WATER USE, YIELD, QUALITY, AND DINITROGEN FIXATION …
Transcript of WATER USE, YIELD, QUALITY, AND DINITROGEN FIXATION …
WATER USE, YIELD, QUALITY, AND DINITROGEN FIXATION OF SAINFOIN
AND ALFALFA UNDER GRADIENT IRRIGATION
by
TERENCE PAUL BOLGER, B.S. in Ag., M.S.
A DISSERTATION
IN
AGRICULTURE
Submitted to the Graduate Faculty of Texas Tech University in
Partial Fulfillment of the Requirements for
the Degree of
DOCTOR OF PHILOSOPHY
Approved
December, 1988
(lop- ?^ ACKNOWLEDGMENTS
I would sincerely like to thank my advisor, Dr. Jerry Matches, for
offering me this opportunity and for his guidance, support and encour
agement throughout ray Ph.D. program. Special thanks also go to Dr. Dan
Krieg for many stimulating and enlightening discussions and Dr. Dave
Wester for advice and constructive criticism in the statistical analy
sis of the data. The assistance of my other graduate committee mem
bers, Drs. Howard Taylor and Ron Sosebee, is truly appreciated.
Much of the field and laboratory work could not have been done
without the able assistance of others, including Owen Clark, Travis
Durham, Tom Griggs, Augustine Forgwe, Peter Karnezos, Saranga Kidambi,
Russell Kitten, Danny Mowrey, Menik Nayakekorala, Steve Peterson, and
John Rascoe; their contributions are greatly appreciated. Additional
thanks go to Kathy Looney for her excellent cooperation in the typing
of the manuscript.
Sincere thanks go to my parents for their support and love through
out my graduate program. Finally, I would like to thank mi amiga,
Lisa, for her support and encouragement during the preparation of the
manuscript.
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CONTENTS
ACKNOWLEDGMENTS
ABSTRACT
TABLES
FIGURES
ABBREVIATIONS
PREFACE
CHAPTER
I.
II.
III.
IV.
V.
REFERENCES
APPENDIX
WATER USE EFFICIENCY AND YIELD OF SAINFOIN AND ALFALFA
Introduction
Materials and Methods
Results and Discussion
Summary and Conclusions
WATER STRESS EFFECTS ON FORAGE QUALITY
Introduction
Materials and Methods
Results and Discussion
Summary and Conclusions
WATER STRESS EFFECTS ON DINITROGEN FIXATION
Introduction
Materials and Methods
Results and Discussion
Summary and Conclusions
WATER RELATIONS OF SAINFOIN AND ALFALFA
Introduction
Materials and Methods
Results and Discussion
Summary and Conclusions
GENERAL SUMMARY AND CONCLUSIONS
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ABSTRACT
Sainfoin (Onobrychis viciifolia Scop.) and alfalfa (Medicago
sativa L.) are perennial forage legumes adapted to the dry, calcareous
soils of the western United States. The objectives were to determine
irrigation and water stress effects on water use, yield, quality, and
dinitrogen fixation of these species. Measurements were made at four
points along an irrigation gradient.
Yield was a linear function of evapotranspiration (ET) for both
species. Maximum sainfoin yields were 85% of alfalfa (20.7 t ha~ ).
With adequate water for growth, sainfoin was ready to harvest 13 d
before alfalfa, and produced 63% of its total season yield in the
first two harvests (taken by late June) compared to alfalfa with 46%.
Total water use of both species was similar. Water-use efficiency
(WUE) of alfalfa was generally higher than sainfoin. Species differ
ences in WUE were largely due to differences in the evaporation (E)
component of ET. Seasonal WUE of sainfoin and alfalfa was similar
(18.2 vs. 16.7 kg ha"- mm""'-) in 1987.
Water stress had no consistent effect on forage quality. Forage
quality generally improved slightly or was unaffected by decreasing ET.
In a few cases forage quality decreased with decreasing ET. Alfalfa
was frequently higher than sainfoin in crude protein and dry matter
digestibility (DMD). Sainfoin and alfalfa were generally similar in
fibrous components. Path analysis revealed that water stress affects
DMD directly, and indirectly through its effect on leaf:stem ratio and
maturity.
Dinitrogen fixation decreased with ET in both species. The pro
portion of plant N derived from N^ fixation (Nsy) in sainfoin generally
decreased at a faster rate with ET than in alfalfa, suggesting that
sainfoin can fix similar Nsy as alfalfa under high irrigation, but that
the N« fixation ability of sainfoin is more sensitive to water stress.
Alfalfa Nsy was 35 to 85% compared to 0 to 72% for sainfoin, depending
on the degree of water stress.
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Sainfoin and alfalfa had generally similar water relations as
measured by water potential (4' ), leaf conductance (G), and leaf-air
temperature (AT) at Harvests 2 and 3 in 1987. A threshold of severe
stress at which G stabilizes at low rates and A T begins to increase
above zero, occurs at -2500 J kg" ^ in both species.
TABLES
1.1. Harvest dates for sainfoin and alfalfa. 10
1.2. Water-production functions for sainfoin and alfalfa by harvest and season. 11
1.3. Alfalfa water-production functions from line source sprinkler irrigation experiments in West Texas and New Mexico. 12
1.4. Relationship of LAI to ET for sainfoin and alfalfa at
first harvest in 1987 and 1988. 12
2.1. Relationship between ET and CP in sainfoin and alfalfa. 27
2.2. Relationship between ET and DMD in sainfoin and alfalfa. 28
2.3. Relationship between ET and NDF in sainfoin and alfalfa. 29
2.4. Relationship between ET and ADF in sainfoin and alfalfa. 30
2.5. Relationship between ET and ADL in sainfoin and alfalfa. 31
2.6. Mean values of forage quality components for sainfoin
and alfalfa (+ SE). 32 2.7. Proportion of variance accounted for and eigenvectors
for principal components. 33
2.8. Path analysis for effects of ET and stem content or maturity on DMD of sainfoin and alfalfa. 34
3.1. Atom percent N is a function of ET for sainfoin and alfalfa. 45
3.2. Proportion (Nsy) and total (Nf) N from fixation for sainfoin and alfalfa in Harvest 3 of 1987. 46
3.3. Seasonal comparisons of yield, N content, and N2 fixa
tion for sainfoin and alfalfa under high and low irri
gation in 1987. 47
A.l. Calibration and validation data for analysis of sainfoin and alfalfa forage quality components by NIRS. 76
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FIGURES
1.1. Total season irrigation applied as a function of distance from the sprinkler line source. 13
1.2. Season total water-production functions for sainfoin and alfalfa. 14
1.3. Water-production functions for sainfoin and alfalfa by harvest, 1986. 15
1.4. Water-production functions for sainfoin and alfalfa by harvest, 1987. 16
1.5. Leaf area development of sainfoin and alfalfa under non-stressed conditions during the second growth cycle in 1988. 17
1.6. Stand survival of sainfoin and alfalfa in fall 1987 as affected by irrigation level. 18
2.1. Principal components ordination of forage quality data, 1986. 35
2.2. Principal components ordination of forage quality data, 1987. 36
2.3. Principal components ordination of forage quality data,
1988. 37
3.1. Atom percent N as a function of ET, 1986. 48
3.2. Atom percent N as a function of ET, 1987. 49 3.3. Atom percent N as a function of 1987 seasonal ET when
water stress was alleviated in Harvest 2 of 1988. 50
3.4. Proportion of N from fixation (Nsy) and total N fixed (Nf) as a function of ET in Harvest 3, 1987. 51
4.1. Diurnal air temperature and vapor pressure deficit (VPD) on 23 June and 28 July 1987. 56
4.2. Diurnal plant water potential of sainfoin and alfalfa at Harvests 2 and 3 as affected by irrigation level. 57
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4.3. Midday plant water potential of alfalfa (A) and sainfoin (S) as a function of plant available water (PAW). Data from 23 June and 28 July. 58
4.4. Diurnal leaf conductance of sainfoin and alfalfa at Harvests 2 and 3 as affected by irrigation level. 59
4.5. Relationship between leaf conductance and plant water potential for alfalfa (A) and sainfoin (S) at Harvests 2 and 3. 60
4.6. Diurnal leaf-air temperature differential for sainfoin and alfalfa at Harvests 2 and 3 as affected by irrigation level. 61
4.7. Relationship between leaf-air temperature and water potential for alfalfa (A) and sainfoin (S) at Harvests 2 and 3. 62
4.8. Profile soil water of alfalfa and sainfoin under low irrigation on 11 June 1986 and 23 June 1987. 63
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ABBREVIATIONS
ADF acid detergent fiber
ADL acid detergent lignin
AT air temperature
CP crude protein
DM dry matter
DMD dry matter digestibility
A T leaf-air temperature
E evaporation
ET evapotranspiration
G leaf conductance
LAI leaf area index
LT leaf temperature
NDF neutral detergent fiber
Nf nitrogen fixed (kg ha )
Nsy proportion of nitrogen from fixation
PAW plant available water
PCA principal components analysis
SW soil water content
T transpiration
VPD vapor pressure deficit
WUE water-use efficiency
y plant water potential
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PREFACE
Forage legumes are important protein, mineral, and energy
sources for ruminant livestock wherever they can be grown. The
increase in animal performance from the inclusion of legumes into
forage-livestock production systems is widely recognized. The capabil
ity of legumes to derive a significant proportion of their nitrogen
needs from symbiotic dinitrogen fixation further contributes to their
usefulness in agricultural ecosystems. With the continual increase in
the price of nitrogen fertilizers and the eventual decrease in natural
gas supplies, there is an increasing interest in the use of legumes as
inexpensive and sustainable sources of nitrogen in cropping systems.
Unfortunately, relatively few legume species are adapted to the arid
and semi-arid regions of the western United States.
Sainfoin (Onobrychis viciifolia Scop.) and alfalfa (Medicago
sativa L.) are perennial forage legumes adapted to t le dry, calcareous
soils of the West where they are grown as irrigated and dryland pasture
and hay crops. It is recognized that certain legumes have a higher
water requirement and use water less efficiently than grain crops, and
native and introduced grasses. Alfalfa is a major irrigated crop in
the Southwest, and there has been increased interest in the use of
sainfoin in this region. In the Southwestern states, agriculture
accounts for 80 to 95% of total water consumption. As the demand for
this limited resource increases, water shortages may become more common
and costs of irrigation water may increase. Clearly, there is a need
for more efficient use of water in agricultural production. However,
little information exists on the effect of water stress on the yield,
forage quality, dinitrogen fixation and water relations of alfalfa and
sainfoin. The objectives were to determine: 1) irrigation and water
stress effects on dry matter production and water-use efficiency, 2)
water stress effects on forage quality, 3) the relationship of water
stress to dinitrogen fixation, and 4) the water relations of these
species under water stress. Results are reported in manuscript form,
with references combined into one section.
CHAPTER I
WATER USE EFFICIENCY AND YIELD OF
SAINFOIN AND ALFALFA
Introduction
Sainfoin (Onobrychis viciifolia Scop.) and alfalfa (Medicago sativa
L.) are perennial forage legumes adapted to the dry, calcareous soils of
the western United States where they are grown as irrigated and dryland
pasture and hay crops. Current interest in sainfoin began with the need
for alternatives to alfalfa, due to spread of the alfalfa weevil [Hypera
postica (Gyllenhal)] and the release of a well-adapted cultivar in
Montana in 1964 (Eslick, 1968). Sainfoin has several attributes which
make it a desirable alternative to alfalfa. Sainfoin's non-bloat induc
ing characteristic gives it an advantage over alfalfa for grazing, and
it is resistant to the alfalfa weevil (Ditterline and Cooper, 1975).
Sainfoin provides earlier spring grazing or hay production than alfalfa
(Melton, 1973; Smoliak and Hanna, 1975). Sainfoin yields have been less
than (Hanna and Smoliak, 1968; Melton, 1973), equal to, or greater than
alfalfa (Carleton et al., 1968b), depending on environment. Sainfoin
has compared favorably to alfalfa in forage quality (Carleton et al.,
1968a) and average daily gain of cattle (Jensen et al., 1968; Parker and
Moss, 1981; Marten et al., 1987).
In the Southwestern states, agriculture accounts for 80 to 95% of
total water consumption (Solley et al., 1983). As the demand for this
limited resource increases, water shortages may become more common and
costs of irrigation water may increase. Clearly, there is a need for
more efficient use of water in agricultural production. Briggs and
Shantz (1914) recognized that legumes had a higher water requirement and
used water less efficiently than grain crops, and native and introduced
grasses. Despite this fact, alfalfa is a major irrigated crop in the
Southwest, and there has been increased interest in the use of sainfoin
in this region (Glover, 1980).
There are various reports of sainfoin yields under irrigated
(Carleton et al., 1968b; Melton, 1973) or dryland (Hanna and Smoliak,
1968; Townsend et al., 1975) conditions, but no information is available
on the relationship of sainfoin yield to irrigation water supply. Only
one study reports on the water-use efficiency (WUE) (yield per unit of
water use) of sainfoin. Sainfoin seasonal WUE was 12.5 kg ha" mm" on
dryland in Colorado (Koch et al., 1972). In contrast, there are numer
ous reports on irrigation-yield relationships and WUE of alfalfa, in
cluding recent reviews by Heichel (1983) and Sheaffer et al. (1988).
Reports of alfalfa WUE range from 11.3 to 18.1 kg ha"" mm"-*-, with WUE
tending to be higher in cooler, more northerly climates (Sheaffer et
al., 1988). Thus alfalfa provides a frame of reference for the evalua
tion of sainfoin. Our objective was to determine yield and WUE of
sainfoin and alfalfa as related to irrigation or water use. Water-
production functions, the relationship between yield and evapotranspira
tion, were developed to describe these relationships.
Materials and Methods
"Renumex" sainfoin and "Cimarron" alfalfa were established in 1985
at Lubbock, Texas, (33° 36' N, 101° 65' W, 990 m elevation) on an Acuff
loam soil (fine-loamy, mixed, thermic Aridic Paleustolls), Seed was
inoculated with the appropriate Rhizobium spp. and seeded in rows 30,5
cm apart and 4 m long at seeding rates adjusted to achieve one pure live
seed per cm of row. Nitrogen (34 kg ha N) and phosphorus (57 kg ha
P) were applied broadcast and disked into the seedbed prior to seeding.
Soil fertility was maintained throughout the study at recommended levels
based on annual soil test results. This required broadcast application
of 65 kg ha"- P in the spring of 1986 and 1987.
The experimental design was a randomized complete block in split-
block arrangement with four blocks. Species were whole plot treatments
and four irrigation levels were subplot treatments as described by Hanks
et al. (1980).
Plots were irrigated uniformly in 1985 to promote stand establish
ment. Beginning in April, 1986, irrigation treatments were applied
using a line source sprinkler irrigation system (Hanks et al., 1976)
oriented parallel to the plant rows. This system produces a water
application pattern which is uniform along the line but decreases lin
early perpendicular to the line in either direction. Neutron probe
access tubes were located in the center of each subplot treatment at
1.8, 5.5, 9.1, and 12.8 m to each side of the sprinkler line. Volumet
ric soil water content (SW) was determined at the onset of spring growth
and at each harvest at 20-cm increments to a 2.8-m depth using a field-
calibrated neutron probe. Applied water (I) was measured with 100-mra
diameter catchment cans placed beside the neutron access tubes. Precip
itation (R) was measured with a rain gauge located adjacent to the plot
area. The plot area was bordered by a 15-m wide strip of tall wheat-
grass [Thinopyrum ponticum (Podp.) Barkw. and Dewey] to minimize varia
tion in microclimate within the experimental area. Evapotranspiration
(ET) was calculated for each growth cycle and for the year using a water
balance method: ET = I + R + ASW. Irrigation water was applied to
maintain SW at the sprinkler line near field capacity. Water applica
tion patterns for 1986 and 1987 are presented in Figure 1.1. Irriga
tions generally occurred at night, when wind speeds tended to be low, to
minimize evaporation losses and distortion of the water application
pattern. Annual precipitation at the site was 667 mm in 1986 and 469 mm
in 1987, 85% of which occurred during the growing season (March through
October).
Alfalfa was harvested for dry matter yield at about 10% bloom.
Sainfoin was harvested at about 50% bloom. When maturity varied along
the irrigation gradient, as was the case for some growth cycles, all
subplots were harvested when the high irrigation treatment reached
harvest maturity. A fall residual harvest was taken after a killing
freeze. A residual harvest of sainfoin was not taken in 1986 because it
forms a low-growing rosette of vegetative leaves in the fall which
remain green throughout the winter in our environment. The importance
of these leaves to spring growth is unknown, but previous work indicates
that residual leaf area is important for rapid regrowth of sainfoin
(Cooper and Watson, 1968). Harvests and harvest dates are listed in
Table 1.1. Two samples consisting of three rows (0.915 m width) 3 m in
length and centered 0.915 m to either side of each neutron tube were
flail-harvested to a 7.5-cm height and weighed, k subsample of about
0.2 kg fresh wt. was taken from each sample, weighed, dried (60°C), and
rsweighed to determine dry matter (DM) content. Yield for each subplot
was expressed as the mean DM yield of the two samples.
A 40-cm row segment from each subplot was clipped to ground level
for determination of leaf area index (LAI) at the first harvest in 1987
and 1988, and at 16, 23, and 27 d regrowth during the second growth
cycle in 1988, Leaves were removed and total leaf area was measured
using a leaf area meter (LICOR 3000), LAI was calculated as the ratio
of leaf area to ground area.
Percent basal cover was determined after the residual harvest in
the fall of 1987. A meter stick was placed along each of three rows in
each subplot. The cm of row occupied by vegetation was measured.
Percent basal cover was expressed as the mean of values from the three
rows within each subplot.
Water-production functions, defined as the relationship between
yield and ET, were developed for years and individual harvests. System
atic arrangement of irrigation levels resulting from the line source
sprinkler system may be expected to result in nonindependent observa
tions. We assume that observations are equally correlated and hence the
usual test statistics are appropriate (Graybill, 1976). Differences in
water-production functions of species within years and harvests and of
harvests within species were determined by testing the homogeneity of
regression coefficients (Graybill, 1976). When differences in slopes
among harvests occurred, slopes were separated using t tests (Steel and
Torrie, 1980). The 0.05 probability level was used for all tests of
significance unless stated otherwise.
Results and Discussion
Yield was a linear function of ET for individual harvests and
season totals (Table 1.2), This indicates that maximum yields may have
been limited by water supply. Maximum alfalfa yields were similar in
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both years, averaging 20673 kg ha" . Sainfoin yields were lower in 1986
than in 1987 due to environmental and management factors (discussed
later), with maximum yields of 8003 and 16815 kg ha"-'" in 1986 and 1987,
respectively. A comparison of our data with lysimeter data from Las
Cruces, NM (Sammis, 1981) indicates that maximum yields were near poten
tial. We obtained 20.7 t alfalfa with 1225 mm ET (Fig. 1.2). Sammis
obtained 23.0 t alfalfa with 1695 mm ET. Seasonal ET rates are deter
mined primarily by length of growing season and temperature regime
(Sheaffer et al., 1988). Sammis (1981) stated that lysimeter studies
are necessary to obtain water use data at the upper end of the water-
production function.
Water use (ET) by sainfoin and alfalfa was similar for individual
harvests and season totals (Figs. 1.2, 1.3, 1.4). Therefore, species
differences in yield are due to differences in water-use efficiency
(WUE) rather than water use per se. Alfalfa seasonal WUE was higher
than sainfoin in 1986 (Table 1.2) as indicated by a comparison of slopes
(units of kg ha mm ). In 1987, seasonal functions had similar slopes
(Table 1.2) but alfalfa had a greater intercept value than sainfoin,
resulting in greater WUE. If the evaporation (E) component of ET is
assumed to be negligible then intercept values should be zero. More
negative intercept values indicate a larger E component of ET. Differ
ences in intercept values, then, indicate differences in WUE due to the
E component of ET. It follows then, that given the intercept, slope
values indicate transpiration (T) efficiency. Improved WUE through
cultural or management practices results from decreased E (intercept
value) as a fraction of ET; T efficiency (slope value) is changed lit
tle, if at all (Tanner and Sinclair, 1983).
Seasonal water-production functions for sainfoin differed in slope
between years. The lower WUE of sainfoin in 1986 seems to be due to
environmental and management factors. March and April of 1986 had
higher temperatures and lower rainfall than normal. Irrigation treat
ments were not begun until 5 April 1986, although spring growth had
begun in early March. This resulted in lower sainfoin yields in the
first and second harvests of 1986 (Fig. 1.3) as compared to 1987
(Fig. 1.4). These reduced yields at a time when sainfoin WUE is highest
(Table 1.2; Koch et al,, 1972) partially account for the lower seasonal
WUE in 1986. Data from 1987 gives a better indication of the seasonal
yield potential (Fig. 1.2) and WUE (Table 1,2) of sainfoin.
Alfalfa seasonal water-production functions for 1986 and 1987 were
statistically similar, indicating that a common function could be devel
oped for alfalfa (Table 1,3). This function is statistically similar to
an alfalfa water-production function developed from the line source
sprinkler data of Sammis (1981) (Table 1.3), The slope of our combined
function (17,4 kg ha imn" ) also agrees with other reports of alfalfa
WUE in North Dakota (15.9 kg ha"" mm"" ) (Bauder et al., 1978) and more
recently in Idaho (17.2 kg ha"" ram""^) (Wright, 1988).
Sainfoin and alfalfa water-production functions for individual
harvests generally differed, with alfalfa having greater WUE due to
slope or intercept differences (Table 1.2). Exceptions were the first
harvest and residual harvest in 1987 when water-production functions for
the two species were similar. Second growth of sainfoin in 1987 had a
higher slope but lower intercept value than alfalfa (Table 1,2) result
ing in sainfoin yields being lower than alfalfa at low ET but equal to
alfalfa at high ET (Fig, 1,4), Sainfoin had lower intercept values than
alfalfa in Harvest 2 of both years and Harvest 3 in 1986 (Table 1.2).
The positive intercept values of alfalfa in Harvests 2 and 3 of both
years (Table 1.2), while biologically unexplainable, indicate very rapid
regrowth and development of leaf area, reducing E. Indeed, differences
in LAI seem to account for differences in intercepts (E) of sainfoin and
alfalfa. Alfalfa and sainfoin had similar LAI as a function of ET
(Table 1.4) at first harvest in 1987 and 1988, corresponding with simi
lar water-production functions (1988 data not presented). Alfalfa had a
higher rate of leaf area development than sainfoin in the second growth
of 1988 (Fig. 1.5), resulting in final LAI of 3.2 and 1.3 for alfalfa
and sainfoin, respectively. Low LAI of regrowth sainfoin could account
for the lower intercept (greater E) values. Similar results were ob
tained by Sheehy and Popple (1981) who found that alfalfa had a higher
rate of leaf area development and LAI after 27 d regrowth (3.3) than
sainfoin (1.5). Therefore, sainfoin WUE and yield may be increased up
to or near that of alfalfa by seeding sainfoin broadcast, or in rows
narrower than 30 cm, to increase LAI and reduce the E component of ET.
Water-use efficiency (slopes) and yield varied among harvests
within a species (Table 1.2; Figs. 1.3, 1.4), Sainfoin WUE was higher
for Harvests 1 and 2 in the spring, and declined in the summer. Har
vests 1 and 2 had higher WUE than Harvests 3 and 4 in 1986 at P = 0.09,
Koch et al, (1972) also found sainfoin WUE to be higher in spring than
summer. In 1987, Harvest 4 had greater WUE than Harvest 3 and was
greater than that of Harvest 4 in 1986 as a result of delaying harvest
to mid-September (Table 1,1) when environmental conditions were more
favorable for growth.
The residual harvest of both sainfoin and alfalfa had lower WUE
than other harvests in 1987, presumably due to increased partitioning of
assimilates to root and crown tissue. Carter and Sheaffer (1983a) also
reported reduced alfalfa WUE in fall due to fall dormancy responses.
However, Sammis (1981) obtained highest alfalfa WUE in the fall. Dif
ferences in alfalfa cultivar fall dormancy response and environment
could account for the different results obtained.
Alfalfa WUE in 1986 was highest in Harvest 1 and then remained
constant through the summer. In 1987, alfalfa WUE was similar among all
harvests except the residual harvest. In the fall of 1986, no relation
ship was found between yield and ET of alfalfa. Large rainfall events
during this period and possible differential runoff from irrigation
treatments caused unaccountable errors in ET calculations for Harvest 5
especially. Lack of water stress across irrigation treatments resulted
in little range of yield or water use in the residual harvest.
Sainfoin yield potential was highest in the spring and declined
thereafter, as indicated by 1987 data (Fig, 1,4), In Harvests 1 and 2
of 1987 maximum sainfoin yields were equal to those of alfalfa. In the
first growth of 1987, sainfoin reached harvest maturity 13 d before
alfalfa (Table 1,1), A comparison of 1987 yields with those of 1986
(Figs, 1.2, 1.3, 1.4) illustrates the importance of having high soil
water availability in early spring to realize early production and high
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yields of sainfoin. Others have reported similar seasonal growth pat
terns and early spring growth of sainfoin (Melton, 1973; Ditterline and
Copper, 1975). Since sainfoin yield potential and WUE is low in summer
(Figs. 1.2, 1.3), seasonal WUE could be increased, at the expense of
some yield decline, by reducing summer irrigation. However, some amount
of summer irrigation may be necessary to prevent severe stand loss of
sainfoin (Fig. 1.6). We observed rapid plant death in both years in low
irrigation plots after harvests followed by hot, dry environmental
conditions. We observed similar sainfoin stand loss on a loamy fine
sand soil, but on a clay loam soil dryland stands remained productive
for 5 years and no rapid stand loss was observed (Bolger and Matches,
1987). The rapid stand loss of sainfoin in our environment appears to
be due to environmental and/or management imposed stress rather than to
crown and root-rot pathogens, blamed for rapid stand losses of irrigated
sainfoin (Ditterline and Cooper, 1975). Hanna and Smoliak (1968) also
observed severe stand loss of sainfoin after an extreme summer drought.
However, at Akron, CO, sainfoin stand survival was 92% after the second
harvest season with below-average rainfall and prolonged late-season
drought during both years (Koch et al., 1972).
In contrast to sainfoin, alfalfa yield potential remained high
through the spring and summer, declining in fall due to dormancy re
sponses (Figs. 1.3, 1.4). Alfalfa yields were not reduced like those of
sainfoin by environmental and management factors in the spring of 1986.
Indeed, first and second harvest alfalfa yields in 1986 were similar to
those in 1987.
Summary and Conclusions
Maximum seasonal sainfoin yields were 85% of alfalfa in 1987.
Water-use efficiencies (slopes) of sainfcxn and alfalfa (18.2 and 16.7
kg ha" mm" , respectively) were similar in 1987. The differences in
yield were due to differences in intercepts (E component of ET). Dif
ferences in LAI seem to account for differences in intercepts between
sainfoin and alfalfa. Therefore, cultural and management factors aimed
at increasing sainfoin LAI, such as broadcast seeding or harvesting at a
higher stubble height to leave some leaf area for more rapid regrowth
(Cooper and Watson, 1968), should reduce the E component of ET resulting
in increased overall WUE and yield of sainfoin.
Sainfoin had maximum WUE and yield in the first two harvests,
whereas alfalfa WUE and yields remained high through the summer. The
seasonal growth patterns of the two species differed with sainfoin
producing 58 to 63% of its total season yield in the first two harvests
compared to alfalfa with 41 to 46% of its yield in the first two har
vests. A comparison of 1986 and 1987 results demonstrates the necessity
of early spring irrigation of sainfoin to realize maximum yields and the
early production advantage of sainfoin over alfalfa. Sainfoin WUE and
yield is lower in summer, so reduced summer irrigation may increase
seasonal WUE for a small decline in yield. However, moderate levels of
summer irrigation may be necessary to prevent rapid stand loss of sain
foin. Reasons for rapid sainfoin stand loss under low irrigation are
unclear and merit further study.
Sainfoin's early production potential suggests that its greatest
utility is as an early-season irrigated pasture or hay crop. Since
sainfoin is a non-bloating legume, it may have more potential for pas
ture usage than alfalfa. Alfalfa would be the best choice of species
when maximum yield is the desired objective, especially for irrigated
hay production.
10
Table 1.1. Harvest dates for sainfoin and alfalfa.
Harvest
1
2
3
4
5
R
Sainfoin
5/2
6/11
7/15
8/26
1986
Alfalfa Sainfoin
Month/day
5/2
6/11
7/15
8/12
9/25
11/7
5/19
6/23
7/28
9/17
11/19
1987
Alfalfa
6/1
6/23
7/28
8/31
10/1
11/19
11
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C • H O
M-i C
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>-l
o
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• H J->
a c :3
c o
•H 4J O :3
O t-i O i
I u 0) 4J CO
cs
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CO H
MH O
C O
m •H V CO
a, S o
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CO 0)
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c •H
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c • f — :
-C 4-J •H ^ CO
cu •H U 0)
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^
12
Table 1.3. Alfalfa water-production functions from line source sprinkler irrigation experiments in West Texas and New Mexico.
Water-production function n r Location and year
kg ha mm
Yield = -1491 + 17.4 ET 32 0.93 Lubbock, TX 1986 to 1987
Yield = -3524 + 16,6 ET 30 0,76 Las Cruces, NM 1978 to 1979
Line source sprinkler (Sanmiis, 1981)
Table 1.4. Relationship of LAI to ET for sainfoin and alfalfa at first harvest in 1987 and 1988.
2 Year Species Equation n r
1987 Sainfoin LAI = -1.369 + 0.014 ET^t 16 0.79
Alfalfa LAI = -2.032 + 0.013 ET^ 16 0.68
1988 Sainfoin LAI = -0.194 -h 0.006 ET^ 16 0.80
Alfalfa LAI = -0.517 + 0.009 ET^ 16 0.81
t Equations followed by the same letter are similar (P > 0.05).
13
E E Q UJ
Q. Q. <
tr LU
<
ouu -
6 0 0 -
4 0 0 -
2 0 0 -
0 -
• •
1986 1987
• El
' 1
#
•
B
j . . . . . . .
• El
B
W
' 1 " - 2 0 - 1 0
SOUTH
1 0
NORTH
2 0
DISTANCE, m
Figure 1,1, Total season irrigation applied as a function of distance from the sprinkler line source.
14
CO
UJ
UJ
• ALFALFA • SAINFOIN
4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0
ET, mm
25000
20000 -
1987
— , — I — I — I — ^ — I — « — [ —
4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0
ET, mm
• ALFALFA • SAINFOIN
Figure 1,2, Season total water-production functions for sainfoin and alfalfa.
15
HARVEST 1
(0 JZ
UJ
ET, mm
n ALFALFA • SAINFOIN
T ^ 1 "-1 0 0 2 0 0 3 0 0
5000 HARVEST 2
ET, mm
HARVEST 3 HARVEST 4
ns
YIE
LD,
5000
4000
3000
2000
1000
3 0 0
5000
3 0 0
HARVEST 5 HARVEST R.
r-
kg h
a Y
IELD
,
5000
4000
3000
2000
1000
ET, mm
5000
4000 -
3000 -
2000 -
1000 -J 2 ^
ET, mm
-1 \ 1 1 , —
1 0 0 2 0 0 3 0 0
Figure 1,3, Water-production functions for sainfoin and a l fa l fa by harvest, 1986.
16
HARVEST 1 HARVEST 2
OJ
>•
5000
4000
3000 -
2000 -
1000 -
0
t r g
a ALFALFA • SAINFOIN
- I — - - T — I — I 1 — I 1 -
1 0 0 2 0 0 3 0 0 4 0 0
5000
1 1 1 [ — ' 1 ^
0 1 0 0 2 0 0 3 0 0 4 0 0
ET, mm ET, mm
CO JZ
UJ >-
5000 -
4000 -
3000 -
2000 -
1000 -
0 -
HARVEST 3
/
B/
/ ilf*
1 - - ( - •'- -I - r - - f I
HARVEST 4
0 1 0 0 2 0 0 3 0 0 4 0 0
5000
T — T 1 1 \ 1 r -
0 1 0 0 2 0 0 3 0 0 4 0 0
ET, mm ET, mm
HARVESTS
1
n SI
YIE
LD,
5000
4000
3000
2000
1000
T — > — I — ' — r 1 0 0 2 0 0 3 0 0 4 0 0
ET, mm
cnnn -.
4000 -
3000 -
2000 -
1000 -
0 -C
HARVEST R
r i j j j l ^ y ^ *
^ ^ — • 1 ' 1
) 1 0 0 2 0 0 3 0 0 4( 30
ET, mm
Figure 1,4. Water-production functions for sainfoin and alfalfa by harvest, 1987,
17
3 -
2 -
ALFALFA SAINFOIN
1 0 2 0 3 0
DAYS REGROWTH
Figure 1,5, Leaf area development of sainfoin and alfalfa under non-stressed conditions during the second growth cycle in 1988,
1.-
Q
<
I-
LU o LU
100
80 -
60 -
40 -
20
ALFALFA SAINFOIN
H MH ML T L
IRRIGATION
Figure 1.6. Stand survival of sainfoin and alfalfa in fall 1987 as affected by irrigation level.
CHAPTER II
WATER STRESS EFFECTS ON FORAGE QUALITY
Introduction
Alfalfa and sainfoin are grown in the semi-arid and arid West under
irrigated and dryland conditions. As such, they frequently experience
some degree and duration of water stress. Water stress has been re
ported to increase forage quality but results have been inconsistent
(Vough and Marten, 1971; Snaydon, 1972; Wilson, 1983; Undersander et
al,, 1987), The increase in forage quality due to water stress is often
attributed in part to the negative effect on stem elongation resulting
in higher leaf:stem ratio (Vough and Marten, 1971; Snaydon, 1972; Brown
and Tanner, 1983). Sainfoin is unusual in that its stems are more
digestible than leaves until early flower (McGraw and Marten, 1986). No
reports were found on the effect of water stress on forage quality of
sainfoin.
Principal components analysis (PCA) is a multivariate technique
which is often used to analyze ecological data and determine environmen
tal gradients responsible for plant community patterns. Stallcup et al.
(1983) showed that PCA can be used to summarize and analyze forage
quality data effectively; however, PCA has rarely been used for this
purpose.
Our objective was to study the effect of water stress on the forage
quality of sainfoin and alfalfa. An additional objective was to assess
the utility of PCA and path coefficient analysis in analyzing and inter
preting the effect of water stress on forage quality.
Materials and Methods
Treatment variables, experimental design, and various procedural
aspects have been described previously (Chapter I). Further details
specific to this study follow.
19
20
In addition to data collected in 1986 and 1987, plots were har
vested twice in 1988, on 18 May and 14 June, to evaluate further the
water stress effects on forage quality. During the second growth cycle,
water stress effects on forage quality. During the second growth cycle,
all plots were irrigated uniformly to alleviate water stress across the
gradient, 2
At each harvest a 1-m area around each neutron tube was clipped to
a 7,5-cm height with hand shears. A subsample of about 0.2 kg fresh wt.
was dried (60 C), ground in a shear mill (2 mm), reground in a cyclone
mill (1 mm), and refrigerated in sealed plastic packets prior to quality
analyses. A subset of sainfoin and alfalfa samples, selected to repre
sent treatment, harvest, and yr effects, was assayed for contents of
crude protein (CP), in vitro dry matter digestibility (DMD), neutral
detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent
lignin (ADL).
Crude protein was determined as Kjeldahl N x 6.25, and NDF, ADF and
ADL were determined according to Goering and Van Soest (1970). Dry
matter digestibility was determined by a modified two-stage pepsin-
cellulase procedure (Clarke et al., 1982). Modification involved sub
stitution of Onozuka 3S cellulase at a cellulase:sample ratio of 1,25
(see McLeod and Minson, 1980),
About 2 g of each sample were placed in sample cups with quartz
windows and scanned with monochromatic radiation (1100-2500 nra). Dif
fuse reflectance (R) was collected with lead sulfide detectors in a
Pacific Scientific Model 6250 near infrared reflectance (NIR) monochrom-
ator and recorded as log R . The NIR spectroscopy (NIRS) calibration
equations for analysis of forage quality were developed by stepwise
multiple regression of each forage quality component (Y) on R~ values
(X's) for sainfoin and alfalfa, A common equation for both species was
developed for ADL, Infrasoft International software (Release 1.1) was
used to develop calibration equations and analyze samples.
Criteria for selecting best analysis equations were 1) F ratio >_ 10
on each selected wavelength; 2) minimum standard error of calibration 2
(SEC) and maximum R ; 3) minimum number of independent variables; and
21
4) minimum mean H for analysis values. The standardized H statistic
indicates how different a sample is from the average sample in the
calibration set. One indication of valid NIRS analysis is a mean H j< 3
(Shenk, 1985). Summary statistics for each prediction equation are
presented in Table A.l.
A 40-cm row segment from each subplot was clipped to ground level
for determination of maturity and stem proportion at the first and
second harvests in 1987 and 1988, Maturity was determined using the
mean stage by count method of Kalu and Fick (1981), Stem content was
expressed as a fraction of total dry wt, by separating leaves and in
florescences from stems, drying (90°C), and determining the dry wt. of
each fraction.
Regression analysis was used to determine relationships between ET
and forage quality components at each harvest. Differences in forage
quality components between species and species by ET interactions were
determined by testing the homogeneity of regression coefficients (Gray
bill, 1976). The 0.05 probability level was used for all tests of
significance. Species and water stress effects on forage quality as
measured by the five component analyses together were investigated using
uncentered, non-standardized PCA on the correlation matrix (Pielou,
1984). Path coefficient analysis (Li, 1956) was used to evaluate the
relative effects of water stress (ET) and maturity or stem content on
forage quality.
Results and Discussion
Regression Analysis
Univariate regressions showed that ET had no consistent effect on
forage quality components (Tables 2.1 to 2.5). In general, forage
quality components improved slightly or were unaffected by decreasing
ET. In a few cases, forage quality improved with increasing ET. For
example, sainfoin CP increased with ET in Harvest 3 of 1986 and Harvest
1 of 1987. Alfalfa CP increased with ET in Harvest 5 of 1987 (Table
2.1). Alfalfa ADL decreased with increasing ET in Harvests 5 and R of
1987 (Table 2.5). In Harvest 1 of 1988, alfalfa forage quality as
22
measured by four of five components improved with increasing ET. Crude
protein and DMD increased with increasing ET, while NDF and ADF de
creased with increasing ET, Acid detergent lignin increased with in
creasing ET (Tables 2.1 to 2.5). These results are consistent with
other reports in the literature. A review by Wilson (1983) indicates
that low soil moisture has either little effect or a beneficial effect
on CP and DMD. In a few cases, water stress had a negative effect on
forage quality, Vough and Marten (1971) found that alfalfa ADF and ADL
generally decreased with water stress. Undersander et al. (1987) re
ported that water stress decreased alfalfa NDF, ADF, and ADL content,
but also reduced the Jji vivo digestibility of these fibrous components
and total organic matter when stress was severe.
The response of sainfoin and alfalfa quality to ET, as indicated by
a test of slopes (Tables 2.1 to 2.5), was generally similar for a given
harvest. Since species by ET interactions were generally not signif
icant, mean values of forage quality components across levels of ET are
presented in Table 2.6. Significant interactions occasionally occurred
when 1) a forage quality component of one species changed with ET but
the other species was not affected, 2) a forage quality component of one
species decreased with ET while in the ot.ier species it increased with
ET, or 3) a forage quality component of one species changed at a faster
rate than in the other species (Tables 2.1 to 2.5). Alfalfa was fre
quently higher than sainfoin in CP and DMD (Tables 2.1, 2.2, 2.6).
Sainfoin and alfalfa had similar contents of NDF and ADF in 1986, but
sainfoin was frequently higher in NDF and ADF in 1987 and 1988 (Tables
2.3, 2,4, 2,6), Sainfoin and alfalfa were generally similar in ADL
content with sainfoin having greater ADL in Harvest 4 of 1986 and Har
vest R of 1987 (Tables 2,5, 2.6). In only one case was sainfoin higher
in forage quality than alfalfa, as measured by any of the forage quality
components. Sainfoin was slightly but significantly lower (9 g kg" ) in
ADF content in Harvest 4 of 1987 (Tables 2,4, 2,6), Carleton et al,
(1986a) reported that at the stage of maximum yield (100% bloom for
sainfoin, 10% bloom for alfalfa) sainfoin had 60 g kg" less CP than
alfalfa, but total digestible nutrient and crude fiber content of the
23
two species was similar, McGraw and Marten (1986) found that 10% bloom
alfalfa and 50% bloom sainfoin had similar DMD content (640 and 620 g
kg , respectively), but alfalfa was higher than sainfoin in CP content
(200 and 147 g kg" , respectively). Our values for CP content of al
falfa and sainfoin are generally higher than those reported by McGraw
and Marten (Table 2,6), while our DMD values are similar to theirs for
sainfoin but generally higher than theirs for alfalfa. Although alfalfa
tends to be higher in forage quality than sainfoin, especially in CP
content, both species are high quality forages, and sainfoin generally
has adequate CP content to meet the needs of high-producing cattle (140
g kg CP or more in the ration). Indeed, average daily gains of cattle
on sainfoin or alfalfa hay or pasture have been similar (Jensen et al.,
1968; Parker and Moss, 1981; Marten et al,, 1987),
Principal Components Analysis
Forage quality is assessed in the laboratory by a variety of dif
ferent analyses, the most conmion being CP, DMD, ADF, NDF, and ADL,
These various measures of forage quality are often correlated to each
other and therefore give similar indications of forage quality. Multi
variate analysis can give a relative measure of forage quality as deter
mined by various forage quality components taken together, taking advan
tage of the intercorrelation among forage quality variables. Principal
components analysis (PCA) is a multivariate ordination technique which
summarizes and projects points in a multidimensional space (in this case
five) into fewer dimensions with minimal loss of information (Gauch,
1982), For example, 84 to 96% of the total variance in our five vari
able data matrices was accounted for by the first two principal compo
nents (PC 1 and PC 2 in Table 2,7), Graphical presentation of treat
ments according to the two principal components facilitates comprehen
sion and evaluation of their relationships to each other in terms of
forage quality. In Figures 2,1 to 2,3, treatments are plotted on a
relative scale of ordination scores such that treatments similar in
quality are close together and treatments differing in quality are
farther apart. For display purposes, the two subplots nearest the
24
irrigation line are designated as high (H) irrigation, and the two
subplots farthest from the line, as low (L) irrigation treatments.
In all ordinations. Principal Component 1 (PC 1) represents a
forage quality gradient with CP and DMD (positively associated with
quality) loading on one side of the axis, and fibrous components (nega
tively associated with quality) loading on the other side of the axis.
The loadings of variables on PCA axes, known as eigenvectors, are shown
in Table 2,7, From 55 to 89% of the total variance is accounted for by
PCI alone (Table 2,7), The nature of PC2 is less clear. For example,
DMD and ADF are ordinated close together on PC 2 in Harvest 3 of 1986
(Table 2,7), Principal Component 2 appears to represent a gradient of
relative composition rather than quality per se and is of lesser impor
tance, accounting for only 7 to 31% additional variance.
The PCA ordinations (Figs. 2,1 to 2,3) generally lead to similar
interpretation of the data as an examination of the separate univariate
regressions (Tables 2,1 to 2,5), The ordinations indicate that forage
quality is usually higher for the low irrigation plots. Exceptions
include Harvests 3 and R in 1986, Harvests 5 and R in 1987, and alfalfa
in Harvest 1 of 1988, In Harvest 2 of 1988, all plots were highly
irrigated, and therefore the ordination reveals no differences in qual
ity due to the previous irrigation treatment (Fig, 2,3), Sainfoin and
alfalfa plots were ordinated into two distinct clusters due to differ
ences in forage quality (PC 1) and/or composition (PC 2). Alfalfa was
higher in quality than sainfoin except for Harvest 3 in 1986 and 1987
when the difference was more compositional.
By taking advantage of the intercorrelation among variables, PCA
revealed trends in forage quality not detected by the individual uni
variate regressions. For example, in Harvest 3 of 1986, none of the
univariate analyses (Tables 2.1 to 2.5) showed differences between
sainfoin and alfalfa, but PCA ordinated the species into two distinct
clusters (Fig. 2.1). Similarly, in Harvests 2 and 3 of 1987, univariate
regressions indicated that sainfoin forage quality was unaffected by ET,
or the responses were inconsistent (Tables 2.1 to 2.5). However, PCA
ordinations indicated that water stress resulted in higher quality in
25
both harvests. In Harvest 5 of 1986, regression analyses indicated no
effect of ET on forage quality except for a slight but significant
increase in ADL with ET (Tables 2.1 to 2.5), Lack of relationships may
have been partially due to errors in ET calculations for this growth
period (discussed in Chapter I), The PCA ordination indicated that the
low irrigation alfalfa was higher in quality (Fig, 2,1), In the PCA,
ordination scores were derived from forage quality data alone. Environ
mental interpretation of PCA ordinations is a separate step. Thus,
environmental factors affecting forage quality can be indicated by the
plants themselves through PCA, without direct measurement.
Path Coefficient Analysis
Path coefficient analyses were conducted using only DMD as the
dependent variable since it is probably the best single indicator of
forage quality and is highly correlated (r = 0,65 to 0,85) with other
forage quality variables. For the multiple regressions and subsequent
path analyses, ET and stem content (stem) were the two best predictors
of DMD for first harvests, and ET and maturity were the two best predic-2
tors for second harvests. Results of path analysis and R values for
multiple regression are shown in Table 2,8, In Harvest 1 of 1987,
increasing ET had a strongly negative, direct effect on sainfoin DMD,
which was greater than the positive direct effect of stem content on DMD
or the positive indirect effect of ET through stem content. The posi
tive influence of increased stem content on whole plant DMD seems back
wards, but McGraw and Marten (1986) found that stems were more digest
ible than leaves of sainfoin until early flower. Sainfoin maturity
ranged from vegetative to mid-bud stage at this harvest. Alfalfa DMD
decreased with increasing ET due to the indirect effect of ET increasing
stem content. Unlike sainfoin, alfalfa stems are less digestible than
leaves at all stages of maturity (McGraw and Marten, 1986). In Harvest
2 of 1987, the direct effect of maturity was twice as important as the
direct effect of ET on DMD for both species. Increasing maturity had a
negative effect on DMD of sainfoin, which ranged from mid-bud to late
flower stage, but had a positive effect on DMD of alfalfa, which ranged
26
from vegetative to early-bud stage. In Harvest 1 of 1988, alfalfa DMD
increased due to a direct effect of increasing ET. Sainfoin also had a
direct effect of ET to increase DMD, but this was less than the direct
effect of stem content to decrease DMD or the negative indirect effect
of ET through stem content. In Harvest 2 of 1988, uniform irrigation
resulted in little effect of ET on DMD, Maturity had a negative effect
on DMD content of both species. These results support those of previous
studies which indicate that water stress increases forage quality in
directly through its negative effect on stem elongation thereby increas
ing leaf:stem ratio (Vough and Martin, 1971; Snaydon, 1972; Bro\vTi and
Tanner, 1983) or by delaying plant maturity (Wilson, 1982; Halim et al.,
1985). Reports also indicate that water stress affects forage quality
directly by reducing fibrous components and increasing digestibility of
stem and/or leaf fractions (Vough and Marten, 1971; Snaydon, 1972;
Wilson, 1983; Undersander et al., 1987).
Summary and Conclusions
Alfalfa was generally higher than sainfoin in forage quality,
particularly in CP and DMD, Water stress had no consistent effect on
individual forage quality components, and this is consistent with other
reports in the literature. However, PCA ordinations indicated that
forage quality, as measured by the individual components taken together,
was generally increased by water stress. Principal components analysis
effectively summarized forage quality data for easy interpretation and
revealed trends in forage quality not detected by univariate analyses.
Path analysis revealed that ET affects DMD, both directly and indi
rectly, through its effect on leaf:stem ratio and maturity. More re
search is needed to determine how the timing, duration, and severity of
water stress is related to its effects on forage quality.
2 Li
Table 2.1. Relationship between ET and CP in sainfoin and alfalfa.
Year
1986
1987
1988
Harvest
1
2
3
4
5
R
1
2
3
4
5
R
1
2
Sainfoin
b
0,18
-0,22**
0,23*
-0.47**
—
—
0,11**
0,06
-0.12
-0.44**
—
-0.10
-0.06
0.06
r2
0.21
0.47
0.31
0.43
—
—
0,46
0,01
0.20
0.47
—
0.13
0.08
0.01
Alfalfa
b
0,00
-0.42**
0.06
-0,25**
-0,03
-0.05
-0,31**
0,00
-0,25**
-0,47**
0,43*
-0,11*
0,14**
0.08
r2
0,00
0.57
0,03
0,46
0,01
0,00
0,76
0,00
0.60
0,61
0,30
0,31
0,58
0,05
Compar: slopes interce a
* *
NS
NS
—
—
* *
* *
•*
NS
—
* *
NS
NS
Lson of and
b
NS
NS
NS
NS
—
—
* *
NS
NS
NS
—
NS
* *
NS
*,** Significant at the 0.05 and 0.01 probability levels, respectively,
28
Table 2.2. Relationship between ET and DMD in sainfoin and alfalfa.
Year
1986
1987
1988
Harvest
1
2
3
4
5
R
1
2
3
4
5
R
1
2
Sainfoin
b
-0.56**
-0.55**
0.08
-0.34*
—
—
-0.19**
-0.26
-0.32
-0.35**
—
-0.09
-0.06
-0.11
r2
0.52
0.64
0.03
0.34
—
—
0.47
0.11
0.20
0.39
—
0.06
0.11
0.03
Alfalfa
b
0.11
-0.32*
0.01
-0.27**
0.03
-0.20
-0.25**
0.00
-0.28**
-0.47**
0.33
0.04
0.35**
0.01
r2
0.06
0.35
0.00
0.52
0.01
0.06
0.57
0.00
0.65
0.63
0.24
0.02
0.77
0.00
Comparison of slopes and intercepts a b
NS
NS
NS ^:;:ic
*•
*
NS
—
* *
*
* *
* *
NS
NS
NS
—
—
NS
NS
NS
NS
—
NS
* *
NS
*,** Significant at the 0.05 and 0.01 probability levels, respectively,
29
Table 2.3. Relationship between ET and NDF in sainfoin and alfalfa.
Year
1986
1987
1988
Harvest
1
2
3
4
5
R
1
2
3
4
5
R
1
2
Sainfoin
b
0.44**
0.81**
0.02
1.01*
—
—
0.24**
0.02
0.62*
1.37**
—
-0.08
0.16**
0.12
r2
0.57
0.77
0.00
0.36
—
—
0.53
0.03
0.26
0.82
—
0.08
0.46
0.04
Alfalfa
b
0.71**
0.68**
0.17
0.65**
0.05
0.28
0.56**
0.49**
0.45**
0.85**
-0.15
0.46*
-0.18*
-0.01
r2
0.48
0.74
0.14
0.72
0.01
0.06
0.82
0.54
0.51
0.76
0.03
0.36
0.38
0.00
Comparison of slopes and
intercepts a b
NS
NS
NS
NS
—
—
* *
* *
NS
*
—
NS
* *
NS
NS
NS
NS
NS
—
—
* *
NS
NS
*
—
« *
* *
NS
*,** Significant at the 0.05 and 0.01 probability levels, respectively.
30
Table 2.4. Relationship between ET and ADF in sainfoin and alfalfa.
Year
1986
11987
1988
Harvest
1
2
3
4
5
R
1
2
3
4
5
R
1
2
Sainf
b
1.03**
0.54**
-0.06
0.67**
—
—
0.42**
0.24
0.38
0.71**
—
0.12
0.14**
0.06
oin
r2
0.80
0.68
0.01
0.41
—
—
0.78
0.06
0.23
0.76
—
0.23
0.48
0.02
Alfalfa
b
0.82**
0.70**
0.24
0.68**
0.03
0.30
0.48**
0.71**
0.45**
0.67**
0.14
0.28
-0.15*
0.03
r2
0.57
0.81
0.23
0.76
0.00
0,08
0,83
0,60
0,55
0,76
0.03
0.17
0.29
0.00
Compar: slopes interce
a
NS
NS
NS
NS
—
—
* *
NS
NS
*
—
NS
* *
NS
Lson of and =»ntR
b
NS
NS
NS
NS
—
—
NS
NS
NS
NS
—
NS
* *
NS
*,** Significant at the 0.05 and 0.01 probability levels, respectively
31
Table 2.5. Relationship between ET and ADL in sainfoin and alfalfa.
Year
1986
1987
1988
Harvest
1
2
3
4
5
R
1
2
3
4
5
R
1
2
Sainfoin
b
0.11**
0.09**
-0.02
0,04
—
—
0,02
0.04
0.02
0.12**
—
0.00
0.02
-0.04
r2
0.60
0.51
0.02
0,05
—
—
0,19
0.05
0.07
0.40
—
0.00
0.06
0.05
Alfalfa
b
0,01
0,04
-0.02
0.05*
0.03*
0.13
0.02
0.05*
0.05
-0.01
-0.14**
-0,06**
0,03*
0,00
r2
0,02
0,18
0,03
0,29
0,28
0,19
0.11
0.27
0,24
0,01
0,55
0,45
0,33
0.00
Compard slopes
.son of and
intercepus a b
*
NS
NS
NS
NS
NS
NS
—
* *
NS
NS
*
NS
NS
NS
—
—
NS
NS
NS
*
—
NS
NS
NS
*,** Significant at the 0.05 and 0.01 probability levels, respectively.
32
w CO
+ i
CO
CO
u-> rH
CO
t 3 C 03
C • H O
CO CO
O U-l
CO 4-J
QJ
O
E o o
4-J • H i H
CO
CJ
CT3 >-( O
CO OJ
i H CO >
c CO
s
CN
OJ i H
CT3
H
en
to
Q
CO c o a. E O
ITS
(V C7>
m
o
Q
t>0
s: o
00
•H-
a.
•M (/)
> I . >a 3C
ifl a>
> -
00 en 00 CM VO en
C3 O O I-H o o
+ 1 +1 +1 +1 +1 +1
o en •-< r~. o <n T-t o •—I <—I I—< o
+ 1 +1 +1 +1 +1 +1 VO VO
1—1
•-I
+ 1 in VO
(M
CM
rH
+ 1
<n o
+ 1
VO U5
p~
I-H
+ 1 in 00
CM in
1
in in
1
VO
00
o +1 +1 +1
VO
CM
CM
+ 1 CM CO
00
CO in
00 00
i n
00
^ en CO
r «s- o • - I CM
VO CO
<n 00 p~ VO CM
en 00 l o 00 «r
VO CO
CO
+ 1 i n i n
VO
+ 1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1
O VO
00 P^
^ t-H i n i n
<j- o i n CO
+1 +1 +1 +1 +1 +(
VO <3- o o en «*• rH l o r^ »H ^ r~ <—I TH
+ 1 +1 +1 +1 +1 +1 r^ 00 CM en CO CO
«a- CO «a- CO
lO VO r H
00 r~
VO
+ 1 +1 +1 +1
• * i n ^ 00 CO eg
in «i-CO
o CO «*
*i-CO ^
in 00 CO
358
VO
in
+ 1 rH cn CO
357
CO
00
+ 1
469
404
I-H
CM t-4
+ 1
409
308
in
rH
+ 1
350
290
1 303
CM
CO
+ 282
VO CM o o 00 i n
CO i n CO i n CO CM
+ 1 1-1 -I-l +1 +1 +\
r H CM en r^ I D VO
VO CO CO VO CO CM
+ 1 -HI -t-l +1 +1 +1
725
CO
VO
+ 1
660
678
«r VD
+ 1
cn rH VO
665
CM
«r
+ 1
619
757
o in
+ 1
619
693
1
775
t
719
p-
^
+ 1
679
730
o VO
+ \
635
706
rH
1—
+ 1
660
CO VO
in
VO
+ 1
709
804
1
806
CM
«s-
+ w-4 in <0
r«. CO i n o r- VO
CO i n CO i n CO CM
+1 +1 +1 +1 +1 +1
r» CO VO 00 CM o
VO CM CO ID ^ CM
+ 1 +1 +1 -t-l +1 -t-l
r~~ CO CM
00 CM CM
•3-VO r-H
rH in CM
00 en rH
T-l
00 CM
00 «T CM
rH >a-CM
r~ o CM
r*-r H
CM
CM rH CO
VO VO CM
CO O VO rH
CO CO CO VO
+ \ +\ +\ -t-l rH in 00 00 00 in
«:J-cn
CM
+ 1 rH
•cf
+ 1
168
CM
+ \ CO 00 rH
r--l-l 1
238
CO
-t-l
186
rH CM CO <»• in QC
VO 00 cn
rH CJ CO
00 cn
in c^
o cn
rH o
-t-l -t-l
p~ in
-t-l -t-l
CM in
in
in
in
in
00 CD CO
o ID
-t-l -t-l 253
CM
cn
-i-I
282
318
o
VO
-t-l
367
382
^ in
-t-l
355
294
o
en
-t-I
rH CO
255
1
214
1
278
o
00
-t-l
300
322
in
r--
•f 1
365
350
en r-
-t-l
318
251
«*
cn
+ 1
242
226
VO cn t—i
<n CM
-t-l
224
249
CO
•a-
-t-l
252
rH cn CM
o
CO
-1-
310
CO
355
CM
in
388
CO
«*•
en in CO
ID
r-«
+ \ in .rt
cn CO
-t-l
648
r H
CM
•t-l
773
CO
«*
-I-l
635
«* CO
+ 1
238
VO
<3-
-t-l
00 r-1
«r CM
-1-
235
CM
^
-t-
203
rH CM
00 00 cn r H
• f —
o V*-c
•f—
<0 y^ +-
(0 «.-r—
m <*-,— <r -t*
33
Table 2.7. Proportion of variance accounted for and eigenvectors for principal components.
Year Harvest
1986 1
2
3
4
5
R
1987 1
2
3
4
5
R
1988 1
2
Principal component
PC 1 PC 2
PC 1 PC 2
PC 1 PC 2
PC 1 PC 2
PC 1 PC 2
PC 1 PC 2
PC 1 PC 2
PC 1 PC 2
PC 1 PC 2
PC 1 PC 2
PC 1 PC 2
PC 1 PC 2
PC 1 PC 2
PC 1 PC 2
Proportion of
variance
- % -
,61 ,25
,81 ,11
.55 ,31
,81 .15
.63
.26
.64
.26
.65
.26
.89
.07
.63
.27
.72
.19
.69
.21
.69
.25
.55
.29
.70
.22
CP
-0.37 0.63
-0,46 0,36
-0.51 0.06
-0.49 0.10
-0.47 0,40
-0,35 0,66
0,45 0.40
-0.45 0.46
-0.51 0.24
-0.49 0.07
-0.47 0.22
0.53 0.02
0.58 -0.04
0.50 0.00
Eig
DMD
-0.49 0,36
-0.47 0.16
-0.39 0.57
-0.45 0.45
-0.48 0.37
-0.51 0.25
0.53 0.03
-0.46 0.34
-0.53 0.20
-0.49 0,32
-0,52 0.08
0.53 0.02
0.56 -0.03
0.51 0.08
envector
NDF ADF
0.50 0.19
0.47 0.04
0.47 0.43
0,45 0,45
0.51 0,24
0.50 0.21
-0,52 0,20
0,47 -0,01
0,47 0.43
0.46 0.36
0.51 0.24
0.24 0.77
0.34 0.75
0.32 0.75
0.53 0.24
0.47 -0.22
0.37 0,60
0,41 0,61
0,51 0,24
0,53 0.11
-0,48 0,35
0.41 0,81
0,27 0,73
0,38 0,66
0,43 0,52
-0,35 0.64
-0.20 0.65
-0.37 0.65
ADL
0.30 0.61
0.36 0,89
0,47 -0,37
0,44 -0,46
0,15 0.77
0.29 0.67
0,10 0,82
0.45 0,08
0,41 -0.42
0.40 -0.58
0.26 -0.78
-0.51 -0.04
-0.43 0.08
-0,50 0,08
34
Table 2.8, Path analysis for effects of ET and stem content or maturity on DMD of sainfoin and alfalfa.
Path analysis Multiple effects regression
2 Year Harvest Species Predictor Direct Indirect R
1987 1 Sainfoin ET -1.220 0.503 0.59
0,64
Sainfoin
Alfalfa
ET
Stem
ET
Stem
-1.220
0,575
-0.162
-0,661
0.503
—
-0.543
Sainfoin ET -0.265 -0.133 0.42
Maturity -0,531
Alfalfa ET -0,234 0,300 0,20
Maturity 0,535 ~
1988 1 Sainfoin ET 0,423 -0,602 0,24
Stem -0,757
Alfalfa ET 0.893 -0.005 0,79
Stem -0,035
2 Sainfoin ET -0,163 -0,215 0.30
Maturity -0.453
Alfalfa ET -0.011 0.008 0.22
Maturity -0,464
35
HARVEST 1
CM O Q.
2 -
0 -
- 2 -
A ^ ° • „ Bl
-4-+ — I — 0
PC1
1^
2
CM o Q.
2 -
0 -
2 -
• 4 -
A
A
t-
HARVEST 2
n ° • % ,
—1 ' T ' I ' 2 0
PC1
A ALFALFA L • ALFALFA H A SAiNFOINL fl SAINFOIN H
HARVEST 3 HARVEST 4
CJ O
a
CM
o
A ALFALFA L n ALFALFA H A SAINFOIN L a SAINFOIN H
PC1 PC1
CM O
4 -
2 -
0 -
- 2 -
-4 T - 4
HARVEST 5
' ^
• 1 — [ • • •
- 2
D
D D
A A A n
A°
1
0
PCI
D D
a
2 ^
PC
2
\
HARVEST R
A ALFALFA L n ALFALFA H
PC1
Figure 2,1, Principal components ordination of forage quality
data, 1986.
.-^^IJgTT^ I nil I I
36
CM O Q.
HARVEST 1 4 '
2
0
-2
ICI
-4 4 - 4
S B A^QA A A
' — I — 0
PC1
- r 2 4
CM o Q.
•4 ~
2-
0-
-2-
-4-
HARVEST2
A M
' r - r • - • ! - T-' •, t •
- 2
PC1
A ALFALFA L D ALFALFA H A SAINFCIi'JL B SA;NFOIN H
HARVEST 3
CM
o Q.
H -
2-
0-
• 2 -
•4-
A • H A
^•" A A A
A
1 1 1 1 T-
•
— , — I - •
CM O
A —. 4
2-
0-
2-
• 4 -
HARVEST 4
^ AA^^° . ,
A A ^ A^ -*
1 1 1 1 T • i--r
A ALFALFA L • ALFALFA h, A SAINFOINL a SAINFOIN H
PC1 PCI
CM O Q.
4 ~
2-
0-
2-
4-
HARVEST 5
^ A A D
A
— 1 — 1 — I — r
A
1 — 1
a
A A
A
HARVEST R
4 - 2 0 2
PC1
CM O
*+ -
2-
0-
2-
4-
A"* B
— ' — 1 — ' — r
•° . a
•
A
- • r I 1
- 2
A Ai.FALFA L n ALFALFA H A SAINFOINL B SAINFOIN H
PCI
Figure 2.2, Principal components ordination of forage quality data, 1987.
37
HARVEST 1
CM O Q.
CM
o 0.
HARVEST 2 4 -
2 -
0 -
2 -
• 4 -
AB
• / / •
A
• 1 1 1
n^^^
^ A D
-1 - r I 1
A ALFALFA L • ALFALFA H A SAINFOIN L a SAINFOIN H
PC1 PC1
Figure 2.3. Principal components ordination of forage quality data, 1988.
CHAPTER III
WATER STRESS EFFECTS ON DINITROGEN FIXATION
Introduction
An important attribute of forage legumes is their ability to fix
atmospheric nitrogen (N) symbiotically. For this reason, they are often
grown in crop rotations with non-legume species. Alfalfa (Medicago
sativa L.) and sainfoin (Onobrychis viciifolia Scop.) are perennial
forage legumes adapted to the dry, calcareous soils of the western
United States where they are grown as irrigated or dryland pasture or
hay crops.
Various studies quantifying the high N2-fixing ability of alfalfa
have been reviewed by LaRue and Patterson (1981) and Heichel (1987).
Information on the N2-fixing ability of sainfoin is inconclusive.
Sainfoin has been cited as having poor N^-fixing ability due to poor
nodulation or ineffective nodules (Burton and Curley, 1968; Sims et al.,
1968; Walsh et al., 1983) and N-deficiency symptoms in inoculated sain
foin have been observed in the field (Ditterline and Cooper, 1975;
Meyer, 1975; Townsend et al., 1975). In contrast, Krall and Delaney
(1982) found that sainfoin acetylene reduction rates were 36 to 75%
greater than alfalfa. However, another study indicates that the acety
lene reduction assay underestimates the nitrogenase activity of alfalfa
relative to sainfoin (Minchin et al., 1983).
Several studies have shown a decline in acetylene reduction rates
of perennial forage legumes with water stress (Engin and Sprent, 1973;
Aparicio-Tejo et al., 1980; Wahab and Zahran, 1983). However, these
studies were done with potted plants and/or plants grown in the green
house or growth chamber, where the stress was allowed to develop rapidly
but was of short duration (3 weeks or less). We are not aware of any
information on the N^-fixing ability of perennial forage legumes to long ^ 15
term stress under field conditions when measured by N isotope dilu
tion. Therefore, the objective of this study was to determine the
38
39
effect of water stress on dinitrogen fixation of sainfoin and alfalfa in
the field.
Materials and Methods
Details of experimental design and treatments, cultural and manage
ment practices, and sampling procedures were described in Chapters 1 and
2. Methods specific to this study follow.
Whole pots of an alfalfa line (MN5847) selected out of "Agate"
which forms ineffective nodules with Rhizobium meliloti were established
to serve as the non-N2-fixing control species for determinations of N2
fixation.
Immediately after Harvest 1, 0,40 g " N as 71 and 60% "'• N-enrichf i
( NH^)2S0^ for a total N addition of 6,2 and 7,3 kg ha" was applied to
0,915 m subplots of the N2-fixing species in 1986 and 1987, respec
tively. Control subplots (0,915 m^) received 0,40 g ^^N as 10% -'•\-
enriched ( NH ) SO. for a total N addition of 43 kg ha~ in both years.
The N rate applied to the fixing species was insufficient to suppress
nodulation or N^-fixation (Heichel and Vance, 1979), The isotope was 15 -1
dissolved in water at a rate of 2.0 g N 1 and injected between the
plant rows at 10-cm increments to a 10-cm depth. The isotope was in
jected using a syringe with a modified 14-guage needle that had holes
along the shaft rather than at the tip.
In subplots of the non-N^-fixing control one plant row was assigned
at random to each of the N^-fixing species and harvested at the same
time as its corresponding species so that plant N was accumulated over
the same time period. Samples for forage quality analysis (Chapter 2)
were also used for isotope analysis of the N2-fixing species. Samples
from control plots were handled the same as those from fixing plots.
Herbage samples could be used for N analysis instead of whole plants
because the isotope is not differentially partitioned among herbage,
crown, and root tissue (Heichel et al,, 1981). All samples for isotope
analysis were reground in a cyclone mill to a 0.25-mm particle size.
Samples were oxidized and subsequently analyzed for N isotope
40
composition by a Dumas combustion unit (ROBOPREP-CN) interfaced for a
Tracermass mass spectrometer (Europa Scientific Ltd, Cheshire, UK),
Symbiotic N2 fixation was calculated as N2 fixed on a land area
basis (Nf) or as the proportion of total plant N derived from symbiosis
(Nsy) using both the isotope dilution (McAuliffe et al,, 1958) and A-
value (Fried and Broeshart, 1975) methods.
Atom percent N, Nsy, and Nf were regressed against ET or the
ratio of actual to potential ET (ETa/ETp) to determine the effects of
water stress on N2 fixation. Potential ET was determined as pan evapo
ration from a class A pan located adjacent to the experimental plots.
Species differences in N2 fixation response to water stress were deter
mined by testing the homogeneity of regression coefficients (Graybill,
1976) when appropriate. The 0.05 probability level was used for all
tests of significance.
Results and Discussion
Values of Nf and Nsy calculated by the isotope dilution or A-value
methods revealed no difference between methods, which were highly corre
lated (r = 0,99) for both measurements. Since both methods gave similar
results, data are shown only for the isotope dilution method of calcula
tion due to its relative ease of comprehension. The similarity between
the two methods indicates that the assumption of isotope dilution that
the fixing species and the non-fixing control be exposed to similar
N/ N ratios from the soil N pool was not operationally violated by
the unequal N addition to the fixing species and the control. The same
result was found by Heichel et al. (1981).
The non-N«-fixing control plants grew poorly despite the applica
tion of high N is compared to the fixing species. Boiler and Heichel
(1983) found that reduced growth of ineffectively nodulated alfalfa was
only partially alleviated by application of 100 kg ha N, As a result,
atom percent N values for the non-fixing control were highly variable
leading to large errors in calculation of Nsy and Nf, There was gener
ally no relationship between Nsy and ET except for Harvest 3 of 1987
(discussed later). The response of N^ fixation to water stress was
41
therefore investigated by regressing the atom percent ^ \ in the fixing
species against ET (Table 3,1, Figs, 3,1 to 3,3), Danso (1986) states
that the isotope dilution method can be used by simply comparing the
atom percent N within treatments, thereby eliminating the problem of
selecting an appropriate non-N2-fixing control species. Phillips et al.
(1986) concluded that qualitative estimates of N2 fixation can be used
to determine treatment effects on N2 fixation. Values of atom percent
N give a relative measure of the proportion of N from fixation (Nsy)
with greater atom percent values corresponding to lower Nsy values.
Atom percent N generally decreased with increasing ET (Figs, 3.1,
3,2), which is consistent with other studies (Sprent, 1972; Aparicio-
Tejo et al,, 1980; Wahab and Zahran, 1983) using the acetylene reduction
technique. The atom percent N of alfalfa was not related to ET in
Harvests 2, 3 and 5 of 1986 and Harvest 2 of 1987 (Table 3.1). In
second harvests, lack of a relationship is probably due to variability
caused by the recently injected isotope not being equilibrated with the
soil N pool. Lack of a relationship in Harvest 5 of 1986 is probably
due to errors in ET determination for this harvest (see Chapter 1). In
Harvest 3 of 1986 precision was good (CV = 6,3%) so lack of a relation
ship seems to suggest that Nsy was unaffected by ET at this harvest.
Atom percent N of sainfoin frequently showed a quadratic response
to ET or declined at a faster rate with ET than alfalfa (Table 3,1,
Figs, 3,1, 3,2), In Harvests 1 and R of 1987 (Table 3,1, Fig, 3,2) atom
percent N is regressed against ETa/ETp to normalize the ET data for
the different time periods over which the plants grew because statis
tical tests of species slopes and intercepts were performed for these
harvests. These results indicate that N2 fixation of sainfoin is
similar to alfalfa under non-stressed or slightly stressed conditions,
but that the N^-fixation process in sainfoin is more affected by water
stress than alfalfa, especially when the stress is severe, Allen and
Allen (1981) concluded that there is a more delicate balance between
sainfoin and its microsymbiont with respect to effectiveness than in
most rhizobiarhost associations, Wahab and Zahran (1983) reported that
acetylene reduction activity of alfalfa was unaffected by mild water
42
stress, and concluded that N2 fixation in alfalfa is less sensitive to
water stress than in other species. These results differ from other
reports in which acetylene reduction rates of sainfoin were greater than
alfalfa (Major et al,, 1979; Krall and Delaney, 1982), However, a more
recent report suggests that these results, obtained using a closed
system acetylene incubation, may be in error, Minchin et al, (1983)
found an acetylene- induced decline in nodular nitrogenase activity
which varied with species. This decline was exhibited by alfalfa but
not by sainfoin. Thus, closed-system assays underestimate acetylene
reduction activity of alfalfa relative to sainfoin.
In Harvest 2 of 1988, all plots were irrigated uniformly to relieve
stress across the irrigation treatments. Atom percent N was regressed
against the season total ET for 1987 to determine the effect of previous
water stress on N^ fixation when stress was relieved (Table 3.1, Fig. 15 3.3). Atom percent N decreased with increasing ET at a similar rate
for both species. This indicates that the N^-fixing ability of plants
was not able to recover rapidly from long term stress once the stress
was relieved. Engin and Sprent (1973) found that the degree and rate of
recovery of acetylene reduction activity in Trifolium repens L. was
related to the duration of the water stress. Wahab and Zahran (1983)
found that it took 3 wk for the acetylene reduction activity of alfalfa
to completely recover upon rewatering after a 3-week stress period.
In Harvest 3 of 1987, a significant response of Nsy and Nf to ET
was detected (Table 3,2, Fig, 3,4), The results indicate that alfalfa
derives 35 to 82% of its N from symbiosis compared to 0 to 72% for
sainfoin, depending on the degree of water stress. These data also
suggest that the N^-fixing ability of sainfoin is more sensitive to
water stress as indicated by the faster rate of decline of Nsy with ET
for sainfoin as compared to alfalfa. These results are consistent with
other reports on the Nsy of legumes. Heichel et al, (1984) found that
fixed N2 accounted for 33 to 80% of the total N in alfalfa, LaRue and
Patterson (1981) reviewed the literature and found that the highest
estimates for Nsy of legumes are about 80%, Total N fixed increased
linearly with ET (Table 3,2, Fig, 3.4), Alfalfa Nf increased at a
43
faster rate than sainfoin with increasing ET, This is partially due to
the higher yields and plant N content of alfalfa (data not shown).
Values of Nf ranged from 23 to 138 kg ha"^ for alfalfa and 0 to 50 kg
ha~ for sainfoin for this harvest.
Season total Nf was projected for high and low irrigation treat
ments from Nsy data of Harvest 3 in 1987 (Table 3.3). Heichel et al.
(1984) found that Nsy of alfalfa did not vary among harvests in the
third and fourth year of the stand. Alfalfa fixed 576 kg ha""*- N with
high irrigation and 121 kg ha~ N under low irrigation, whereas sainfoin
fixed 304 and 0 kg ha~ N under high and low irrigation, respectively
(Table 3,3), The value for Nf of alfalfa under high irrigation is
greater than other reports, but is in agreement with other results when
differences in yield are accounted for, Heichel et al. (1984) reported
224 kg ha"- N fixed with 9,1 t ha"" yield (24.6 kg N t~^). Our results
show 576 kg ha"" N fixed with 19,0 t ha"" yield (30,3 kg N t""^).
The value of 0 kg ha~ N fixed by low irrigation sainfoin raises
the question of whether the low irrigation sainfoin plants were effec
tively nodulated. Observations made on sainfoin plants dug in March of
1988 confirmed that the roots were nodulated. However, the small, young
nodules were often the only ones which contained the red hemoglobin
pigment associated with effectiveness. This was observed at all irriga
tion levels. A similar observation was made by Burton and Curley
(1968).
Sunmiary and Conclusions
Dinitrogen fixation decreased with ET in both species. The atom
percent N in sainfoin generally decreased at a faster rate with in
creasing ET than alfalfa, suggesting that sainfoin can fix a similar
proportion of plant N as alfalfa under high irrigation but that the N^
fixation ability of sainfoin is more sensitive to water stress, espe
cially when the stress is severe. Atom percent N of both species
increased with decreasing level of previous ET after water stress was
relieved, indicating that the N«-fixing ability of the two species was
not able to recover rapidly from long term stress.
44
Alfalfa fixed a greater total amount of N than sainfoin. In Har
vest 3 of 1987, N2 fixation was 23 to 138 kg ha"" N for alfalfa and 0 to
50 kg ha N for sainfoin under low and high irrigation treatments,
respectively. Projected values of season total N2 fixation for 1987
were 121 to 576 kg ha"" N for alfalfa and 0 to 304 kg ha"-"" N for sain
foin under low and high irrigation treatments, respectively. The
greater total N fixed by alfalfa was partially due to its greater yields
and generally higher N content than sainfoin.
Contrary to other reports, the results indicate that sainfoin has
the ability to derive up to 72% of its N needs from symbiotic N2 fixa
tion. Nitrogen deficiency symptoms were not observed in sainfoin in
this study. More research is needed on factors affecting the N^ fixa
tion ability of sainfoin.
The decline in N2 fixation with ET suggests that irrigation level
or soil water supply should be considered when including legumes in crop
rotations for their N benefit to subsequent crops. Legumes may not fix
as much N under water limiting conditions as has been assumed.
CO
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45
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46
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CNJ
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;z:
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T H
>-. 4J •H i H • H i j a CO
Xi o Ul a.
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i n o
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4-) CO
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pq
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4«-
U l
Table 3,3. Seasonal comparisons of yield, N content, and N^ fixation
for sainfoin and alfalfa under high and low irrigation in 1987.
Variable
DM Yield (t ha~^)
Total N (g kg"- )
Nsy (%)t
Nf (kg ha"-'-) :
High
14.8
28.5
72.0
304
Sainfoin
Low
5.3
29.3
0.0
0
High
19.0
37,0
82,0
576
Alfalfa
Low
8,6
40,1
35,0
121
t Proportion of N from symbiosis, projected from Harvest 3,
+ Total N from symbiosis, projected from Harvest 3,
48
HARVEST 2
E o
"co
in
u -
4 -
3 -
2 -
1 -
. ITn * ^ T
I 1 1 1 ,
100 200
ET, mm
300
• ALFALFA • SAINFOIN
HARVEST 3 HARVEST 4
5? E o
^-> C3
ET, mm ET, mm
E o
in
0.50 "
0.48-
0.46-
0.44-
0.42-
0.40-
HARVEST 5
D
•
^ ' ^ 1
D
• y^ va<a
y^u
— 1 — 1 — 1
HARVEST R
1 0 0 2 0 0 300
ET, mm
E
"co
\Cl
0.50
0.46-
0.42-
0.38 1 00 1 50
15 Figure 3.1. Atom percent N as a function of ET, 1986.
A9
S5 E
"ro
in
HARVEST 1 n AC
0.44-
0.42-
0.40-
0.38-
0.36-
• •
1 r — ' — 1 — ' —
• •
ALFALFA SAINFOIN
N,
ato
m %
i n
0 . 2 0 . 3 0 . 4 0 . 5 0 . 6
ETa/ETp
HARVEST 2
2 0 0
HARVEST 3
S5 E
in
T ' 1 <-1 0 0 2 0 0 3 0 0
ET, mm
HARVEST 4
1 0 0 2 0 0
ET, mm
3 0 0
HARVEST 5
E o
• ^ CO
m
T ' T
100 120 140 160 180
ET, mm
E o
"co
in
0.7 -
0.5 -
0.3 -
HARVEST R
\ *
• \ #
i
0 . 0 0 . 2 0 . 4
ETa/ETp
0 . 6
Figure 3 . 2 . Atom percent ^ \ as a function of ET, 1987.
50
E o + ^ CO
m
0.6
0,5 -
0.4 -
HARVEST 2
• ALFALFA • SAINFOIN
0.3 i 1 1 • 1 r 4 0 0 7 0 0 1 0 0 0 1 3 0 0
ET, mm
Figure 3.3. Atom percent N as a function of 1987 seasonal ET when water stress was alleviated in Harvest 2 of 1988.
51
to
• ALFALFA • SAINFOIN
100 200
ET, mm 300
200
• 150 H CQ
sz O) 100
100 200
ET, mm 300
Figure 3.4. Proportion of N from fixation (Nsy) and total N fixed (Nf) as a function of ET in Harvest 3, 1987.
CHAPTER IV
WATER RELATIONS OF SAINFOIN AND ALFALFA
Introduction
Alfalfa and sainfoin are perennial forage legumes grown under
irrigated and dryland conditions in the arid and semi-arid West. Al
though alfalfa is an important forage crop in this region, limited
information is available on the effect of water stress on the plant
water relations of alfalfa. There has been increased interest in sain
foin in recent years, but there is little information on the water
relations of sainfoin. Sheehy and Popple (1981) reported that sainfoin
water potential {^ ) remained very high throughout their study and as
solute potential decreased, turgor potential increased. No explanation
was given for the unusual pattern of ^ in sainfoin, but it was noted
that stomatal conductance of sainfoin and alfalfa was similar. We know
of no reports on the effect of water stress on water relations of sain
foin. Therefore, our objective was to study and compare the water
relations of sainfoin and alfalfa as affected by soil water deficits.
Materials and Methods
Experimental design and treatments, cultural and management prac
tices, and various procedural aspects were described in previous chap
ters. Further details specific to this study follow.
Water relations of sainfoin and alfalfa were assessed on two clear
days at the end of the second (23 June) and third (28 July) growth
cycles in 1987. Measurements were made at four points along the irriga
tion gradient (subplots) designated as high (H), medium high (MH),
medium low (ML), and low (L) irrigation treatments. Diurnal measure
ments of plant water potential (? ), leaf conductance (G), leaf (LT) and
air (AT) temperature were made on one replicate of sainfoin and alfalfa
at intervals shown in Figure 4.2. At midday (1200 h), three replicates
were sampled. Measurements were made on one sample per plot.
Leaf conductance, LT, and AT were measured with a steady-state por-
ometer (LICOR Model 1600). Leaf conductance was measured on adaxial and
52
53
abaxial leaf surfaces assuming that the two surfaces acted as parallel
resistors. The same tiller then was excised about 15 cm from the apex
and transferred to a pressure chamber (Model 3005, Soilmoisture Equip
ment Corp.) for measurement of ^ according to the techniques described
for alfalfa by Brown and Tanner (1981). Plant available water (PAW) was
calculated from measurement of volumetric soil water content (described
in Chapter 1), and determination of the upper and lower limits of soil
water availability according to Ritchie (1981).
Results and Discussion
Air temperature and vapor pressure deficit (VPD) for the two sam
pling dates are presented in Figure 4.1. The atmospheric conditions
were more stressful on 23 June than 28 July. Maximum AT and VPD occur
red at 1500 h when they were 36 vs. 31°C and 26,1 vs, 17,5 millibars
(mb) on 23 June and 28 July, respectively.
Plant water potentials for all treatments were greatest at or
before sunrise and least at midday (Fig. 4.2). Water potentials were
generally decreased with decreases in irrigation level. Water poten
tials declined to lower levels at Harvest 2 compared to Harvest 3 due to
the greater midday AT and VPD (Fig, 4,1), Idso et al, (1981) reported
that alfalfa ^ declined with increased air VPD, Sainfoin f followed a
similar diurnal course as alfalfa, with alfalfa ^ being lower than
sainfoin in MH, ML, and L irrigation treatments due to generally lower
PAW under alfalfa and the decline in ^ with PAW at values of PAW less
than about 50% (Fig, 4.3), These results differ from those reported by
Sheehy and Popple (1981), They reported that sainfoin m remained
essentially constant throughout the day, whereas alfalfa m followed a
typical diurnal pattern. The two species showed similar diurnal pat
terns in solute potential, but the turgor potential of sainfoin actually
increased as solute potential decreased. No explanation was given for
the unusual pattern of "V in sainfoin, but it was noted that stomatal
conductance of the two species was similar.
Sainfoin and alfalfa showed generally similar diurnal patterns of G
(Fig. 4,4), Highly irrigated sainfoin and alfalfa maintained G at high
54
levels (0,025 to 0.04 m s"" ) until 1200 h when G declined during the
midday period. Maximum sainfoin and alfalfa G values of up to 0.04 m
s were high compared to those generally measured on other crop spe
cies, although Hodgkinson (1974) reported conductance as high 0.05 m
sec for alfalfa. Conductance of MH, ML, and L treatments, with the
exception of MH sainfoin, declined in the morning and remained low
through the midday period. Frequently G showed some recovery during the
evening period, but this response was not consistent. Similar diurnal
patterns of alfalfa G in response to water stress have been reported by
van Bavel (1967) and Carter and Sheaffer (1983b),
The relationship between ^ and G for sainfoin and alfalfa is shown
in Figure 4,5. Leaf conductance declined in an exponential manner with Y
for the two species at Harvest 2. Conductance declined sharply with m
until about -2500 J kg"-*". Below -2500 J kg"""" H', conductance stabilized
at low rates (0.005 m s~ ), A similar response was reported for alfalfa
by Carter and Sheaffer (1983b). Conductance declined linearly with 4*
for both species at Harvest 3. Sainfoin conductance declined more
rapidly with m than alfalfa. The lack of an exponential response at
Harvest 3 is probably due to less severe stress at this harvest. Sain
foin m declined to a minimum of -2200 J kg" and alfalfa ^ to a minimum
of -2900 J kg . The different responses may have been due in part to
differences in the air VPD between the two days. Turner et al. (1985)
found that the G vs. V relationship of Helianthus annuus L. changed with
air VPD. At lower VPD the relationship was essentially linear. At
higher VPD G decreased exponentially with ^ below a threshold W of
about -700 J kg" . This is in general agreement with our results. A
threshold ^ for G sensitivity was not detected in our study, but there
is a tendency for one at about -1000 J kg for sainfoin at Harvest 2.
Diurnal responses of leaf-air temperature differential ( A T) are
shown in Figure 4.6. Both species had similar responses. High irriga
tion treatments remained below ambient temperature (-AT) all day. Low
irrigation treatments were above AT for most of the day or the midday
period. Sainfoin MH and ML treatments generally remained at or below
AT, while alfalfa MH and ML treatments were above AT for the midday
55
period or most of the day. A linear relationship existed between a T
and 'i'with A T increasing as m decreased (Fig. 4.7). The relationship
was similar for species and harvests and showed that A T became zero at
^ of -2470 J kg" which is similar to the value at which conductance
stabilized with further decline in T in Harvest 2. Thus, -2500 J kg"-*"
m appears to be a threshold of severe stress in sainfoin and alfalfa.
Soil water extraction patterns for low irrigation sainfoin and
alfalfa are shown in Figure 4.8. Data are presented for mid-June of
1986 and 1987 because this is the time of year when the soil profile was
most dry. Sheaffer et al. (1988) state that less water is extracted
from deeper soil layers when water is available in the upper profile,
but that the drought resistance of alfalfa is related to its ability to
extract water from deep within the soil profile. Figure 4.8 shows that
water-stressed alfalfa was able to extract more water from depths below
190 cm than sainfoin. Observation made on soil cores while installing
neutron access tubes in February 1986 (after the establishment year)
indicated rooting depths of 1.94 m for sainfoin and 2.64 m for alfalfa.
This suggests that the greater drought resistance of alfalfa relative to
sainfoin in this study (see Fig. 1.6) may be related to its greater soil
water extraction below 190 cm.
Summary and Conclusions
Sainfoin and alfalfa had generally similar water relations as
measured by ¥ , G, and A T. This contrasts with reported differences in
patterns between sainfoin and alfalfa (Sheehy and Popple, 1981), A
threshold of severe stress, at which conductance stabilizes at low rates
and leaf temperature begins to increase above air temperature, occurs at
about -2500 J kg" m in sainfoin and alfalfa. The similarity in water
relations was reflected in similar WUE of sainfoin and alfalfa in 1987
(see Chapter 1). The greater drought tolerance exhibited by alfalfa in
this study may have been due to its greater soil water extraction below
190-cm depth relative to sainfoin rather than to differences in water
relations per se.
56
O o
UJ
<
E d a. >
<
300 600 900 1200 1500 1800 2100
1 1 1 1 1 r 300 600 900 1200 1500 1800 2100
TIME, h
Figure 4.1. Diurnal air temperature and vapor pressure deficit (VPD) on 23 June and 28 July 1987.
57
X - I X S S _i
•J" I " ^
X - I X S S -1
•{•IM
CM
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60
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A = 0.063 * 10'^{3.632e-4x) r = 0.85
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a ALFALFA • SAINFOIN
A = 0.040+1.219e-5x r = 0.93
8 = 0.049+1.935e-5x r = 0.90
• ALFALFA • SAINFOIN
Figure 4 . 5 . Relationship between leaf conductance and plant water po ten t ia l for a l fa l fa (A) and sainfoin (S) a t Harvests 2 and 3 .
61
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62
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-3000 -2000 - 1 000 0
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Figure 4.7. Relationship between leaf-air temperature and water potential for alfalfa (A) and sainfoin (S) at Harvests 2 and 3.
63
CO
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ou
20 -
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6-11-86 LOW IRRIGATION
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1 70
DEPTH, cm
Figure 4.8. Profile soil water of alfalfa and sainfoin under low irrigation on 11 June 1986 and 23 June 1987.
CHAPTER V
GENERAL SUMMARY AND CONCLUSIONS
Alfalfa and sainfoin are perennial forage legumes adapted to the
dry, calcareous soils of the western United States where they are grown
as irrigated and dryland pasture and hay crops. However, little in
formation exists on the effect of water stress on the yield, forage
quality, dinitrogen fixation, and water relations of these species. The
objectives were to determine: 1) irrigation and water stress effects on
dry matter production and water-use efficiency, 2) water stress effects
on forage quality, 3) the relationship of water stress to dinitrogen
fixation, and 4) the water relations of these species under water
stress. Species were grown under an irrigation gradient in 1986, 1987,
and spring of 1988. Measurements were made at four points along the
gradient.
Yield was a linear function of ET for both species. Maximum sain
foin yields were 85% of alfalfa (20673 kg ha~ ). The seasonal growth
patterns of the two species differed with sainfoin producing 58 to 63%
of its total season yield in the first two harvests compared to alfalfa
with 41 to 46% of its yield in the first two harvests (taken by late
June). A comparison of 1986 and 1987 results demonstrates the necessity
of early spring irrigation of sainfoin to realize maximum yields and the
early production advantage of sainfoin over alfalfa. With adequate
water for growth in the spring of 1987, sainfoin was ready to harvest
two weeks earlier than alfalfa, but with a lack of water in 1986, spring
growth for both species occurred concurrently.
Total water use of both species was similar. Water-use efficiency
of alfalfa was generally higher than sainfoin. Species differences in
WUE were largely due to differences in the E component of ET as indi
cated by the intercept of water-production functions. Sainfoin WUE was
high in spring and declined in summer. Alfalfa WUE remained high
through the spring and summer. Sainfoin's pattern of high spring growth
followed by low growth rates during periods of high summer temperature
64
65
is apparently responsible for these differences in WUE between alfalfa
and sainfoin, since water use was similar for both species at all har
vests. Both species had low WUE in the fall due to fall dormancy re
sponses. Season long WUE of alfalfa (18.3 kg ha"" mm"" ) was greater
than sainfoin (10.7 kg ha"" mm"" ) in 1986 due to a lack of irrigation
water in spring when sainfoin yield potential and WUE is highest. In
1987, seasonal WUE of sainfoin and alfalfa was similar (18.2 vs. 16.7 kg
ha imn , respectively), but alfalfa had a smaller E component giving
it greater overall WUE and yield. Differences in LAI seem to account
for differences in E (intercepts) between sainfoin and alfalfa. There
fore, cultural and management factors aimed at increasing sainfoin LAI,
such as broadcast seeding or harvesting at a higher stubble height to
leave some leaf area for more rapid regrowth, should reduce the E com
ponent of ET resulting in increased overall WUE and yield of sainfoin.
Sainfoin WUE and yield was lower in summer, so reduced summer irrigation
may increase seasonal WUE for a small decline in yield. We observed
rapid death of sainfoin plants under low irrigation in summer. Moderate
levels of summer irrigation may be necessary to prevent rapid stand loss
of sainfoin. Reasons for rapid sainfoin stand loss under low irrigation
are unclear and merit further study.
Sainfoin's early production potential suggests that its greatest
utility is as an early-season irrigated pasture or hay crop. Since
sainfoin is a non-bloating legume, it may have more potential for pas
ture usage than alfalfa. Alfalfa would be the best choice of species
when maximum yield is the desired objective, especially for irrigated
hay production.
Water stress had no consistent effect on individual forage quality
components. In general, forage quality improved slightly or was unaf
fected by decreasing ET. In a few cases forage quality decreased with
decreasing ET. Alfalfa was frequently higher than sainfoin in CP and
DMD. Sainfoin and alfalfa were similar in fibrous components in 1986,
but sainfoin was frequently higher in fibrous components in 1987. Al
though alfalfa tended to be higher in forage quality than sainfoin,
especially in CP content, both species are high quality forages, and
66
sainfoin generally had adequate CP to meet the needs of high-producing
cattle (140 g kg"""" CP or more in the ration).
Principal components analysis effectively summarized forage quality
data for easy interpretation and revealed trends in forage quality not
detected by univariate regression analyses. The PCA ordinations indi
cated that forage quality, as measured by the individual components
taken together, was generally increased by water stress. Path coeffi
cient analysis revealed that ET affects forage quality (as measured by
DMD), both directly and indirectly, through its effect on leaf:stem
ratio and maturity. More research is needed to determine how the tim
ing, duration, and severity of water stress is related to its effects on
forage quality.
Dinitrogen fixation decreased with ET in both species. The propor
tion of plant N derived from N2 fixation in sainfoin generally decreased
at a faster rate with ET than in alfalfa, suggesting that sainfoin can
fix a similar proportion of plant N as alfalfa under high irrigation,
but that the N„ fixation ability of sainfoin is more sensitive to water
stress, especially when the stress is severe. The proportion of plant N
from fixation decreased with level of previous ET after water stress was
relieved in the second growth cycle of 1988, indicating that the N«-
fixing ability of the two species was not able to recover rapidly from
long term stress. Alfalfa derived 35 to 82% of its N from symbiosis
compared to 0 to 72% for sainfoin, depending on the degree of water
stress.
Alfalfa fixed a greater total amount of N than sainfoin. In Har
vest 3 of 1987, N« fixation was 23 to 138 kg ha~ N for alfalfa and 0 to -1
50 kg ha N for sainfoin under low and high irrigation treatments,
respectively. Projected values of season total N^ fixation for 1987 -1 -1
were 121 to 576 kg ha N for alfalfa and 0 to 304 kg ha N for sain
foin under low and high irrigation treatments, respectively. The
greater total N fixed by alfalfa was partially due to its greater yields
and generally higher N content than sainfoin.
Contrary to other reports, the results indicate that sainfoin has
the ability to derive up to 72% of its N needs from symbiotic N^
«x
67
fixation. More research is needed on factors affecting the N2 fixation
ability of sainfoin. The decline in N2 fixation with ET suggests that
irrigation level or soil water supply should be considered when includ
ing legumes in crop rotations for their N benefit to subsequent crops.
Legumes may not fix as much N under water-limiting conditions as has
been assumed.
Sainfoin and alfalfa had generally similar water relations as
measured by ^ , G, and AT at Harvests 2 and 3 in 1987. This contrasts
with reported differences in m patterns between sainfoin and alfalfa. A
threshold of severe stress, at which conductance stabilizes at low rates
and leaf temperature begins to increase above air temperature, occurs at
about -2500 J kg" m in sainfoin and alfalfa. The similarity in water
relations was reflected in similar WUE of sainfoin and alfalfa in 1987.
The greater drought tolerance exhibited by alfalfa in this study may
have been due to its greater soil water extraction below 190-cm depth
relative to sainfoin rather than to differences in water relations per
se.
The results indicate that sainfoin has good potential as an alter
native perennial forage legume in the Southwest. Sainfoin is not des
tined to replace or compete with alfalfa. Rather, because of differ
ences in seasonal growth patterns, sainfoin and alfalfa occupy different
niches in potential forage production systems. Many of the agronomic
problems of sainfoin could be overcome with further research and breed
ing efforts.
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APPENDIX
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76
Table A.l. Calibration and validation data for analysis of sainfoin and alfalfa forage quality components by NIRS.
Forage quality component
CP
DMD
NDF
ADF
Species
Sainfoin
Alfalfa
Sainfoin
Alfalfa
Sainfoin
Alfalfa
Sainfoin
Alfalfa
N
65
60
59
68
62
71
58
73
Calibration
SEC
1.84
1.11
1.86
2.30
1.34
1.60
1.61
2.27
R2
0.91
0.92
0.97
0.92
0.99
0.92
0.98
0.87
samples
Wavelengthst
3
3
3
3
5
6
3
4
Prediction samples
H
1.1
1.2
1.6
1.2
1.4
1.2
1.2
1.0
ADL 66 0.89 0.91 0.9
t Number of independent variables in the analysis equation.
•^N
i t