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.

11

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

11

iv

vi

vii

ix

X

1

1

2

4

8

19

19

19

21

26

38

38

39

40

43

52

52

52

53

55

64

68

75

111

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.

iv

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

VI

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

Vll

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

Vlll

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

IX

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

5

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

8

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 CO

C • H O

M-i C

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>-l

o

a o

• H J->

a c :3

c o

•H 4J O :3

O t-i O i

I u 0) 4J CO

cs

0) rH

CO H

MH O

C O

m •H V CO

a, S o

CJ

^3 C CO

CO 0)

a, o

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c •H

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• H O (U

C/D

CO M- l

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• H

o c

• H CO

CM

• H

CO

cr

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• o 13 C CO

i n

o •

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x: 4->

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c

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CO

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•^ a ^ O

I—

r-t

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c • f — :

-C 4-J •H ^ CO

cu •H U 0)

u CO

cu >-.

u o CO

cu •H

u <u ex CO

CO

c •H r"

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c 0) (U :*

00 4J •H

cn * ^

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r-^ CO

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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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46

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i n

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vD

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+

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I

II MH

:z;

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W

00 CO

CNJ

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;z:

0) >

•H 4J O a) CO 0) JH

cn 0) > CU

T H

>-. 4J •H i H • H i j a CO

Xi o Ul a.

i H

o •

o XJ c CO

i n o

• o (U

rC 4-)

4-) CO

4J c CO u •H

MH •H c:: 00

•H C/3

•?(• ^

• CO <u •H u 0) Ok CQ

c cu cu :5 4-> <u

pq

4 -

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

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X - I X S S -1

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58

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59

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60

HARVEST 2

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-4000

0.04 HARVESTS

T ' r 3000 -2000 -1000 0

WATER POTENTIAL, J kg

A = 0.063 * 10'^{3.632e-4x) r = 0.85

S = 0.088 * 10^(4.521 e-4x) r = 0.91

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

HARVEST 2

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• ALFALFA • SAINFOIN

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S = -2.759-0.001 Ix r=0.63

Q ALFALFA • SAINFOIN

-3000 -2000 - 1 000 0

WATER POTENTIAL, J kg -1

Figure 4.7. Relationship between leaf-air temperature and water potential for alfalfa (A) and sainfoin (S) at Harvests 2 and 3.

63

CO

m

CC LU h-<

o CO

ou

20 -

10 -

0 -

6-11-86 LOW IRRIGATION

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1 0 5 0 9 0 1 30 1 70 21 0 2 5 0

6-23-87 LOW IRRIGATION

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.

REFERENCES

Allen, 0. N., and E. K. Allen. 1981. The leguminosae. Univ. of Wisconsin Press, Madison, WI.

Aparicio-Tejo, P. M., Manuel F. Sanchez-Diaz, and J. I. Pena. 1980. Nitrogen fixation, stomatal response and transpiration in Medicago sativa, Trifolium repens, and T\_ subterraneum under water stress and recovery. Physiol. Plant. 48:1-4.

Bauder, J. W., A. Bauer, J. M. Ramirez, and D. K. Cassel. 1978. Alfalfa water use and production on dryland and irrigated sandy loam. Agron. J. 70:95-99.

Bolger, T. P., and A. G. Matches. 1987. Yield, quality, and water use of alfalfa and sainfoin, p. 105. ^ Agronomy abstracts. ASA, Madison, WI.

Boiler, B. C., and G. H. Heichel. 1983. Photosynthate partitioning in relation to N^ fixation capability of alfalfa. Crop Sci. 23:655-659. ^

Briggs, L. J., and H. L. Shantz. 1914. Relative water requirements of plants. J. Agric. Res. 3:1-64.

Brown, P. W., and C. B. Tanner. 1981. Alfalfa water potential measure­ment: A comparison of the pressure chamber and leaf dewpoint hygro­meters. Crop Sci. 21:240-244.

Brown, P. W., and C. B. Tanner. 1983. Alfalfa stem and leaf growth during water stress. Agron. J. 75:799-804.

Burton, J. C , and R. L. Curley. 1968. Nodulation and nitrogen fixa­tion in sainfoin (Onobrychis sativa. Lam.) as influenced by strains of rhizobia. p. 3-5. ^ C. S. Cooper and A. E. Carleton (ed.) Sainfoin symposium. Mont. Agric. Exp. Stn. Bull. 627.

Carleton, A. E., C. S. Cooper, R. H. Delaney, A. L. Dubbs, and R. F. Eslick. 1968a. Growth and forage quality comparisons of sainfoin (Onobrychis viciaefolia Scop.) and alfalfa (Medicago sativa L.). Agron. J. 60:630-632.

Carleton, A. E., C. S. Cooper, C. W. Roath, and J. L. Krall. 1968b. Evaluation of sainfoin for irrigated hay in Montana, p. 44-48. In C. S. Cooper and A. E. Carleton (ed.) Sainfoin symposium. Mont. Agric. Exp. Stn. Bull. 627.

68

~\

69

Carter, P. R., and C. C. Sheaffer. 1983a. Alfalfa response to soil water deficits. I. Growth, forage quality, yield, water use, and water-use efficiency. Crop Sci. 23:669-675.

Carter, P. R., and C. C. Sheaffer. 1983b. Alfalfa response to soil water deficits. II. Plant water potential, leaf conductance, and canopy temperature relationship. Crop Sci. 23:676-680.

Clarke, T., P. C. Flinn, and A. A. McGowan. 1982. Low-cost pepsin-cellulase assays for prediction of digestibility of herbage. Grass and Forage Sci. 37:147-150.

Cooper, C. S., and C. A. Watson. 1968. Total available carbohydrates in roots of sainfoin (Onobrychis viciaefolia Scop.) and alfalfa (Medicago sativa L.) when grown under several management regimes. Crop Sci. 8:83-85.

Danso, S. K. A. 1986. Review: estimation of N.^-fixation by isotope 15

dilution: an appraisal of techniques involving N enrichment a their application—comments. Soil Biol. Biochem. 18:243-244.

Ditterline, R. L., and C. S. Cooper. 1975. Fifteen years with sain­foin. Mont. Agric. Exp. Stn. Bull. 681.

Engin, M., and J. I. Sprent. 1973. Effects of water stress on growth and nitrogen-fixing activity of Trifolium repens. New Phytol. 72: 117-126.

Eslick, R. F. 1968. Sainfoin—its possible role as a forage legume in the West. p. 1-2. LS. C» S. Cooper and A. E. Carleton (ed.) Sain­foin symposium, Mont. Agric. Exp. Stn. Bull. 627.

Fried, M., and H. Broeshart. 1975. An independent measurement of the amount of nitrogen fixed by a legume crop. Plant Soil 43:707-711.

Gauch, H. G. 1982. Multivariate analysis in community ecology. Cam­bridge Univ. Press, Cambridge.

Glover, C. R. 1980. Sainfoin shows promise in New Mexico. Rangelands 2:54-55.

Goering, H. K., and P. J. Van Soest. 1970. Forage fiber analysis. USDA Agric. Handb. 379. U.S. Gov. Print. Office, Washington, DC.

Graybill, F. A. 1976. Theory and application of the linear model. Duxbury Press, North Scituate, MA.

i i ----

70

Halim, R. A., D. R. Buxton, M. J. Hattendorf, and R. E. Carlson. 1985. Water stress effects on growth and forage quality of alfalfa, p. 125. j[n Agronomy abstracts. ASA, Madison, WI.

Hanks, R. J., J. Keller, V. P. Rasmussen, and G. D. Wilson. 1976. Line source sprinkler for continuous variable irrigation-crop production studies. Soil Sci. Soc. Am. J. 40:426-429.

Hanks, R. J., D. V. Sisson, R. L. Hurst, and V. M. Sorensen. 1980. Statistical analysis of results from irrigation experiments using the line source sprinkler system. Soil Sci. Soc. Am. J. 44:886-888.

Hanna, M. R., and S. Smoliak. 1968. Sainfoin yield evaluations in Canada, p. 38-43. ^ C. S. Cooper and A. E. Carleton (ed.) Sain­foin symposium. Mont. Agric. Exp. Stn. Bull. 627.

Heichel, G. H. 1983. Alfalfa, p. 127-155. In I. D. Teare and M. M. Peet (ed.) Crop-water relations. John Wiley and Sons, New York.

Heichel, G. H. 1987. Legume nitrogen:symbiotic fixation and recovery by subsequent crops, p. 63-80. Jii Z. R. Helsel (ed.) Energy in plant nutrition and pest control. Elsevier Science Publ., Amster­dam.

Heichel, G. H., D. K. Barnes, and C. P. Vance. 1981. Nitrogen fixation of alfalfa in the seeding year. Crop Sci. 21:330-335.

Heichel, G. H., D. K. Barnes, C. P. Vance, and K. I. Henjum. 1984. N^ fixation, and N and Dry Matter Partitioning during a 4-year alfalfa stand. Crop Sci. 24:811-815.

Heichel, G. H., and C. P. Vance. 1979. Nitrate-N and Rhizobium strain roles in alfalfa seedling nodulation and growth. Crop Sci. 19:512-518.

Hodgkinson, K. C. 1974. Influence of partial defoliation on photosyn­thesis, photorespiration, and transpiration by lucerne leaves of different ages. Aust. J. Plant Physiol. 1:561-578.

Idso, S. B., R. J. Reginato, D. C. Reicosky, and J. L. Hatfield. 1981. Determining soil-induced plant water potential depressions in alfalfa by means of infrared thermometry. Agron. J. 73:826-830.

Jensen, E. H., C. R. Torell, A. L. Lesperance, and C. F. Speth. 1968. Evaluation of sainfoin and alfalfa with beef cattle, p. 97-99. ^H C. S. Cooper and A. E. Carleton (ed.) Sainfoin symposium. Mont. Agric. Exp. Stn. Bull. 627.

—^r\

71

Kalu, B. A., and G. W. Fick. 1981. Quantifying morphological develop­ment of alfalfa for studies of herbage quality. Crop Sci. 21:267-

Koch, D. W., A. D. Dotzenko, and G. 0. Hinze. 1972. Influence of three cutting systems on the yield, water use efficiency, and forage quality of sainfoin. Agron. J. 64:463-467.

Krall, J. M., and R. H. Delaney. 1982. Assessment of acetylene reduc­tion by sainfoin and alfalfa over three growing seasons. Crop Sci. 22:762-766.

LaRue, T. A., and T. G. Patterson. 1981. How much nitrogen do legumes fix? Adv. Agron. 34:15-38.

Li, C. C. 1956. The concept of path coefficients and its impact on population genetics. Biometrics 12:190-210.

Major, D. J., M. R. Hanna, S. Smoliak, and R. Grant. 1979. Estimating nodule activity of sainfoin, alfalfa, and cicer milkvetch seed­lings. Agron. J. 71:983-985.

Marten, G. C , F. R. Ehle, and E. A. Ristau. 1987. Performance and photosensitization of cattle related to forage quality of four legumes. Crop Sci. 27:138-145.

McAuliffe, C , D. S. Chamblee, H. Uribe-Arango, and W. W. Woodhouse, Jr. 1958. Influence of inorganic nitrogen on nitrogen fixation by

legumes as revealed by N. Agron. J. 50:334-337.

McGraw, R. L., and G. C. Marten. 1986. Analysis of primary spring growth of four pasture legume species. Agron. J. 78:704-710.

McLeod, M. N., and D. J. Minson. 1978. The accuracy of the pepsin-cellulase technique for estimating the dry matter digestibility in vivo of grasses and legumes. Anim. Feed. Sci. Technol. 3:227-287.

Melton, B. 1973. Evaluation of sainfoin and cicer milkvetch in New Mexico. New Mexico Agric. Exp. Stn. Res. Rep. 255.

Meyer, D. W. 1975. Yield, regrowth, and persistence of sainfoin under fertilization. Agron. J. 67:439-441.

Minchin, F. R., J. F. Witty, J. E. Sheehy, and M. Muller. 1983. A major error in the acetylene reduction assay: decreases in nodular nitrogenase activity under assay conditions. J. Exp. Bot. 34:641-649.

^ . ^

i. —

72

Parker, R. J., and B. R. Moss. 1981. Nutritional value of sainfoin hay compared with alfalfa hay. J. Dairy Sci. 64:206-210.

Phillips, D. A., M. B. Jones, and K. W. Foster. 1986. Advantages of the nitrogen-15 dilution technique for field measurements of symbi­otic dinitrogen fixation in legumes, p. 11-21. Tn R. D. Hauck and R. W. Weaver (ed.) Field measurement of dinitrogen fixation and denitrification. SSSA Spec. Publ. 18. ASA, CSSA, and SSSA, Madi­son, WI.

Pielou, E. C. 1984. The interpretation of ecological data, a primer on classification and ordination. John Wiley and Sons, NY.

Ritchie, J. T. 1981. Soil water availability. Plant Soil 58:327-338.

Sammis, T. W. 1981. Yield of alfalfa and cotton as influenced by irri­gation. Agron. J. 73:323-329.

Sheaffer, C. C , C. B. Tanner, and M. B. Kirkham. 1988. Alfalfa water relations and irrigation. Ln A. A. Hanson et al. (ed.) Alfalfa and alfalfa improvement. Agron. 29:373-409.

Sheehy, J. E., and S. C. Popple. 1981. Photosynthesis, water rela­tions, temperature and canopy structure as factors influencing the growth of sainfoin (Onobrychis viciifolia Scop.) and lucerne (Medicago sativa L.). Ann. Bot. 48:113-128.

Shenk, J. S. 1985. Monitoring analysis results, p. 27-28. Iji G. C. Marten et al. (ed.) Near infrared reflectance spectroscopy (NIRS): analysis of forage quality. USDA Agric. Handb. 643. U.S. Gov. Print. Office, Washington, DC.

Sims, J. R., M. K. Muir, and A. E. Carleton. 1968. Evidence of in­effective rhizobia and its relation to the nitrogen nutrition of sainfoin (Onobrychis viciaefolia). p. 8-12. j[n C. S. Cooper and A. E. Carleton (ed.) Sainfoin symposium. Mont. Agric. Exp. Stn. Bull. 627.

Smoliak, S., and M. R. Hanna. 1975. Productivity of alfalfa, sainfoin, and cicer milkvetch on subirrigated land when grazed by sheep. Can. J. Plant. Sci. 55:415-420.

Snaydon, R. W. 1972. The effect of total water supply, and of fre­quency of application, upon lucerne. II. Chemical composition. Aust. J. Agric. Res. 23:253-256.

Solley, W. B., E. B. Chase, and W. B. Mann IV. 1983. Estimated use of water in the United States in 1980. Circular 1001. U.S. Geologi­cal Survey, Alexandria, VA.

73

Sprent, J. I. 1972. The effects of water on nitrogen-fixing root nodules. IV. Effects on whole plants of Vicia faba and Glycine max. New Phytol. 71:603-611.

Stallcup, 0. T., C. J. Brown, Z. B. Johnson, D. L. Kreider, and J. 0. York. 1983. Use of principal-component analysis in summarizing nutritive and analytical characteristics of forages, p. 494-497. j[n. J. A. Smith and V. W. Hays (ed.) Proc. 14th Int. Grassl. Congr., Lexington, KY, 15-24 June, 1981. Westview Press, Boulder, CO.

Steel, R. G. D., and J. H. Torrie. 1980. Principles and procedures of statistics. 2nd ed. McGraw-Hill Book Co., New York.

Tanner, C. B., and T. R. Sinclair. 1983. Efficient water use in crop production:research or re-search, p. 1-27. Li H. M. Taylor et al. (ed.) Limitations to efficient water use in crop production. ASA, CSSA, and SSSA, Madison, WI.

Townsend, C. E., G. 0. Hinze, W. D. Ackermann, and E. E. Remmenga. 1975. Evaluation of forage legumes for rangelands of the central Great Plains. Colo. Agric. Exp. Stn. Gen. Ser. 942.

Turner, N. C , E. D. Schulze, and T. Gollan. 1985. The responses of stomata and leaf gas exchange to vapour pressure deficits and soil water content. II. In the mesophytic herbaceous species Helianthus annuus. Oecologia 65:348-355.

Undersander, D. J., N. A. Cole, and C. H. Naylor. 1987. Digestibility and rate of passage by lambs of water-stressed alfalfa. J. Anim. Sci. 64:1813-1820.

van Bavel, C. H. M. 1967. Changes in canopy resistance to water loss from alfalfa induced by soil water depletion. Agric. Meteorol. 4:165-176.

Vough, L. E., and G. C. Marten. 1971. Influence of soil moisture and ambient temperature on yield and quality of alfalfa forage. Agron. J. 63:40-42.

Wahab, A. M. A., and H. H. Zahran. 1983. The effect of water stress on N2(C2H2)-fixation and growth of Medicago sativa L. Acta. Agron.

Acad. Sci. Hung. 32:114-118.

Walsh, S. F., D. F. Bezdicek, A. M. Davis, and D. L. Hoffman. 1983. Nitrogen fixation capabilities of plant introduction accessions of pasture and range forage legumes. Agron. J. 75:474-478.

Wilson, J. R. 1982. Environmental and nutritional factors affecting herbage quality, p. 111-131. In. J. B. Hacker (ed.) Nutritional limits to animal production pastures. CAB, Farnham Royal, U.K.

^v

74

Wilson, J. R. 1983. Effects of water stress on herbage quality, p. 470-474. In J. A. Smith and V. W. Hays (ed.) Proc. 14th Int. Grassl. Congr., Lexington, KY, 15-24 June, 1981. Westview Press, Boulder, CO.

Wright, J. L. 1988. Daily and seasonal evapotranspiration and yield of irrigated alfalfa in southern Idaho. Agron. J. 80:662-669.

i >

APPENDIX

75

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