Effect of moisture and nitrogen on growth and yield of fababean (Vicia faba L.) by David Allen Buss A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Agronomy Montana State University © Copyright by David Allen Buss (1984) Abstract: Fababean (Vicia faba L.) is being investigated for its potential as a rotational crop with cereals in the Northwestern region of the United States. Fababean is capable of a symbiotic relationship with Rhizobium bacteria that can convert atmospheric nitrogen to a usable plant form, therefore decreasing the demand for nitrogen fertilizer. Soil moisture stress is one of the most limiting factors affecting fababean production in semiarid areas. The objectives of this research were to determine the effect of soil moisture and soil nitrogen at various levels on fababean growth and yield. Field experiments were established in 1982 and 1983. Main treatments of increasing moisture (non-irrigation, low, intermediate and high irrigation) were applied with a modified line-source sprinkler system. Moisture treatments were divided into subplots of applied nitrogen and non-applied nitrogen. Fababean roots penetrated to 135 cm in all irrigation regimes. Higher root density was found in deeper soil layers in the non and low irrigation regimes compared to intermediate and high regimes. Plant height, shoot dry weight, total plant N, seed yield, seed number pod-1, pod number plant-1, harvest index, grain and total yield WUE were not affected by N application. N application inconsistently affected 1,000 seed weight and leaf-water potential. Fababean utilized applied NO3- in preference to N2 -fixation when NH4NO3 was applied. Plant height, shoot dry weight, total leaf-water potential and total plant N increased with increased ET. Seed yield, harvest index and WUE increased in 1982 and decreased in 1983 with increased ET. The decrease in 1983 was attributed to the short growing season and the effect of moisture on delayed maturation.  EFFECT OF MOISTURE AND NITROGEN ON GROWTH AND YIELD OF F AB ABE AN ( VICIA FABA L.) by David Allen Buss A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Agronomy MONTANA STATE UNIVERSITY Bozeman, Montana - August 1984 APPROVAL of a thesis submitted by David Allen Buss This thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, format, citation, bibliographic style, and consistency, and is ready for submission to the College of Graduate Studies. Date Chairperson, Graduate Committee Approved for the Major ^partm ent Date 7 Z Head, Major Department Approved for the College of Graduate Studies Date Graduate Dean iii STATEMENT OF PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a master’s degree at Montana State .University, I agree that the Library shall make it available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Permission for extensive quotation from or reproduction of this thesis may be granted by my major professor, or in his absence, by the Dean of Libraries when, in the opinion of either, the proposed use of the material is for scholarly purposes. Any copying or use of the material in this thesis for financial gain shall not be allowed without my permission. Signature__ Date__ $ / a / Z tJ- ACKNOWLEDGMENTS I wish to express my sincere appreciation to the following: My family, for their encouragement and support during my graduate education. Dr. Ronald H. Lockerman for his assistance, guidance and friendship while serving as my major professor and during the preparation of this thesis. Drs. R. L. Ditterline, G. L. Westesen and H. A. Ferguson for their advice while serving on my graduate committee. Dr. D. G. Miller for arranging my research assistantship and for his concern for gradu­ ate studies and agronomic research. The Plant and Soil Science and Cooperative Extension Service secretaries for then- assistance and friendship. My close friends and fellow graduate students for their friendship and stimulating dis­ cussions. Mrs. Jean Julian for preparation of the final manuscript. The Montana Agricultural Experiment Station and the Plant and Soil Science Depart­ ment for providing financial support and facilities for my studies and research program. vi TABLE OF CONTENTS Page APPROVAL............................................... ii STATEMENT OF PERMISSION TO USE........................................................................ Li VITA.................................................................................................................................... iv ACKNOWLEDGEMENTS.................................................................................................. v TABLE OF CONTENTS.................................................................................................... vi LIST OF TABLES........................................................................................... viii LIST OF FIGURES............................................................................................................. ix ABSTRACT........................................................................................................................ xi Chapter I. INTRODUCTION................................................................................................ I II. LITERATURE REVIEW..................................................................................... 2 C ro p ................................ 2 Water Stress Effects on Seed Y ield .............................. .............................. 6 Water Stress Effects on Seed Quality........................................................... 8 Water Stress Effects on Dry Matter Production......................................... 8 Water Stress Effects on Plant Height........................................................... 9 Water Stress Effects on Leaf and Internal W ater....................................... 10 Water Stress Effects on Water Use............................................................... 11 Water Stress Effects on Root Growth and Depth of Soil Water Extraction..................................................................................... . 12 Water Stress Effects on Nodulation and N2 -F ixation............................... 13 Water Stress Effects on N Uptake............................................................... 16 Nitrogen Effects on Nodulation and N2 -Fixation..................................... 16 Nitrogen Effects on Nitrogen U ptake......................................................... 19 Nitrogen Effects on Seed Yield.................................................. 20 Nitrogen Effects on Seed Quality............................................................... 20 Nitrogen Effects on Shoot Dry Matter Production................................... 21 Nitrogen Effects on Forage Quality.............................. 21 Nitrogen Effects on M aturity ...................................................................... 22 TABLE OF CONTENTS-Continued . Page III. MATERIALS AND METHODS.......................................................................... 23 Site Description................. 23 Experimental Design.................................. 24 Planting................. ' ....................................................................................... 25 Meteorological Observations........................................................................ 25 Irrigation System................. : ....................................................................... 25 Soil Moisture Determination............................ 27 Growth and Yield Measurements................................................................. 29 Leaf Internal Moisture................................................................................... 30 Statistical M ethods............................ . '........................................................ 31 IV. RESULTS AND DISCUSSION.......................................................................... 33 Environments................................................................................................ 33 Evapotranspiration.............................. 33 Plant Available W ater............................ 34 Root Growth......................................................................................... 37 Soil NO3- ..................................................................................................... 39 Plant Analysis................................................................................................ 41 Plant H eight.................................................................................................. 41 Shoot Dry Weight............... -........................................................................ 41 Leaf-Water Potential.............................. 45 Total Plant N (Aerial)................................................................................... 47 Seed Yield........... ....................................................................... ; ................. 49 Seed Weight.................................................................................................... 52 Total Seed Number....................................................................................... 54 Immature Seed N um ber................... 55 Seed Number Pod-1 ................................ 55 Pod Number Plant- 1 ..................................................................................... 56 WUE ............................................................................................................... 59 Harvest Index ........................................................................................... .. . 61 V. SUMMARY AND CONCLUSIONS. . .,............................................................ 63 LITERATURE CITED...................................................................................................... 65 APPENDIX TABLES........................................................................................................ 75 vii viii ' LIST OF TABLES Tables Page 1. Weekly Environmental Data for Horticultural Farm at Bozeman, MT and John Schutter Farm at Manhattan, MT in 1982 and 1983, Respectively.......................................................................................................... 26 2. Irrigation Regimes for Fababean Field Experiments at Bozeman and Manhattan, MT in 1982 and 1983, Respectively......................................... 28 3. Percent of Total Water Used by Fababean with Increasing Soil Depth at Four Irrigation Regimes in 1983 at Manhattan, M T...................• • • • 38 4. Fababean Forage Yield at Bozeman and Manhattan, MT in 1982 and 1983................................................................................................................. '4 5 5. Effect of Irrigation Level on Maturation of Fababean at Bozeman and Manhattan, MT in 1982 and 1983, Respectively......................................... 52 6. Correlations of Fababean Seed Parameters to Seed Yield in 1982 and 1983 at Bozeman and Manhattan, MT, Respectively........................................ 59 Appendix Tables 7. Daily Environmental Data for Horticultural Farm at Bozeman, MT, 1982 .........: ................................................................................ ............................ 76 8. Daily Environmental Data for John Schutter Farm at Manhattan, MT, 1983 ......................................................................... 80 9. Water Budget for the Four Irrigation Regimes for Fababean Field Experiments in 1982 at the Horticultural Farm at Bozeman, M T.................... 84 10. Water Budget for the Four Irrigation Regimes for Fababean Field Experiments in 1983 (Exp. I) at the John Schutter Farm at Manhattan, M T...................................................................................................... 85 11. Water Budget for the Four Irrigation Regimes for Fababean Field Experiments in 1983 (Exp. 2) at the John Schutter Farm at Manhattan, M T.................................. 86 12. Significance Table of the Nitrogen and Moisture X Nitrogen Interaction for Each Parameter Measured in 1982 and 1983 at Bozeman and Manhattan, MT, Respectively...................................................... 87 ix LIST OF FIGURES. Figures Page 1. Diagram of pressure cham ber.............................................................................. 31 2. Relationship of seasonal evapotranspiration (ET) to water applied at four irrigation levels (no, low, intermediate, high) to fababeah in 1982 and 1983 at Bozeman and Manhattan, MT, respectively................................... 34 3. The effect of fababean on plant available water from emergence to harvest at four irrigation levels in 1982 at Bozeman, MT................................... . 35 4. The effect of fababean on plant available water from emergence to harvest at four irrigation levels in 1983 at Manhattan, M T .............................. 36 5. Relationship of soil NO3- (0-30 cm depth) at harvest to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes at two NH4 NO3 application rates (0 and 99 kg ha-1) in 1983 at Bozeman and Manhattan, MT, respectively............................ 40 6. Effect of time and irrigation level on fababean plant height in 1982 ' and 1983 at,Bozeman and Manhattan, MT respectively..................................... 42 7. Relationship of fababean plant height at harvest to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes in 1982 and 1983 at Bozeman and Manhattan, MT, respectively................................................................................ 43 8. Relationship of fababean shoot dry weight at harvest to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes in 1982 and 1983 at Bozeman and Manhattan, MT, respectively................................................................................................... 44 9. Relationship of fababean total leaf water potential (^ t ) to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes at two NH4 NO3 application rates in 1982 and 1983 at Bozeman and Manhattan, MT, respectively......................................... 46 10. Relationship of fababean total plant N (aerial) at harvest to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes in 1982 and 1983 at Bozeman and Manhattan, MT, respectively 48 X Figures Page 11. Relationship of soil NO3- difference (between planting and harvest).at 0-60 cm depth at harvest to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes at two NH4 NO3 application rates (0 and 99 kg ha-1) in 1982 and (0 and 157 kg ha-1) in 1983 at Bozeman and Manhattan, MT, respectively...................... 50 12. Relationship of fababean seed yield to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes in 1982 and 1983 at Bozeman and Manhattan, MT, respectively...................... 51 13. Relationship of fababean seed weight to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes at two NH4 NO3 application rates in 1982 and 1983 at Bozeman and Manhattan, MT, respectively................................................................................ 53 14. Relationship of fababean seed number to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes in 1982 and 1983 at Bozeman and Manhattan, MT, respectively. .................... 54 15. Relationship of immature fababean seed number to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes in 1982 and 1983 at Bozeman and Manhattan, MT, respectively....................................................... •........................................... 56 16. Relationship of fababean seed number pod-1, to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes in 1982 and 1983 at Bozeman and Manhattan, MT, respectively.................................................................................................... 57 17. Relationship of fababean pod number to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes in 1983 at Manhattan, MT..................................................................................... 58 18. Relationship of fababean grain water use efficiency (WUE) to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes in 1982 and 1983 at Bozeman and Manhattan, MT, respectively................................................................■........................................... 60 19. Relationship of fababean harvest index to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes in 1982 and 1983 at Bozeman and Manhattan, MT, respectively...................... 62 xi ABSTRACT Fababean (Vicia faba L.) is being investigated for its potential as a rotational crop with cereals in the Northwestern region of the United States. Fababean is capable of a sym­ biotic relationship with Rhizobium bacteria that can convert atmospheric nitrogen to a usable plant form, therefore decreasing the demand for nitrogen fertilizer. Soil moisture stress is one of the most limiting factors affecting fababean production in semiarid areas. The objectives of this research were to determine the effect of soil moisture and soil nitro­ gen at various levels on fababean growth and yield. Field experiments were established in 1982 and 1983. Main treatments of increasing moisture (non-irrigation, low, intermediate and high irrigation) were applied with a modi­ fied line-source sprinkler system. Moisture treatments were divided into subplots of applied nitrogen and non-applied nitrogen. Fababean roots penetrated to 135 cm in all irrigation regimes. Higher root density was found in deeper soil layers in the non and low irrigation regimes compared to inter­ mediate and high regimes. Plant height, shoot dry weight, total plant N, seed yield, seed number pod™1, pod number plant™1, harvest index, grain and total yield WUE were not affected by N application. N application inconsistently affected 1,000 seed weight and leaf- water potential. Fababean utilized applied NO3" in preference to N2 -fixation when NH4NO3 was applied. Plant height, shoot dry weight, total leaf-water potential and total plant N increased with increased ET. Seed yield, harvest index and WUE increased in 1982 and decreased in 1983 with increased ET. The decrease in 1983 was attributed to the short growing season and the effect of moisture on delayed maturation. I CHAPTER I INTRODUCTION Cereal cropping systems in Montana have historically consisted of wheat and barley monocultures. Annual legume crops are being investigated for their potential in rotation with cereals to increase soil fertility; break weed, insect and disease cycles; and increase market stability. Fababean {Vicia faba L.) is a low oil, high protein crop that can be used as either grain or forage for livestock or food for human consumption. Work in Canada has shown fababean to fit well in cereal crop rotations. Fababean is being investigated as an alterna­ tive and rotational crop in Montana. Fababean, like other legume crops, is capable of a symbiotic relationship with Rhizo- bium bacteria. Rhizobium converts atmospheric nitrogen to a usable plant form, with the plant providing carbohydrates for the bacteria. Fababean is self-sufficient from symbiotic nitrogen (N2)-Hxation in low NO3' soils (Salih, 1980; Sprent and Bradford, 1977). There­ fore, fababean may decrease the demand for nitrogen fertilizer. Fababean is well adapted to a cool climate and short growing season common in Montana. Its production in Montana should be limited either to irrigated areas or where rainfall is above 38 cm (Lockerman et al., 1982). However, limited research information is available in Montana on irrigation management of fababean. Soil moisture stress is one of the most limiting factors affecting fababean production in Montana. This study was initiated to determine the effect of: (I) soil moisture levels on growth and yield of fababean; and (2) soil nitrogen at various soil moisture levels on growth and yield of fababean. 2 CHAPTER II LITERATURE REVIEW Crop Fababean {Vicia faba L.) is an Old World crop referred to as the bean of antiquity. Probably native to the Near East, fababean is now cultivated in Europe, South America, North Africa, China, Asia and more recently in Canada and the United States. China is the leading producer of fababean, with an estimated production of 4,660,000 metric tons in 1975 (Duke, 1981). In 1975, Switzerland reported the highest yields with 4,000 kg ha-1 (Duke, 1981). Fababean was introduced into Canada in 1972 and production has increased steadily (Anonymous, 1975; Rowland and Drew, n.d.). Fababean is classified into three groups; major, minor and equina. The small to med­ ium seeded cultivars are grown for livestock feed and belong to the minor and equina groups, while the larger seeded cultivars are used for human consumption and belong to the major group (Duke, 1981; Witcombe, 1982). Common names for fababean include broadbean, horsebean, fava bean, Windsor bean, tickbean and Scotchbean (Duke, 1981; Janick et al., 1981). Fababean is a coarse, upright annual legume with indeterminate growth (Duke, 1981). It has large, unbranched, hollow stems 0.3 to 2 m tall, with I or more stems from the base (Duke, 1981). The leaves are compound, usually having 6 large, broad, oval leaflets (Duke, 1981). Indeterminate flowering is prolific with a limited number of set pods (Anonymous, 1975). The white axillary flowers with dark purple markings are born on short pedicels in clusters of I to 5 (Duke, 1981). Each flower cluster produces one to four pods 8-20 cm 3 long, 10-30 cm broad, containing 3 to 4 seed initiating approximately 20 cm above ground level (Duke, 1981). The smooth seed may be either oblong, oval, flattened or rounded. Seed color varies from bright reddish brown, light to dark greenish brown, light to dark purple, and may be obscurely mottled or dotted with colors similar to the base colors (Duke, 1981). Cultivated varieties in the U.S. and Canada are pale buff to buff in color when mature. Seed size varies from 350,000 to 550,000 mg per thousand seed (Anonymous, 1975). Although fababean are mainly self-pollinated, they may be highly cross-pollinated given favorable conditions and appropriate insect populations (Anonymous, 1975; Duke, 1981). Rooting depth ranges from 80 to 120 cm with 70 to 80% of the root mass in the soil plow-depth layer (Hebblethwaite, 1982; Naim ark, 1976). Growth rate of the root system exceeds that of the stem up to the flowering stage (Naimark, 1976). Sprent et al. (1977) reported that root growth ceases when the pods begin to fill. Fababean is exposed to varied photoperiod, precipitation and thermal regimes since its cultivation ranges from approximately 9 N to more than 40 N longitude and from near 0 to more than 2,000 m above sea level (Saxena, 1982). It is grown as a winter-season crop in subtropical regions with mild winters, at high elevations, under tropical conditions, and as a spring-season crop in temperate areas. Fababean is best adapted to moist growing areas and does best under relatively cool growing conditions (Anonymous, 1975; Rowland and Drew, n.d.). Dantuma et al. (1982) evaluated eight fababean cultivars grown at 22 environments in Western Europe. They con­ cluded that favorable factors for optimum fababean production are moderate temperatures, average amounts of solar radiation and the absence of a long, dry period. They also con­ cluded that water supply was probably the major yield determining factor. Keatinge and Shaykewich (1977), in a study at 9 locations in Manitoba, reported that seasonal soil-heat accumulation (above 5 C) needs to be greater than 1,000 degree days for 4 satisfactory dry matter production. High ambient temperatures (above 20 C) appeared to be deleterious to crop growth. Hot, dry conditions with low humidity may have a detri­ mental effect on seedset (Anonymous, 1975; Lockerman et al., 1982; Rowland and Drew, n.d.; Skjelvag, 1981a). Skjelvag (1981a) found that dry matter and seed yields decreased with increasing temperature. Growth was mainly affected by day temperature while night temperature had less effect (Skjelvag, 1981b). The amount of solar radiation has a differential effect on fababean growth. Increasing insolation reduced plant height, especially at high day temperatures (Skjelvag, 1981e). Crude fiber and nitrogen content increased with temperature at low insolation levels, but decreased at high levels (Skjelvag, 198Id). Skjelvag (1981c) also reported increased seed yields with high insolation during early growth and flowering. However, yields decreased with increased temperature and soil moisture deficit. Frost tolerance and growing season length are comparable to barley (Lockerman et al., 1982). Time needed for fababean maturation varies because of its indeterminate growth habit. Maturity ranges from 100 to 115 days depending on cultivar, location and year (Lockerman et al., 1982). Late maturity of fababean can be largely offset by early plant­ ing since the seedlings are frost tolerant (Anonymous, 1975). Additionally, some fababean cultivars can withstand low Fall temperatures. ‘Ackerperle’ was not frost killed until the temperature dropped below -4 C in Bozeman, MT during the Fall (1981) season (Locker­ man et al., 1982). Fababean is grown in North America primarily as a high protein supplement or high protein silage for on-the-farm use or for sale to local markets (Lockerman et al., 1982). When supplemented with methionine, fababean is an excellent protein source for livestock (Anonymous, 1975; Lockerman, et al., 1982; Rowland and Drew, n.d.). ^Protein in the present world collection ranges from 6.9 to 34.4% (El Sayed et al., 1982). Protein content of commonly cultivated cultivars often approaches 30% with a low 5 fat content of 1-2% (Marquardt, 1978). Fababean contains 60% less crude protein than soybean {Glycine Max (L.) Merrill) meal, but 27 and 147% more than field peas {Pisum sativum L. subsp. arvense L. Poir.) and barley {Hordeum vulgare L.), respectively (Mar­ quardt, 1978). Digestible energy content of fababean is similar to or slightly less than that of corn {Zea mays L.) silage (Ingalls et al., 1976; Ingalls et ah, 1979). According to Blair (1977), approximately 900 g of fababean are equivalent in feeding value to 450 g of soy­ bean meal plus 450 g of barley. Whole-plant fababean silage intake by dairy heifers and lactating cows is significantly higher than that of grass/legume silage or grass silage (Bareeba, 1980; Ingalls et al., 1976; Ingalls et al., 1979). Marquardt (1978) reported that daily liveweight gains of calves fed fababean, com and grass/legume silage were 1544,1317 and 1226 g, respectively. However, Ingalls et al. (1976 and 1979) reported no difference in average daily liveweight gains in dairy heifers fed fababean or grass/legume silage. Milk yields and milk composition were not significantly different when dairy cows were fed grass/legume or com silage untreated or treated with urea or Pro-sil or whole- plant fababean silage untreated, direct cut, wilted or treated with formaldehyde (Bareeba, 1980). Ingalls et al. (1980) also found no significant differences in milk yield when faba­ bean replaced soyameal in the diet. Additionally, with similar amounts of dietary fiber, replacing soya by fababean had no apparent effect on milk, fat, but milk protein was sig­ nificantly reduced. Thorlacius and Beacom (1981) reported high energy digestibility and voluntary intake of whole crop fababean silage by lambs. Additionally, dry matter intake and average daily gain was significantly greater for lambs given fababean than those fed on corn or oat {Avena sativa L.) silage (Thorlacius and Beacom, 1981). Ingalls et al. (1976) reported that dry matter digestibility of silages for sheep was 60.3, 59.7, 65.9 and 69.0% for barley, grass, com and fababean, respectively. 6 Mateos and Puchal (1981) studied the nutritional value of fababean for swine and sug­ gested that fababean may be used safely in diets for starting and finishing pigs at 20% sup­ plemental levels. Fababean is also being utilized as a protein source in human diets. In Egypt, fababean occupies a prominent position in the national diet (Gabrial, 1982). In 1978, fababean pro­ vided 250,000,000 of the 376,000,000 kg of pulse, nut and seed crops produced in Egypt (Gabrial, 1982). Eighty-one and six-tenths g of the daily per capita protein intake of 94.9 g is of vegetable origin (Gabrial, 1982). Approximately 14 g of fababean is consumed daily per capita accounting for 3 g of protein (Gabrial, 1982). Fababean in Egypt are prepared and eaten in several ways. Green immature seeds are eaten fresh, fresh immature pods are boiled and dried seeds may either be stewed, germi­ nated and cooked, or soaked and made into a paste and fried (Gabrial, 1982). Fababean seed amino acid balance is good, except for the sulphur amino acids, in par­ ticular methionine (El Mubarak et al., 1982). El Mubarak et al. (1982) also concluded that 100 g of germinated, cooked or baked fababean would supply, with the exception of meth­ ionine and threonine, a major proportion of the human daily requirement for essential amino acids. Water Stress Effects on Seed Yield According to Sprent et al. (1977), water supply may be a more important factor con­ trolling fababean yield than either solar radiation or plant competition. Montana fababean production should be limited either to the irrigated areas or areas where rainfall exceeds 38 cm (Lockerman et al., 1982). Seed yield rarely exceeds 1344 kg ha-1 in Montana when precipitation is below 38 cm. 7 Seed yield increases with increased irrigation (El Nadi, 1970; Farah, 1981a; Keatinge and Shaykewich, 1977; Krogman et al., 1980; McEwen et ah, 1981; Olivares and Recalde- Martinez, 1982; Stock and El Naggar, 1980). Yield may decrease as a result of water stress at any growth stage, however, some growth stages are more sensitive than others (El Nadi, 1970). Most researchers agree that the greatest detrimental effect of moisture stress is during the early reproductive development phase (El Nadi, 1970; Keatinge and Shaykewich, 1977; Stock and El Naggar, 1980). El Nadi (1970) applied four irrigation treatments [(wet, wet), (dry, wet), (wet, dry) and (dry, dry)] to fababean at two different growth phases from emergence to early fruit set and from early fruit set to harvest. Plants not stressed had the highest number of pods plant-1 and seed weight. Plants stressed early had higher yields than plants stressed late due to high seed weight and more seeds pod-1. The number of pods plant-1 were higher in the later stressed plants. Annual legume crops other than fababean have not shown consistent results from water applications. Zablotowicz et al. (1979) working with cowpea (Vigna unguiculata (L.) Walp.) and Robertson et al. (1980) with soybean found no difference in yield between well-watered and draughted treatments. Summerfield et al. (1976) reported that repeated wilting prior to flowering of cowpea markedly reduced seed yields compared with the unstressed controls, whereas wilting after flowering did not reduce yield. Turk et al. (1980a) reported no effect of water stress during the vegetative stage when environmental conditions were conducive to rapid recovery in field grown cowpea. However, water stress during flowering and pod fill reduced yields. Other studies have found that irrigation of pea {Pisum sativum L.) and soybean at pod fill increased yield more than irrigation at any other growth stage (Ashley and Ethridge, 1977; Doss et al., 1973; Miller et al., 1977; Pumphrey and Schwanke, 1974; Rathore et al., 1981). Mederski arid Jeffers' (1972) reported that soil moisture effects on soybean seed yield varied among cultivars. 8 Literature addressing the effect of water stress on pea, cowpea and soybean seed qual­ ity is limited and inconsistent. At Vauxhall, Alberta from 1974 to 1977, seed crude pro­ tein yield was strongly dependent upon increased water supply (Krogman et ah, 1980). Seed crude protein content increased from 30.8 to 33.2% as irrigation level increased. However, at Brooks, Alberta in 1974 and 1976 there was no response of seed crude protein content with increased irrigation (Krogman et ah, 1980). Additionally, 1,000 seed weight was not dependent upon total water received. Farah (1981b) reported that water shortage reduced amounts of seed nitrogen (N), phosphorus (P) and potassium (K). Results on the effect of water stress on pea, cowpea and soybean seed quality are also inconsistent. Moisture stress did not affect oil or protein content of pea, cowpea or soy­ bean at any growth stage (Hunt et ah, 1980; McLean et ah, 1974; Rathore et ah, 1981; Sionit and Kramer, 1977). Miller et ah (1977) reported a relationship between water used and seed size at constant water applications. However, Pumphrey and Schwanke (1974) found irrigated peas to have lower processing quality than non-irrigated peas. Water Stress Effects on Dry Matter Production Irrigation increases fababean total dry matter and moisture stress reduces dry matter production (Farah, 1981a; Krogman et ah, 1980; McEwen et ah, 1981; Shaaban et ah, 1979). McEwen et ah (1981) predicted fababean forage yields of at least 5,000 kg ha"1 at ■ Rothamsted without irrigation and 6,000 kg ha-1 with above average rainfall or irrigation. According to Lockerman et ah (1982), Canadian reports indicate that irrigated fababean has a forage potential of 8,960 to 17,920 kg h a '1. In the Sudan, EI Nadi (1970) reported reductions in fababean relative growth rate when water stress was applied from emergence until early fruit set. Additionally, more Water Stress Effects on Seed Quality 9 crown branches were produced when drought up to early fruit set was followed by water­ ing. In contrast, soybean plants suffered less injury when the plants were stressed before flowering (Sionit and Kramer, 1976). Pea and cowpea dry matter production respond to water stress similar to fababean (Lee et ah, 1973; McLean et ah, 1974; Miller et ah, 1977; Pumphrey and Schwanke, 1974; Shouse et ah, 1981; Turk and Hall, 1980c). A greenhouse study where four constant moisture levels were applied to pea showed a relation between water used and total dry matter (Miller et ah, 1977). Shouse et al. (1981) reported that dry matter production was linearly related to transpiration. . Water Stress Effects on Plant Height Limited information is available on the effect of water stress on fababean plant height. Most of the literature relates plant growth mainly to shoot dry matter. El Nadi (1970) reported that water stress from emergence to early fruit set resulted in a relative growth reduction. Fababean is reported to have a strong stem (Anonymous, 1975). However, McEwen et al. (1981) reported that fababean grain in 1977, in a field study at the Rotham- sted experiment station, could not be harvested because of lodging. Therefore, it is sug­ gested that plant height, internode number and length may have serious implications if they are affected by high precipitation or irrigation. Pea and cowpea plant height increased with increased water application and water use efficiency (Manning et al., 1977; Miller et al., 1977). Irrigation timing may also affect plant height. Miller et al. (1977) in a greenhouse study applied combinations of two water levels of high (80 to 100% of field capacity) and low (40 to 60%) to pea over each of three different growth stages. Greatest plant height occurred when high water was applied during flowering to early pod fill. 10 Water Stress Effects on Leaf and Internal Water High moisture stress reduced fababean leaf area (El Nadi, 1970; Farah, 1981a). Farah (1981a) applied constant field irrigation treatments designated as wet, medium and dry to fababean. Leaf area was reduced as well as rate of leaf appearance and leaf longevity as moisture stress increased. In another field experiment, water stress from emergence to early fruit set reduced leaf area (El Nadi, 1970). Additionally, water stress applied from emergence to early fruit set decreased moisture content of shoot tissue compared with the well-watered plants. In a growth room experiment, moisture content of shoot tissue at the permanent wilting point was only 2% less than that of plants growing at field capacity (El Nadi et ah, 1969). This suggests a tendency toward drought resistance.in fababean. Water stress decreased leaf area, leaflet number and average leaflet area of cowpea, although water stress increased specific leaf weight (Turk and Hall, 1980c). Manning et al. (1977), in a greenhouse experiment, found water use efficiency (WUE) positively corre­ lated with leaf area. WUE represents yield per unit of water used by the plant. Water stress also affects other structural components of pea leaves. Increased soil moisture stress increased the stomatal density, while upper leaves had more stomata per area than lower leaves (Manning et al., 1977). Additionally, the cross-sectional diameter of the xylem cor­ related with WUE (Manning et al., 1977). Plant responses (leaf-water potential, leaf-air temperature differential and leaf-diffusion resistance) are sensitive to water deficits during the late vegetative stage in southern pea (Vigna sinensis L.) (Clark and Hiler, 1973). All three plant measurements indicated water deficit to some degree, however, leaf-water potential was most responsive and leaf-diffusion resistance was least responsive (Clark and Hiler, 1973). Additionally, plant response was less sensitive during the pod development stage (Clark and Hiler, 1973). Predawn leaf-water J ■1 11 potential was a better indicator of crop water stress than midday in cowpea (Shouse et ah, 1981; Turk and Hall, 1980b). The literature does not explain the effect of water stress levels on leaf-water potential of fababean. More work should be done to examine the utility of leaf-water potential as an index of fababean water stress. Water Stress Effects on Water Use Water use by a crop may be expressed as WUE, evapotranspiration (ET) or crop trans­ piration (T). Additionally, water use efficiency may be based either on evapotranspiration or crop transpiration. The difference may be important since suppression of soil evapora­ tion and prevention of weed transpiration, may improve WUE based on ET, but may not improve WUE based on T (Tanner and Sinclair, 1983). However, ET is easier to measure than T and is the most commonly used. Evapotranspiration for the growing season is higher in fababean than cereals. At Leth­ bridge, Canada from 1974 to 1977, evapotranspiration of fababean receiving high irrigation averaged 544 mm, which was 16% greater than irrigated cereals (Krogman et ah, 1980). El Nadi (1970), in field studies at the University of Khartoun in the Sudan, reported the highest WUE in well-watered fababean. Water stress affects WUE of pea and-cowpea similar to fababean. When constant water applications were applied, WUE was positively correlated with moisture regime in pea (Manning et ah, 1977) and Cowpea (Turk and Hall, 1980d). However, the growth stage in which stress is applied niay result in either an increase or decrease in WUE. Shouse et ah (1981) and Turk and Hall (1980d) found that WUE in cowpea increased with vegetative stage drought and decreased with flowering and late season drought. WUE was also posi- lively correlated with total dry matter, seed yield, seed size, seed number plant"1, plant 12 height and leaf area of pea (Manning et ah, 1977; Miller et ah, 1977). Therefore; WUE should be a good parameter to measure plant response to various moisture levels. Water Stress Effects on Root Growth and Depth of Soil Water Extraction Root system size and water extraction depth are extremely important since yield and growth parameters are closely related to total water use. There are conflicting reports on the maximum rooting depth of fababean. Naimark (1976), on a dernopodzolic soil in Belorussia, reported rooting depths to 120 cm. However, Hebblethwaite (1982) reported that no roots could be found below 80 cm. Although there is disagreement on the maximum depth of rooting, most researchers agree on the depth where most of the water is absorbed. Tawadros (1982), Naimark (1976) and Hebblethwaite (1982) reported that the upper 30 cm of the soil profile is the most important absorption area for fababean, since it contains approximately 70% of the active roots. Literature involving the effect of soil moisture levels on root growth and soil extrac­ tion patterns of fababean is limited. El Nadi et al. (1969), in growth chamber experiments, observed that the drier the soil, the deeper the roots penetrate in the growing medium. Additionally, soil moisture influenced root distribution in the profile, but did not affect root weight. Roots reduce the harmful effect of water stress by growing and branching deeper where the soil is less dry. A physiological explanation has been suggested for compensatory growth of fababean roots in deep layers in dry soils. Growth rate depends on carbohydrate supply and on external conditions. Carbohydrates flowing from the shoot are distributed to all growing parts of the root. Plant parts growing most rapidly constitute the most active sink. Higli 13 soil moisture is more favorable for rapid growth than low soil moisture, with subsequently more root growth in deeper soil layers of high moisture content (El Nadi et ah, 1969). Soil moisture effects are variable among many crops. Peanut (Arachis hypogaea L.) and soybean root growth was not affected by water management, however, corn root growth increased in length with irrigation (Robertson et ah, 1980). Water management treatments of (I) rain-fed, no irrigation; (2) light, frequent irrigation-soil wetting depth of 30 cm; (3) medium, infrequent irrigation-soil wetting depth of 60 cm; and (4) light, infre­ quent irrigation-soil wetting depth of 30 cm were applied to field grown corn. Corn root growth increased in length with irrigation with the largest root length values corresponding to light, infrequent irrigations (Robertson et al., 1980). Water Stress Effects on Modulation and N2 -Fixation Molecular nitrogen (N2) composes almost 80% of the earth’s atmosphere (Havelka et al., 1982). However, the two triple-bond atoms of the N2 molecule have to be cleaved into single atoms before they combine with hydrogen or oxygen to form either ammonia (NH3) or nitrate (NO3-) compounds for plant use (Havelka et al., 1982). One method of bond cleavage is by the commercial Haber-Bosch process which requires high temperature and pressure (Havelka et al., 1982). Another method is through symbiotic biological N2- fixation, a unique system possessed by a few prokaryotic organisms in association with legume plants. Nitrogenase catalyzes the conversion of N2 to NH3 under mild temperature and normal atmospheric pressure. The best known and most agriculturally important microorganism capable of biologi­ cal N2 -fixation is Rhizobium bacteria. Rhizobium infect the root of legumes, form nodules and conduct a symbiotic relationship with the host plant. The host plant (macrosymbiont) supplies the bacterium (microsymbiont) with an energy supply, and the bacterium supplies the plant with reduced N2. However, symbiotic N2 -fixation is not without cost to the host 14 plant. Estimates suggest that from 15 to over 30% of the total assimilatory capacity of a plant may be utilized to sustain the process of N2 -fixation and NH*+ assimilation (Schu­ bert, 1982). Fababean has a symbiotic relationship with Rhizobium leguminosarum. However, water stress is a major factor affecting nodulation and nitrogen fixation in fababean (Day et al., 1980a; Sprent, 1972; Sprent, 1976a and b; Sprent and Bradford, 1977). Water poten­ tial gradients exist in nodules. Water is lost from the surface and resupplied by the vascular system of the root (Sprent, 1972; Sprent, 1976b). Sprent (1972) showed a high degree of correlation between soil-water content and nitrogen-fixing activity in field grown fababean. Slow natural drying over 6 weeks progressively reduced N2 -fixation and was restored by irrigation (Sprent, 1972). Maximum nitrogen fixation occurs at field capacity, however, nodule formation and nitrogen fixation are reduced by waterlogging (Sprent, 1972; Sprent, 1976a). Day et al. (1980b) working with fababean and Zablotowicz et al. (1979) with cowpea reported that irrigation increased nodule dry weight, total and specific nitrogenase activity and total N content. Nodulation and nitrogenase activity are differentially affected by water stress, depending on the plant growth stage. Summerfield et al. (1976) observed that nitrogenase activity of cowpea decreased with repeated wilting prior to flowering and was less affected when wilting occurred after flowering. Several hypotheses explaining how nitrogen fixation is affected by water stress have been suggested. Sprent (1976b) suggested two alternatives: (I) depressed O2 uptake inhibits oxidative phosphorylation which produces ATP and NADPH2 required for the metabolic reduction of NO3" to NH3 and (2) water stress affects membrane characteristics which in turn affect the function of the membrane bound enzyme essential for N2 -fixation. Effects of moderate stress may be overcome by increasing the O2 concentrations (Sprent, 1976b). 15 Pate et al. (1969) suggested that limitations in water supply to the nodule may affect nodule activity by restricting fixation products which may accumulate in inhibitory con: centrations. Sprent (1971) observed a close link between nitrogen-fixing and respiratory activities. However, other researchers have reported that inhibition of shoot photosynthe­ sis accounts for the inhibition of nodule acetylene-reduction at low water potentials (Finn and Brun, 1979; Huang et al., 1975a; Huang et al., 1975b). Huang et al. (1975a), in a con­ trolled environment experiment, observed that as soil was desiccated below -0.2 MPa acetylene-reduction decreased and the decrease was correlated with decreased photosyn­ thesis and transpiration. It was concluded that either photosynthesis, transpiration or some direct effect on the nodule other than that caused by respiration was more likely the reason for acetylene-reduction inhibition at soil-water potentials below -0.2 MPa. In further experiments, Huang et al. (1975b) found that acetylene-reduction inhibition caused by low soil-water potentials could be reproduced by depriving shoots of atmospheric CO2 even though the soil-water potentials were favorable for rapid acetylene-reduction. Additionally, the inhibition of acetylene-reduction at low soil-water potentials could be reversed by exposing shoots to high concentrations of CO2. It was concluded that inhibi­ tion of shoot photosynthesis accounted for acetylene-reduction inhibition at low soil-water potentials. Other effects of water supply may be on multiplication and movement o tRhizobium in the soil. Shimshi et al. (1967) found that shallow placement of inoculum in soils gave best nodulation in peanut at depths of 3-4 cm, despite higher soil moisture at greater depth. They also concluded that Rhizobium multiply rapidly following irrigation, and migrate in the soil while sufficient moisture is available. Soil-water tensions o f -0.8 MPa reduced the movement of Rhizobium trifolii, and migration cessation occurred when water-filled soil pores became discontinuous (Hamdi, 1970). 16 Research on the effects of water stress on fababean N uptake are limited and incon­ sistent. Water shortage reduced plant levels of N, P and K throughout the growth period and for seed at harvest (Farah, 1981b). However, Shaaban et al. (1979) reported that plant N, NH4+ and NO3- contents were highest at soil moisture contents of 60% and lowest at 80% of water holding capacity. Moisture stress reduces N uptake by soybean (Rathore et al., 1981). However, in the same experiment, moisture stress at all growth stages did not alter N status of the roots. Hunt et al. (1980) reported that water level had no effect on seed N content of field grown soybean. Nitrogen Effects on Nodulation and N2 -Fixation Inhibitory effects of NO3- on nodulation and N2 -fixation of fababean have been well documented (Day et al., 1980a and b; Dean, 1976; Dean and Clark, 1977; Hill-Cottingham and Lloyd-Jones, 1980; Kishaet al., 1980; McEwen et al., 1973; Richards and Soper, 1982; Salih, 1980; Vondrys and Biedermannova, 1980). However, results have been inconsistent and there is some disagreement as to the extent to which nitrogen fertilization affects N2 -fixation. Dean and Clark (1977) reported that symbiotic N2 -fixation of fababean on low nitrate soils accounted for a maximum of 67.5 to 70.0 kg N ha-1 in 1975 and 146.0.kg N ha-1 in 1976. However, on high N soils, acetylene-reduction was 37% less than the maximum rate found at the low N sites. Day et al. (1980a) reported that the amount of N fixed was 235 kg ha-1 without added N and declined linearly to 50 kg ha-1 with 450 kg N ha-1 . Hill-Cottingham and Lloyd-Jones (1980) grew fababean plants in a complete nutrient solution with either 1.5 or 6 mM of 15N labelled nitrate. They reported that N2 -fixation Water Stress Effects on N Uptake 17 was slightly reduced at the higher N rate, but still made a substantial and increasing con­ tribution to total plant N. In a further study by Hill-Cottingham and Lloyd-Jones (1980), plants grown in 1.5 mM nitrate were suddenly exposed to a high nitrate solution (18 mM) during initial pod fill. The high nitrate solution had no effect on plant total N content, but N2 -fixation ceased. NO3- uptake and nodule growth returned to normal when the nitrate concentration was returned to 1.5 mM. Stimulatory effects of low rates of combined N on soybean symbiosis have been indi­ cated (Sistachs, 1976). Additions of up to 50 kg N ha-1 at planting to inoculated plants qutyielded noninoculated plants with similar N rates, but N added after cotyledon exhaus­ tion had a depressive effect. Additionally, application of 56 kg ha-1 NH4NO3 to soybean grown in the field had no effect on N2 -fixation (Bhangoo and Albritton, 1975). However, Dean and Clark (1980) reported that the addition of 20 kg N ha-1 as NH4NO3 depressed nodulation and acetylene-reduction of fababean, pea, black bean (Phaseolus vulgaris L.) and soybean. The time of NH4 NO3 application was not reported. The degree of effect also depends on the form of applied N and time of application. Ammonium depressed nodulation and N2 -fixation more than N 03--N in fababean (Salih, 1980). No effects of timing of N application on N2 -fixation have been reported for faba­ bean. However, fertilizer applied at planting in excess of 45 kg N ha-1 reduced the symbiot- ically fixed N fraction in soybean, whereas delayed fertilizer application had no such influ­ ence at any N rate (Deibert et al., 1979). Beard and Hoover (1971) reported fewer nodules per soybean plant when more than 56 kg N ha-1 was applied at planting. However, up to 112 kg N ha-1 did not affect nodule number when applied at flowering. Soybean cultivars differ in their tolerance to fertilizer N with respect to N2-fixation. Nitrogen fixation was constant as N fertilizer increased from 0 to 80 kg ha-1 , but decreased by 24% when 160 kg N ha-1 was applied to soybean accession ‘X005’. Nitrogen fixation 18 was constant as N fertilizer increased from 0 to 40 kg ha"1 but decreased 21% when 80 or 160 kg ha"1 ofN was applied to soybean cv ‘Maple Presto’ (Rennie et al., 1982). Several hypotheses have been suggested to explain why applied nitrogen sources or high fertility levels cause decreased nodulation and subsequent N2 -fixation. One hypothe­ sis is that photosynthate deprivation occurs in the nodule. This may occur because carbon is being used in the NO3" assimilatory pathway. Carbon comes from the photosynthate normally used for N2-fixation, therefore, N2 -fixation may be inhibited (Oghoghorie and Pate, 1971). Other researchers suggest that nitrite, the product of nitrate reductase, strongly inhibits nitrogenase activity in bacteroids. Nitrite may complex with leghemoglobin to destroy the O2 regulating activity, and inhibit nitrogenase activity (Kennedy et al., 1975; Rigaud et al., 1973). Additionally, Dazzo and Brill (1978) suggest that fixed N ions may play a role in regulating the early recognition process in the Rhizobiumlhost symbiosis. As concentrations of either NO3- or NH4+ increased, binding of Rhizobium trifolii bacteria to root hairs of clover {Trifolium repens L.) declined. Additionally, plant lectins (trifoliin) on the root hair surface, which are involved in recognition, declined. Evidence indicates that fababean utilizes soil and fertilizer N sources in preference to fixed atmospheric N (Dean, 1976; Hera, 1976; Richards and Soper, 1979). The reason for this preference is uncertain. Fababean are self-sufficient from symbiotic N2 -fixation in low NO3- soils and the potential for N2 -fixation in fababean is considered to be sufficient to sustain high yields (Salih, 1980; Sprent and Bradford, 1977). Possibly the high energy costs to the macrosymbiont by N2 -fixation may cause it to preferentially use soil N. Mahon (1977) estimated the energy requirement for N2 -fixation to be equivalent to 17 g of carbohydrate consumed per gram of N2 fixed. However, Schubert (1982) and Mahon (19.77) suggested that the energy cost for reduction of NO3- (from fertilizer) to NH4+ (form usable by plant) was similar to the costs for N2 -fixation. 19 Other environmental factors which may have a role in the inconsistent response of N fertility on N2 -fixation and growth of fababean are light quantity, temperature, soil pH, organic matter and micronutrient nutrition (Silver and Hardy, 1976). These environmental and nutritional factors normally affect N2 -fixation through photosynthate production, but some environmental factors may exert a direct influence on N2 -fixation itself (Havelka etal., 1982). Nitrogen Effects on Nitrogen Uptake There is some disagreement on the effect of nitrogen fertilization on nitrogen uptake of fababean. Vondrys and Biedermannova (1980) reported that applied N had no effect on the total-N content, even though nitrogenase activity and symbiotic N2 -fixation decreased. Contradictory results were reported by Day et al. (1980a) and Graman et al. (1978). They found that total-N in fababean increased with increased N fertility, even; though N2 -fixation decreased (Day et al., 1980a). Hill-Cottingham and Lloyd-Jones (1980) reported that after pod fill, plants given higher NO3" contained slightly more total-N than those receiving a lower concentration and took up four times as much NO3'. Additionally, N2 -fixation was slightly reduced at the higher N rate; but still made a substantial and increasing contribution to total plant N. The same inconsistent response of N on total-N uptake was observed in soybean. Bhangoo and Albritton (1975) and Deibert et al. (1979) reported that nitrogen fertiliza­ tion resulted in an increase in. N uptake by the plant. Conversely, Rennie et al. (1982) reported no response in N uptake. Variable effects may have been caused by differential location and other environmental conditions. 20 Richards and Soper (1982) observed that seed yield of nodulated fababean was infre­ quently and unpredictably affected by N application rate, application type, and applica­ tion time. Most researchers agree that there are no significant seed yield differences of fababean with N application (Islam and Afandi, 1981; Kisha et ah, 1980; Scherer and Danzeisen, 1980). However, Hamissa (1980) and Salih (1980) reported increased yields with N application whereas Graman et al. (1978) reported decreased yields with an appli­ cation of 120 kg N ha-1 . Similar unpredictable effects have been found for soybean and pea. Most research indicates that N application rates have no effect on soybean seed yield (Beard and Hoover, 1971; Criswell et al., 1975; Hera, 1976; Semu and Hume, 1979). However, depending on location, environment, and amount of N applied, soybean seed yield may either increase (Bhangoo and Albritton, 1975; Sosulski and Buchan, 1978; Trevino and Murray, 1975) or decrease (Trevino and Murray, 1975). Nitrogen Effects on Seed Quality Most research on seed quality of legumes is based on seed protein content. Research is limited on the effect of nitrogen fertility on fababean seed protein. Richards and Soper (1982) found that fababean seed protein was unaffected by applied N up to 150 kg ha-1, but was significantly increased by 300 kg N IiaT1 in nine field trials in Manitoba. Similar results have been found for pea, where seed protein progressively increased with increased N fertility (Browning and George, 1981; Trevino and Murray, 1975). Nitrogen Effects on Seed Yield , 21 Results have been sporadic regarding the effect of nitrogen fertility on legume dry matter production. Several researchers found no significant increase in fababean dry matter production with N fertilization (Dean and Clark, 1980; Richards and Soper, 1982; Vondrys and Biedermannova, 1980). However, some reports indicate increased vegetative growth with increased N fertility of fababean (Graman et al., 1978; Hill-Cottingham and Lloyd-Jones, 1980; Salih, 1980). Graman et al. (1978) reported that application of 40 and 80 kg N ha"1 increased fababean fresh and dry matter yield. However, dry matter yield decreased with the application of 120 kg N h a '1. More consistent results have been reported for soybean, dry bean (Phaseolus vulgaris L.) and pea dry matter production (Bethenfalvay et al., 1978; Bhangoo and Albritton, 1975; Edje et al., 1975; Sosulski and Buchan, 1978). Forage dry matter yields increased as N fertility increased. Nitrogen Effects on Forage Quality Forage protein content of fababean was variably affected by N application (Richards and Soper, 1982), although results are limited. Edje et al. (1975) working with dry bean, and Sosulski and Buchan (1978) with pea noted that protein percentage and protein yield were closely related to applied N. However, these crops are relatively poor nitrogen fixers, which may account for this response. However, if environmental conditions are favorable, fababean is relatively self-sufficient in N2 -fixation (Dean and Clark, 1977; Sprent and Bradford, 1977). This may account for its variable response to N fertility. Nitrogen Effects on Shoot Dry Matter Production 22 Nitrogen fertilizer response on fababean maturity has not been addressed and very little research has been reported on maturity effects of other legumes. Trevino and Murray (1975), at Idaho, reported a delay in maturity, of pea by N application in all winter culti- vars tested except one. However, three ‘spring type’ cultivars showed no maturity differ­ ence due to N application. When there was a delay in maturity, the delay occurred between first flower and harvest, resulting in a lengthening of the pod filling period. In many areas of Montana, frost free days can vary considerably from year to year. A ten year average (1973-1982) for Bozeman is 94 frost free days, however, this number varied from 74 days in 1976, to 131 days in 1980 (Caprio, 1973-1982). Any factor which increases days to maturity may affect fababean production considerably in Montana. Nitrogen Effects on Maturity 23 \ CHAPTER III MATERIALS AND METHODS Effects of moisture level and nitrogen fertilization on growth and yield of fababean (Vicia faba L. cv ‘Ackerperle’) were evaluated in field experiments in 1982 at the Montana State University Horticultural Farm near Bozeman, MT and in 1983 on the John Schutter Farm near Manhattan, MT. Site Description The experiment in 1982 was on a Bozeman silt loam (fine-silty, mixed, Argic Pachic Cryoborolls). Composite soil samples of 8 cores per replication were taken on 24 April at depths of 0 to 30 and 30 to 60 cm to determine initial soil fertility. Samples were oven- dried at 80 C with forced-air for 48 hours and analyzed by standard soil test methods in the Montana State University Soil and Plant Testing Laboratory. The soil contained 81, 1,026, and 9,430 kg ha-1 , respectively of N, P, and K, Bulk densities at depths of 0 to 30 and 30 to 60 cm were 1.23 and 1.30 Mg m-3, respectively'. The experimental site was fal­ lowed the year before planting. Two field experiments at the same location in 1983 were conducted on a Manhattan very fine sandy loam (coarse-loamy, mixed, Typic Calciborolls). Initial soil samples were taken on 25 April, processed, and tested as described for 1982. The analysis indicated the presence of 23, 94, 2,110, 381, 45, and 0.9 kg ha-1, respectively of N, P, K, Ca, Mg and Na. The soil had a conductivity (Ec) of 0.7 mmhos, medium effervescence, and pH and O.M. content at 0 to 30 and 30 to 60 cm of 8.1, 8.4 and 1.0 and 0.5%, respectively. Bulk 24 densities at depths of 0 to 30, 30 to 60, and 60 to 90 cm were 1.28, 1.24, and 1.28 Mg n r 3, respectively. The area was previously cropped to barley. Experimental Design A modified randomized complete block, split-block design was utilized in all experi­ ments. In 1982, four main treatments (2.4 X 6 m) of increasing moisture (non-irrigation, low, intermediate, and high irrigation) were applied and replicated three times. Main plot irrigation treatments were fixed due to the limits of the line-source system, and cannot be statistically tested by analyses of variance (ANOVA) (Hanks et al., 1980). Moisture data were analyzed by regression. Moisture treatments in 1982 were divided into subplots (2.4 X 3 m) for applied nitro­ gen, and non-applied nitrogen. The non-applied nitrogen subplots had an intermediate level (81 kg ha"1) of indigenous nitrate nitrogen. Prior to seedling emergence, 99 kg ha"1 NH4NO3 were applied to the applied nitrogen subplots to increase the NO3" level to 180 kg ha"1. Nitrogen subplot treatments were randomized, and ANOVA is statistically valid in identifying nitrogen effects and moisture X nitrogen interactions (Hanks et al., 1980; Sorensen et al., 1980; Stewart et al., 1977). In 1983, two experiments with four main plots (2.4 X 4.8 m) of increasing moisture levels of non-irrigation, low, intermediate, and high irrigation were applied and replicated four times. Moisture treatments were divided into subplots (1.2 X 4.8 m) for applied nitro­ gen and non-applied nitrogen. The non-applied nitrogen subplots had a low level (23 kg ha"1) of indigenous nitrate nitrogen. Prior to seedling emergence, 157 kg h a '1 NH4NO3 was applied to the applied nitrogen subplots to increase the nitrogen level to 180 kg h a '1. Statistical analyses were the same as in 1982. 25 Planting Seed were planted 7 May 1982 in eight row plots and 26 May 1983 in 4 row plots, 2.5 cm deep, with a coneseeder. Rows were 30 cm apart with 13 seed m-1. Seed were sized to minimize seedling variation. Commercial granular Rhizobium inoculum (strain Q, Nitra- gin Co., Milwaukee, WI) was seed applied at 17 kg ha-1 . Plots were hand weeded when necessary. Meteorological Observations Growing season precipitation, temperature, humidity, and solar radiation were measured with standard weather instruments and recorded daily in 1982 (Appendix, Table 7) and 1983 (Appendix, Table 8) and summarized in Table I. Irrigation System Water treatments in 1982 and 1983 were applied with a line-source sprinkler irriga­ tion system similar to the one described by Hanks et al. (1976). My system used a Model 25 sprinkler with a 4 mm nozzle (Rain Bird Sprinkler Manufacturing Company of Glen­ dora, California). The sprinklers were operated in 1982 at approximately 414 kPa produc­ ing a wetted radius of 15 m and a discharge rate of 0.35 I s"1 per sprinkler head. In 1983, the sprinklers were operated at 379.5 kPa giving a wetted radius of 15 m and a discharge rate of 0.34 I s-1 per sprinkler head. Initially, sprinklers were placed on 2.5 X 60 cm risers spaced 4.6 cm apart on 5 cm diameter aluminum pipe with hook and latch couplings. Sprinklers were later placed on 120 cm high risers to compensate for crop growth. Evaporation pans (No. I wash tubs), similar to the one described by Bauder et al. (1982), were placed within the intermediate water treatments to determine irrigation 26 Table I. Weekly Environmental Data for Horticultural Farm at Bozeman, MT and John Schutter Farm at Manhattan, MT in 1982 and 1983, Respectively. Temperature $ Humidity Week Precipitation Mean High Mean Low Mean Mean Mean High Mean Low Solar Radiation mm ------ C - - - 1982 — % ------ Wm"2 5/ 7-5/ 8 7.7 14 3 9 92 39 — 5/ 9-5/15 8.2 12 I 7 81 35 — 5/16-5 /22 7.4 20 5 13 86 29 — 5/23-5 /29 43 .9 16 3 10 84 47 — 5/30-6 / 5 13.2 14 3 9 90 41 — 6/ 6-6/12 46.5 18 4 11 85 30 — 6/13-6/19 26.1 23 8 16 89 . 34 — 6 /2 0-6 /26 13.2 24 10 17 86 38 6/27-7/ 3 8.2 25 12 18 89 38 — 7/ 4-7/10 16.6 22 9 16 88 33 — 7/11-7/17 11.8 24 8 16 77 32 30 ,852 ' 7/18-7/24 2.0 28 ■ 11 20 74 27 49 ,977 7/25-7/31 ■ 4.6 27 13 20 73 24 53,048 8 / 1-8/ 7 . 2.7 28 8 18 78 22 53,537 8 / 8-8/14 1.6 27 11 19 76 23 45 ,998 8/15-8 /21 7.2 29 10 20 83 24 45 ,230 8 /22 -8 /28 9.6 27 8 18 81 22 45,928 8 /29 -9 / 4 4.6 25 9 17 77 24 41,461 9/ 5-9/11 12.7 24 6 15 69 19 40 ,624 9/12-9/17 24.1 10 J _ _6 92 49 11,587 5/ 7-9/17 271.6 22 7 1983 15 82 31 418,242t 5/26 -5 /28 0 28 6 17 — — — 5 /2 9 -6 / 4 0 21 5 13 — — - 6/ 5-6/11 0 24 8 16 — — - 6/12-6/18 6.0 19 6 13 — — — 6/19-6/25 7.0 23 9 16 -7- — — 6 /2 6 -7 / 2 43:3 23 11 17 . 60 24 . — 7/ 3-7/ 9 4.7 25 10 18 54 18 10,679' 7/10 -7 /16 35.5 24 10 17 54 18 52,490 7/17-7/23 0 27 9 ' 18 54 17 56,329 7/24-7/30 6.0. 28 11 20 57 17 51,792 7/31-8/ 6 2.5 31 12 22 56 16 50,116 8/ 7-8/13 12.8 29 14 21 55 21 . 7,818' 8/14-8/20 0 26 11 19 55 20 - 8/21-8/27 12.8 27 10 19 56 17 - 8 /2 8 -9 / 3 10.1 28 10 19 52 13 ” 9/ 4-9/10 7.6 23 6 15 50 14 - 27 Table I (continued). Temperature^ Humidity Week Precipitation Mean High Mean Low Mean Mean Mean High Mean Low Solar Radiation mm ----- C- - - 1983 — % ----- Wm-2 9/11-9/17 0 22 4 14 53 17 — 9/18-9/19 0.0 5 -4 I 54 32 — 5/26-9/19 148.3 25 9 17 55t 19^ 229,224t —Data not available. ^ Partial total. t Temperatures for 5/26/83 to 6/22/83 are from Belgrade, MT. timing. Approximately 15 cm of water was placed in the pans at planting and irrigation was applied when half the plant available water was depleted. Cumulative evaporation from the pan is a good estimate of crop water use (Bauder et al., 1982). Plant available water in 1982 and 1983, based on available water capacity (Kresge and Westesen, 1980) X rooting depth was 13.3 cm. Therefore, plots were irrigated until the water level in the evaporation pans reached 15 cm after approximately 6.7 cm of water was evaporated. Irrigation was applied when the wind speed was I to 2.4 m s_1 to control drift, and at successive intervals to reduce runoff. Plastic collection cups were placed within each main plot at canopy level to monitor the amount of water applied to each plot. Soil Moisture Determination Soil moisture measurements were taken at seedling emergence, prior to and 24 hours after each irrigation, and at harvest in 1982 and 1983. Gravimetric method Was used in 1982 at depths of 0 to 30, and 30 to 60 cm to determine soil moisture. Soil moisture at emergence was at field capacity (28% by weight). Irrigations based on moisture depletion were applied at 50, 69 and 90 days after planting. 28 Soil moisture was measured in 1983 with a neutron moisture probe (Troxler, Model 1257) at depths of 23, 38, 53, 68, 83, 98, 113, and 128 cm. Aluminum access tubes with an inside diameter of 38 mm were placed in the center of each main plot. Soil moisture at emergence was approximately 17% by weight, .or 85% of field capacity. Irrigations based on moisture depletion were applied at 48, 58, 76, and 100 days after planting. Plant available water in 1982 and 1983 was the difference between the soil moisture content and the permanent wilting point (PWP). PWP in 1982 was 12.0%, based on the average soil moisture percentage at the 30 to 60 cm depth in the non-irrigated plot at har­ vest. PWP in 1983 was 9-8, 8.8 and 8.7% at 0 to 15, 15 to 60 and 60 to 120 cm, respec­ tively determined by pressure plate extraction methods. Data at specific time periods for ET, irrigation and rainfall levels in 1982 and 1983 are given in Appendix, Tables 9-11. Seasonal irrigation regimes and corresponding ET values used to regress all soil and plant growth parameters are summarized in Table 2. Seasonal ET was determined for each irrigation regime by the following equation: ET= soil mois­ ture content at planting + precipitation + irrigation - soil moisture content at harvest. Table 2. Irrigation Regimes for Fababean Field Experiments at Bozeman and Manhattan, MT in 1982 and 1983, Respectively. Experiment Irrigation Regime Total Water Applied (precip. + irrigation) Seasonal ET 1982 None ...............................mm — 272 354 Low 292 371 Intermediate 418 484 High 485 551 1983 (No. I) None 148 261 Low 208 -320 Intermediate 345 457 High 442 523 1983 (No. 2) None 148 256 Low 264 373 Intermediate 388 479 High 458 525 29 Growth and Yield Measurements Stand counts were taken from the two center rows of each subplot on 2 1 June in 1982 and 1983. Counts were also taken at harvest from a i m 2 area in the center of each subplot. Plant height in 1982 was measured 32, 51,62, 75 and 92 days after emergence. Plant height in 1983 was measured 19 days after emergence and weekly until harvest. Shoot dry weights were taken at harvest in 1982 and 47, 69, 92 and 102 days after emergence in 1983. Shoot dry weights were based on three plants subplot-1 during the growing season and from a m2 at harvest. Samples were randomly selected, weighed, dried at 80 C with a forced-air drier for 24 hours, and reweighed to determine dry weight and moisture per­ centage. Plots were harvested in 1982 and 1983 when 30 percent of the basal pods turned black. The non-irrigation, low, intermediate, and high irrigation treatments in 1982 were harvested on I September, 10 September, 17 September, and 17 September, respectively. Plant number, height, shoot dry weight and seed dry weight were taken from a I m2 area in the center of each plot. Plant material was weighed, dried at 80 C with a forced-air drier for 48 hours and re weighed to determine moisture percentage and dry matter plant-1. Seeds were removed from the pods with a Vogel rubber-roller thresher. Cracked seed were removed and weighed. Noncracked seed were sized through 4.0, 5.6, 6.8 and 7.5 mm standard sieves, categorized, counted and weighed. Seed < 4.0 mm in diameter were con­ sidered immature. Seed number pod-1 was based on six randomly selected pods plot"1. AU plots were harvested in 1983 at the same time due to a killing frost (-8 C) on 19 September. The non-irrigation treatment matured 17 September, and all other treat­ ments had not fully matured before frost kill. Plant number, height, shoot and seed dry weight were taken from a I m2 area in the center of each plot. Shoot and seed dry matter 30 plant™1 were determined as described for 1982. Seeds were removed from the pods with a Vogel rubber-roller thresher, sized, counted and weighed as described for 1982. Pod num­ ber plant™1 was based on four plants plot"1. Seed number plot™1 was calculated by divid­ ing seed number plant™1 by pod number plant™1. Harvest index, expressed as the ratio of seed yield to above-ground plant yield, grain and biomass WUE, expressed as yield per cm3 of ET, were determined in 1982 and 1983. Plant material in 1982 and 1983 were ground in a Wiley mill with a I mm mesh screen and analyzed for total N by the micro-kjeldahl method. Soil samples after harvest in 1982 and 1983 were taken in each subplot at 0 to 30 and 30 to 60 cm depths dried at 80 C with a forced-air drier, ground, and analyzed for NO3™-N by the Montana State University Soil and Plant Testing Laboratory. Leaf Internal Moisture Total leaf-water potential was measured 83 days after emergence in 1982 and 1983 with a pressure chamber (PMS Instrument Co., Corvallis, Oregon). Measurements were taken at predawn (0400 to 0600 h) and again at midday (1100 to 1300 h). Three repli­ cations were sampled in 1982 and two replications were sampled from each experiment in 1983. Three leaves (approximately 5 cm long) from each subplot were cut from the upper portion of the plant with a razor blade and immediately placed between moistened cardboard sheets. Total leaf-water potential measurements were taken immediately after removal from the plant. A razor blade was used to make a cut approximately 2 cm from the base toward the tip of the leaf on both sides of the midvein. The midvein was inserted through a sili­ cone stopper with the aid of a syringe needle and placed in the pressure chamber as shown in Figure I. Pressure was increased until sap began to exude from the end of the midvein. 31 COVER SILICONE INSERT REGULATED PRESSURE SUPPLY INLET AND EXHAUST Figure I. Diagram of pressure chamber. Statistical Methods The MSUSTAT computer program developed by Richard E. Lund was used for all statistical analyses. Data were analyzed on the Plant and Soil Science Discovery computer system. Main plot effects were analyzed by linear regression. Subplot and the main plot by subplot interaction effects were analyzed by ANOVA. Means for Experiments I and 2 in 1983 were regressed together because moisture X location was non-significant. Additionally, location in 1983 had no effect on any recorded soil or plant parameter. 32 Stand differences occurred in several subplots in 1983. Covariance analyses were used to adjust treatment means. Adjusted treatment means, are reported only when the covari­ ant fit was significant at p=0.05. 33 CHAPTER IV RESULTS AND DISCUSSION Environments Growing season precipitation was higher at Bozeman in 1982 with 271.6 mm com­ pared to 148.3 mm at Manhattan in 1983 (Table I and Appendix, Tables 7 and 8). Most of the rainfall in 1982 occurred from 23 May to 12 June and no rainfall occurred during this time period in 1983. Additionally, most of the precipitation in 1982 occurred early whereas rainfall in 1983 was more evenly distributed throughout the growing season. Temperatures were cooler early in the growing season in 1982 than in 1983. Humidity was higher in 1982. Growing season length was 155 and 117 days in 1982 and 1983, respectively. The shorter growing season in 1983 resulted from delayed planting due to spring rains. Evapotranspiration Evapotranspiration (ET) expressing water use by a crop, is a measure of crop transpi­ ration plus soil surface evaporation. There was a good relationship between ET and applied water (precipitation and irrigation) at four irrigation regimes in 1982 and 1983 (Fig. 2). ET increased from 354 to 551 and 256 to 525 mm in 1982, and 1983, respectively with increased irrigation. The high irrigation regime was similar to conditions at Lethbridge, Canada from 1974 to 1977 where ET of fababean receiving high irrigation averaged 544 mm (Krogman et ah, 1980). 34 1982 • y = 82.8 + 1.15x r2 = 0.99 1983 Exp. I m 9 = 132.8 + 0.89x Exp. 2 A I2 = 0.99 320 WATER A PPLIED (mm) Figure 2. Relationship of seasonal evapotranspiration (ET) to water applied at four irriga­ tion levels (no, low, intermediate, high) to fababean in 1982 and 1983 at Boze­ man and Manhattan, MT, respectively. Plant Available Water Plant available water was based on water depletion data. Four irrigation regimes resulted in marked differences in plant available water in 1982 (Fig. 3) and 1983 (Fig. 4). Plant available water at emergence in 1982 was approximately 12.2 cm (Fig. 3). Plant avail­ able water determinations in 1982 were restricted to 0 to 60 cm due to sand and gravel layers below 60 cm. Available water in the 0 to 30 cm depth for the non and low irrigation treatments declined until 81 and 76 days after emergence, respectively. Available water at 0 to 30 cm 35 o 3.75 -------High irrigation ------ In term ed ia te irrigation ......... Low irrigation — No irrigation <£ 7.50 — 30-60< 3.75 DAYS AFTER EM ER G EN C E Figure 3. The effect of fababean on plant available water from emergence to harvest at four irrigation levels in 1982 at Bozeman, MT. Arrows indicate time of irrigations. increased from 76 to 81 days to harvest for the non and low irrigation treatments, respec­ tively. The increase is attributed to replenishment by late season rainfall (Appendix, Table I). Available water in the low, intermediate and high irrigation treatments were replenished to varying degrees with irrigations at 36, 55 and 76 days after emergence. Less soil water depletion occurred in the 0 to 30 cm depth, compared with 30 to 60 cm. Available water in the 30 to 60 cm depth was depleted 76 days after emergence in the non-irrigation treatment. Greater depletion in the 30 to 60 cm depth is attributed to high root density. Plant available water at emergence in 1983 to a depth of 135 cm was approximately I 2.6 cm (Fig. 4). Rooting depth was not limited by root restricting soil layers. Plant availa­ ble water was depleted in the 0 to 30 cm depth within 61 days after emergence in the non. 36 O 30 - 60 90 120 5 .0 0 -J- - - - - - - - - - - - - - - - - - - - - - 1---------------------- 1- - - - - - - - - - - - - - - - - - - - - - 1--- - - - - - - - - - - - - - - - - - - - h DAYS AFTER EMERGENCE Figure 4. The effect of fababean on plant available water from emergence to harvest at four irrigation levels in 1983 at Manhattan, MT. Arrows indicate time of irrigations. Data represent the average of experiments I and 2. SO IL D EPTH (cm ) 37 low and intermediate irrigation treatments. However, available water in the low, intermed­ iate and high irrigation treatments were replenished to varying degrees with irrigations at 34, 44, 62 and 86 days after emergence. Plant available water was depleted to the 45 cm depth in all irrigation regimes at harvest. Residual plant available water at harvest from 45 to 135 cm was 2.1, 2.2, 2.8 and 4.2 cm for non, low, intermediate and high irrigation regimes, respectively. Consumptive use rate (CU) is indicated by the steepness of the line between irriga­ tions (Fig. 4). Fababean have a characteristic CU curve. CU was relatively low at emergence, gradually increased to an optimum during peak vegetative and reproductive growth, and then slowly declined at harvest. Root Growth Rooting depth was not analyzed in 1982 because of the root restricting sand and gravel layers below 60 cm. Rooting depth in 1983 was interpolated from plant available water depletion at various soil depths (Fig. 4). These data indicate that roots penetrated to 135 cm at harvest with all irrigation regimes. However, the magnitude of water deple­ tion indicated less root proliferation with increased depth. Most researchers agree that the upper 30 cm of the soil profile is the most important absorption area for fababean since it contains approximately 70 to 80 percent of the root mass (Tawadros, 1982; Naim ark, 1976; Hebblethwaite, 1982). My experiment showed similar results. However, depth of major water absorption varied depending on irrigation regime. In 1983, 28, 32, 44 and 48 percent of the total water used by fababean was absorbed from the upper 30 cm of the soil profile in the non, low, intermediate and high irrigation regimes, respectively (TaGle 3). Approximately 70 percent of the total water used was 38 absorbed within 75, 75, 60 and 45 cm from the soil surface in the non, low, intermediate and high irrigation regimes, respectively. Table 3. Percent of Total Water Used by Fababean with Increasing Soil Depth at Four Irri­ gation Regimes in 1983 at Manhattan, MT. Total Water Used^ Irrigation Regime Soil Depth None Low Intermediate High cm ____.......................................... 0-30 28 32 44 48 0-45 44 48 63 70 0-60 60 62 76 84 0-75 73 74 85 91 0-90 84 84 91 95 0-105 91 91 95 98 0-120 96 96 . 98 100 0-135 100 100 1 100 100 ^Data represent the average of Exps. I and 2. These data suggest higher root density in deeper soil layers in the non and low irriga­ tion regimes compared to intermediate and high regimes. High soil moisture is more favor­ able for.root growth than low soil moisture (El Nadi et ah, 1969). Root penetration and branching is deeper in non-irrigated and low rainfall areas because of more favorable con­ ditions in deeper less dry soil layers. El Nadi et ah (1969) reported that deep root penetration resulted from dry upper soil layers. However, Hebblethwaite (1982) reported that no fababean roots could be found below 80 cm. Variable root penetration may be a result of soil type, annual precipitation levels and soil moisture at planting. My experiments in 1983 were on a fine sandy loam soil with growing season precipi­ tation of 163 mm. Hebblethwaite’s experiments at Rothamsted experiment station were on a clay-with flints soil with growing season precipitation levels of 232, 183, 230 and 183 mm in 1966, 1967,1968 arid 1971, respectively. Plant available water was probably greater 39 at Rothamsted because of higher precipitation levels and greater soil water holding capaci­ ty. Shallow rooting depth would be expected, corresponding to the higher irrigation regimes at Manhattan, MT in 1983. These data indicate that roots reduce the harmful effects of water stress by growing and branching deeper where soil is moist (El Nadi et ah, 1969). Soil NO3- The relationship of soil NO3- to ET at harvest at the O to 30 cm depth in 1982 and 1983 are shown in Figure 5. Nitrogen application in 1982 had no effect on soil NO3- level at the O to 30 cm depth at harvest. This may be attributed to the intermediate level of residual soil NO3- (81 kg ha-1) at planting in 1982. Soil NO3- decreased 358% in 1982 with increased ET at the O to 30 cm depth. There was a low level of residual soil NO3- (23 kg ha-1) at planting in 1983. Applied N at the O to 30 cm depth increased soil NO3- at harvest approximately 325 and 93% at ET levels representing non and low irrigation regimes, respectively. Applied N had no effect on soil NO3- at harvest at ET levels representing intermediate and high irrigation regimes. NO3- is soluble and moves with the convective flow of soil water (Olson and Kurtz, 1982). Therefore, leaching of soil NO3- may be suspected for the decrease in soil NO3- level with increased ET. However, N application had no effect on soil NO3- levels at harvest at the 30 to 60 cm depth. Additionally, soil NO3- levels from the 30 to 60 cm depth were not influenced by increased ET in I'982 or 1983. Consequently, if leaching were a major source of NO3- loss, the soil NO3- level would be expected to be influenced at the 30 to 60 cm depth. Tawadros (1982), Naimark (1976) and Hebblethwaite (1982) reported that the O to 30 cm depth is the most important soil water absorption zone for fababean. I suggest that most of the applied NH4NO3 was absorbed from the 0 to 30 cm depth. S O IL N O ; (k g h a " at 0 -3 0 cm ) 40 r! = 0.97 1983 No Nitrogen Exp. I ■ NS Exp. 2 A NS □ Nitrogen Exp. I D 9 = 249.9 - 1.03x + 0.001 X1 Exp. 2 A r 2 = 0.90 ET (mm) Figure 5. Relationship of soil NO3" (0-30 cm depth) at harvest to four seasonal evapotran- spiration (ET) levels representing no, low, intermediate and high irrigation regimes at two NH4NO3 application rates (0 and 99 kg ha"1) in 1983 at Boze­ man and Manhattan, MT, respectively. Means for 1982 and 1983 represent the average of 6 and 4 soil samples, respectively. Nitrogen treatments were combined when not significantly different @ .05 level. NS indicates zero slope coefficient @ .05 level. Plant Analysis Nitrogen and the interaction with moisture were significant for only a few parameters measured (Appendix, Table 12). Means for soil and plant data were combined when nitrogen was non-significant. Means for experiments I and 2 in 1983 were regressed together because moisture X location was non-significant. Plant Height The effect of time and irrigation level on fababean plant height are shown in Figure 6. Nitrogen application had no effect on plant height 51,62, 75 and 92 days after emergence and at harvest in 1982. Irrigation level had no effect on plant height until 54 days after emergence in 1983. However, increasing irrigation levels from 54 to 102 days after emerg­ ence increased plant height. Irrigation had the greatest effect on plant height during the intermediate growth and development stages in 1982 and 1983. There was a 37 and 95% increase in plant height at harvest in 1982 and 1983, respec­ tively with increased ET levels (Fig. I). El Nadi (1970) reported that water stress from emergence to early fruit set in fababean resulted in a relative growth reduction. Manning et al. (1977) and Miller et al. (1977) reported that plant height had a positive relationship with increased water application in pea. My data indicate that irrigation management is extremely important in maximizing vegetative growth and development of fababean. Further investigations are warranted to determine irrigation effects on lodging incidence and harvestability. Shoot Dry Weight Nitrogen application had no effect on shoot dry weight at harvest in 1982 and 1983. This agrees with results from several researchers (Dean and Clark, 1980; Richards and PL A N T H EI G H T (c m ) 42 High irrigation V = irrigation Intermediate irrigation Low irrigation No irrigation Y = irrigation High irrigation Intermediate irrigation Low irrigation • * # # No irrigation DAYS AFTER EMERGENCE Figure 6. Effect of time and irrigation level on fababean plant height in 1982 and 1983 at Bozeman and Manhattan, MT, respectively. Means for 1982 and 1983 represent the average of 12 and 16 plants, respectively. 43 190 1982 # 9 = 47.5 + 0.24x r2 = 0.98 1983 Exp. I ■ 9 = -2 4 .3 + 0.44x - 0.0002X1 '250 320 -L 390 460 ET (mm) 530 600 Figure 7. Relationship of fababean plant height at harvest to four seasonal evapotranspira- tion (ET) levels representing no, low, intermediate and high irrigation regimes in 1982 and 1983 at Bozeman and Manhattan, MT, respectively. Means for 1982 and 1983 represent the average of 18 and 24 plants, respectively. Soper, 1982; Vondrys and Bierdermannova, 1980), although other reports indicate increased fababean vegetative growth with increased N fertility (Graman et al., 1978; Hill-Cottingham and Lloyd-Jones, 1980; Salih, 1980), Dean and Clark (1977) and Sprent and Bradford (1977) reported that fababean is relatively self-sufficient in N2 -fixation if environmental conditions are favorable. Differential environmental conditions may account for variable response of fababean to N fertility. 44 I Shoot dry weight at harvest increased 93 and 97% in 1982 and 1983, respectively with increased ET (Fig. 8). Several researchers have reported that increased irrigation levels increased fababean total dry matter and high levels of moisture stress markedly reduced dry matter production (Farah, 1981a; Krogman et ah, 1980; McEwen et ah, 1981; Shaaban et ah, 1979). • 9 =-11.7 + 0.09x r2 = 0.99 1983 Exp. 1 S y = 1.57 + 0.08x Exp. 2 A r» = 0.86 O 2 8 - ET (mm) Figure 8. Relationship of fababean shoot dry weight at harvest to four seasonal evapotran- spiration (ET) levels representing no, low, intermediate and high irrigation regimes in 1982 and 1983 at Bozeman and Manhattan, MT, respectively. Means for 1982 and 1983 represent the average of plants from 6 and 8 m2, respectively. 45 Fababean forage dry matter production increased with increased irrigation (Table 4). According to Lockerman et al. (1982), Canadian reports indicate that irrigated fababean has a forage potential of 8,960 to 17,920 kg ha-1. These results suggest that irrigation has a tremendous potential for increasing fababean forage production. Table 4. Fababean Forage Yield at Bozeman and Manhattan, MT in 1982 and 1983. Experiment Irrigation Regime Forage Yieldt 1982 None kg ha-1 5,571 Low 7,022, Intermediate 9,873 High 11,110 1983 (No. I) None 5,397 Low 6,874 Intermediate 9,349 High 10,713 1983 (No. 2) None 5,419 Low 7,072 ' Intermediate 9,462 High 11,105 "i"Projected from shoot dry weight m 2 . Leaf-Water Potential ■ Nitrogen application increased midday total leaf water potential (V̂t ) in 1982 (Fig. 9). • This may indicate that nitrogen may reduce plant stress. However, this is inconclusive since there were no differences in ^ ̂ due to NH4NO3 application in 1983, even though there was a greater difference in NH4 NO3 application rate between the non-applied and applied N treatments in 1983 as compared to 1982. \pj is sensitive to water deficits during the late vegetative stage in southern pea (Clark and Hiler, 1973). There was a positive relationship of ipj to ET at the four irrigation regimes in 1982 and 1983 (Fig. 9). i//T increased in both years with increased ET. As expected, midday plant stress was higher than predawn stress due to the higher evaporative 46 Predawn Midday (no nitrogen) O Midday (nitrogen) # =-31.9 + OOSx r! = 0.95 =*34.9 + OOSx r' = 0.99 =-32.7 + 0.04x r2 = 0.99 Predawn Midday MiddayZ -1.0 1983 Predawn J = -1 0 .4 + 0.01 x Midday y = -19 .1 + 0.01 x Exp. I m Exp. 2 A r2 = 0.85< 0 r2 = 0.74 Predawn Midday ET (mm) Figure 9. Relationship of fababean total leaf water potential (\pT) to four seasonal evapo- transpiration (ET) levels representing no, low intermediate and high irrigation regimes at two NH4NO3 application rates in 1982 and 1983 at Bozeman and Manhattan, MT, respectively. V/T was measured at predawn (0400-0600 h) and midday (1100-1300 h) 83 days after emergence. Means for predawn and midday measurements in 1982 represent the average of 18 and 9 plants, respectively. Means for 1983 represent the average of 12 plants. Nitrogen treatments were combined when not significantly different @ .05 level. demand during that period. However, predawn and midday i//T increased at the same rate with increased ET in each year. Shouse et al. (1981) and Turk and Hall (1980b) reported that predawn i//T was a better indicator of crop water stress than midday in cowpea, because of less variability in readings at predawn. In 1982, midday \pj appeared to be as good an indicator of crop 47' water stress as predawn \pj, since the regressions accounted for 95 and 99% of the variabil­ ity in j for predawn and midday, respectively. However, predawn \pT in 1983 was a bet­ ter indicator of crop water stress than midday since the regressions accounted for 85 and 74% of the variability in i//T for predawn and midday, respectively. at the high ET level was similar for both years. However, plants in the non­ irrigation or lowest ET levels were stressed more in 1982 than 1983. This maybe attributed to lower plant available water in 1982 because of restricted rooting depth. Plant available water 83 days after emergence was estimated to be 0.8 and 2.7 cm, respectively in 19.82 and 1983 (Figs. 3 and 4). Additionally, plant available water in 1982 was depleted in the 30 to 60 cm root zone and roots may have been restricted to this water depleted zone because of sand and gravel layers below 60 cm. In 1983, there were no root restricting soil zones. Therefore roots were able to grow deeper where the soil was less dry. Total Plant N (Aerial) N application had no effect on total plant N at harvest in 1982 and 1983. Total plant N was positively related to ET (Fig. 10). Total plant N increased 75% with increased ET in 1982. These data agree with previous research on fababean (Farah, 1981b) and soybean (Rathore et al., 1981). The increase in total plant N corresponds to a 358% decrease in soil NO3- at the 0 to 30 cm depth (Fig. 5) with increased ET level. This response would be expected since most N movement occurs as NO3- in the convective flow of soil to the roots in response to transpiration in the above-ground portion of the crop (Olson and Kurtz, 1982). Total plant N increased 276% with increased ET in 1983 (Fig. 10). The greater increase in total plant N in 1983 compared to 1982 may be due to greater N application rate and lower residual soil NO3- level at planting in 1983. The increase in total plant N corre­ sponded to a 456% decrease in soil NO3- with applied N at the 0 to 30 cm depth with 48 1982 y =-0.06 + 0.0008X r‘ = 0.98 1983 Exp. I ■ 9 = -0 .4 4 + 0.003x Exp. 2 A rl = 0-84 Q. 1.2 ET (mm) Figure 10. Relationship of fababean total plant N (aerial) at harvest to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes in 1982 and 1983 at Bozeman and Manhattan, MT, respec­ tively. Means for 1982 and 1983 represent the average of plants from 6 and 8 m 2, respectively. increased ET in 1983 (Fig. 5). However, soil NO3" was not influenced by increased ET in the non-applied N treatment at the 0 to 30 cm depth. NO3 movement by mass soil water flow becomes less important and movement by diffusion locally to the root surface becomes more important when soil NO3" levels are low 49 and the potential uptake by the plant exceeds supply. Therefore, increases in ET may not necessarily increase NO3- uptake (Olson and Kurtz, 1982). The relationship of soil NO3- difference between planting and harvest at the O to 60 cm depth to increased ET in 1982 and 1983 are shown in Figure 11. Addition of 99 and 157 kg ha-1 NH4NO3 in 1982 and 1983, respectively resulted in a significant increase in the soil NO3- difference in both years. However, there was no significant difference in total plant N with differences in N application rate. Evidence indicates that fababean utilizes soil and fertilizer N sources in preference to fixed atmospheric N (Dean, 1976; Hera, 1976; Richards and Soper, 1979). However, the reason for this preference is uncertain. Fababean are self-sufficient from symbiotic N2 - fixation in low NO3- soils and the potential for N2 -fixation in fababean is considered to be sufficient to sustain high yields (Salih, 1980; Spfent and Bradford, 1977). My data suggest that N2 -fixation was apparently sufficient to supply the plant with needed N. However, the plant utilized applied NO3- in preference to N2 -fixation when NH4 NO3 was applied. Seed Yield Nitrogen application had no effect on seed yield in 1982 and 1983. Richards and Soper (1982) reported that seed yield of nodulated fababean is infrequently and unpredict- ably affected by rate of N application. Most researchers agree that there are no significant seed yield differences of fababean with N application (Islam and Afandi, 1981; Kisha et ah, 1980; Scherer and Danzeisen, 1980). Seed yield in 1982 increased 125% with increased ET (Fig. 12). Previous reports on fababean have shown increased seed yield with increased irrigation (El Nadi, 1970; Farali, 1981a; Keatinge and Shaykewich, 1977; Krogman et ah, 1980; McEwen et ah,' 1981; Olivares and Recalde-Martinez, 1982; Stock and El Naggar, 1980). However, seed yield in SO IL N O ; D IF FE R E N C E (k g ha *1) 50 1982 No Nitrogen # NS Nitrogen O 9 = 1983 No Nitrogen Exp. I ■ NS Exp. 2 A, NS Exp. I D 9 = 176.2 - 1.46x + 0.002X1 Exp. 2 A r> = 0.87 Nitrogen ET (mm) Figure 11. Relationship of soil NO3" difference (between planting and harvest at 0-60 cm depth at harvest to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes at two NH4NO3 application rates (0 and 99 kg ha"1) in 1982 and (0 and 157 kg ha"1) in 1983 at Bozeman and Manhattan, MT, respectively. Means for 1982 and 1983 represent the average of 3 and 4 soil samples, respectively. NS indicates zero slope coefficient @ .05 level. 51 1982 9 ="5.3 + 0.03x r1 = 0.95 1983 Exp. I ■ 9 = 11.8 - 0.02x Exp.2 A r 2 = 0.81 ET (mm) Figure 12. Relationship of fababean seed yield to four seasonal evapotranspiration (ET) levels representing no, low, intermediate and high irrigation regimes in 1982 and 1983 at Bozeman and Manhattan, MT, respectively. Means for 1982 and 1983 represent the average of plants from 6 and 9 m2, respectively. 1983 decreased 106% with increased ET. The decrease in 1983 is attributed to the rela­ tively short growing season in 1983 as compared with 1982 and the effect of moisture on delayed maturation. Growing season length was 155 and 117 days for 1982 and 1983, respectively. Length of the growing season was calculated as the number of days from planting to the first kill­ ing frost (-2 C). Increased ET, representing irrigation levels from non to high in 1982, 52 progressively increased time to maturity from 118 to 134 days (Table 5). The non-irrigation treatment in 1983 matured in 113 days. However, the low, intermediat