBM—M
Curve F it
AWP:
y=-7.03+2.37x-0.OI^81 ^ 8=O.94
GBM:
y=4.20-1.65x+0.13x , R =0.82
P a ir e d C o m p a r is o n s ( p = 0 . 0 5 )
GBM:
B
O A W P -L
V
G B M -L
Cumulative ET (cm )
Fig.
35.
N g - fix a tio n vs. c u m u la tiv e ET in 1994. Com parisons
b etw een AWP and GBM a t each seeding ra te .
68
Curve Fit
H:
y=23.71— 7.88x+0.48x3, R 2=0.92
M: y=27.55-9.62x+0.67x22, R 2=O.96
L: y=20.57— 5.89x+0.29x , R =0.73
Paired C o mparisons (p=0.05)
M:
L:
O AWP-H 1993
• AWP-M
V AWP-L
B
C
Curve Fit g z
H:
M:
L:
y=11.72-3.4x+0.17x2 R Z=0.89
y=22.86-7.04x+0.37x , R =0.95
y=2.68-0.73x+0.03x2, R 2=0.43
Paired Compar i s o n s (p=0.05)
O IHL-H
• IHL-M
V IHL-L
H:
M:
L:
A
B
C
Curve Fit
H:
y=16.55-5.76x+0.36x2, R Z=0.90
L:
y=5.90-2.17x4-0.15% , R =0.91
Paired C omparisons (p=0.05)
O GBM-H
• GBM-M
V
GBM-L
0
5
H:
M:
U
A
B
C
10
15
20
25
Cumulative ET (cm )
Fig.
36.
N g - fix a tio n vs. c u m u la tiv e ET in 1993. Com parisons
b etw een seeding ra te s fo r AWP, IHL, and GBM.
30
69
Curve F it
200
H:
y=-6.43+1.14x+0.07x2, p 2=0.93
O A W P -H 1994
• AW P-M
V
AW P-L
M: y=7.16-2.79x+0.32x
R =0.94
L: y = - 7 . 0 3 + 2 . 3 7 x — O.Olx , R =0.94
o
_c
Paired C o mparisons (p=0.05)
150
O)
XS
CD
X
U-
H:
A
M
L:
B
A
100 -
I
CN
Z
Curve F it
2
200
2
H:
M:
y=0.42— Q.BOx+0.13x , R =0.93
y = 1.38— i.08x+0.14x , R =0.96
L:
y=4.2 0 — 1.65x4-0.13x , R =0.82
O G B M -H
GBM—M
•
G B M -L
V
CS
.C
150
Paired C omparisons (p=0.05)
CO
H: A
M: A
L: B
-X
XS
CD
X
100
I
CN
Z
Cumulative ET (cm )
Fig.
37.
N g -fix a tio n vs. c u m u la tiv e ET in 1994. Com parisons
betw een seeding ra te s fo r AWP and GBM.
70
seeding rates.
Water use efficiency in IHL was
substantially below AWP and GBM levels.
In 1994, there were slight but detectable differences
at the 5% level between AWP and GBM at high and low seeding
rates only.
Wright (1993) found, in a year of low
transpirational demand, AWP to have higher WUE in terms of
!^,-fixation than G B M , followed by IH L . However, in.a year of
higher transpirational demand, he found that GBM instead of
IHL was not able to exceed accumulated canopy N levels in
spring wheat.
Comparisons of seeding rates within species (Figs. '36
and 37) in 1993 reveal in all three species WUE was
significantly different at all three seeding rates.
Highest
WUE occurring in the medium seeding rate, and lowest in the
low seeding rate.
This trend did not carry through to 1994.
In A W P , the
medium seeding rate had lowest W U E , while there was no
detectable difference between the high and low seeding
rates.
In G B M , high and medium seeding rates had similar
W U E , detectably above the low seeding rate at the 5% level.
71
Chapter 5
APPRAISAL OF METHODS FOR, MANAGEMENT OF GREEN MANURE
Plant Height
An important aspect of this study was to explore green
manure management methods which would be of practical use to
producers and agriculture consultants (Sims,- 1989)=
One
method considered was using plant height to predict
cumulative E T f biomass and canopy N accumulation=
Data from
1993f 1994 and a composite of 93/94 data was fit to the
equation y=a+bxf to model these relationships =
Regressions for plant height as a predictor of
cumulative ET showed good fit both years (Figs= 38 and 39)
for all species at all seeding rates =
Indianhead lentil
showed greatest fit, with most R 2 values equaling 0=99=
Austrian winterpea R2 values ranged from 0=96 to 0=98=
Lowest fit was found in G B M f with values ranging from 0=88
to 0=97=
Differences in rainfall between 1993 and 1994 caused
plant height to vary widely between years=
Austrian
winterpea grew to 150 cm in height in 1993, using 24 cm of
water, but only reached 60 cm in 1994, using 16 cm of water =
The other two species also varied in height but not as
72
O A W P-H 1993
• IH L -H
V
G B M -H
Line F it
AWP:
IHL:
GBM:
z
y=4.49+0.131x, R 2=O.96
y =0.35+0.509x, R 2=0.99
y=4.85+0.414x, R =0.92
O AW P-M
# IH L -M
V
GBM -M
Line F it
A V P : y=3.e+0.135x, R =0.97
IHL:
y=0.84+0.478x, R 20.99
GBM: y=4.36+0.461x, R S=0.92
O A W P-L
• IH L -L
V GBM—L
Line F it
AWP:
IHL:
GBM:
y=3.73+0.145x, R g=0.98
y=0.48+0.534x, R =0.98
y=4.99+0.425x, R 2= 0.88
Plant Height (cm )
Fig.
38.
C u m u la tiv e ET vs. p la n t h e ig h t regressions in 1993 fo r
AWP, IH L1 and GBM a t each seeding ra te .
73
O A W P -H 1994
• IH L -H
V
G B M -H
Line F it
A W P : y=0.91+0.301x, R 2=C^.98
IHL:
y = — 0.828+0.5 ISxlgR =0.99
GBM: 7 = — 2.15+ 1.14x, R =0.92
O AWP-M
• IH L -M
V
GB M -M
Line F it
A W P : y=1.23+0.267x, R 2=0.96
IHL:
y=-1.08+0.547x, R =0.99
GBM: y=-3.01 + 1.09x, R 2=O.96
O AW P-L
S IH L -L
V
G B M -L
Line F it
q
AWP:
7= — 0.10+0.266X, R g=0.97
IHL:
GBM:
y = - 2 . 0 5 + 0.622x, R =0.99
y = — 1.47+ 1.02x, R Z=0.97
y m _________I_____________ I____________ I_____________I_____________I_____________I----------- 1—
0
20
40
60
80
100
120
140
Plant Height (cm )
Fig.
39.
C u m u la tiv e ET vs. p la n t h e ig h t regressions in 1994 fo r
AWP, IHL, and GBM a t each seeding ra te .
74
30
25
20
15
Line F it
10
A W P : 7=5.52+0.132x. R =0.84
IHLy=-0.41+0.519x, R =0.98
GBM: y=4.90+0.439x, R =0.81
5
0
30
25
/
20
GBM—M /'
AW P-M
z z IH L -M
/
15
Line F it
10
A W P : 7=4.83+0.135x, R^= 0.88
IHL:
y=0.20+0.495x, R 3=O.98
GBM: 7 = 3 .22+0.517x, R =0.85
5
0
30
25
20
15
10
5
0
i
Plant Height (cm )
40
C u m u la tiv e ET vs. p la n t h e ig h t regressions fo r 1 9 9 3 /1 9 9 4
fo r AWP, IHL, and GBM a t each seeding ra te .
75
dramatically„
Because the cool wet year of 1993 was
extremely unusual, whereas 1994 had average precipitation
and temperatures, it may not be advisable to use the
composite regression of 93/94 ((Fig, 40) .
Partitioning of
water between evaporation and transpiration during the two
unlike years appeared to vary too widely=
0=98 for IHL were still quite high.
The R2 values of
However , AWP values
dropped to a range of 0=84 to 0=93, and GBM had the lowest
values, ranging from 0=81 to 0=85=
It is interesting to note Wright's (1993) pooled
regression constants for ET as a function of plant height=
For AWP y=l =16+0 =19x, R2=O =85 =
R2=O =96=
For IHL y = - l .04+0.46x,
For GBM y = l .46+0.52x, R2=O =92 =
Slopes are quite
similar in all cases to those found in this study, and R 2
values show similar trends =
This suggests that plant height
may be a good predictor of cumulative ET across a variety of
soil groups and climates =
Regression lines modeling plant height as a predictor
of biomass production (Figs. 41 and 42) were fit with good
results.
Once again, IHL showed highest fit with R 2 values
ranging from 0.96 to 0=99=
Values for AWP ranged from 0=91
to 0=96, and GBM values ranged from 0=82 to 0=99=
Composite 93/94 R2 values for AWP and G B M , in some
cases, exceeded those for individual years (Fig. 43)=
This
suggests that plant height is a good predictor of biomass in
these two species despite climatic differences.
The slope
76
15000
12000
9000
6000
3000
0
15000
12000
9000
6000
3000
0
15000
12000
9000
6000
3000
0
Plant Height (cm )
ig.
41
Biomass vs. p la n t h e ig h t regressions fo r 1993, fo r AWP,
IH L1 and GBM at. each seeding ra te .
77
15000
O A W P-H 1994
S IH L -H
V
G B M -H
12000
9 0 00
6000
Line F it
A V P : y = — 495.8+82.98x, R * = 0.96
IHL:
y=-770.3+115.4x, R =0.99
G B M : y = — 1225+240.5x, R 2=O.92
3000 -
Biomass (k g /h a )
15000
O AW P-M
• IH L -M
V
GBM -M
12000
9000
6000
—
3000
A W P : y=-563.5+78.0x, R 8=0.94
IHL:
y = — 997.9+125.lx, R =0.96
GBM: y = — 1402+274.7x, R =0.93
15000
Line F it
O A W P-L
• IH L -L
V
G B M -L
12000
9000
6000
3000
^
Line F it
A V P : y = — 804.8+82.4x, R S=0.92
IHL:
y=-1050+130.9x, R 3=O.97
GBM: y — — 1 4 5 7 + 2 5 6 .4x, R 2=O.82
Plant Height (cm )
Fig.
42.
Biom ass vs. p la n t h e ig h t regressions fo r 1994, fo r AWP,
IH L1 and GBM a t each seeding ra te .
78
15000
1 9 9 3 /1 9 9 4
IH L -H
12000
9000
A W P-H
G B M -H
6000 -
Line F it
A W P : y = - 178.3+65.lx, R *=0-95
IHL:
y=-1728+174.5x, R =0.94
G B M : y = — 621.1 + 185.3x, R =0.97
3 0 00
15000
Biomass (k g /h a )
IH L -M
12000
AWP-M
GB M -M
9000
6000
3000
Line F it
AWP: y = — 659.6+76.6x, R =0.92
IHL:
y=— 1730+172.9x, R 2=0.94
G B M : y=-857.8+225.5x, R 2=O.98
15000
IH L -L
12000
9000
AW P-L -
6000
Line F it
3000
AWP:
IHL:
GBM:
y = — 476.9+65.4x, R 3=0.92
y = — 1 6 0 5 + 172.3x, R Z=0.95
y = — 446.9+171.Ox, R =0.89
Plant Height (cm )
Fig.
43.
Biom ass vs. p la n t h e ig h t regressions fo r 1 9 9 3 /1 9 9 4 ,
fo r AWP, IHL, and GBM a t each seeding ra te .
79
for AWP at the medium seeding rate is almost identical for
individual years =
The AWP composite R 2 values reflect this
relationship, ranging form 0.92 to 0=95.
Highest composite
values were in G B H , ranging from 0=89 to 0.97.
The IHL
values dropped slightly to a range of 0.94 to 0.95.
Using plant height as a predictor of canopy N
accumulation (Figs. 44 and, 45) once again produced
relatively good results.
Data for AWP fit well both years,
with R2 values generally ranging form 0.97 to 0.99.
The IHL
data fit better in 1993 with values of 0.97 as compared to
the range found in the 1994 data of 0.90 to 0.93.
The GBM
data had lowest f i t , with a range of 0.86 to 0.87.
Since canopy N is so closely correlated with biomass,
it is not surprising that R2 values in the composite 93/94
graphs (Fig..46) are quite good.
This is especially true in
AWP where values range form 0.94 to 0=96.
The GBM values of
0.95 and 0.94 for the medium and high seeding rates
respectively, were also quite good.
Indianhead lentil
showed a marked reduction in quality of fit, with values
dropping to a range of 0.81 to 0.89.
The compact growth
habit of IHL may reduce the precision of using plant height
as a predictor of canopy N accumulation. •
Growth Stage
Another method of green manure management is to use
growth stage as a predictor of cumulative E T , biomass and
80
O A W P-H 1993
* IH L -H
V
G B M -H
Line F it
A W P : y=2.21+1.47x, R 2=0.99
IHL:
y=-25.B+3.63x, R^=0.97 .
GBM: y=-7.33+4.65x, R 2=O.96
-c
300
O AW P-M
• IH L -M
V
G B M -M
250
Line F it
_
100
A W P : y = — 2.77+1.7lx, R =0.93
IHL: y=-2B.7+3.91x, R =0.97
GBM: y=-13.72+5.B4x, R =0.96
O A W P-L
# IH L -L
V G B M -L
O
Line F it
A W P : y = — 10.8+1.52x, R 2=O.98
IHL:
y=-25.7+3.74x. R =0.97 _
GBM: y=0.4fl+4.27x. R =0.86
Plant Height (cm )
Fig.
44.
Canopy N a c c u m u la tio n vs. p la n t h e ig h t regressions fo r
1993, fo r AWP, IHL, and GBM a t each seeding ra te .
81
O A W P-H 1994
• IH L -H
V
G B M -H
Line F it
A W P : y =z-0.54+1.68%, R^= 0.98
IHL:
y=-1.07+1.86x, R =0.90
GBM: y = — 32.3+6.76x, R =0.94
-E
O AW P-M
• IH L -M
V
GBM -M
300
250
Line F it
A W P : y=-3.28+1.59x, R =0.98
IHL:
GBM:
y=-7.36+2.22x. R Z=0.93
y = — 34.25+7.2lx, R =0.97
O A W P-L
S IH L -L
V
GBM- L
Line F it
A W P : y=-6.19+1.58x, R^=0.97
IHL:
y=-6.65+2,04x, R^=0.90
GBM: y=-39.1+7.24x, R =0.87
__________ i
__________ I
---------- 1---------- 1---------- 1--------- 1—
q
0
20
40
60
80
100
120
140
Plant Height (cm )
Fig.
45.
Canopy N a c c u m u la tio n vs. p la n t h e ig h t regressions fo r
1994, fo r AWP, IHL, and GBM a t each seeding ra te
82
1 9 9 3 /1 9 9 4
IH L -H
200
AW P-H
G B M -H
-
^—
Line F it
A V P : y=1.01 + 1.47x, R 8=0.97
IHL:
y = — 26.09+3.28s:, R 3=O-Bl
GBM: y=-12.74+4.78x, R 3= 0.95
50 350 -
IH L -M
AWP-M
GBM -M
Line F it
A W P : y=-9.42+1.73x, R 2=0.94
IHL:
y=-31.92+3.69x, R g=0.89
GBM: y=-20.78+5.97x, R =0.94
IH L -L
AW P-L
G B M -L z
_—
Li ne Fi t
A W P : y=-9.7+1.49x, R 2=O.96
IHL:
y = — 26.8+3.42x, R 2=O.86
GBM: y = — 9.12+4.Six, R =0.85
Plant Height (cm )
Fig.
46.
Canopy N a c c u m u la tio n vs. p la n t h e ig h t regressions fo r
1 9 9 3 /1 9 9 4 , fo r AWP, IHL, and GBM a t each seeding r a te
83
canopy N accumulation.
Results for A W P f IHL and GBM are
reported for both 1993 and 1994 (Figs, 47 through 52),
It
should be noted that scales on the y axes of these graphs
vary, so that distinctions can be made between seeding rates
in the 1994 data.
Curve fit information for data displayed
here is the same as that reported in previous sections.
In general, various stages of growth occurred earlier
after emergence in 1994 than in 1993, for all species.
Despite this, there may be a good correlation between
certain growth stages and cumulative E T ,
For example, at
the time of the first flower in 1993, AWP at medium seeding
rate had used approx. 11 cm of water.
In 1994, approx = 10
cm had been used at the time of first flower.
Comparisons
between.later growth stages do not show as close a
correlation of cumulative water use between years.
By the time of the first flower in 1993, IHL had used
approx. 16.5 cm of water at the medium seeding rate.
1994,, only approx. 11 cm had been u s e d .
In
Growth stage may
not be as good a predictor of cumulative ET for I H L .
In 1993, GBM had a cumulative ET of approx. 6 cm at the
time of first flower and 10 cm by the time of seed set.
In
1994, almost 6 cm of water had been consumed by the time of
first flower and approx. 10 cm by the time of seed set. It
would appear that growth stage may also be a good predictor
of cumulative ET in G B M , despite differences in climatic
conditions.
Actual water use is also a function of soil
84
texture, therefore, JLt is uncertain whether values from this
study would apply across all soil groups =
More research
would need to be conducted before absolute values could be
determined for various growth stages =
Using growth stage to predict biomass and canopy N does
not show as close a relationship between years as in the
case of cumulative ET=
This is true for all species, not
surprising in view of the fact that climate has a large
effect on partitioning of water between evaporation and
transpiration, hence biomass production =
85
15000
Biomass (k g /h a )
12500
O A W P-H 1993
• AWP-M
V AW P-L
10000
7500
5000 2500
O A W P-H
• AW P-M
V AW P-L
O A W P-H
• AW P-M
V AW P-L
80
Tendrils
1 s t F lo w e r
Fig.
47.
I 90
100
P o d F i l lin g
F u l l B lo o m
Pod Set
Biom ass, ET and N a c c u m u la tio n a fte r em ergence fo r AWP
a t each seeding r a te in 1993, by grow th stage.
86
5000
4000
g'
3000
O
2000
O A W P -H
• AWP-M
V AW P-L
1994
1000
O A W P-H
e AW P-M
V AW P-L
-A
10
• AW P-M
V AW P-L
10
201
5 Nodes
T e n d r ils
Fig.
48.
40
ISO
1 s t F lo w e r
F u l l B lo o m
13 N o d e s
I
70
I 80
P o d F illin g
I 90
IC
P o d S h a tte r
P o d S e t / E n d F lo w e r in g
Biom ass, ET and N a c c u m u la tio n a fte r em erg en ce fo r AWP
a t each seeding r a te in 1994, by grow th stage.
87
15000
12500
O IH L - H
• IH L -M
V IH L -L
1993
10000
7500
5000
2500
O IH L -H
S IH L -M
V IH L -L
u
20
O IH L -H
• IH L -M
V IH L -L
4 0 1 5 0 6 0
2 B ra n c h e s
4 B ra n c h e s
1 s t F lo w e r
P o d Fill
Fig.
49.
Biom ass, ET and N a c c u m u la tio n a fte r em ergence fo r IHL
a t each seeding r a te in 1993, by grow th stage.
88
5000
4000
^
O IH L -H
• IH L -M
V IH L -L
1994
3000
2000
1000
O IH L -H
# IH L -M
V IH L -L
•_£
10
O IH L -H
• IH L -M
V IH L -L
20
70
UO
2 Branches
4 B ra n c h e s
1 s t F lo w e r
F u l l B lo o m
I
I 80
P o d F ill
P o d S h a tte r
Pod Set
Fig.
50.
Biom ass, ET and N a c c u m u la tio n a fte r em ergence fo r IHL
a t each seeding r a te in 1994, by grow th stage.
89
15000
O G B M -H 1993
• GBM -M
V GBM—L
12500
10000
7500
5000
2500
20
O G B M -H
• G B M -M
V G B M -L
-
O G B M -H
# GBM -M
V G B M -L
100
-
1st true leaf
se e d s e t/flo w e r in g
1 s t p o d s b la c k /s h a tte r
1st Flower
Fig.
51.
Biom ass, ET and N a c c u m u la tio n a fte r em ergence fo r GBM
a t each seeding r a te in 1993, by grow th stage.
90
5000
O GBM-H 1994
S GBM-M
V GBM-L
4000
^
3000
2000
1000
O GBM-H
S GBM-M
V GBM-L
-A
10
O GBM-H
• GBM-M
V GBM-L
20
-
IlO
1 s t t r u e le a f
20
30
5 leaves
40l
50
60
70
80
I 90
100
1 s t p o d s b la c k /s h a tte r
seed set/flowering
1st pods b r o w n
Fig.
52.
Biom ass, ET and N a c c u m u la tio n a fte r em ergence fo r GBM
a t each seeding r a te in 1994, by grow th stage.
91
Chapter 6
SUMMARY ASfD CONCLUSIONS
The objective of this study was to determine the WUE of
three' legume species, Austrian winterpea, Indianhead lentil,
and George black medic in terms of dry matter production,
canopy N accumulation and !^,-fixation, as a function of
stand density.
It was hypothesized that increasing stand
density from low to medium to high would more quickly
achieve canopy closure, and therefore increase W U E .
Measurements were taken on field plots at Logan, Montana
over the 1993' and 1994 growing seasons.
From these data,
WUE regressions were constructed, comparing all species at
each seeding rate.
In addition, plant height data was used
to construct regressions, which would predict cumulative E T ,
dry matter production and canopy N accumulation.
Thirdly,
growth stage data was used to generate curves which would
predict these three elements.
Across both years, AWP consistently maintained highest
WUE in terms of percent canopy closure, biomass production,
canopy N accumulation and N2-fixation.
As reported
previously, AWP and field peas in general, have consistently
been ranked as the green manure legume with the highest
water use efficiency.
George black medic often had similar
92
WUE to A W P f in this study, and IHL consistently exhibited
lowest WUE of the three species =
Differences between
species were quite apparent during the cool wet year of
1993, but smaller during the more average year of 1994 =
This study was a culmination of several years of
research devoted to examining the effects of integrating
green manure into crop-fallow systems in semi-arid areas.
Originally, many hundreds of legume species were screened
for use as green manure crops.
Promising species were then
grown in rotation with small grains.
Green manure was shown
to substantially increase subsequent barley grain yield and
protein content.
In other studies, green manure crops were
terminated after using a previously determined amount of
water, and subsequent small grain yields were recorded.
Results from these studies using IH L > showed that
intermediate water use (4 to 6 inches) produced highest
grain yields, significantly above yields produced under a
classic fallow system (Sims and Slinkard, 1991). ' The
results of the current study, reported in this thesis, serve
to further refine the above mentioned research studies.
Results enable producers to determine which legume species
provides the greatest amount of biomass and canopy N with
the least investment of water.
Although AWP did display
higher WUE than other species, other criteria will influence
species selection by producers =
As suggested by other
researchers, factors such as seed cost and a desire for only
93
intermediate N production may make certain species such as
IHL more desirable for use in a green manure rotation,
despite having lower WUE than some of the other legume
species (Townley-Smith et a l , 1993)
No consistent trends emerged in within species
comparisons of WUE at high, medium and low seeding rates =
During both years, the medium seeding rate often emerged as
having highest W U E , with some exceptions,
It would appear
that the medium seeding rate generally has optimum potential
when these three species are used as green manure=
Plant height regressions exhibit good correlation with
cumulative E T , biomass and canopy N accumulation in all
three species =
It is exciting to see the similarity between
regression equations generated in this study and those from
Wright's research (.1993),
Regression slopes were almost
identical, despite broad differences in climate and soils =
A simple management tool such as these plant height
regressions will be very valuable to producers and
consultants for management of green manure crops.
There was good correlation between certain growth
stages for AWP and GBM in predicting cumulative E T , but not
for I H L .
More research needs to be conducted to determine
if these correlations will hold over a variety of climates■
and soil groups.
Growth stage was not a good predictor of
biomass or canopy N accumulation in any of the three
species.
94
LITERATURE CITED
Alessi , J= and J=F= Power= 1982= Effects of plant and row
spacing on dryland soybean yield and water-use
efficiency. Agron= J= 74:851-854=
Allison, F=E= 1973= Soil organic matter and its role in crop
production= Elsevier Scientific Publishing Company= New
York =
American Public Health Association. 1981= Automated cadmium
reduction method, pp. 376-379= In standard methods for
the examination of waste and wastewater. American
Public Health Association, Washington, DC=
Army, T=J= and J=C= Hide= 1959= Effects of green manure
crops on dryland wheat production in the great
plains area of Montana. Agron= J= 51:196-198=
A u l d , D=L=, B=L= Bettis, M=J= Dial, and G=A= Murray.
1982= Austrian winter and spring peas as green
manure crops in Northern Idaho= Agron= J= 74:10471050 =
Biederbeck, V=O=, and O=T= Bouman= 1994= Water use by annual
green manure legumes in dryland cropping systems.
Agron= J= 86:543-549=
Biederbeck, V=O=, O=T= Bouman, J= Looman, A=E= Slinkard,
L=D= Bailey, W=A= Rice, and H=H= Janzen= 1993=
Productivity of four annual legumes as green manure in
dryland cropping systems= Agron= J= 85:1035-1043=
Bremer, E=, R=J= Rennie, and D=A= Rennie= 1988=
Dinitrogen fixation of lentil, field pea and
fababean under dryland conditions= Can= J= Soil
Sci= 68:553-562=
Bremer, E=, and C= van Kessel= 1992=.Plant-available
nitrogen from lentil and wheat residues during a
subsequent growing season= 1992= Soil Sci= Soc= Am= J=
56:1155-1160.
Bremner, J=M= and C=S= Mulvaney= 1982= Nitrogen-total, pp=
595-624= In A=L= Page, R=H= Miller, and D=R= Keeney
(eds =) Methods of soil analysis. American Soc= of
Agron=, Madison, WI=
Campbell, C=A=, G=P= LaFond, A=J= Leyshon, R=P= Zentner, and
H=H= Janzen= 1991= Effect of cropping practices on the
95
initial potential rate of N mineralization in a thin
Black Chernozem= Can = J= Soil Sci= 71:43-53 =
Campbell , C=A=, and W= Souster= 1982= Loss of organic matter
and potentially mineralizable nitrogen from
Saskatchewan soils due to cropping= Can. J= Soil Sci=
62:651-656=
Ford, G =L= and J =L= Krall= 1979 = The history of summer
fallow in Montana = Montana Agric= Exp= Stn= Bul= 704 =
Hanks , R =J= 1985= Crop Coefficients for transpiration = p.
431-438= In Advances in evapotranspiration= Proc=
National Conference on Advances in Evapotranspiration,
Chicago, IL= 16-17, Dec. 1985= Am. Soc= Agric= Eng=,
St= Joseph, MI=
Hanks, R=J= 1983= Yield and water-use relationships: An
overview= p. 393-411= In H=M= Taylor et'al= (ed=)
Limitations to efficient water use in crop production.
ASA, CSSA and SSSA, Madison, WI=
Henson, R = A = , and G=H= Heichel= 1984. Dinitrogen, fixation of
soybean and alfalfa: comparison of the isotope dilution
and difference method = Field Crop Research. 9:333-346 =
Janzen, H = H = , J=B= Bole, V=O= Biederbeck, and A=E= Slinkard=
1990 = Fate of N applied as green manure or ammonium
fertilizer to soil subsequently cropped with spring
wheat at three sites in Western Canada = Can = J= Soil
Sci= 70:313-323=
Jenson, M=E= (ed=)= 1974= Consumptive use of water and
irrigation water requirements = Am. Soc= Civil Eng= New
York.
Koala, S= 1982= Adaptation of Australian ley farming to
Montana dryland cereal production = M=S= thesis, Montana
State University.
Knudsen, D=, G=A= Peterson, and P=F= Pratt= 1982= Lithium,
Sodium, and Potassium, pp. 225-246= In A=L= Page, R=H=
Miller, and D =R= Keeney (eds =) Methods of soil
analysis = American Soc= of Agron=, Madison, WI =
Kuc e y , R =M =N= 1989 = Contribution of N2 fixation to field
bean and pea N uptake over the growing season under
field conditions in Southern Alberta = Can. J= Soil Sci =
69:695-699=
LaRue, T =A= and T =G= Patterson = 1981= How much nitrogen do
legumes fix= Adv= Agron= 34:15-38=
96
Loomis, R=S= 1983 = Crop manipulation for efficient use of
water: An overview= p= 345-374= In H=M= Taylor et a l =
(ed =) Limitations to efficient water use in crop
production= ASA, CSSA, SSSA, Madison, WI=
Mahler, R =L = , and D =L= Auld= 1989 = Evaluation of the green
manure potential of Austrian winter peas in Northern
Idaho = Agron= J= 81:258-264 =
Mahler, R =L= and H= Hermamda= 1993 = Evaluation of the
nitrogen fertilizer value of plant materials to spring
wheat production = Agron= J= 85:305-309 =
Milthorpe, F =L= and J= Moorby, 197.4= An introduction to crop
physiology= Cambridge University Press, London =
Olsen, S =R= and L =E= Somners= 1982= Phosphorus = pp= 403-430 =
In A =L= Page, R =H= Miller, and D =R= Keeney (eds =)
Methods of soil analysis= American Soc= of Agron=,
Madison, WI=
Power, J=F= 1991= Growth characteristics of legume cover
crops in a semiarid environment = Soil Sci= Am= J =
55:1659-1663 =
Power, J =F= 1983 = Soil Management for efficient water use:
Soil fertility, p, 461-470= In H=M= Taylor et a l = (ed=)
Limitations to efficient water use in crop production =
ASA, CSSA, and SSSA, Madison, WI=
Power, J=F= and V=O= Biederbeck= 1991= Role of cover crops
in integrated crop production systems = p= 167-174= In
W =L= Hargrove (ed=) Cover crops for clean water = Proc =
Int= Conf= West Tennessee Exp= Stn= Apr= 9-11, 1991=
SWCS = Ankeny, IA =
Ritchie, J =T= 1983 = Efficient water use in crop production:
Discussion on the generality of relations between
biomass production and evapotranspiration = p. 29-44= In
■ H=M= Taylor et a l = (ed.) Limitations to efficient water
use in crop production. ASA, CSSA, and SSSA, Madison,
WI =
Ritchie, J =T = , and B =S= Johnson = 1990=
factors affecting evaporation= p.
Irrigation of agricultural crops =
30= ASA, CSSA, and SSSA, Madison,
Soil and plant
363-390 = In
Agron= Monogr =
WI=
Sims, J =R= 1989 = CREST farming: A strategy for dyrland
farming in the Northern Great Plains-Intermountain
region = Am= J= Alternat = Agric= 4:85-90 =
97
Sims, J=R= and V=A= Haby= 1971= Simplified colorimetric
determination of soil organic matter = Soil Sci =
112;137—141=
Sims, J = R = , and G=D= Jackson= 1971= Field measurement of pan
evaporation. Agron= J= 63:339-340 =
Sims, J = R = , S= Koala, R=L= Ditterline, and L=E= Wiesner=
1985= Registration of 'George' Black Medic= Crop Sci=
25;709-710 =
Sims, J =R = , S= Koala, D =W= Wichman, and D =E= Baldridge =
1989= Seeding dates for cool season and warm season
grain legumes in the Northern Great PlainsIntermountain region. Appl= Agric= Res= 4:208-212 =
Sims, J=R= and A=E= Slinkard= 1991= Development and
evaluation of germplasm and cultivars of cover crops =
■P= 121-129= In W =L= Hargrove (ed =) Cover crops for
clean water. Proc= Int= Conf= West Tennessee Exp= Stn=
Apr. 9-11, 1991= SWCS= Ankeny, IA=
Tanaka, D=L= and J=K= Aase= 1987= Fallow method influences
on soil water and precipitation storage efficiency.
Soil Till= Res= 9:307-316.
Tanner, C =B = , and T =R= Sinclair = 1983 = Efficient water use
in crop production: Research or re-search? p. 1-26= In
H =M= Taylor et al» (ed =.) Limitations to efficient water
use in crop production = ASA, CSS A , and S S S A , Madison,
WI =
Townley-Smith, L=, A=E= Slinkard, L=D= Bailey, V=O=
Biederbeck, and W=A= Rice= 1993= Productivity, water
use and nitrogen fixation of annual-legume green-manure
crops in the Dark Brown soil zone of Saskatchewan = Can.
J= Plant Sci= 73:139-148=
Welty, L = E = , L=S= Prestbye, R=E= Engel, R=A= Larson, R=H=
Lockerman, R=S= Speilman, J=R= Sims, LiI= Hart, G=D=
Kushnak, and A=L= Dubbs= 1988= Nitrogen contribution of
annual legumes to subsequent barley production = Appl =
Agric= Res= 3:98-104=
Wright, A =T= 1990 = Yield effect of pulses on subsequent
cereal crops in the Northern Prairies = Can= J= Plant
Sci= 70:1023-1032=
Wright, C=K= 1993= The water use efficiencies of five legume
green manure species = M =S= thesis, Montana State
University, Bozeman=
98
Zachariassen, J=A= and J=F= Power= 1991= Growth rate
and water use by legume species at three soil
temperatures = Agron= J= 83:408-413 =
I
99
APPENDIX
Water fcm
O C u m u la tiv e E v a p o ra tio n 1993
• C u m u la tiv e P re c ip ita tio n
Water (cm )
O C u m u la tiv e E v a p o ra tio n 1994
• C u m u la tiv e P re c ip ita tio n
Days A fter May I
Fig.
53.
Cum. pan e v a p o ra tio n and p re c ip ita tio n fo r 1 9 9 3 /1 9 9 4 .
MONTANA STATE VNWERSfTY UBRARfES
3 1762 10266200 2