(A; ’ \- LIBRARY Michigan State University X j PLACE IN RETURN BOX to remove thie checkout from your record. TO AVOD FINES return on or before die due. DATE DUE DATE DUE DATE DUE MSU Is An Affirmative Action/Equal Opportunity Institution extwmpm-pi EFFECT OF SOIL WATER DEFICITS ON THE GROWTH AND DEVELOPMENT OF DRY BEANS (W W L.) AT DIFFERENT STAGES OF GROWTH BY Abelardo Nunez Barrios A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Crop and Soil Sciences 1991 ABSTRACT EFFECT OF SOIL WATER DEFICITS ON THE GROWTH AND DEVELOPMENT OF DRY BEANS (ghasegulus vulgaris L.) AT DIFFERENT STAGES OF GROWTH BY Abelardo Nunez Barrios Soil dehydration adversely affects crop productivity. An increased understanding of the whole plant response to water deficits is a prerequisite to increase production under water- limited environments. A rain shelter facility and two different-textured.soils (sandy and loamy) were used to impose terminal drought on dry beans at various growth stages under field conditions. Results indicated that in the sandy soil water deficits hastened flowering and seed filling while delaying leaf appearance. In ‘both soils, the deficits diminished leaf and pod expansion resulting in a small plant size. The duration of leaf growth and internode elongation was not affected as much as the growth rate of these organs. Changes in leaf ‘area due to reduced leaf growth and accelerated leaf senescence appear to be one of the main mechanisms by which dry bean plants adapted to the declining soil water availability. Flowers and pod abscision were greater in the stress treatments decreasing final yield and harvest index. Photosynthetic rates were reduced to a lesser extent than stomatal conductances during progressive soil dehydration. Paraheliotropic leaf movement decreased light interception in a diurnal cycle. Above ground dry matter production. was linearly related to the intercepted photosynthetic active radiation. However, the efficiency of energy conversion was slightly lower for the deficit treatments. Rapid root expansion was observed at the beginning of the water deficits followed by root death and compensatory root growth in deeper soil layers. Difference in rooting patterns changed the amount and timing of water extraction at various soil depths. A mi querida Lily iv ACKNOWLEDGEMENTS I wish to express my sincere appreciation to the people and institutions that made possible for me to reach this goal in my professional career. First, I would like to extend my gratitude to the Mexican Government (CONACYT - INIFAP) for providing me with the advise and economic support before and during my Ph.D. program in Michigan State University. I also wish to express my gratitude to my advisor Dr. Joe T. Ritchie. His philosophy and pragmatic approach to real- world problems had a profound influence on reshaping my way of thinking. I would like to tank Dr. Alvin Smucker for his advise and constant support on my research" His door was always open for me. I am also grateful to Dr. Eunice Poster for her genuine interest on my investigation. Sharing with her some field research was for me an additional learning experience. I am grateful to Dr. Jim Flore and Andrew Hanson for serving on my committee. I would like to recognize the help and contribution of the many people involved in my field research and in the completion of this document. Specially to Sharlene Rhines, Paul Wilkens, Peter Grace, and Jim Bronson. I was very lucky to meet so many good friends in Michigan State University. In particular, I would like to mention Scott NeSmith and Avner Carmi. I wish to thank my wife for her continuous support and encouragement during the long hours of work and fatigue. Liliana you are the most important person in my life. vi TABLE OF CONTENTS Page ListOfTableSOOOOOOOOOOOOO0...........OOOOOOIOOOO. ....... ix List of Figures........................ ......... . ...... ... x IntrOductiODOOOOOOO......OOOOOOOOOOOOOOOO0.0.0.0000000000001 List OfReferenceSOOOOCCOO......OOOOOOOOOOOOOOOOO.......... 8 Chapter 1. Chapter 2. Chapter 3. Chapter 4. Effect of soil water deficits on Dry Beans (Bhaseolns yglgaris L.). I. Growth and elongation of different organs................ 11 Abstract.................................11 Introduction...................... ....... 12 MaterialsandMethods.................... 14 Results andDiscussion................... 18 ListofReferences....................... 44 Effect of soil water deficits on Dry Beans (We L-)- 11- Reproductive organsandyield.............................. 47 Abstract............................ ..... 47 Introduction........ ........ ... .......... 48 MaterialsandMethods.................... 49 Results..................................51 Discussion...............................64 ListofReferences....................... 69 Effect of soil water.deficits on Dry Beans (Ehaseolus yglgazis L.). III. Stomatal conductance, photosynthesis, light interception, and.dry matter production....... 71 Abstract........................... ..... .71 Introduction.............................72 Materials andMethods.................... 73 Results..................................75 Discussion...............................84 ListofReferences....................... 90 Effect of soil water deficits on Dry Beans (Phaseolus vulgaris L.). IV. Root growth ...... 92 Abstract......................... ........ 92 Introduction..... ........................ 93 Materials and Methods .................... 94 vii ResultSOOOOOODOCOOOOOOOO0......0.0.00.00096 Discussion........ .............. ........108 List of References ...................... 113 Summary'and.Conclusions.................... .............. 115 Appendix 1. Description of the soil profile for Spinks andKalamazoosoils.......................... 121 Appendix 2. Weather data for the 1988 growing season at the Kellogg Biological Station............... 122 Appendix 3. Weather data for the 1989 growing season at the Kellogg Biological Station............... 125 viii LIST OF TABLES Page Table 1.1. Number of leaves, pods, and dry matter production of different plant parts at maturity for various soil water deficit conditions.................................... 42 Table 2.1. Yield components in dry beans for various soil water deficit conditions. . . . . . . . . . . . . . . . . 63 Table 2.2. Total dry matter, seed yield, and harvest index of dry beans for various soil water deficitconditions..................... ....... 65 5 ix Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure LIST OF FIGURES Page Irrigation amounts applied to different treatments during 1988 and 1989 . . . . . . . . . . . ..... 16 Seasonal patterns of minimum and maximum temperatures during 1988 and 1989 . . . . . . . ....... 19 Seasonal patterns of solar radiation during 1988and19890000......OOOOOOOOOO0.0.00.0000...20 Soil water content with depth at several dates for early and mid stress treatments for Spinks soilduring1988......................... ...... 21 Soil water content with depth at several dates for mid and late stress treatments for Spinks saildurin919890000000000............OOOOOOOOO23 Soil water content with depth at several dates for mid and late stress treatments for Kalamazoo soil during 1989 . . . . ................. 24 Seasonal changes in leaf appearance on the main stem for different water deficit treatments for Spinks soil during 1988. Arrows represent initiationofwaterdeficit.................... 26 Seasonal changes in area of leaf 6 on main stem in different water deficit treatments for Spinks soil during 1988. Deficit treatments started 15 DAP for ES, and 29 DAP for'MS.... ........... 27 Seasonal changes in area of leaf 7 (n7) on main stem and leaf 2 (Br) on the first branch for Spinks soil during 1989. Deficit treatment started27DAP........................... ...... 28 Seasonal changes in area of leaf 7 on main stem, for Kalamazoo soil during 1989. Deficit treatment started 27 DAP ....... . ............... 3O Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure 1.11 1.15 1.16 during 1989.00.00...00......00.000.000.000...OO Seasonal changes in leaf area distribution along nodes of the main stem on 45 DAP for different water deficit treatments for Spinks soildurin91988...............................31 Seasonal changes in leaf area index for different water deficits treatments for Spinks (A,B) and Kalamazoo soil (C). Arrows represent initiation of water deficits. . . . . . . . . 33 Seasonal changes in internode elongation for MS and control treatments for Spinks soil 35 Length of different internodes on the main stem at 46 DAP for MS and control treatments forSpinkssoilduring1989.................... 36 Seasonal changes in individual pod length for MS and control treatments for Spinks and Kalamazoosoilsduring1989.................... 37 Seasonal changes in total pod length for MS and control treatments for Spinks and Kalamazoo soils during 1989. . . . . . . . . . . . . . ...... 39 Relative elongation rates of different plants organs as influenced by the percentage of plant extractable water (PAW) in the root zone for Spinks soil during 1989. . . . . . . . . . . . . . . 40 Relative elongation rates of different plants organs as influenced by the percentage of plant extractable water (PAW) for Kalamazoo soilduring1989...............................41 Seasonal changes in number of flowers for different water deficits treatments for Spinks (A,B) and Kalamazoo (C) soils. . . . . . . . . . . ....... 52 Distribution of flowers along the main stem in MS and control treatments, on the day when maximum flowers number occurred. . . . . . . 54 Seasonal changes in pod number as affected by different water deficit treatments for Spinks (A) and.a Kalamazoo (B) soils during 1989 ...... 55 Pod distribution along nodes of the main stem at 50 and 65 DAP for Spinks soil during 1989... 57 xi Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure 2.5. Seasonal changes in dry weight of seeds (A) and pods walls (B) for different water deficit treatments for Spinks soil during 1989 . . . . . . . . . 58 Seasonal changes in dry weight of seeds (A) and pod walls (B) for different water deficit treatments for Kalamazoo soil during 1989 . . . . . . 6o Seed weight distribution for different water deficit treatments for Spinks soil during 1989.00.00.0000000.......OOOOOOOOOOOOOOOO...... 61 Seed weight distribution for different water deficit treatments for Kalamazoo soil during 1989.00.00.000000......OOOOOOOOOOOOOOOO0.00.... 62 Stomatal conductances at different days during late stages of growth in MS and control treatments during 1988 and 1989. . . . . . . . . . . . . . . . 77 Photosynthesis rates at different days during late stages of growth in MS and control treatments during 1988 and 1989. . . . . . . . . . . . . . . . 78 Relationship between stomatal conductance and photosynthesis rate in MS and control treatments during 1988 and 1989. . . . . . . . . . . . . . . . 79 Seasonal changes in light interception at mid day for control and.MS treatments during 1989.. 81 Diurnal changes of leaf angle and light interception for MS and control treatments at 36DAPin1989000000000 ........ ...... 0000000000 82 Relationship between leaf area index and light interception for the control and MS treatments ................ . .................... 83 Seasonal changes in dry matter production for different soil water deficits treatments during 1988 and 1989 ................ . . . ........ 85 Relationship between biomass and cumulative intercepted photosynthetic active radiation (IPAR) measured in 1989 .............. 86 Total root length in the soil profile for different water deficit treatments. Arrows show the beginning of water deficits during 1988 and 1989 .................................. 97 xii Figure Figure Figure Figure Figure Figure Figure Figure Root length density for three dates in the Spinks soil for different soil water regimes in1988.00.00.00000000.00.00...0.00.00.00.00... 99 Root length density for three dates in the Spinks soil for different soil water regimes in1989..0.........OOOOOOOOOOOOOO.....OOOOOOOO 10]- Changes in root growth between 42 and 58 DAP for different water deficit treatments and soildepthsduring1988....................... 102 Changes in root growth between 42 and 59 DAP for different water deficit treatments and soildepthsduring1989....................... 103 Dynamics of root density (RLD) and soil water content at 20, 60 and 100 cm depth in the ES treatmentduringlsas.........................104 Dynamics of root density (RLD) and soil water content at 20, 60 and 100 cm depth, in the MS treatment during 1989 . . ..... . ........ . ........ 105 Fraction of the total water absorption for different soil layers in ES and MS in Spinks soilduring1988..............................107 Fraction of the total water absorption for different soil layers in MS and L8 in Spinks saildurin91989...OOOOOOOOOOOOOOOOOOOOOOOO0.0109 xiii INTRODUCTION Environmental stresses may reduce crop yield to levels that are a third of the potential production in intensive agriculture, and to much lower values in less intensive systems such as those in developing countries (Vaadia, 1984). The extent of yield losses to disease is estimated to be about 12%, and the loss to insects can be as high or higher depending on the year, crop, and management practice (James, 1981). However, unfavorable physicochemical factors such as water shortages have one of the most detrimental effects on crop production. Boyer and McPherson (1975) estimated that low water availability may account for 50% of the decrease in yield observed in the main crops grown in the USA. In semiarid zones, water deficits may depress yield by more than 80% as compared to irrigated conditions (Fisher and Turner, 1978). Countries like Mexico have a large proportion of its agricultural land (75%) under poor rainfed conditions (Acosta, 1988). Common bean, which originated in the Americas (Gentry, 1969), is an important crop in dryland farming that provides most of the protein consumed by low income families (Adams, et al., 1985). Solving production constraints in this water-limited 1 2 environment is a difficult task to achieve. For instance, genetic improvement programs have largely focused on the selection and breeding of genotypes solely based on grain yields. Temporal distribution of available water from year to year, however, influences the expression of different characters related to crop performance and yield. In addition, management practices that increase yield, often fail to account for the temporal and spatial variability of rain and crop water availability during the growing season. The strategies adopted.by the plants in response to the changes in soil water content are also not well known. In general, there are three basic strategies through which plants cope with limiting water regimes: escape, avoidance, and tolerance (Levitt, 1972). Plants may escape drought conditions by rapid growth and development, completing their life cycle before the water supply is exhausted. The avoidance strategy is related to plants more sensitive to dehydration. The plants avoid water deficits whenever they occur. Plants may also have tissues that tolerate water deficiencies. However, it is recognized that plants generally may posses a wide range of responses that include the use of several strategies at the same time (Fisher and Ludlow, 1984). An increased. understanding of a whole plant response to 'water deficits is needed to improve crop productivity. One of the most important factors to consider is the phenological stage of growth at the time of the deficit. Ludlow and Muchow (1989) stated that genotypic 3 variation in growth duration is one of the most obvious means of matching seasonal transpiration with the supply of water in the soil profile. They outlined several alternatives to explore. For instance, early flowering tends to give higher yield and greater'yield stability than later flowering if rain does not occur during the later half of the growing season. Developing short season varieties may provide benefits for higher crop production. However, the sensitivity of crops to stress conditions at any stage of growth varies with the degree, duration, and timing of the stress (Begg and Turner, 1976). Early water deficits reduce the rate of leaf expansion and hence, leaf area accumulation. A reduction of leaf area in. dry' beans has. been associated. with. smaller size of individual leaves rather than leaf number (Bonnano and Mack, 1983). Leaf senescence, on the other hand, is considered to be a drought avoidance mechanism that allows the plant to survive dry periods (Kramer, 1983). Rapid senescence rates, however, may be detrimental to final yield. Laing et al. (1983) found that leaf duration was correlated with the variation in seed yield. Although temperature and photoperiod are the most important environmental stimuli for most of the phenological events, water deficits also play a role in affecting initiation of such events. Flowering is usually slightly hastened by water deficits (Turner and Begg, 1977). Water deficits during grain filling will usually hasten seed 4 maturation and increase leaf senescence (Mott and McComb, 1975). Drought stress may also interfere with pollination and fertilization as well as with the abortion of young seeds and the abscission of young fruits (Fisher, 1973; Slatyer, 1973). This change in the number of reproductive structures may seem wasteful in terms of carbon efficiency because carbon is lost during organ abscission. This phenomenon, however, is likely the mechanism insuring adequate seed size and viable seeds at the end of the growing season. In dry beans, water deficits early in the season reduce the number of pods per planta 'When the deficit occurs at flowering, pod number and number of seeds per pod is diminished. Seed weight decreased when the deficit began late in the season, during the pod filling stage (Robins and Domingo, 1956; Dubetz and Mahalle, 1969). Stomatal conductance has been reported to have a significant effect on transpiration and photosynthetic rate under a limited supply water (O'Toole, et al., 1977). Some investigators, however, suggest that an increase in transpiration efficiency with stomatal closure rarely occurs under field conditions because of the resulting rise in leaf temperature which increases the air-leaf vapor pressure difference, lowering transpiration efficiency (Ludlow and Muchow, 1989). In some instances, stomatal conductance has a small impact on photosynthesis. Farquar and Sharkey (1982) concluded that, apart from some transient hormonal effect on rapid stomatal closure, stomatal conductance is rarely the main cause of the decrease in assimilation rate that occurs 5 with a declining plant water supply. There is a growing consensus among crop physiologists that the decrease in plant stomatal conductance under deficit condition is related to the avoidance of desiccation (Blum, et al. , 1981; Ludlow, et al. , 1983). Much of our understanding of the relationship between water deficit and plant processes has evolved from container experiments. .Ritchie (1981) pointed out that differing sensitivity of various plant processes to water deficits and the unrealistic rooting volume are the primary reasons for the difference between container-grown plants and field-grown plants. He emphasized that in the field, water deficits occur gradually, allowing the plant to acclimate to the drought. Container plants lose the water supply so rapidly that they do not have this opportunity to acclimate. One of the mechanisms in drought tolerance is osmoregulation. Osmotic adjustments result from the accumulation of solutes within the cell allowing turgor driven processes, such as expansion growth and stomatal opening, to continue at reduced rates at progressively lower soil water contents (Turner and Jones, 1980; Morgan, 1984). Under increasing soil dehydration, differences in rooting patterns may change the amount and timing of water availability to crops (Ludlow and Muchow, 1989) . Deeper root systems are advantageous when water is available lower in the soil profile. When water is not replenished in lower depths by rainfall, deep rooting patterns will not be useful to 6 improve water supply. Sometimes, investment of carbon in roots under water deficit conditions may occur at the expense of shoot growth (Hoogenboom et al., 1987). In the context of root—shoot relationships, there is an increasing amount of information showing that root signals control leaf and stem elongation (Passioura, 1988) as well as changes in stomatal conductance (Blackman and Davies, 1985). Root signals resulting from soil water deficits may occur without significant changes in bulk leaf water status. The nature of root signals generated.by'a¢drying soil has recently been the subject of considerable speculation. A reduced supply of cytokinins, which are known to be produced in the roots, was thought to be responsible for stomatal closure in fully turgid leaves (Blackman and Davies, 1985) . Other investigators have shown that abscisic acid is produced in roots in response to soil and root dehydration. When the abscisic acid.moves to the leaves, it reduces extension growth and stomatal conductance (Hubick and Reid, 1988; Lachno and Backer, 1986). Root signals are important mainly because of their influence on leaf growth, light interception and hence dry matter production and economic yield. The complexity of the different processes occurring between roots and shoots as well as their interaction with the atmospheric demand for water needs more detailed investigation at a whole plant level, especially under field conditions. This information should improve our capability to predict management strategies that optimize water use and selection of 7 genetic material that will cope‘with.the seasonal availability of water. This wholistic approach will improve the decision making process to increase economic yield under limited water conditions. The objective of this investigation was to study dry bean response to water deficits imposed during different stages of growth under field conditions. LIST OF REFERENCES Acosta, J. 1988. Selection of common bean (Phaseolus vulgaris L). Genotypes with enhanced drought tolerance and biological nitrogen fixation. Ph. Diss. Michigan State University. Adams, M.W., D.P. Cayne, J.H.C. Davies, P.H. Graham, and C.A. Francis. 1985. Common bean (Bhaseglgs yulganis L). In: R.J. Summerfield. and. E.H. iRoberts (Eds), Grain. Legume Crops. William Collins and Sons & Co. Ltd. pp 433-476. Begg, J.E. and.N.C. Turner. 1976. Crop water deficits. Adv. in Agron. 28:161-217. Blackman, P.G. and W.J. Davies. 1985. Root to shoot communication in maize plants of the effects of soil drying. J. Exp. Bot. 36:39-48. Blum, A. Gozlan, G. and J. Mayer. 1981. The manifestation of dehydration avoidance in wheat breeding germplasm. Crop Sci. 21:495-499. Bonanno, A.R. and H.J. Mack. 1983. Yield components and pod quality of snap beans growth under differential irrigation. J. Amer. Soc. Hort. Sci. 105:869-873. Boyer, J.S. and H.G. McPherson. 1975. Physiology of water deficits in cereal crops. Adv. Agron. 27:1-23. Dubetz, S. and P.S. Mahalle. 1969. Effect of soil water stress on bush beans W W, L. at three stages of growth. J. Am. Soc. Hort. Sci. 94:479-481. Farqhuar, G,D. and T.D. Sharkey. 1982. Stomatal conductance and photosynthesis. Ann. Rev. Plant Physiol. 33:317-345. Fischer, R.A. 1973. The effect of water stress at various stages of development on yield processes in wheat. In plant response to climatic factors. Proc. Uppsala Symp. 1970. pp. 505-511. Paris: UNESCO 574 pp. Fischer, R.A. and N.C. Turner. 1978. Plant.productivity in the arid and semiarid zones. Ann. Rev. Plant Physiol. 29:277-317. 9 Fischer, M.J. and M.M. Ludlow. 1984. Adaptation to water deficits in Stylosanthes. In: Stace, H.M. and Edye, L.A. (eds). The Biology and Agronomy of Stylosanthes. pp. 163-179. Academic Press, Sydney. Gentry, H.S. 1969. Origin of common bean, Phaseolus vulgaris L. Econ. Bot. 23:55-69. Hoogenboom, G., M.G. Huck, and C.M. Peterson. 1987. Root growth rate of soybean as affected by drought stress. Agron. J. 79:607-614. Hubick, K.T. and D.M. Reid. 1988. Effect of drought on transpiration and.metabolism of abscisic acid in aerponically grown Heliantngg anggs. Physiol. Plant. 74:317-325. James, C.W. 1981. Estimated losses of crops from plant pathogens. In Pimentel (ed): "CRC Handbook of Pest Management in Agriculture", Boca Raton, Florida: CRC Press Inc., p 79. Kramer, P.J. 1983. Water relations of plants. Academic Press, Inc. pp. 342-389. Lachno, D.R. and D.A. Baker. 1986. Stress induction, of abscisic acid in maize roots. Physiol. Plant. 68:215-221. Laing, D.R., P.J. Kretchmer, S. Zuluaga, and.P.G. Jones. 1983. Field bean. In: W.H. Smith and S.J. Banta (Eds). Symposium of Potential Productivity of Field Crops Under Different Environments. Los Banos, Philippines. 1980 (Procedings) IRRI pp. 227-248. Levitt, J.V. 1972. Responses of jplants to environmental stresses. Academic press, New York. Ludlow, M.M., A.C.P. Chu, R.J. Clements, and R.G. Kerslake. 1983. Adaptation of species of Centrosema to water stress. Austr. J. of Plant Physio. 10:119-130. Ludlow, M.M. and R.C. Muchow. 1989. A critical evaluation of traits for improving crop yields in water-limited environments. Adv. Agron. 43:107-153. Morgan, J.M. 1984. Osmoregulation and water stress in higher plants. Ann. Rev. Plant Physiol. 35:299-319. Mott, J.J., A.J. McComb. 1975. Effects of moisture stress on the growth and reproduction of three annual species from an arid region of western Australia J. Ecol. 63:825-834. 0' Toole, J.C., J.L. Ozbun, and D.H. Wallace. 1977. Photosynthetic response to water stress in Phaseolus vulgaris. Physiol. Plant. 40:111-114. 10 Passioura, J.E. 1988. Root signals control leaf expansion in wheat seedlings growing' in. drying soil. Aust. J. Plant Physiol. 15:687-693. Ritchie, J.T. 1981. Water dynamics in the soil-plant- atmosphere system. Plant and Soil. 58:81-96. Robins, J.S. and C.E. Domingo. 1956. Moisture deficits in relation to the growth and development of dry beans. Agron. J. 48:67-70. Slatyer, R.O. 1973. The effect of internal water status on plant growth development and yield. In plant response to climatic factors. Proc. Uppsala Symp. 1970. pp. 505-511. Paris: UNESCO. 574 pp. Turner, N.C. and J.E. Begg. 1977. Response of pasture plants to water deficits. 1n Wilson J.R. (ed). Plant Relations in Pastures pp. 50-56. Canberra, Australia. CSIRO. Turner, N.C. and M.M. Jones. 1980. Turgor maintenance by osmotic adjustment: A review and evaluation. In Turner N.C. and P.J. Kramer (Eds). Adaptation of Plants to Water and High Temperature Stress. pp. 155-172. New York: Wiley-Interscience. Vaadia, Y. 1984. The impact of plant stresses on crop yields. Mexico-Israel. Taller sobre sequia, memoria (Proceedings). pp 69-90 e CHAPTER 1 EFFECT OF SOIL WATER DEFICITS ON DRY BEANS (P. vulgaris L.). I. EXTENSION GROWTH OF LEAVES, STEMS, AND PODS. AW Soil dehydration adversely affects the growth of different organs in the plant and hence, crop productivity. This study was conducted to examine the effect of water deficits on the elongation of leaves, stems, and pods under field conditions in a Spinks soil (Psammentic Hapludalfs) and a Kalamazoo soil (Typic iHapludalfs). The research. was conducted in Michigan utilizing a rain shelter to control the water regimes. In 1988, an early (ES) and mid season (MS) water deficit treatment began 15 and 29 days after planting (DAP). The mid season treatment in 1989 started 27 DAP. Leaf appearance was slightly decreased by the water deficit conditions in the Spinks soil. Leaf, pods, and internode elongation were sensitive to a decrease in water content in both soils. leaf expansion decreased when plant available water (PAW) declined. by' about. 30%; IElongation. of stem internodes lagged behind the control after about 40% of the PAW was depleted. The growth of individual pods was observed 11 12 to be less sensitive than that of leaves and internodes. However, total pod elongation was much greater in the control than in ES and.MS because of an increase on pod abortion under advancing drying conditions. Total pod elongation decreased when more than 40% and 60% of PAW was depleted in the Spinks and Kalamazoo soils, respectively. In the Spinks soil, dry matter production of stems and leaves decreased by about 38%, 34% and 15% in ES, MS and LS, respectively. In the Kalmazoo soil, leaf and stem dry matter decreased by about 23% and 11% for MS and LS, respectively. Number of leaves was less affected by the deficits than the pod number. Additional information on reproductive growth is reported in Chapter 2. INIBQDQQIIQN Organ expansion is one of the earliest discernible effects of soil water deficits on cropigrowth.when compared to other plant processes (Hsiao, 1973). Processes such as stomatal conductances and.photosynthesis become progressively more affected as the deficits become greater in the soil. The magnitude of the water deficit required to reduce growth varies with the timing of the deficit and.the conditions under which plants are grown. leaf extension of plants grown in pots has been found to decline at leaf water potentials below -0.2 MPa and to cease at potentials of -0.7 to -0.9 MPa (Acevedo et al., 1971; Boyer, 1970). On the other hand, field experiments have shown that a decline in leaf water potential 13 to -1.2 MPa had little effect on the rate of leaf expansion in soybean (Bunce, 1977). For maize, Watts (1974) found that water'potentials of -0.8 MPa.did.not.decrease leaf elongation. These attempts to find a general trend relating plant water status to organ expansion have not been successful. Ludlow (1987) suggested that the lack of a unique relationship between leaf water potential and critical physiological processes has led to a greater use of measurements of soil water status to understand shoot performance. Recent investigations have indicated that plants growing in a drying soil may reduce leaf and stem elongation independently of the shoot turgidity (Passioura, 1988; Blackman and Davies, 1985). However, changes in soil water content, as well as plant water availability, are largely influenced by the physical and chemical soil conditions (Larson, et al., 1983). Russell and associates (ICRISAT, 1978) showed that a coarse-textured alfisol had less PAW'and.produced less dry matter than a fine- textured 'vertisol ‘when. compared. under’ the same climatic conditions. More information is still needed on the water availability in the field for different soils and its effect on shoot and root growth processes during advancing drought conditions. The objective of this investigation was to study the effects of decreasing plant water availability in two contrasting soils on elongation and expansion of leaves, internodes and pods in dry bean plants. 14 RI D OD A field study was conducted at the Kallogg Biological Station near Kalamazoo, MI, during the summers of 1988 and 1989. Weather data for both years is reported in Appendices 2 and 3. Dry bean plants (W L. , cv. Seafarer) were grown in a rainout shelter facility (Martin, et al., 1988). The experimental unit consisted of a plot of 6 rows, 6m long with an inter-row spacing of 0.71m. Each plot had an independent control system for irrigation. Soils types included were a Spinks sand (Psammentic Hapludalfs) with an average plant water availability of 104 mm in the upper 1.5 m profile and a Kalamazoo loamy soil (Typic Hapludalfs) with an average of about 118 mm. Plant available water (PAW) is defined as the difference between the highest volumetric water content in the field after drainage and the lowest measured water content when plants are very dry and leaves are dead or dormant (Ritchie, 1981). Some physical and chemical characteristics for both soils are described in Appendix 1. A dry bean variety (cv. Seafarer), was planted on.July 8, 1988 and June 12, 1989. The variety belongs to a navy bean class, also referred to as the pea bean. Seafarer is an early bush type plant with white flowers and.chalky white roundish seeds. It is resistant to both common.bean.mosaic and anthracnose and is widely accepted by Michigan growers because of its high yield and earliness (Adams, 1982). The two planting dates provided different thermal regimes during the seasons for 15 beans to grow. In the experiment, seeds were planted in excess and thinned out after emergence to a density of 16 plants/m2 . Fertilizer was applied in doses of 120 Kg/ha N, 100 Kg/ha P, and 100 Kg/ha K. Nitrogen supply was split in two applications, at planting and 20 DAP. The irrigation system (NeSmith, et al., 1990) was operated 2-3 times a week to keep the soil water content close to the drained upper limit (DUL)(Figures 1.1A and 1.18). In 1988, soil water deficits began at 15 DAP and 29 DAP, resulting in an early season (ES) and a mid season (MS) water deficit commencing during the vegetative and flowering stages, respectively. In 1989 the mid season deficit began 27 DAP. Water content at five different soil depths (25, 50, 75, 100, 125 and 150 cm) was monitored at 7-day intervals using the neutron scattering technique. These readings provided estimates of the DUL and lower limit (LL) of plant water availability. Leaf initiation on the main stem.was recorded as soon as each small trifoliate leaf began to unfold (about 1 cm length). Three small initial leaves were selected in each treatment to determine leaf extension. Leaves were tagged at node 6 and 7 on the main stem and at node 2 of the first lateral branch, the branch emerging from the first node. Measurements were taken daily on the length (L) and width (W) of individual leaflets. Leaf area (LA) was estimated utilizing a regression equation determined for this variety using L and W: 16 4O - control [:1 early stress SSS] mid stress 1988 AEEV LcaoE< c0509; - control [:1 mid stress SSS late stress 1989 O O nu O O 4, 3 7. l AEEV choE< cozoot: 4O 5O 60 70 DAP 30 Irrigation amounts applied to different treatments during 1988 and 1989. Figure 1.1. 17 LA = 0.603 + 0.581 (L*W), (18- 0.98). To determine the equation, the length and. width of 40 individual leaves of different sizes were correlated with the leaf area obtained in a leaf area meter (Licor, model 1500, Lincoln NB). iLeaves were randomly selected from irrigated.and stress treatments. This equation facilitated the non- destructive measurements of leaf area during the growing season. Elongation of the internodes on the main stem was measured in the 1989 study only on three plants of MS and control treatments on 7-day intervals after the appearance of the third trifoliate leaf. Individual pod elongation was determined in both soils in 1989 on a daily basis for both the MSiand.control treatments, taking into account the position of the pod within the plant. Three different pods were selected for measurement between nodes 8 and 9 of the main stem. Total pod length was estimated at 5-day intervals using the total number'of pods per plant.and the average pod length" Relative extension was determined by dividing the rate of elongation of the stressed treatments by those of the control. Dry matter production of various plant parts was measured at the end of the season. Leaves, stems, and pods from 6 plants in each treatment were separated into paper bags and dried in a forced air oven at 70 °C for 72 hours before weighing. Weather information of maximum and minimum temperature and radiation was collected near the rainout shelter using a Licor model 12008 data acquisition system. 18 CUSO Different climatic conditions were obtained in both years by planting late in 1988 and early in 1989. In 1988, maximum and minimum temperatures as well as solar radiation tended to decrease from 42 DAP to the end of the season, reaching lower values than the ones observed in 1989 (Figures 1.2A and 1.28). However at the beginning of the season, the same climatic factors were slightly higher in 1988 (Figures 1.3A and 1.38). Irrigation ceased 15 and 29 DAP in 1988, and 27 and 45 DAP in 1989, initiating a terminal water deficit at different stages of phenological development. In the first year, the soil water content for ES (Spinks soil) rapidly decreased in the upper 50 cm followed by water uptake from deeper layers 43 DAP (Figure 1.4A). Toward the end of the season, soil water content began to reach the lower limits of PAW. For the MS treatment, the pattern of water extraction was different. The decrease of soil water content in the first 15 days after the onset of the drought.period was greater than those observed in ES (Figure 1.43). However, the total water depletion in the upper 75 cm was greater for the ES than for the MS treatment. For soil depths below 75 cm, the water content in MS reached lower values than that in ES. This suggested greater root activity of E8 in the upper soil layers decreasing with depth as the water deficit progressed during the season. The opposite action seemed to occur with the MS treatment (see 19 45“ Planting date July 8 /\ 1988 0 maximum 8, 35-- o L 3 25-- —&-J O 6 Q. 15" E rnmknum +93 5- -5 .L : : 45- Planting date June 12 A 1989 O 6 EL 35" mammum Q) L 3 25. ...: O 6 g? 15-- Q) . e . F— 5 mwmnum -5 g : § Figure 1.2. DAP Seasonal patterns of minimum and maximum temperatures during 1988 and 1989. 20 /_\ 40 (\I E 1988 \ p 30- IE v S 5 20-- .9. 13 O (I. 10... L S O 2 o . . = (\l 40- E 1989 \\ .3 2 30- v c .9 .5. 13 O L. L 10- 2 O U") 0 l l l O 20 4O 60 80 DAP Figure 1.3. Seasonal patterns of solar radiation during 1988 and 1989. Depth (cm) 0 7157 43 29 15 DAP 25- CIA A 'e O A \\ \ \ \ 50- DA A O O \\ \ \ / 75- DA ADO \ \l/ 100- DAD \\\ 125- DH) 1988 \\\l\ 150 -- early stress m 0 ' 7157'43 '29 DAP 504- B . O // / / 75- DA C O I \ \/ 100— [:1 A0 \ \\\ 125- DAOO 1988 \\ lSO-- mid stress UK) 0 0.05 0.10 0.15 0.20 Soil water (cm3/cm3) Figure 1.4. Soil water content with depth at several dates for early and mid stress treatments for Spinks soil during 1988. 22 Chapter 4). In 1989, the MS treatment of the Spinks soil resembled the patterns of water extraction of those in the MS of the previous year. Rapid water depletion was observed in the top 75 cm at the beginning of the water deficit followed by increased water uptake from deeper layers as the upper soil dried out (Figure 1.5A) . In the LS treatment, a greater decrease in soil water content was observed in the upper 75- 100 cm 2 weeks after the last day of irrigation. By the end of the season, most of the water available to the plant was found in the region of the soil below 75 cm depth (Figure 1.58). In the Kalamazoo soil, both the initial soil water content after the last irrigation and the patterns of water extraction were different to those same treatments in the Spinks soil. The DUL reached average values of 0.27 cma/cma in the top 50-75 cm. A decrease in soil water content was observed after the onset of the water' deficit in both treatments (Figures 1.6A and 1.68). By 50 DAP, soil water began to be depleted below' 75 cm in the MS treatment. In contrast, changes in the water content of LS were very small below 75 cm depth. The soil water deficits imposed in the 1988 season slightly changed leaf appearance and final number of leaves in the main stem. Leaf number in the ES treatment began to lag one leaf behind the control after the unfolding of leaf number 6. In the MS treatment, leaf number lagged behind the 23 0 S . 69 55 41 27 DAP 25 ~~ A A A O O \\ \ \ E 50~- AA C O 0 \\ \ / V 75» A A e O _c . \ \ \ \ a 100- A A00 8 , ill; b 1989 \\\! 150“ mid stress Ad. 0 l l 71 65 59 45 DAP 25- 8 AA 0 O \\\ \ E 50" AA. 0 o \\\ / v 75- AA. 0 L l \ l / '5. 100- A A00 8 \\QA " 1989 \ l/ 150 __ late stress Al. 0 0.05 0.30 0'15 Soil water (cm3/cm3) Figure 1.5. Soil water content with depth at several dates for mid and late stress treatments for Spinks soil during 1989. 0.20 24 O I DAP '69 55 4127 25- A A A O O A 50-- \A\ \e\o E // 3 75- A O .5 1..-- A! O. <1) \\ Q 125- 1989 21/7 150“ mid stress . O 'r l l i i DAP 71 59 45 25- B A O O \ \ \ E 50.- A O O \9/ 75-- A e/ O/ _C (/// 45- 10'0--- A g A?! 1989 \\\ 150“ late stressw 0 0.05 0.70 0.15 0.20 0.25 0.30 3) Soil water (ems/cm Figure 1.6. Soil water content with depth at several dates for mid and late stress treatments for Kalamazoo soil during 1989. 25 control by one leaf after leaf number 9 (Figure 1.7). The near-linear response observed in leaf appearance, as well as the small effect of water deficits on this process, has been shown for other legumes (Sinclair, 1984: Huck et al., 1983). Leaf appearance and other developmental events are much more influenced by temperature than by limited water conditions (Hesketh et al., 1973). Leaf expansion was greatly affected by all water deficit treatments in both years. In 1988, leaf area in MS (leaf 6, main stem) began to differ from the control 5 days after the initiation of the soil water deficits (Figure 1.8). Leaf 6 for the ES treatment began to grow when the plants had been under stress conditions for 14 days. The rate of leaf expansion for this treatment was 5.0 cmz/day as compared to 16.7 and 27.8 cmz/day in the MS and control treatments, respectively. In 1989, expansion of leaves in the main stem differed from that observed in the leaves of branches (Figure 1.9) . Under irrigated conditions, leaves from branches became a competitive sink for assimilates with those growing on the main stem. Leaf expansion in branches was more affected than in the main stem as soil water deficit progressed in the season, indicating a priority for the main stem. Leaf number 7 on the main stem was 70% smaller in the MS treatment than in the control and leaf area of number 2-branch decreased by about 75% when subjected to drought stress. Under the same water deficit treatment, plants in the Kalamazoo soil had a greater rate of leaf expansion than the I; 26 DJ 1 l C) i Main stem leaf number O—O control 1988 0—0 early stress A—A mid stress O l// J [ale ’6/. ’6’. @O u/ / P /I Q / I Figure 1.7. Seasonal changes in leaf appearance on the main stem for different water deficit treatments for Spinks soil during 1988. Arrows represent initiation of water deficit. 27 200 A O—Ocontrol 1988 B 0—0 mid stress 2 1 50 __ A—A early stress \ - 1' N . 6,/9r9 E 5/ " \./ 1 OO " 1_/.‘. T 3‘; O 9 T/t/J. .L m ~/-/? 5 /9/2 :5 5K37' <5//I' cu /’ .. . _l o/ " T T/A—A «- / ‘5 v 1" A A J. ‘L ¢° 5-5’9 A * L O eéfi"? T i 1 1 1 . 30 31 32 33 34 35 36 3‘7 3'8 3'9 40 DAP Figure 1.8. Seasonal changes in area of leaf 6 on main stem in different water deficit treatments for Spinks soil during 1988. Deficit treatments started 15 DAP for ES, and 29 DAP for MS. 28 200 /'\ ‘4— 0—0 N7 control C 0—0 Br control 1 989 m A——AN7MS —- 150 __ A—A Br MS - ;§\ 3-9-9 E 5/5/9752 0 - 5/ \_/ 100 -- /8/ - 0 g/- 8 ”5* O / ‘ 50 -- . - - 4. /. - - g-A”é‘é‘é .3 :A,x-‘ O-——$§ ? i i i i i i i t i i 40 4142 43 44 45 4 47 48 49 50 51 DAP Figure 1.9. Seasonal changes in area of leaf 7 (n7) on main stem and leaf 2 (Br) on the first branch for Spinks soil during 1989. Deficit treatment started 27 DAP 29 comparative one in the Spinks soil (Figure 1.10). Leaf number 7 in the main stem was growing at a rate of 9.4 cm?/day as compared to 4.7 cm3/day observed in the one from the Spinks soil. The sensitivity of leaf expansion to soil water deficits is the result of twoigrowth.components, cell division and cell expansion (Hsiao et al., 1976). Boyer (1970) showed differing sensitivity to water deficits for the major metabolic processes in maize, soybean, and sunflower, with expansion growth being the most sensitive. Under field conditions, NeSmith (1990) found that maize growing under water deficit in a sandy soil had a measurable decrease in leaf extension within five days after withholding water. Hoogenboom et a1. (1987) , showed that leaf extension in soybean declined.as soon as soil water'potential began.to fall below 0.03 MPa in the upper 40 cm of the soil. The greater effect of soil water deficit on the extension of branch leaves resulted in different profiles of leaf area along the main stem (Figure 1.11). In general, total leaf area.measured 45 DAP“was greater’in.the first nodes decreasing toward node 10-11. The main effect of the water deficit occurred in the first nodes where most of the branches are located. In node number one, leaf area diminished by 45% and 67% for MS and ES treatments, respectivelyx These differences in leaf area greatly affected ground cover and light interception (Chapter 3). The effect of soil water deficit on leaf area index (LAI) was observed in plants grown in the Spinks sail a few days 3O 200 A 0—0 control 1989 “'5 0—0 m1d stress 2 150- \ Tie.) 61 .. 5/9 1 E 6/1 - 0 .all", 8 T/L T/l l L. (3 T/,Cl (j 1 ‘T,/CD L 4— ‘5C) &;/:;/’1P l O _- T/O/J. (D Q/* ..J safigi / /.L O-r—Q 1 1 1 1 ' . ' 1 1 40 41 42 43 44 45 45 47 DAP 484 Figure 1.10 Seasonal changes in area of leaf 7 on main stem, for Kalamazoo soil during 1989. Deficit treatment started 27 DAP. 31 12 GE) 0 1988 _,_. 1 m 10 e o 45 DAP \\ \ g: A. 0 0—0 control 6 8 “23‘ 0—0 mid stress \ i\ — E /A.\O\ A A early stress 23 (3--kAfi H.1H34 _Q 1-/ /__4 \ é; 14-m1—£y«‘n H34 C 1-\A-1>.-1 \1-04 (D 2 ~- No- 1? / | \\\\\\\\ C) 1——Ay—4 H.4 1—Cya Z O 1 1 1 1 0 100 200 300 400 500 Leaf area (cmz) Figure 1.11 Seasonal changes in leaf area distribution along nodes of the main stem on 45 DAP for different water deficit treatments for Spinks soil during 1988. 32 after the onset of the drought treatments (Figure 1.12A and 1.123). A rapid senescence rate was observed as the drought progressed in the MS treatments in both years causing low LAI values compared to the control. Rapid senescence rate was also observed in LS after the onset of the deficit. The MS and LS deficits had less effect on the LAI of plants growing in the Kalamazoo soil, both in the rate of increment until 50 DAP and in the rate of leaf area decrease from 50 DAP until the end of the season. On the other hand, the effect of the ES treatment resulted in an apparent preconditioning of the plants by the early season soil water regime, resulting in less senescence beyond 50 DAP (Figure 1.12A). Morgan (1984) showed that wheat undergoing water deficits at an early stage of growth will increase solute accumulation which leads to the maintenance of turgor and hence continued plant growth. Rapid senescence rate is also a plant adaptation mechanism to decreasing soil water content (Turner, 1979). However, rapid loss of leaves in short season dry bean varieties may be detrimental to yield (Laing, et al., 1983). Although internode length on the main stem of dry beans is influenced by genetic factors (Acosta, 1988), soil water deficits also affected the growth rate (Figure 1.13) as well as the final size of each internode (Figure 1.14). Internode 7 was the longest internode on ‘the :main stem. for’ both treatments, with a growth rate of 0.62 and 0.39 cm/day for the control and MS treatment, respectively. Elongation rate for internode 9 was 0.38 and 0.21 cm/day under irrigated and MS 33 1933 0—0 control 5... A-A mid stress A A—A early stress LAI ‘I‘ 'O—O' control 5" 1989 41—1. mid stress B A—A lots stress LAI 4p. ’4/ 5 <1- 1989 C 4. .. i 3 1’ . 2 <1- 0 — 0 control a—a mid stress e—A late stress L J 1 1 1 1 L r r I T ' 1'5 22 29 36 43 50 57 84 71 DAP Figure 1.12 Seasonal changes in leaf area index for different water deficits treatments for Spinks (A,B) and Kalamazoo soil (C). Arrows represent initiation of water deficits. 34 conditions, respectively. In general, soil water deficits reduced internode length an average of 41% in comparison to the control. This reduction was mainly observed above internode number 4 (Figure 1.14). These results agree with those of Hoogenboon et al. (1987) who showed that internodes of soybeans elongated significantly slower during drought periods. Elongation of individual pads in the plants of the Spinks soil was less affected than the elongation of internodes and the expansion of leaves. Individual pods in the control reached an average length of 8.4 cm, with a growth rate of about 0.93 cm/day (Figure 1.15A) . Under the stress conditions of the MS treatment, the rate of pod elongation was 0.78 cm/day, reaching a final' pod length of 7.1 cm. This difference is rather small considering that more than 50% of PAW was already depleted from the upper 50 cm of soil. The number of pods per plant is an important factor explaining the lower sensitivity of individual pads to soil water deficits. Drought stress during flowering and pad filling increased the rate of flower and pad abortion (Chapter 2). In this experiment the control in the Spinks soil had 14.5 pods per plant versus 6.5 in the MS treatment (1988- 1989) . The reduction in pod number also decreased the competition for plant resources resulting in a greater rate of elongation on main stem pods as compared to that observed in leaves and internodes. In the Kalamazoo soil, individual pod elongation in MS was not significantly different when compared 35 15 E mid stress 1989 control internode 89 A/A 7 S 10" internode " / -~ 8‘ - 4 0’ 4...... 7 0—0-1 8 _ / / 43 A: 5 (3"" '__—C> 4 o 5- ngr’g 4 -- 9 ~- C: .... ___. L /O O / 9 A E] H .03 C) ‘1 A 0 O C 1 1 Ofl/e/Q/1 1 1 /Q, E/ 1 1 25 32 39 46 53 25 32 39 46 53 50 DAP DAP Figure 1.13 Seasonal changes in internode elongation for MS and control treatments for Spinks soil during 1989. 36 21% 45; 12 "' 1989 O C 1011-0310 0 L. 53'“ t-dD-1 . O"I Q) 1.-1 :RD—i Q t— l ES 6‘* 1.H 1—«35:// :2 ;;.V1 #434 Q) 4.". H.4 FCH 13 p‘fi6}//// 4f3[DA$D g / / O—O control a 2 " ”((34 0—0 mid stress . £9, 16)- .E O 1 1 1 1 1 1 1 0 2 4 6 8101214 lnternode length (cm) Figure 1.14 Length of different internodes on the main stem at 46 DAP for MS and control treatments for Spinks soil during 1989. 37 10 A 1989 A 9“ 8—8 control -- 'd t E 8i m1 sress L) V 7‘- .C ...) CT) 6-- CI .9. 5.- 13 CD 4~~ O. 3.. 2 1 1 1 e1 1 1 1 1 1 10" . B 1989 9“ 0—0 control A ‘ O—O mid stress E O 8“ v .c 7“ ‘81 c 6" Q) — 5‘- 8 a. 4" 3.- 2 1 1 1 1 1 1 1 1 1 4'1 4‘2 43 4'4 45 4‘6 47 4'8 49 D A P Figure 1.15 Seasonal changes in individual pod length for MS and control treatments for Spinks (A) and Kalamazoo (B) soils during 1989. 38 totcontrol plants (Figure 1.158), however total.pod elongation for MS was significantly lower than that of the control for both soils. Total pods in the Kalamazoo soil had an elongation rate of 3 cm/day compared to 1 cm/day observed in the corresponding treatment in the Spinks soil (Figures 1.16A and 1.163). Plant available water in the soil profile influenced organ elongation in dry beans in both soils (Figures 1.17 and 1.18). In the Spinks soil, relative leaf expansion in terms of LAI, fell when PAW decreased to 68%, but reached a lower value of 0.34 when PAW decreased to 42%. Relative total pod elongation decreased at 62% of PAW. Stem elongation began decreasing at 60% of PAW; In.the Kalamazoo soil, relative leaf expansion began declining at 70% of PAW, however, the relative elongation of total pods decreased at PAW values of 45%. Different.patterns of organ expansion affected the final accumulation of dry matter (Table 1). In 1988, dry matter of stems and total leaves in the Spinks soil was greater for the control than for'ES and.MS, where branches were most affected. The number of pods on the control plants was greater compared to the ones in the deficit treatments. However, leaf number was less affected by the drought condition. In 1989, dry matter production as well as leaf number and pods were consistently greater for the Kalamazoo soil as compared to the Spinks soil. For the MS treatment in Spinks soil, the number of pods was 54% less than those in the MS of the Kalamazoo soil. For the same treatment, dry matter Figure 1.16 39 1989 A 0—0 control O—O mid stress —8 —a h) .9 O O '_—'l‘ 100‘ 0 60- lotol pod length (cm) C O .3. o i m 1989 0—0 control . o—o mid stress —t ...-1 O N 0 i O i 60- Totol pod length (cm) 8 20- I 4o 45 5'0 5'5 6'0 6'5 7'0 DAP -Seasonal changes in total pod length for MS and control treatments for Spinks (A) and Kalamazoo (B) soils during 1989. Relative elongation rate 40 1.0 0.8-- 0.6-- 0.4-- -- O stems 0 leaves 0.2-- A pods -- A O 1 1 1 1 O 20 4O 60 80 100 PAW Figure 1.17 Relative elongation rates of different plants organs as influenced by the percentage of 'plant extractable water (PAW) in the root zone for Spinks soil during 1989. 41 Figure 1.18 1.0 ‘ A cu .. Koldmozoo 7 . O L' 0.8" c .9 “ A E -- O, 0.6 / C -- 2 ‘D 0.4-- 3 1:: . n 0 leaves 2 0.2" A pods <1) 0: -- o = = l i 0 2o 40 60 so 100 PAW Relative elongation rates of different plants organs as influenced by the percentage of plant extractable water (PAW) for Kalamazoo soil during 1989. 42 Table 1.1. Number of leaves, pods, and dry matter production of different plant parts at maturity for various soil water deficit conditions. Dry Weight Number/plant Treat. (g/Plant) IMain Stem. Branches Leaves Leaves Final pods 1988 Spinks Soil Control 1.99:0.17 3.84:0.141 6.20:0.35 42.7:1.9 15.2:2.0 Mid 1.6510.09 2.15:0.07 4.39:0.43 39.2il.6 6.4il.8 stress Early 1.59:0.13 1.85:0.09 4.03:0.51 34.8:2.8 9.ltO.9 stress 1989 Spinks Soil Control 1.90:0.10 3.21:0,19 5.28:0.29 40.6r1.3 16.1:l.1 Late 1.83:0.07 2.61:0.15 4.49:0.31 39.1:1.7 9.9:0.9 stress Mid 1.48:0.22 1.83:0.08 3.36:0.38 36.2:2.1 5.9:1.4 stress ” —i 1989 Kalam. Soil Control 2.10:0.21 3.5710.24 6.3010.19 43.2:1.5 17.5:1.6 Late 1.79:0.15 2.98:0.13 5.8810.29 41.4:0.9 15.4:l.2 stress Mid 1.52:0.18 2.59:0.20 5.07:0.27 40.3il.7 12.7:1.1 stress ___— 43 accumulation in branches was 43% lower in the Spinks soil. In summary, deficit water conditions in both soils adversely affected the growth and expansion of different organs in dry beans. Leaf appearance for plants grown in the Spinks soil was slightly delayed in ES and MS. Significant reductions in leaf, stem and pod elongation were observed with relatively small decreases in soil water contents Leaves were the most susceptible organs, followed by pods and stems. Along the plant.main axis, the.greatest reduction in leaf area and stem dry weight was observed in the branches of the first four nodes. Dry beans became more susceptible to periods of drought as canopy size increased. Mid season water deficits caused a rapid senescence rate. However, plants experiencing early stress showed better adaptation to the deficit conditions. LIST OF REFERENCES Acevedo, E., T.C. Hsiao, and D.W. Henderson. 1971. Immediate and subsequent growth responses of maize leaves to changes in water status. Plant Physiol. 48:631-636 Acosta, J.A. 1988. Selection of common bean (Phaseolus W) genotypes with enhanced drought tolerance and biological nitrogen fixation. Ph.D. Diss. Michigan State University, MI. Adams, M.W. 1982. Bean varieties. In Dry Bean Production - Principles and Practices, ed. L.S. Robertson, R.D. Frazier. Extension bulletin. Extension Service. pp. 143-151. Mich. State Univ. Blackman, P.G. and W.J. Davies. 1985. Root to shoot communication in maize plants of the effects of soil drying. J. of Exp. Bot. 36:39-48. Boyer, J.S. 1970. Differing sensitivity of photosynthesis to low leaf water'potentials in.corn.and.soybeans. Plant Physiol. 46:236-239. Boyer, J .S. 1970. Leaf enlargement and metabolic rates in corn, soybeans and sunflower at various leaf water potentials. Plant Physiol. 46:233-235. Bunce, J.A. 1977. Leaf elongation in relation to leaf water potential in soybean. J. Exp. Bot. 28:156-161. Hesketh, J.D., D.L. Myhre, and C.R. Wiley. 1973. Temperature control of time intervals between vegetative and reproductive events in soybeans. Crop Sci. 13:250-254. Hoogenboom, G., C.M. Peterson, and M.G. Huck. 1987. Shoot growth rate of soybean as affected by drought stress. Agron. J. 79:598-607. Hsiao, T.C. 1973. Plant responses to water stress. Ann. Rev. Plant Physiol. 24:519-570. 44 45 Hsiao, T.C., E. Acevedo, E. Fereres, and D.Wx Henderson. 1976. Water stress, growth and osmotic adjustment. Phil. Trans. R. Soc. London 273:479-500. Huckq M.G., K. Ishihara, C.M. Peterson, and.T.‘Ushijima. 1983. Soybean adaptation to water stress at selected stages of growth. Plant Physiol. 73:422-427. INTERNATIONAL CROPS RESEARCH INSTITUTE FOR THE SEMI-ARID TROPICS. 1978. Report of work, 1977-1978. Environmental physics, farming systems research program. Hyderabad, India. Laing, D.R., P.J. Kretchmer, S. Zuluaga, and P.Gw Jones. 1983. (Field bean. In W.H. Smith and S.J. Banta (Eds). Symposium on Potential Productivity of Field Crops Under Different Environments. Los Banos, Philippines, 1980 (Proceedings) IRRI pp. 227-248. Larson, W.E., J.B. Swan, and M.J. Shaffer. 1983. Soil management for semiarid regions. Agric. Water'Mgmt. 7:89-114. Ludlow, M.M. 1987. Defining shoot water status in the most meaningful way to relate to physiological processes. In Hanks and Brown (ed.). Measurement of soil and plant water status. Proc. Inter. Conf., Logan, UT. 6 July - 10 July 1987. Utah State University, Logan, UT, USA. Martin, E.C., J.T. Ritchie, S.M. Reese, T.L. Loudon, and B. Knezek. 1988. A large area, light-weight rainshelter with programmable control. Trans. Am. Soc. Agric. Eng. 31:1440- 1444. , Morgan, J.M. 1984. Osmoregulation and water stress in higher plants. Ann. Rev. Plant Physiol. 35:299-319. NeSmith, D.S. 1990. Growth responses of corn (Zea mayg L) to intermittent soil water deficits. Ph.D. Thesis. Michigan State University, MI. NeSmith, D.S., A. Miller, and J.T. Ritchie. 1990. An irrigation system.for plots under'a rain shelter. Agric. Water Mgmt. 17:409-414. Passioura, J.B. 1988. Root signals control leaf area expansion in wheat seedlings growing in drying soil. Aust. J. Plant Physiol. 15:687-693. Ritchie, J.T. 1981. Water dynamics in the soil-plant- atmosphere system. Plant and Soil 58:81-96. Sinclair, T.R. 1984. Leaf area development in field-grown soybeans. Agron. J. 76:141-146. 46 Turner, N.C. 1979. Drought resistance and adaptation to water deficits in crop plants. In Stress Physiology in Crop Plants, ed. H. Munssell and R.G. Staples, pp. 181-194. New York: Wiley-Interscience. Watts, W.R. 1974. Leaf expansion in Zea mays L. III. Field measurements of leaf extension in response to temperature and leaf water potential. J. of Exp. Bot. 25:1085-1096. CHAPTER 2 EFFECT OF SOIL WATER DEFICITS ON DRY BEANS (P. vulgaris L.) II. REPRODUCTIVE ORGANS AND YIELD. ABSTRACT Little is known about the effect of soil water deficits on the setting and distribution of pods and flowers along the different axes of the dry bean plant. The objective of this study was to investigate the effect of water deficit treatments, during different growth stages, on the number and distribution.of pods and flowers on the main stem.and.branches as well as the dry matter production and yield under field conditions. A rainout shelter facility was used to control the water regimes of early (ES), mid (MS), and late (LS) season treatments. A Spinks soil (Psammentic Hapludalfs) and a Kalamazoo soil (Typic Hapludalfs) were utilized in the experiment. Soil water deficits in the Spinks soil decreased total flower formation by about 32%. Branches on the first four nodes were most severely affected. Flower formation at those nodes declined by more than 40% and pod abortion reached nearly 100% in the MS treatment. For LS, a decrease in soil water content, 10 days after the onset of the deficit, induced 47 48 substantial (48%) pod abortion. In the Kalamazoo soil, the number' of flower' and. pods, as ‘well as seed. dry 'matter production, were diminished in the water deficit treatments. Results indicated that the rapid water deficits observed in the Spinks soil reduced the number of flowers and pods growing on branches, suggesting that under drought stress the main stem had priority for the plant resources. In the Kalamazoo soil, water'deficits effect on the number of flowers and pods was small when compared to those observed in the Spinks soil. INIBQDHQIIQE Soil water deficits occurring during the reproductive stages of growth are considered to have the most adverse effect on crop production (Begg and Turner, 1976: Herrero and Johnson, 1981). Bean plants are sensitive to drought stress during flowering and pod filling. Robins and Domingo (1956) found that water deficits imposed during flowering reduced both pod number and the number of seeds per pod and that water stress imposed prior to harvest was observed to decrease seed weight. Dubetz and Mahalle (1969) also reported that severe stress at flowering resulted in inhibition of subsequent flower formation, but water stress imposed during pod filling resulted in a higher percentage of empty seeds. Harvest time and pod length were not affected. The rate of seed growth decreases under limiting soil 49 water conditions (Spaeth and Sinclair, 1983: Snyder et al., 1982) . Rate and duration of seed growth are important components in determining whole plant yield from the contribution of individual pods and seeds. To improve yield predictions, however, additional information is needed to understand the effect and severity of soil water deficits on the setting, production, and distribution of individual pods along the different plant axes, such as the main stem and branches. The objective of this investigation was to determine the effect of different soil water deficits on flower and pod production and the distribution between the main stem and branches in dry beans. MAIEBIAL§_AHD_MEIHQD§ During the summers of 1988 and 1989, dry bean plants (Ehasggnlns ynlggzis L. cv. Seafarer) were grown in a Spinks soil in a rain shelter at the Kellogg Biological Station near Kalamazoo, MI. A Kalamazoo soil was included in the second year. In 1988, a control and a mid season water deficit treatment (M8) were established in the Spinks soil, The water deficit treatment started 29 DAP at the time of flower initiation. In the second year (1989), a Spinks and Kalamazoo soil were utilized. The mid season deficit began 27 DAP and an additional water deficit treatment (LS) was imposed late in the season (45 DAP) at the beginning of pod filling. The control was well irrigated throughout the growing season in 50 both years. Soil water content for this treatment was maintained close to the drained upper limit of approximately 0.16 cma/cma for the Spinks soil and 0.27 cm"/cma for the Kalamazoo soil (upper 75 cm). Irrigation schedule, soil water contents, and the experiment establishment are described in Chapter 1. During flower initiation, three plants per treatment were tagged and measured for changes in the total number of flowers. Flowers were counted every other day on the main stem and branches. At 40-42 DAP, when flowering reached a maximum in Spinks soil, flower number was determined for each node on the main stem, and the branches of the first 4 nodes. This approach provided a profile of flower and pod distribution along the main axis of the bean plant at different dates during the growing seasons (40 DAP, 1988: 42, 50, 65 DAP, 1989) . Three more plants per treatment were randomly selected in both soils in 1989 to measure the effect of water deficits on pod setting through maturity. The number of pods per plant was counted at 5-day intervals. Dry matter production of individual pods was measured in both soils (1989) during the reproductive period of the bean plants. Thirty pods, about the same age, were tagged in each treatment at the beginning of the pod filling stage. A sample of five pods was harvested at 5-day intervals. Pods were then placed in an oven to dry at 70 °C for 72 hours. After drying, seeds from each pod were removed from the shell and weighed separately. At the end of the season, six plants were sampled 51 in each treatment to calculate an average number of pods per plant. A sub-sample of ten pods was used to determine the number of seeds per pod as well as the weight of individual seeds. The frequency distribution for individual seed weight was estimated for both soils in MS and control treatments. This was accomplished by weighing 100 individual seeds categorized in 0.02 9 increments. For final dry matter production, an area of 4 m2 per plot was harvested. BEEQLIfi Soi1.water'deficits imposed.at flowering time (MS) had an adverse effect on leaf extension and cumulative leaf area (Chapter 1).. In the Spinks soil, the early and mid season deficit treatment slightly hastened flower initiation and decreased the total number of flowers per plant observed in both years (Figures 2.1A and 2.18). Flowering was hastened from 1 to 4 days. Flower number in MS reached a maximum of 26 and 32 (42 DAP) in 1988 and 1989, respectively. In contrast, there were 39 and 44 flowers for the control at 42 and 44 DAP, respectively. The rate of flowering increase was 2.1 and 2.3 for MS and 3.3 and 3.8 flowers/plant/day for the control during the period from flower initiation to pod set in 1988 and 1989, respectively; In the Kalamazoo soil, flower initiation was not affected by the deficit, however total number of flowers in MS was significantly lower than that of the control. In MS, the rate of growth was about 3.5 52 $0 1 1 H g 45" 1988 33 40“ A l l T O 2 35" o/ 1\r/o o O l 3 30" T i 1. 2 1 i , I: ’/ ” RA ' o 20» 1/ / 1 3.12 8 154- T/ / (L '0 10" lg/ / O—O COH‘U'OI E A /.l. .—O mid stress g y-fl A—Awmmm 0 Q 50 1 1; 1 H 1: 45- T T ‘2 1mm 0 7.; a 40-- B l /l\0 (f \ l. E 35“ §,/f T o d. \ g 30 1/0/1 .\T : 25-1- 1 t ‘5 20.. T T/ B ... ...- 1 .2 15 1 O-Ocmmd E 10" O—O mid stress 3 r 7 Z 5“ . é/? so ‘ 1 1 1 1 *’ 45 S " 1989 g\, _. fl r Q 4° C l/1 ?\o a: 351- T L B i/O’?\r ; 30" L ? =3 25» l ‘5 20.. L o 15" i g 10.. /1 0—0 control 3 T é O—O mid stress :2 5“ 7’ 0 Q 1 1 1L 1 30 34 .38 42 46 50 DAP Figure 2.1. Seasonal changes in number of flowers for different water deficits treatments for Spinks (A,B) and Kalamazoo (C) soils. 53 flowers/plant/day as compared to 4.1 flowers/plant/day in the control (Figure 2.1C). For MS treatments in the Spinks soil, the number of flowers was described along the main stem in day 40 and 42 for 1988 and 1989, respectively. This corresponds to the time of maximum flowering. All flowers counted on the first 4 nodes of the main stem were located in branches and these flowers were the most severely affected by the water deficit" In.node number’l, the number of flowers decreased.by 43% and 50% when compared to the control (Figures 2.2A and 2.23). In nodes 2 and 3, flowers decreased by an average of 45%. Above node number 5, all flowers for the MS treatment were found on the main axis and the differences between the two treatments were small. The total number of pods in both soils decreased with time for all treatments, including the control (Figures 2.3A and 2.38). From a maximum of 23 initial pods in the Spinks soil, the irrigated treatment decreased to 16 pods by the end of the season, a decrease of 36% due to pod abortion. Soil water conditions in the late stress treatment caused a rapid decline in the number of pods. Pod number decreased 39% between 50 DAP and 55 DAP. For the MS treatment, a total of 12 pods were counted during pod initiation. Between 55 DAP and 70 DAP, a decrease of about.1 pod/day was observed in this treatment reaching a final number of 6 pods/plant (Figure 2.3A). In the Kalamazoo soil, pod number decreased from.25 to 18 and from 20 to about 13 in the control and MS treatment, respectively (Figures 2.3A and 2.3B). 54 ._.A N ‘ a—n— A 40 DAP, 1988 0—0 control 0—. mid stress a 0 Node number 0) T o l 52 \\\. 2 .1.— .._.-< h—O\—-¢ 1—.—1 1—0-1 o 1 1 1 1 1 12" B 42 DAP.'1939 O—O control L. 10 -- 0Q O—O mid stress (D >0 -0 / / E a-- o o 3 ‘80 C 6..- |—\.—1\kO-1 Q) n—pé—u 'C) / \ O 4 -— 1—‘\—1 *0" 2: h—CP-1 P—43:f‘ \ 2 -- 1—0—1 »——o- Number of flowers Figure 2.2. Distribution of flowers along the main stem in MS and control treatments, on the day when maximum flowers number occurred. 55 4O 1 s 1 1 1 1989 0—0 control .35 '- A 0—0 mid stress A—A lote stress 1— 30 -- Q) Q 75 -- 1 E o 3 20 -- I \ T '8 15 "' 1' A\ f t ‘9 x ‘ A-— A - CL- 1C)"' !’ !l\\\i‘ 4>“‘z§ O\ T I 5 .- * O—O l - 4O : 1 . . 1 1 _ 1.959 0—0 control .35 -- . B 0—0 midstress L 30 ~- 2 1 ‘2 25 J- g 2\é\ T C 20 -- .L \; 9‘9-‘6 ‘0 15 -- .1. \ T I : 0 9‘9“? O. 10 -- 5 .. O 1 5'0 5‘5 6'0 6’5 7‘0 DAP Figure 2.3. Seasonal changes in pod number as affected by different water deficit treatments for Spinks (A) and a Kalamazoo (B) soils during 1989. 56 Pod abortion.occurred mainly in.the branches of the first 4 nodes (Figures 2.4A and 2.4B). For the MS treatment of the Spinks soil, almost 100% of the pods were aborted from node 1 to node 4 between 50 DAP and 65 DAP. From node 5 to node 10, the abortion rate in the same period of time was only 15%, largely pods growing on the main stem. For the control, the decrease in pod number in the first branches was 32%. Duration and rate of seed growth were different for MS as compared to late stress (LS) and control treatments in the Spinks soil (Figure 2.5A). The MS treatment seemed to hasten the initiation of seed growth. Seeds began to grow 3 to 4 days earlier for MS than for LS and the control. Seed growth in MS had an estimated duration of about 12 days with a growing rate of 0.045 g/pod/day. The duration of growth in the control was about 14 days with a growth rate of 0.06 g/pod/day, about 20% greater than the one observed in the MS treatment. Differences in seed dry matter accumulation were not significant between control and LS treatments. During pod elongation, there was significant growth in pod walls. For the MS treatment, the dry matter of pod walls increased at a rate of 0.028 g/pod/day from 50 DAP to 55 DAP and decreased significantly between 55 DAP to 60 DAP (Figure 2.5B). In the Kalamazoo soil, the MS treatment did not hasten the initiation of seed growth when compared to the control, but significantly decreased seed weight per pod at the end of the season (Figure 2.6A). Seed growth rate was 0.05 and 0.06 g/pod/day for MS and control, respectivelyu The dry weight of 57 12 l l l l 1 A 50 DAP O—O control 'Ol-O-l O—O mid stress Nodernnnber 03 i_ o 1 9 O l l l l l ‘2" B 65 DAP O—O control \ \ O—O mid stress Noderuunber O 1 1 I 1 1 l 7 l l I l I 0 2 4 6 8 10 12 Number of pods Figure 2.4. Pod distribution along nodes of the main stem at 50 and 65 DAP for Spinks soil during 1989. 58 1.0 seeds A T pod wdlls B A Q g 0.8 .- / + " O—O control " Q A .—. mid stress } / l A—A late stress O» 0.6- -- .- v ....J -_c .9 0.4-- .- -- g .. 1.): T<8§ §- :3 0'2" , "’ % awg-fi " 9/ s * 0 213/? 1 1 1 A 1 1 1 1 50 55 60 65 7O 50 55 60 65 70 DAP DAP Figure 2.5. Seasonal changes in dry weight of seeds (A) and pods walls (B) for different water deficit treatments for Spinks soil during 1989. 59 the pod wall was lower but not significantly different in MS compared to the control (Figure 2.6B). Seed weight distribution was more affected in the Spinks than in the Kalamazoo soil. The range of seed weight for the MS treatment in the Spinks soil was between 0.04 and 0.18 g/seed with a maximum frequency in the 0.12-0.14 class size. The control had a range between 0.16 and 0.24 g/seed with a maximum frequency in the class size between 0.18 and 0.20 (Figure 2.7). For the Kalamazoo soil, the range of seed weight in MS was between 0.8 and 0.22 g/seed as compared to the 0.14-0.24 range observed in the control treatment (Figure 2.8). Both.treatments had the maximum frequency in the second class size, 0.16-0.18 and 0.18-0.20 g/seed in MS and control, respectively. Pods per plant, seeds per pod, and seed weight were decreased by the soil water deficit treatments in both years (Table 2.1). In the Spinks soil, MS decreased total seed weight by an average of 77% in both years. This is the result of lower seed weight and less seeds/pod and pods/plant. For instance, pod number reached a maximum of 6 and 7 for 1988 and 1989, reflecting a reduction of 40% and 46% compared to their respective controls. The early stress treatment had more pods per plant than MS, reaching a higher total seed weight (1988) . When compared to the control, the MS treatment had 33% and 38% less seeds per pod in the first and second year, respectively. Seed weight was 20% less in MS than in the centrol. The late stress treatment resulted in a lower number of pods/plant and 60 1.0 T - B Cl) pod wolls U 03“ T " Q—O ntrl " 8. 9 .—. gidsctress E o 0.6- -- -- v E .9” 0.4-1 -- -- § 6 1 .>_~ 9 2: <3 1:) 0.2“ ~- - 1 \. *- ./ - 9 O 1 1 1 1 1 1 1 1 1 1 5O 55 60 65 7O 5O 55 6O 65 70 DAP DAP Figure 2.6. Seasonal changes in dry weight of seeds (A) and pod walls (B) for different water deficit treatments for Kalamazoo soil during 1989. 61 Percentage of grain - Mid strns Control 501 40 - 30-” 20 - 10 " fi—I l l I I I -—r 0.12 0.14 0.18 0.18 0.20 0.22 0.24 Grain size class (g/seed) Figure 2.7. Seed weight distribution for different water deficit treatments for Spinks soil during 1989 . 62 Percentage of grain - Mld stress Control 601 2 I / é - ¢ 40- ........... / ................................ é . , // g / g 30‘ .~ ........ Z % -m/ 1/ ¢ ¢ 1/ | ¢ ¢ 15" 5‘ ” .47 :/ . / / r 20-” --.... 1/1 g l g . é ¢ ’ ¢ 1% % ¢ ¢ 1% ¢ .. ¢ 1 ¢ ¢ ¢ ¢ ¢ é / 1°" '¢ ' ¢ -/ ¢ l? 2 lg a o r I I l l 0.18 0.18 0.20 0.22 0.24 Grain size class (g/seed) Figure 2.8. Seed weight distribution for different water deficit treatments for Kalamazoo soil during 1989. 63 Table 2.1. Yield components in dry beans for various soil water deficit conditions. Treatment Pods/Plant Seeds/Pod Seed wt Tot. seed wt ___ _ __ __._-_.____- _ (g) (p/lant) 1988 Spinks Soil Control 15.212.00 4.6:0.40 0.185i0.012 12.93i1.50 Mid 6.4il.60 3.110.32 0.148i0.008 2.93:0.90 stress Early 9.1io.90 2.610.25 0.163i0.009 3.85:0.06 Control 16.1rl.10 4.5:0.23 0.180i0.009 13.04il.90 Late 9.910.90 4.210.41 0.171:0.010 7.11:2.10 stress Mid 5.911.40 3.210.15 0.150r0.006 2.8rl.60 1989 Kalamazoo Soil Control 17.5r1.60 5.1:0.20 0.189:0.07 16.86i1.80 Late 15.411.20 4.710.36 0.178i0.08 12.88i2.60 stress Mid 12.7i1.10 4.510.17 0.172:0.09 9.82:1.20 stress 64 seeds/pod as well as lesser weight per seed than the control. However, the only value significantly different was the number of pods/plant, with.a decrease of 29%. In the Kalamazoo soil, the yield components were lower in LS but not significantly different to those in the control. However, the effect of MS significantly decreased seed weight, seed/pod and pods/plant as compared to the control. Pods/plant was the most affected component, with a reduction of 28% compared to a decrease of 12% and 9% in seeds/pod and seed weight, respectively. The adverse effect of soil water deficits on total seed weight (and hence harvest index) was greater for MS in both soils. Harvest index decreased by 27% and 15% in the Spinks and Kalamazoo soil, respectively. This reduction was lower for E8 and LS treatments (Table 2.2). W Results indicated that soil water influenced the dynamics of flower and pod production. iEarly and mid stress treatments hastened flowering in the Spinks soil. Robins and Domingo (1956) showed.that.plant.development.in dry beans was retarded by stress before blooming and hastened when deficits occurred during flowering and maturity. ES and MS deficits decreased the total number of flowers in the spinks soil. The MS treatment also decreased the number of flowers, though to a less extent, in the Kalamazoo soil. Dubetz and.Mahalle (1969) found that water deficits at flowering resulted in inhibition 65 Table 2.2. Total dry matter, seed yield, and harvest index of 1988 1989 1989 dry beans for various soil water deficit conditions. Soil Spinks. Spinks Kalamazoo Stress — —I=l—===—_==: Total Dry Seed Harvest Treatment Weight Weight Index Kg/ha Control 4868 1850 0.38 Mid 1467 411 0.28 Stress Early 1906 572 0.30 Stress Control 4884 1905 0.39 Late 2776 913 0.33 Stress Mid 1372 398 0.29 W m Control 5821 2387 0.41 Late 4862 1799 0.37 Stress Mid 3428 1201 0.35 66 of subsequent flower formation” In'this study, the inhibition of the formation of new flowers occurred mainly on the branches of the first 4 nodes in the main stem (Spinks soil). Water deficits imposed at the beginning of flowering (MS) induced flower abortion and subsequent lower percentage of pod setting, reducing the total number of pods at the end of the season. Vittum et al. (1963) found that irrigation of snap beans and lima beans increased.the percentage of flowers that set fruits. The adverse effect of water deficits in pod setting was mainly observed in the branches of the bean plant. Results of water deficit treatments imposed prior or during flowering were shown by Robins and Domingo (1956) and Stoker (1974). They found that the total number of pods per plant decreased significantly when deficits began 15 days prior to blooming, but that the greatest decrease was observed with the onset of water deficits at the time of flowering. Soil water retention capacity had a significant effect on the dynamics of flowering and pod setting. For the deficit treatments in the Kalamazoo soil, total number of flowers and pods were less affected than in the Spinks soil. Dubetz and Mashalle (1969) found no changes in flower abscission of bush beans in a fine-textured soil when soil water potential reached values of about -0.8 MPa both before and during flowering. A decrease in seed weight was found to be one of the main effects of late season water deficits (Classen and Shaw, 1970: Couto, 1978; Robins and Domingo, 1956). However, the timing 67 of the deficit may change its effect on a given yield component. In this experiment, the drought stress of the LS treatment began at pod initiation, and although seed weight values were lower than those in the control, the main effect of the deficit was a rapid decrease in pod number. Rate and duration of seed growth are important components in determining its final mass. Growth rate in the irrigated control was greater than that in the MS treatment in both soils, affecting final seed size and seed yield. Water deficits during seed formation have been reported to lower the rate of seed growth resulting in yield reductions (Sionit and Kramer, 1977: Constable and Hearn, 1978). A.longer'duration.of seed growth was also observed in the Spinks soil control as compared to ZMS. However, this measurement was extrapolated from the linear response of seed growth. Difficulties in estimating duration of seed growth have been discussed by Spaeth and Sinclair (1983). Pod length was more restricted by the mid season stress treatment in the Spinks than in the Kalamazoo soil (Chapter 1) . Pod length may have an effect on seed size. Corner (1951) and Duncan et a1. (1978) suggested that pod size determines seed size in legumes and it has been shown that physically restricting fruit size significantly reduces seed size (Egli et al., 1987). The effect of soil water deficits on seeds and pods caused a reduction in the harvest index. It has been shown that patterns of water supply have a large influence on the 68 partitioning of assimilate between seeds and other organs. Bond et al. (1964) observed in sorghum that an adequate water supply until heading, followed by drought, gave a large biomass and small harvest index. The reverse sequence in the supply of water resulted in nearly as much grain with much less biomass. For crops that rely on stored water, the harvest index is highly correlated to the amount of water available after anthesis (Passioura, 1977). W Soil water deficits hastened flowering in the Spinks, but not in the Kalamazoo soil. Deficits decreased the formation of pods and flowers. This effect was mainly observed on the branches growing in the lower 4 nodes of the main stem. Branches, as growing sites for pods and flowers, were more susceptible than the main stem.to the drought conditions. Pod number was the yield component most severely affected by the stress in both years, followed by seed.weight and seed number. Rate of growth was more affected than duration of growth. Harvest index decreased considerably when the deficit began at the time of flowering. More information is needed to understand the effect of water deficits on stem branching and yield production. This may increase the predictive capabilities of the bean model and enhance management practices and genetic programs seeking an improvement of grain yield under drought conditions. LIST OF REFERENCES Begg, J.E. and N. C. Turner. 1976. Crop Water deficits. Adv. Agron. 28:161-217. Bond, J.J., T.J. Army and 0.R. Lehman. 1964. Row spacing, plant population and moisture supply as factors in dryland sorghum production. Agron. J. 56:3-6. Classen, M.M. and R.H. Shaw 1970b. Water deficit effects on corn. II. Grain Components. Agron. J. 62:652-655. Constable, G.A. and A.B. Hearn. 1978. Agronomic and physiological responses of soybean and sorghum crops to water deficits. I. Growth, development and yield. Aust. J. Plant Physiol. 5:159-167. Corner, E.J.H. 1951. The leguminous seed. Phytomorphology 1:117-150. - - Couto, L. 1978. Effects of water stress on growth, reproductive development, dry matter partitioning and yield components of beans (Phageglg§_yulga;1§ L.) in the field. Ph. Diss. University of California, Davis. Dubetz, S. and P.S. Mahalle. 1969. Effect of soil water stress on bush beans W W L. at three stages of growth. J. Am. Soc. Hort Sci. 94:479-481. Duncan, W.G., D.E. McCloud, R.Lu McGrawy and.K.J. Boote. 1978. Physiological aspects of peanut yield improvement. Crop Sci. 18:1015-1020. Egli D.B., R.A. Wiralaga, T. Bustamam, Yu Zhen-Wen, and D.M. TeKrony. 1987. Time of flower opening and seed mass in soybean. Agron. J. 79:697-700. Herrero, M.P. and R.R. Johnson. 1981. Drought stress and its effects on maize reproductive systems. Crop. Sci. 21:105-110. Passioura, J.B. 1977. Grain yield, harvest index, and water use of wheat. J. of Australian Inst. of Agric. Sc. 43:117-121 69 7O Robins, J.S. and C.E. Domingo. 1956. Moisture deficits in relation to the growth and development of dry beans. Agron. J. 48:67-70. Sionit, N., and P.J. Kramer. 1977. effect of water stress during different stages of growth of soybean. Agron. J. 69: 274-277. Snyder, R.L., R.E. Carlson, and R.H. Shaw. 1982. Yield of indeterminate soybeans in response to multiple periods of soil water-stress during reproduction. Agron. J. 74:855-859. Spaeth, S.C. and T.R. Sinclair. 1983. Soybean seed growth. I. Timing of growth of individual seeds. Agron. J. 76:123-127. Spaeth, S.C. and.T.R. Sinclair. 1983. Soybean seed growth. II. Individual seed mass and component compensation. Agron. J. 76:128-133. Stoker, R. 1974. Effect on dwarf beans of water stress at different phases of growth. N.Z.J. Exp. Agric. 2:13-15. Vittum, M.T., R.E. Alderfer, B.E. Janes, C.W. Reynolds, and R.A. Struchtmeyer. 1963. Crop response to irrigation in the Northeast. N.Y., Agr. Exp. Sta., Bull. 800. 1-66. CHAPTER 3 EFFECT OF SOIL WATER DEFICITS ON DRY BEANS (P. W L.) III . STOMATAL CONDUCTANCE , PHOTOSYNTHESIS , LIGHT INTERCEPTION, AND DRY MATTER PRODUCTION. AE§IBAQI Soil water deficits adversely affect light interception, and hence, assimilate production in plant canopies. However, the interaction of factors highly correlated with assimilate production such as leaf area, leaf movement, photosynthesis, etc. is not well understood. The objective of this study was to investigate the effect of soil dehydration on the changes in light interception, photosynthesis, and stomatal conductance as related to the production of dry matter. Research was carried on in the field utilizing a rain shelter facility. A mid season (MS) water deficit treatment began 27 DAP and 29 DAP in 1988 and 1989 respectively. An irrigated control was used for comparison. Stomatal conductance in both years rapidly declined after the onset of the water deficit, remaining significantly lower'than the control for’most.of the dry period. In 1989, midday partial stomatal closure was observed at 42 DAP and 52 DAP. Photosynthetic rates (Pn) were less 71 72 affected by the water deficit than stomatal conductances. Pn rates were lower in MS than in the control at the end of the season and.during stomatal closure. ZLight interception in the MS treatment was decreased during the drought period when compared to the control. Heliotropic leaf movement in MS contributed to the reduction in the diurnal amount of light intercepted, providing the plant with a mechanism to reduce energy load at the same LAI as an irrigated treatment. Dry matter production was closely related to the cumulative intercepted.photosynthetic active radiation (IPAR), although, MS had slightly less biomass than the control at the same IPAR. W Dry matter accumulation in plants is largely a function of net photosynthesis rates and light interception by the canopy. Monteith (1977) showed that with an adequate supply of water, the accumulated interception of light by a wide variety of crops, such as apples, barley, potatoes and sugar beet, was closely related to biomass production. Gallagher and Biscoe (1978) reported that dry matter accumulation in cereals was found to be linearly correlated to the seasonal cumulative light interception at different stages of growth. Leaf expansion, and to some extent assimilation rates, are adversely affected by water deficit conditions. They limit both the amount of light that can be intercepted by the 73 foliage (Monteith, 1965) and the total uptake of carbon dioxide through the stomata (Moldau, 1973: Hall and Schultz, 1980) . Light interception in a plant canopy is largely a function of leaf area (size and. distribution) and leaf movement (Blaine and Baker, 1972). Stomatal closure, on the other hand, has been reported to have a significant effect on photosynthesis during periods of drought stress (O'Toole et al., 1977: Througthon and Slatyer, 1969). However, there is a growing question about the real limitations of a reduction in stomatal conductance on plant dry matter production. After an extensive literature review, Farquhar and Sharkey (1982) concluded that apart from some transient hormonal effects on rapid stomatal closure such.as that of abscisic acid, stomatal conductance is rarely the main cause of the decrease in assimilation rate that may occur with a declining soil water supply. The objective of this experiment was to investigate the effect of soil water deficits on stomatal conductance and photosynthetic rates as well as light interception and dry matter production in dry beans. MAIEBIAL§_AND_MEIHQQ§ A two-year investigation (1988-1989) was carried on at Kellogg Biological Station, near Kalamazoo, MI. Dry bean plants (Phaseolus vulgaris L. cv. Seafarer) were grown in a rain shelter facility in a Spinks sandy soil (Psammentic 74 Hapludalfs). A. mid season 'water’ deficit treatment. was established in both years a few days before the beginning of flowering. Irrigation was halted 27 and 29 days after planting (DAP) in 1988 and 1989, respectively. An irrigated treatment was kept throughout the growing season for comparison. Irrigation schedule, soil water content, weather and other experimental details are described in the Chapter 1. Stomatal conductance and.photosynthesis were measured in the upper leaves of bean plants using an ADC portable open gas exchange system (Analytical Development Company, Haddesdon, UK). Four completely expanded leaves that were fully exposed to solar radiation, were randomly selected in each treatment. The instrument was clamped onto the leaf and exposed to the incoming solar radiation in a perpendicular orientation. Each reading took approximately 30 seconds before reaching a stable value. Measurements were taken between 10 and 12 am EDT for several days. Photosynthesis was calculated as described by Moon and Flore (1986). Light interception was measured in 1989 at about solar noon by evaluation of shaded areas with a meter stick (Adams and Arkin, 1977) . They found that measurements of light interception by this method were closely correlated with those measured by spatial traversing quantum sensors. This procedure was thought to work well because a sunny leaf absorbs about 95% of PAR. Readings of shade accumulation were taken with the meter stick at 7-day intervals from late ‘vegetative stage to 75 maturity. At noon, the meter stick was placed on the soil surface perpendicular to the plant row. The shaded area on the meter stick was measured and summed to the nearest centimeter. Then the stick was moved for repeated measurement along the row covering 1.6 m length at space intervals of 20 cm. The same segment of row in each treatment was used for subsequent measurements. Intercepted photosynthetically active radiation was estimated by taking 48% of the solar radiation as measured near the experimental site (Monteith, 1977). A daily pattern of leaf angle was determined on one day at the beginning of the stress period. A protractor with a small level (5 cm long) attached to it was used.to measure the angle of 10 randomly selected upper leaves. Leaves with a parallel orientation to the soil surface were considered to have zero angle. Leaves, stems, and pods of three plants were harvested.at a 7-day interval throughout the drought period to determine dry matter production. They were separated into paper bags and placed in a forced air oven dryer at 70 °C for 72 hours before weighing. RESULTS Stomatal conductance and photosynthesis. Changes in volumetric soil water content for both years are described in Chapter 1. Stomatal conductances observed 36 DAP were lower 76 in the mid stress treatment (MS) than in the control (Figure 3.1). This difference was also significant at 46 DAP, but not at 55 DAP. In 1989, the water deficit created a similar response to stomatal action. As soon as soil water content decreased in the upper layers, stomatal conductance in MS began to lag behind the control. In 1989 at 42 DAP and 52 DAP, very low stomatal conductances with values less than 0.06 cm/sec were observed in the water deficit treatment. Those two days were hot with.a maximum air temperatures of 30 and 32 °C, respectively. The sharp decrease in stomatal conductance for 42 and 52 DAP had an adverse effect on carbon assimilation. Photosynthesis rates in MS were diminished 60- 80% in comparison to the control. However, the difference lessened toward the end of the season. In 1988, the low values for stomatal conductance were not observed and the difference in photosynthetic rate between the control and MS treatment was significant only at 55 DAP (Figure 3.2). The effect of stomatal conductance on Pn is best depicted in Figure 3.3. For the irrigated treatment, there is an increase of Pn between stomatal apertures of 0.6 and 1.8 cm/sec reaching a maximum of 25.5 mg C02/dm2/hr. Under drought stress, the maximum Pn observed was near 20 mg C02/dm2 /hr. However, photosynthesis was not significantly different between treatments in the range of stomatal conductance from 0.6 to 1.4 cm/sec. The values for MS below 10 mg C02/dm2/hr represent the amount of C02 fixed at the time of near stomatal closure as shown in Figure 3.1. Stomatal Conductance 77 2.0-- control mld stress 1.5-- 1 ,1 < 51.0-- 8, l O 1 1 1 1 . 1r¥1 1"11 1 36 46 55 33 42 52 61 DAP 1988 DAP 1989 Figure 3.1. Stomatal conductances at different days during late stages of growth in MS and control treatments during 1988 and 1989. 78 30 control 25 -- mid stress é .‘2 U) 1: Q G) c -- z 1:20 Si § 4" s \ \ >\\J5-- 3 \ § § W 8‘ \ § \ \ +4 0» \ \ § N 0 E10" \ § \ \ s v t x t 1 CL t 1 t t 5-— § § \ \ \ \ W] E x \ N x \ \ \ O 1 . 1 1 \1 1 t1 1 36 46 55 33 42 52 61 DAP 1988 DAP 1989 Figure 3.2. Photosynthesis rates at different days during late stages of growth in MS and control treatments during 1988 and 1989. 79 30 1988 and 1989 O .(2 25 "- m ’c Q) r: __ _C c} 20 ‘E E .0 U>)\ R 15- o 8 -*-’ m 10- 0 control 8 \E/ '. 0 mid stress 0_ 5__ O O 1 1 1 O 0.5 1.0 1.5 2.0 Stomatal conductance (cm/sec) Figure 3.3. Relationship between stomatal conductance and _photosynthesis rate in MS and control treatments during 1988 and 1989. 80 t t c 'c>. The effect of soil water'deficits on leaf extension is shown in Chapter 1. Leaf area growth rate decreased after the beginning of the drought stress affecting the total amount of light intercepted by the canopy. Light interception for MS lagged behind the control, reaching a maximum of 52% at 46 DAP (Figure 3.4). The maximum mid day light interception in the control was 92% achieved at 53 DAP. After 46 DAP, a rapid decrease in the percentage of light interception was observed in the MS treatment because of leaf senescence. Between 46 and 60 DAP, light interception decreased from 52% to 24%. By the end of the season, interception of light was less than 18% in MS as compared to 76% in the control. Heliotropic leaf movements were also observed in this experiment for both treatments. Leaf angle in the upper leaves of MS increased from less than 10 degrees at 0700 hrs to nearly 62 degrees by noon (Figure 3.5). In the control, a maximum ‘value of 30 degrees 'was observed at 1300 hrs, declining toward the end of the day. These differences in leaf orientation produced a daily pattern of light interception with lowest readings around midday (Figure 3.5A) . The difference in heliotropic leaf movements had an effect on the percentage of light interception between MS and control at approximately the same LAI. .At an LAI of 2.5 the MS treatment was intercepting about 50% of the light at mid day as compared to 60% in the control (Figure 3.6). Dry matter accumulation decreased after the onset of the water deficits (Figure 3.7). 81 1 OO ./-\ 1§H39 T",,gg‘\‘.r 0C, 3? l C)\\\.T v 80 -_ / J. O C: T 1 £2 <3 23. 60-- l 33 T T <1) -_ \ T E 40 _ i/ 1 . "' T % .L l \ T I: 20«- $2 ‘T\\w$ g 1 0—0 control 1 'J _ .—. mid stress 0 1 1 1 1 1 1 1 25 35 59 46 53 ab 63 DAP Figure 3.4. Seasonal changes in light interception at mid day for control and MS treatments during 1989. 82 80 /o\ C: 6C)"’ \\\\ l 0 =5. -/ \ - - Q) - 5” 8 4O * \?\Q/Q/9 .52 9\a/§ .S " LAI = 2.1 E 20 .. O—O control .9 O—0 mid stress _J O t t t t l t l 75‘ - 80 -- Q) g; 1 (1) 60 ~- 1. \T 13 {. \./ T l\\\\ <1) 0 ‘61 4O " i T 3 c: Ox T C3 //’l S?‘\\g;\\\ HP- 7 T .l\\\- C) 2C)"’ ‘. C) 83 <1) é/ED/l l ..J ”'J- O l l l t t t l 7 9 l l 13 15 17 19 EDT Figure 3.5. Diurnal changes of leaf angle and light interception for MS and control treatments at 36 DAP in 1989. 83 100 '- 0 control 3? 90 __ C mid stress v 80 __ 1989 C: ,9 70-- “'5. q) 60-- 8 50-- .3 .9; 4O" E 3O" o .9 20 ~- _J 10‘- O 1 1 1 1 O l 2 3 4 5 Leaf area index Figure 3.6. Relationship between leaf area index and light interception for the control and MS treatments. 84 In 1988, ES had an average growth rate (until maximum growth) of about 0.16 g/plant/day as compared to 0.022 g/plant/day of MS. However, the duration of growth was about a week longer before a decrease in dry matter (64 DAP). In 1989, MS increased at a growth rate 0.24 g/plant/day, compared to 0.33 and 0.40 g/plant/day for' the LS and control treatment, respectively. The relationship between cumulative IPAR and total biomass production is depicted in Figure 3.8. Dry matter production in MS began to lag behind the control after about 100 MJ/m? of cumulative PAR was intercepted. This is when the soil water deficit began to have effect on the MS treatment. DI§§H§§IQH The results indicate that stomata respond to a decrease in soil water content as well as an increase in the evaporative conditions of the atmosphere. Lower stomatal conductances were measured in MS at the beginning of the dry period in both.years and.near stomatal closure was observed in 1989 during days with high air temperature. There is evidence that changing air temperature and humidity affect stomatal movement. Losch (1977) was able to induce stomatal closure in an isolated epidermis by increasing temperature and/or decreasing humidity. In the field, midday stomatal closure has been observed in several crops (Turner and Kramer, 1980). 85 20 T C 0—0 control T O T C .—. mid stress O/1\O .9 A—A early stress T / i J- O' 15» o E 1988 /1 v g T ‘2 10-- L ' T T o ,/ 514:4 E l O 5/ ¥ / * . , .L >‘ , /. / * 9 L. .. .’ ‘T// 13 5‘" -‘/’:,/€> 32' i 6’ ¥ A o /A/é 1— 9x. 0 . 1 1 1 1 1 1 e. 1 ’3 20 ‘_ O—O control _ C .—. mid stress 1’ . , .0. A—A late stress .- /C2“O {1 /9 " cm 15-- 1959 $5) 5.1; T v - \ L T/‘ ‘L 9 as ./Z} :5 1o / 3 " ‘ 6/*\o\. E ; 6/ i J. 9 5 5 - i 6/ i _ - / L g ééé l.— i O 1 1 L 1 1'5. 2'2 2'9 3'6 4‘ 5'0 5'7 6'4 7'1 DAP Figure 3.7. Seasonal changes in dry matter production for different soil water deficits treatments during 1988 and 1989. 86 1989 O—O control 0 0—0 mid stress 0/ I I l L A 350 ‘E \ 300-- 3 C 250-- O ‘5 200-L 3 8 1550-- \— O. (n 100-- U) C E I 50-- .9. GD 0 0 Figure 3.8. so 150 1530 260 250 300 350 Cummulotive IPAR (Md/m2) Relationship between biomass and cumulative intercepted photosynthetic active radiation (IPAR) measured in 1989. 87 In the current experiment, stomata response to atmospheric conditions seems to be occasional and related to days where air temperatures are high. However, the effect of decreasing soil water content seems to affect stomata,for“most of the days where measurements were made. There is evidence from field studies that stomata responses correlate with soil water supply but not with leaf water status (Bates and Hall, 1981) . This independent control of leaf conductance by changes in soil water status was shown by Turner et al. (1985). Gollan et al. (1986) claimed that leaf 'water potential could be substantially changed without altering leaf conductance; however, stomata did temporary close when soil extractable water was depleted by 30%. Gollan et al., (1986) also found that stomata closed when full turgor was maintained in wheat and sunflower leaves while soil dried, suggesting a direct signal from the root to the stoma. Photosynthesis was less affected than stomatal conductance. The largest difference between the control and the MS treatment was observed in 1989 with midday stomatal closure (42 and 52 DAP). For the other days of measurements, the difference between treatments was relatively small. Shultz and Hall (1982) found that with drying soil, stomates of C3 plants generally decreased their aperture prior to changes in their photosynthetic capacity. Wong (1979) found that stomatal conductance adjusted to changes in mesophyll resistance under stress so that variation in internal C02, and hence photosynthesis, is minimized. 88 Interception of radiation was less than the control after the onset of the ‘water' deficit. Light interception ‘was influenced by a rapid decrease in leaf expansion (Chapter 1) and by heliotropic movements observed with the upper leaves of the. bean. canopy; Solar radiation jpenetrated. deeper“ in canopies with a leaf orientation toward the sun such as soybean and dry beans (Lemeur, 1973) . Leaf movement also affects the daily pattern of light interception by increasing leaf angle with respect to the soil surface. The difference in light interception between treatments was greatest around noon. The midday depression of light interception has been shown fer several crops (Shell and Lang, 1976; Blaine and Baker, 1972). This difference in leaf movement is a plant mechanism geared to reduce energy load and allows plants under soil water deficit conditions to intercept less solar radiation at the same LAI than well watered plants. Biomass production was highly correlated to the interception of photosynthetic active radiation by the dry bean canopy (Figure 3.8) . The same relationship has been shown for several crops such as apples, barley, potatoes, sugarbeet, and wheat (Monteith, 1977; Gallagher and Biscoe, 1978). However, when we compare MS and the control in this experiment, there is a small but increasing difference of above ground dry matter accumulation with time at the same percentage of PAR interception. The control produced slightly more dry matter than the MS treatment and this may be due to an increase in the translocation of a assimilates to the root 89 system during periods of water deficits. This effect of water deficit on rapid root growth is shown in Chapter 4. Hoogenboom et al. , (1987) found that during a declining water content, root growth increased at the expense of shoot growth. W Soil water deficits decreased stomatal conductance and to a lesser extent, photosynthesis rate. Light interception was adversely affected by drought conditions, mainly because of a decrease in leaf area expansion growth (Chapter 1), but also because heliotropic leaf movements. Leaf movement in MS decreased light interception at the same LAI than the control. Above ground dry matter production was highly correlated to the amount of PAR intercepted by the plant canopy in both treatments. However, at the same value of IPAR, the MS treatment had slightly lower shoot biomass production as compared to the control, suggesting a possible increase in the translocation of assimilates to the root system. The prediction capabilities of the dry bean model may be improved if we take into account the differential amount of assimilates translocated to the root system during water deficit conditions. LIST OF REFERENCES Adams, J.E. and G.F. Arkin. 1977. A light interception method for measuring row crop ground cover. Soil. Sci. Soc. Am. J. 41:789-792 Bates, L.M., and A.B. Hall. 1981. Stomatal closure with soil water depletion not associated with changes in bulk leaf water status. Oecologia. 50:62-65. Blaine, L.B. and D.S. Baker. 1972. Orientation and distribution of leaves within soybean canopies. Agron. J. 64: 26-29. Farqhuar, G.D. and T.D. Sharkey. 1982. Stomatal conductance and photosynthesis. Ann. Rev. Plant Physiol. 33:317-345. Gallagher, J.M. and P.V. Biscoe. 1978. Radiation absorption, growth and yield of cereals. J. Agric. Sci., Camb. 91:47-60. Gollan, T., Passioura, J.B., and R. Munns. 1986. Soil water status effects the stomatal conductance of fully turgid wheat and sunflower leaves. Aust. J. Plant Physiol. 13:459-464. Gollan, T., N.C. Turner, and.E.D. Schulze. 1985. The responses of stomata and leaf gas exchange to vapor pressure deficits and soil water content III. Oecologia. 65:356-362. Hall, A.B. and E.D. Schulze. 1980. Stomatal response to environment and a possible interrelation between stomatal effects on transpiration and C02 assimilation. Plant, Cell Environ. 3:467-474. Lemeur R. 1973. A method for simulating the direct solar radiation regime in sunflower, jerusalem artichoke, corn and soybean canopies using actual stand structure data. Agri. Met. 12:229-247. Losh, R. 1977. Responses of stomata to environmental factors. Experiments ‘with isolated, epidermal strips of Polypodium yulgarg. I. Temperature and humidity. Oecologia 29:85-97. Moldau H. 1973. Effects of various water regimes on stomatal and mesophyll conductances of bean leaves. Photosynthetica 7: 1-7. 90 91 Monteith, J.L. 1965. Light distribution and photosynthesis in field crops. Ann. Bot. N.S. 29:17-37. Monteith” J.Iu 1977. Climate and efficiency of cropjproduction in Britain. Phil. Trans. Roy. Soc. London, Ser. B. 281:277- 294. Moon, J.W. and J.A. Flore. 1986. A BASIC computer program for calculation of’ photosynthesis, stomatal conductance, and related parameters in an open gas exchange system. Photosynt. Res. 7:269-279. O'Toole, J.C. , J.L. Ozbun, and D.H. Wallace. 1977. Photosynthetic response to water stress in Phaseolus vulgaris. Physiol. Plant. 40:111-114. Schulze, E.D. and A.B. Hall. 1982. Stomatal responses, water loss and C02 assimilation rates of plants in contrasting environments. Encycl. Plant Physiol., Vol 123:181-230. Shell, 6.8. and A.R. Lang. 1976. Movements of sunflower leaves over a 24-H period. Agri. Met. 16:161-170. Troughton, J.H. and R.G. Slatyer. 1969. Plant water status, leaf temperature and the calculated mesophyll resistance to carbon dioxide of cotton leaves. Aust. J. Biol. Sci. 22:815- 827. Turner, N.C. and P.J. Kramer. 1980. Adaptation of plants to water and high temperature stress. Wiley Interscience, New York. pp. 87. Turner, N.C., E.D. Schulze, and T. Gollan. 1985. The response of stomata and leaf gas exchange to vapor pressure deficits and soil water content. II, In the mesophilic herbaceous species Helianthgg anngng. Oecologia 65:348-355. Wong, J.E., I.R. Cowan, and G.D. Farguhar. 1979. Stomatal conductance correlates with photosynthetic capacity. Nature. 282:424-482. CHAPTER 4 EFFECT OF SOIL WATER DEFICITS ON DRY BEANS (P. yglgaris L.) IV. ROOT GROWTH AND WATER EXTRACTION. W Soil water deficits may influence the dynamic of root growth in dry beans. This investigation was performed to study the response of root growth to different terminal drought conditions. Research was conducted in the field using a rain shelter facility. Early (ES) and mid stress (MS) treatments were imposed in 1988. In 1989, the treatments were a MS and a late stress (LS). An irrigated control was used in both years. Root growth was monitored with a system of minirhizotron tubes. Total root length in ES and MS treatments rapidly increased at the onset of the water deficits reaching a peak length of 650 m and 700 m, respectively. The control reached a maximum root growth of about 780 m. Rapid root growth in the upper soil layers occurred when soil water content fell below the drained upper limit. This rapid growth was followed by root death and compensatory root proliferation in deeper layers. Root death was observed when the soil water content approached the lower limit. The 92 93 fraction of water supplied by different soil layers changed with increasing total soil water use. lAfter the initiation of the water deficits, most of the water absorbed (>70%) came from the upper 75 cm of soil, but toward the end of the season there was an increasing fraction of water depleted from lower depths. Total root growth in the control reached greater value than the one in the deficit treatments. IHowever, plants grown under water deficits had more roots in lower depths by the end of the season. INIBQDHQIIQN Roots play an important role in the growth and survival of plants during periods of drought stress (Stypa et al., 1987; Sheriff and Ludlow, 1984). Elongation of primary roots becomes an important factor influencing the framework of future root distribution within the soil profile (Passioura, 1982) as well as plant water uptake, particularly for seedlings growing in a drying soil (Sharp and Davies, 1979). Under"water' deficit. conditions, root. growth. in. the surface soil layers is relatively slow while the growth of new roots in deeper, wetter layers is hastened (Garay and Wilhelm, 1983). Newman (1966) claimed that the total length of flax roots decreased markedly as total soil water potential declined from about -0.2 to -0.7 MPa. Taylor and Klepper (1971) observed a significant decrease of cotton roots in the top part of a drying soil followed by compensatory growth in 94 deeper layers where water was more available. The rapid proliferation of roots observed during drought periods seems to occur at the expense of shoot growth (Hoogenboom et al., 1987). However, the fraction of assimilates partitioned to the root system is not a constant value, but varies with the stage of plant growth and the severity of the water deficit (Smucker, 1984). Progressive soil dehydration influences the changes in rooting pattern growth, thus affecting the amount and timing of water availability (Ludlow and.Muchow, 1989: Nunez-Barrios et al., 1991). However, the dynamic nature of root growth and the timing of the water deficit at different phenological stages is not well understood. The objective of this investigation was to study the dynamics of root growth and water extraction in dry beans under terminal drought conditions including’an.earlyy mid, and late season soil water deficit. MAIEBIAL§_AND_NEIHQD§ A field study was conducted at the Kellogg Biological Station, near Kalamazoo, MI. A rain shelter facility was utilized to control the water regimes for the different treatments. The soil was a Spinks sandy soil with an average drained upper limit (DUL) of about 0.16 cm3/cm3. A dry bean variety was planted on July 8, 1988 and June 12, 1989. Early season (ES) and mid season (MS) water deficit treatments were 95 established in 1988, beginning at 15 and 29 days after planting (DAP), respectively. In 1989, the. MS and LS treatments began 27 DAP and 45 DAP, respectively. Soil water content was monitored for the control and the water deficit treatments using a neutron probe technique. Experimental establishment, irrigation schedule, and soil water contents are described in Chapter 1. A system of non-destructive minirhizotron plastic tubes (5 cm ID) were set in place to determine root growth at multiple depths. Establishment was done by hand using an auger with a diameter similar to that of the minirhizotron 'tube. The hole was augured at a 45 degree angle with respect to the soil surface. After the soil cores were removed, the cavity was cleaned up with a steel brush and tubes were installed by pushing them into the soil. Three replications were used in each treatment. Observations of roots intercepting the minirhizotron tubes were recorded on video tape using a video camera. The camera was lowered into the tube until the deepest observable root appeared intercepting the minirihzotron tube and the camera was then pulled up at equal space intervals (1.2 cm) until reaching the soil surface. Root growth was monitored by recording the number of roots intercepting the upper surface of the minirhizotron tube. The counts were independent of the length or the diameter of the root at the interface. Root counts were converted to root length densities using the equation 96 described by Upchurch and Ritchie (1983): RLD = Nd/Ad where N is the number of intersecting roots, d the outside tube diameter, and A the area of the tube observed. The assumption was that growing roots intersect the tube at various angles with equal probability and the average length of root displaced.by the tube if the roots could continue grow at the angle of the interception, was equal to the tube outside diameter. Each root interception then corresponds to a root length of d, therefore the total root length displaced is Nd. The volume associated with this length is Ad. Root growth was recorded at 26, 42, and 58 DAP in 1988 and at 28, 42, and 59 DAP in 1989 in the Spinks soil. BE§HLI§ During the summers of 1988 and 1989, dry bean plants were subjected to soil water deficits at different stages of phenological development. Irrigation ceased 15 and 29 DAP in 1988 and 27 and 45 DAP in 1989, initiating terminal drought for ES, MS, and LS treatments. Soil water content details are provided in Chapter 1. Total root length at 26 DAP was greater for the Es :tzreatment than for MS or the control (Figure 4.1A). From 26 51:) 42 DAP, MS had a greater growth than ES and the control. Totolrootlength Totolrootlength Figure 4. 1. 97 ‘ l 50-- J i/ i s l 1 <1 E 40 -- l / l 9 3 § O—O control 20 " .—. mid stress A—A eorly stress 0 1 1 1 T 6‘ o 1 l 50‘- ‘ T <3 1 40.- l 3 O—0 control 20 " l O—. mid stress A—A lote stress 0 1 re 1 O 20 4O 60 DAP Total root length in the soil profile for different water deficit treatments. Arrows show the beginning of water deficits during 1988 and 1989. 98 Total root length in MS increased at a rate of 25 m/day as compared to 7 m/day and 10 m/day in ES and control, respectively. At 42 DAP, root death or turnover was observed in ES and MS. However, the roots in the irrigated treatment continued to grow at a rate of 23 m/day. In 1989, the results were similar for the MS treatment (Figure 4.1B). From 28 to 42 DAP, plants in MS experienced an increase in root.growth of 27 m/day. From 42 to 59 DAP total root growth in MS had a significant decrease due to root death. The LS treatment also had decreased root length. Meanwhile the control continued to grow until the last day of readings (59 DAP) . The rapid increase in total root growth in the ES and MS treatments was consistently observed after the onset of the soil water deficit. Root distribution within the soil profile was affected by the water regimes. In 1988, maximum root growth in the control was observed at.a depth of 20-40 cm (Figure 4.2A). In this treatment, roots continued to grow in most of the profile until 58 DAP. For MS, maximum growth in the upper 40 cm of soil was achieved 42 DAP (Figure 4.2B), 13 days after the initiation of the water deficit. At 50 DAP, there was rapid death in the upper region of the soil followed.by compensatory root growth below the 60 cm depth. Similar changes in root growth were observed in ES (Figure 4.2C). Changes of root growth in the upper 70 cm between 26 and 42 DAP were not significant for E3. There was however, a significant decrease in root density at the same depth from 42 to 58 DAP. 99 Raatlengflidenshy (cm/cm3) O (15 ‘L0 L5 20 2J5 £10 0 ' ‘ ' ' ' I ' r - Ar . .\ 1 A . J E I )— ' <3 -40-- v v _C - 3 i a -50- -’ 3 -. control ... - o- °:° g g” '5 8 - :....: 111 (D ' . —100-- -120 : 1 1 1 1 1 Mid stress -20.. 1 B /"\ E 3, ~40- J: '5. -50- o O .-.-_ -80 O U? -100 -120 3 + . i . i ‘r i : i c " earl stress _20" \ YC A ‘ E 1 ~59 ‘40“ v" _C 1" *5- _60__ A m C3 ___ -so‘ 0 U7 —100«- —120 r i l Figure 4.2. Root length density for three dates in the Spinks soil for different soil water regimes in 1988 100 In 1989, roots in the irrigated treatment continued to grow during the growing season in most of the soil profile until 59 DAP (Figure 4.3A). Roots in the MS and LS treatments began to die in the upper layers between 42 and 59 DAP, followed by compensatory root growth at lower depths (Figures 4.3B and 4.3C). Changes in root length density are better depicted in Figures 4.4 and 4.5. Root death between 42 and 58 DAP was low in the control (Figure 4.4A) . Root death in the control treatments was mainly observed in the upper 20 cm of soil. In MS, root death in the upper 50 cm was greater than the one observed in ES and control treatments. This rapid root death in the water deficit treatments occurred when water content in the top regions of the soil neared the lower limits of soil water availability. Root death in MS was also greater than the one observed in the LS treatment (Figures 4.5B and 4.5C). Soil water' content after’ the onset. of the drought decreased rapidly in the top 20 cm, followed by a slower decline at 60 and 100 cm depths (Figures 4.6 and 4.7). In the ES treatment, soil water content began to decrease 15 DAP, with a resulting rapid response in root growth (Figure 4.6A). At a depth of 20 cm, root growth reached a value of 1.0 cm/cm3 at 26 DAP, followed by rapid root death when the soil water content was near 0.07 cm3/cm3. The rate of root growth decreased at 20 cm depth between 26-42 DAP, followed by a rapid increase observed at the 60 cm depth (Figure 4.6B). When root growth rate began to decrease at the 60 cm depth, a 101 Rootlength densky (cm/cm ) 0 0.5 1.0 1.5 2.0 2.5 3.0 0 1 1 N 1989 E t—OHQ—I r——A U —40 ~- r-—O/—4 \b—.—d \h—‘fi *" 60 \o \o A] D. — '1- U- -C -—d —( g —?—éO¢l/v—/A/ — “80"“ ‘7 :-2 221s ._ — 4 O "’7‘“ A—A 59 DAP U7 —100--1-lA-' 1—‘—o —120 1 1 1 1 /_\ _20. late stress E \9/ —40- E. Q -50- 8 _ -80- '5 (f) -100‘ -120 ' = = nfid stress /'\ -20 " ”EC-4x \—' E o—O-o—A—c |-—.—4 C 0 \ I / V -40-- v—e—A: -—o———+ _C r-O-I —‘ .—" / .5— —60-—O+.XIA—O Q) |—.-—1 t—-‘——l Q -80~-o/-o '—\A—' 1: /’ U0) |—-l‘—0 -1oo-- —A—' 1—‘—/ -120 Figure 4.3. Root length density for three dates in the Spinks soil for different soil water regimes in 1989 102 Root change rate (cm/ems) -2.0 -1.5 -‘|.0 -0.5 0 D 2 5 1 . 06 ... .... .. 80808080909: ,. ’0 "O o’o . O o 0 0’0... ’9 0'0 9' D D w .05 ‘0 o o 9 9 9'9 0 o‘c‘o’o’o’o’ofifl 0". one 000 006 900 090 000 00. 000 000 090 000 9'0 000 O a o r 900 .9 o 0 s .0. S .0, 3 . . P P M 3M. . W A my. A 1- 1 l D l r 0 1 a D o t 8 8 8 u no. 5 5 W, 5 a m _ w L. m L. 1 1 N. c M. 1 m 4 e 4 n n w u u u u u u “ u a u u u 0 0 0 0 O 0 O U 0 0 0 0 0 0 0 0 0 O m 4 6 8 0 2 2 4 6 8 0 2 2 4 6 8 0 2 _ _ _ _ ..I ._1 _ _ _ _ 4.1 ..I _ _ _ _ ..1 ..1 A88 £80 :8 A88 £85 :8 A88 £95 :8 t treatments and soil t growth between 42 and 58 DAP lCl in roo for different water def depths during 1988. Changes Figure 4.4. 103 Root change rate (cm/cm 62.0 -1.5 -i.0 -0.5 0 0.5 1.0 1.5 2.0 J l 1989 -20.. 999 9999 9'. ’9’9‘9‘93’93‘99c _40 -_ -50 ._ I 0) O L I control -1 00 -- 42—59 DAP Soil Depth (cm) —120 t ‘1 -20 .. -40 .. -50-- .......‘..'C - 80 - - ..O...........‘.O?‘ 99 999'99'999'99‘9 99991 9’9‘9‘9’999.9.1.9”’9’9’9’9’9’9’9’4 late stress -100-— 42—59 DAP Soil Depth (cm) 9 9 9 9'99 9'9 9" 9’9‘9’9‘9’9’9‘9’95 -120 l 1 l 9 9'9 9 9 9 9 9 9 4 9.39.39.39.39" "O...’......O....I 1'9’9’9‘9.9.9’9'9'9’9’9’9’9’9'9'9‘9'4 -20 .. 99999999999999". '9'9'9.9.9.9R’o’9’9’9’9’9’9‘9’9’a «9999999991 ’9’9’9’9’9’9‘9’9’9’9‘4 -40 .. '9 9 9 9 9'9 91 ’9’9’9’9’9‘9’9’: -50 .- -30 .. mid stress —100~- 42-590AP Soil Depth (cm) —120 l t ‘ l 1 1 i . Figure 4.5. Changes in root growth between 42 and 59 DAP for different water deficit treatments and soil depths during 1989. (120 c 1 1 1 v, 17? A early stress "1'5 E 20cm 0 .1 .. 1} ° 5 a E -1 02 8, 0.10» § . s 3 3 0 1~05 (,1 3 0.05- V '5 U) (120 1 1 1 - 0 A -- N) 8 L5 E 60cm 0 l \ 0.15 E ”E «1 02 3 0.101- (33 L E *3 .5 3 un- . U 3 0.05» V '6 (fl (120 +* 1 e7 17 O .r\ «-L5 ,3 C E 100cm 0 db \ 0.15 m l") 1 O E E s 3 0.10» 3 5 8 44 3 o "0.5 (,4 3 0.05» V '5 (f) O 1 1 e 1 1.. 1 1 1 O 0 20 40 60 80 DAP Figure 4.6. Dynamics of root density (RLD) and soil water content at 20, 60 and 100 cm depth in the ES treatment during 1988. 105 (120 1 1 1 1 . 1 - g;‘ A rTfid stress ’1'5 E 20 cm 0 0.15-- \ I) n '6 g ’5‘ ~\/ 0A01- :1 g o B 3 O U 3 0.05 1- V "5 00 020 1 1 1 1 1 1* 1 05 A "1. N) B E 60 cm 0 O.15«~ \ g PO _1 O O E ”a \‘L 0.10-- 3 g \ m 0 4a 3 0 +0.55 (,1 3 0.05-- V '5 U3 0.20 1 1 1 1 1 1 1 $5 A 4- N) C E 100 cm 0 O.15~- \\. g2 7") _1 0 C7 8 6‘ ii o.10«- i a 0 .... 3 0 "0.5g 3 0.051- '6 (f) O t 1 1 1' ¢ i i O O 20 4O 60 80 DAP Figure 4.7. Dynamics of root density (RLD) and soil water content at 20, 60 and 100 cm depth, in the MS treatment during 1989. 106 rapid expansion of root growth was observed at 100 cm depth (Figure 4.60). For the MS treatment, the root response to declining soil water content in different layers was similar to that in ES. When water depletion began in the top 20 cm of soil, a rapid increase of root growth was observed (Figure 4.7A). Between 28 DAP and 42 DAP, root growth reached a density of 1.51 cm/cm3. When roots began to die at 20 cm, a surge of root growth (0.97 cm/cm3) was observed at 60 cm (Figure 4.78). At 42 DAP, soil water content at 20 and.60 cm was approaching the lower limits of plant available wateru .At this time, roots at a depth of 100 cm started to grow reaching values of 0.7 cm/cm3 at 59 DAP. The increase in root proliferation in deeper layers, as soil at upper layers dried out influenced the fraction of water absorbed in each layer. In the ES treatment (1988), more than 40% of the water uptake between 15 and 29 DAP came from the upper 25 cm (Figure 4.8A). From 29 to 43 DAP, the fraction of water absorption decreased in the top 25 cm and increased in the 50 cm layer. Toward the end of the season, increases in.the fractions of“water extracted.were observed in depths below 100 cm, coinciding'with.a1concomitant increase in root growth. Water extracted in depths of 125 and 150 cm began increasing 57 DAP. In the MS treatment, water was mostly absorbed from the upper'75 cm two weeks after the onset of the water deficit. Between 57 DAP and 71 DAP, more than 60% of the water absorbed came from depths below 100 cm 107 c eorw sUess o S \o .8 0-4“ \ depth 0 5 0 3 / +4 ' "1.———«. O . 10 3 W O/ i /e ‘9 -- / 5 >55 / Lt lkfiagé!4:_:_;__. 0" I i i .5 rnid stress E- 0.5 -- -. a o "’ 0.4.-. . O L /.\ .95) 03" /. /A 100 3 1. /ll150 C 0.2-- D125 .9 a/A:Af§E 0 OJ-- (A u. 0 1 1 15 22 29 56 DAP0 Figure 4.8. Fraction of the total water absorption for different soil layers in ES and MS in Spinks soil during 1988. 108 (Figure 4.88). Similar patterns of water extraction per soil layer“were observed.in the deficit.treatments of 1989 (Figures 4.9A and 4.98). For the MS treatment, more than 70% of the water'was absorbed from the upper 50 cm.a*week.after the onset of the deficit. However, toward the end of the season these two depths contributed less than 20% to the total water extraction. Plants were absorbing water from layers below 100 cm depth. 0159055193 Results indicated that soil water deficits influenced the dynamics and. spatial distribution. of roots in. the soil profiles for both years of study. Rapid root growth was observed for the ES and MS treatments in the upper layers of the soil at the beginning of decreasing soil water contents. Sharp and Davies (1979) found that plants growing in a drying soil exhibited a greater net increase in root growth when compared to plants growing in soil regularly supplied with water. This phenomenon was shown in both dry weight and root length. Hoogenboom et al. (1987) found that a period of drought stress during vegetative development caused a marked increase in root growth rate of non-irrigated soybean plants. After the first response of rapid root growth with declining soil water, roots began to die when plant available water in the upper soil reached values near the lower limit. Compensatory growth of new roots in deeper, wetter layers was 109 g rnid stress a 0.5 ._ 1989 S O A “O _‘é 0 4~- \ L O depth 3 0 3 -- ./O\ 0 .--—~-* 0 a 100 3 A 125 8 O 2 "" . A 75 '4: 4:A/-‘*’§/ I 150 8 01" “ ///E] II :8 L: E]-——E}-1I/”llfl—— o - 1 1 1 1 8 late stress "a 0.5 -- B ‘6 ‘3 0.4-- 0‘0 0 5 o 3 ./.\O E? 100 3 0 2 a 125 g ' " 75 .. A——g,...r—§ 21 E 0.1 " a/ /I/ 150 L“ l;i{_1__.__ 0 : - . 1 - Figure 4.9. Fraction of the total water absorption for different soil layers in MS and LS in Spinks soil during 1989. 110 observed. for all water' deficit treatments, suggesting a significant effect of soil water'in.the reallocation of1carbon in the soil profile. Lang and Thorpe (1986) found that under drought stress, portions of the plant with the lowest water potential attracted most of the assimilates. At the end of the season in both years, more total roots were observed in the irrigated treatments. These observations coincided with the ones shown by Robertson et al. (1980) . They found that total root length was greater for irrigated treatments, although non-irrigated.plants produced more roots in the deeper part of the soil profile. Arya et a1. (1975) reported that under field conditions, where rewatering occurred after a water deficit, most of the root mass was found in the upper soil layers for both irrigated and non- irrigated treatments. Root death was greater for the MS treatment than for 88 and LS. Plants in the MS treatment also experienced a rapid decline in leaf area (Chapter 1) caused by a rapid senescence rate. In dry beans, leaf senescence usually begins from the bottom to the top nodes in the plant. Waters et al. (1980), using radioactive 1‘COZ, found that during flowering in dry beans more than 45% of the carbon fixed in the leaves of the first nodes was recovered in the root system. Upper leaves translocated more than 85% to the pods during the pod filling stage. However, the fraction of photosynthetically derived carbohydrates partitioned into the roots is not a constant value (Smucker, 1984) but varies with the timing and severity 111 of the drought experienced by the plant. Changes in root growth differentially affected the amount of water being extracted at different depths. In the ES treatment, water uptake from the bottom layers was postponed until the last part of the season, reflecting a conservation in water use allowing the plant to survive and produce some yield during the long dry spell. Plants in the MS treatment, because of their larger size, rapidly depleted the water available in the upper portions of the soil. They began water uptake from.below a 1 m depth at least a week before those in ES. This rapid.water absorption from lower depths in the soil indicated a lower adaptation process in the plants of the MS treatment as well as a possible slower downward root growth in, the plants of E8. Ludlow and Muchow (1989) reported that changes in rooting patterns at different stages of growth affected the amount and timing of water availability in the soil profile. The increase in root growth was closely coupled to the decrease in the rate of shoot growth. This type of plant adaptation to water deficits has been shown to help maintain absorption of sufficient water to meet the evaporative demand (Huck et al., 1983). CONCLUSIONS Soil water regime affected the dynamics of root growth and root distribution within the soil profile. Total root 112 growth at the end of the season was greater in the control than in ES, MS, and LS, however, these deficit treatments produced more roots in deeper soil layers“ Roots in the upper regions of the soil increased rapidly in response to a decrease in soil water content and died shortly thereafter. Rooting patterns affected the amount and timing of water extraction in different soil depths. For the ES treatment, the differential water extraction suggests a conservative approach to water use where the available water in the lower regions of the soil was only used at the end of the season during the seed filling stage. The MS treatments had the highest rate of root death which largely coincided with the rapid senescence rate observed in leaves. The description of shoot conditions, in terms of leaf area, is important in explaining the rooting patterns of plants undergoing water deficit conditions. REFERENCES Arya, L.M., G.R. Blake, and D.A. Farrell. 1975. A field study of soil water depletion pattern in presence of growing soybeans roots III. Rooting characteristics and root extraction of soil water. Soil Sci. Am. Proc. 39:437-444. Garay, A.F., and. ‘W.W. ‘Wilhelm. 1983. Root system characteristics of two soybeans isolines undergoing water stress conditions. Agron. J. 75:973-977. Hoogenboom G., M.G. Huck, and C.M. Peterson. 1987. Root growth rate of soybean as affected by drought stress. Agron. J. 79: 607-614. Huck, M.G., K. Ishihara, C.M. Peterson, and.T.'Ushijima. 1983. Soybean adaptation to water stress at selected stages of growth. Plant Physiol. 73:422-437. Lang, A., and M.R. Thorpe. 1986. Water potential, translocation, and assimilate partitioning. J. Exp. Bot. 37: 495-503. Ludlow, M.M., and R.C. Muchow. 1989. A critical evaluation of traits for improving crop yields in water-limited environments. Agronomy 43:107-153. Newman, 8.1. 1966. Relations between root growth of flax (him WM) and soil water potential. New Phytol. 68: 273-293. Nunez-Barrios, A., J.T. Ritchie, A.J.M. Smucker, and D.S. NeSmith. 1991. Soil water deficits and the root dynamics of maize (Zea mays L.) in late growth stages. In review. Passioura, J.8. 1982. Roots and drought resistance. Agric. Water Mgmt. 7:265-280. Robertson, W.R., L.C. Hammond, J.T. Johnson, and R.J. Boote. 1980. Effects of plant water stress on root distribution of corn, soybeans, and peanuts in sandy soil. Agron. J. 72:548- 550. 113 114 Sharp, R.E. and W.J. Davies. 1979. Solute regulation and growth by roots and shoots of water-stressed maize plants Planta 147:43-49. Sheriff, D.W. and M.M. Ludlow. 1984. Physiological reactions to an imposed drought by Macroptil 1' gm atropugpureum and anghrug 91111115 in a mixed sward. Aust. J. Plant. Physiol. 11:23-34. Smucker, A.J.M. 1984. Carbon utilization and losses by plant root system. In Roots Nutrients, Water Influx, and Plant Growth. Barber S.A. and Bouldin D.R., pp. 27-46. Spec. Pub. 49. American Society of Agron., Madison, WI. Stypa M., A. Nunez-Barrios, D.A. Barry, M.M. Miller, and W.A. Mitchell. 1987. Effects of subsoil bulk density, nutrient availability and soil moisture on corn root on corn root growth in the field. Can. J. Soil Sci. 67:293-308. Taylor, H.M. and 8. Klepper. 1971. Water uptake by cotton roots during a drying cycle. Aust. J. Biol. Sci. 24:853-859. Waters, L., P.J. Breen, and H.J. Mack. 1980. Translocation of 14C-Photosynthate, carbohydrate content and.nitrogen fixation in Enasgglgfi yglggzifi L. during reproductive development. J. Amer. Soc. Hort. Sci. 105:424-427. SUMMARY AND CONCLUSIONS The objective of this investigation was to study under field conditions the effect of water deficits on dry beans at different stages of growth. The results obtained from these experiments indicate that soil dehydration hastened flowering and seed filling stages while delaying leaf appearance. This seems to be a plant mechanism related to earliness, which under drought conditions, is associated with a reduced vegetative phase. Water deficits diminished leaf, internode, and pod expansion growth resulting in a small plant size. Reduced leaf growth and accelerated leaf senescence were a common response to the drought conditions and combined to decrease leaf area. Changes in leaf area appear to be one of the main means by which dry bean plants adapt to a declining soil water availability. This response enhances survival by conserving water as observed in ES and MS treatments. However, this mechanism was detrimental to yield because of the decrease in light interception when LAI was below 3. Organ expansion and LAI were more affected in sandy soil than in loamy soil. Paraheliotropic leaf movement decreased the interception of solar radiation per unit leaf area between treatments. Under terminal stress conditions, these paraheliotropic 115 116 movements may enhance yield by reducing the energy load on the plant and hence the rate of water loss. This allows the crop to have more water available during late stages of growth such as flowering and/or seed formation. Excess production of flowers and pods was observed for all treatments, assuring that the plants had enough reproductive structures to cope with the uncertainties of the environment. Flower and pod abscision was greater in the MS and LS treatments. Organ shedding appears to be a wasteful process because of the loss of carbon. Under water deficits the plant priority seems to be focused on having fewer pods with more viable seeds at the end of the season. Flower and pod abscision occurred mainly in the plant branches indicating higher priority for the reproductive structures growing on the main stem. Photosynthesis rate was reduced to a lesser extent than stomatal conductance in the MS treatment. Stomata remained “partially open during progressive soil dehydration, with observable midday closures occurring mainly when the temperature and the atmospheric demand for water was high. The main response to reduced stomatal conductance in the field seems to be the avoidance of plant desiccation. Above ground dry matter production was linearly related to the intercepted PAR. However, the efficiency of energy conversion was slightly lower for the deficit treatments as compared to the control. This suggests that there is an increase in the allocation of assimilates to the root system 117 with a decreasing soil water content. Further investigation is needed to determine the dynamics of carbon allocation in the root/shoot system with advancing soil dehydration. This information is needed to better model dry bean production under deficit conditions. A rapid response in root growth was observed shortly after the onset of the water deficit treatments. Root proliferation increased root density, allowing the plant to continue water absorption from the upper soil layers. As soon as the soil water’content.approached.the lower limits of plant available water in the top regions of the soil profile, root death rapidly occurred followed by compensatory growth in deeper, wetter layers. Differences in the rooting patterns changed the amount and timing of water extraction at different soil depths. For example, the plants in the ES treatment managed to have a conservative strategy for water absorption. They used most of the water in the upper soil profile at the beginning of the deficit, leaving the water available in deeper layers to be used later in the season to complete the seed filling stage. Rapid expansion of root growth was observed during soil dehydration and coincided with a decrease in leaf elongation as well as with a partial decline in stomatal conductance. This suggests that root proliferation (more root branches and root tips) results in some type of communication between root and shoot. More research is needed to describe the effect of the root-to-shoot signals on the whole plant carbon balance 118 under field conditions. The main conclusions drawn from this investigation may be summarized in terms of the duration and rate of growth under soil water deficits. v o e ° Water deficits hastened flowering and seed filling, reducing the vegetative phase. This phenomenon lowered water requirements allowing the plant to reach maturity with a limited supply of water. Production of new leaves, internodes, flowers, and pods decreased with soil dehydration. The duration of leaf growth and internode elongation was not affected as much as the growth rate of these organs. EIQEED_I§§§1 Leaf growth and flower and pod production were more affected on branches than on main stem during acclimation of the dry beans to water deficits, indicating a priority for the plant to allocate resources in the main stem. Leaf size, leaf senescence, and leaf paraheliotropic movements greatly influenced light interception and water absorption. In the water deficit treatments, stomata seemed to have little control on photosynthesis rates and on total crop evapotranspiration. . Plants under increasing soil dehydration may conserve soil water through two means: a) extracting water more slowly as 119 the soil water approached LL in the upper soil layers and b) changing the dynamics of root.growth.in the soil profile to use available water from deeper depths at late stages of growth. 8. Plants showed.evidence of stress in the sandy soil as early as five days after the onset of the deficit when much of the available water was still in the soil. Roots expanded rapidly, apparently because the water could not move fast enough to the existing root system. The rapid expansion increased the total root surface bringing roots to a closer proximity with the water, especially when the rate of absorption was fast. 9. Roots death occurred when soil water content reached the LL, allowing plants to increase the growth of new roots in deeper layers where water was more available. 10. Dynamics of root growth patterns during soil dehydration implied a greater partitioning of assimilates to the root system at the expense of shoot growth and yield. 11. There is no simple solution to improve yield of dry beans under drought conditions. Defining the physical environment and matching phenology and plant growth to the patterns of water supply is one of the first steps to maximize water availability and yield. 12. The use of simulation models will provide a tool for integrating the information collected in the field under different drought scenarios. Models facilitate the 120 decision making process for the selection and improvement of varieties as well as for the use of management.practices directed at optimizing the water availability during the growing season. 8W Based on the experience acquired through the conduction of this investigation, a further understanding of the plant response to water deficits may be obtained by: 1. Quantifying the partitioning of assimilates to the root system using radioactive isotopes such as 1"C02. This is an expensive and cumbersome goal to achieve under field conditions but it will provide a whole carbon balance needed to better understand the system. 2. Estimations of ET based on the neutron probe data seemed biased, primarily because the inaccurate readings near the soil surface. The use of more appropiate instruments such us TDR may help to improve ET estimations. 3. Although stomata did not have much effect on photosynthesis and ET in this investigation, more measurements describing the diurnal cycles of stomatal conductance may provide a better understanding of the role of stomatal action on plant productivity under drought conditions. APPENDICES Appendix 1. Description of the soil profile for Spinks and Kalamazoo soils. Kalamazoo soil Spinks soil Ap. 0-11 inches: light brownish gray (day): weak medium granular structure: friable 81. 11-16 inches: dark yellowish brown: weak medium subangular blocky structure: friable. 821t. 16-20 inches: dark yellowish brown clay loam: moderate medium subangular blocky structure. 822t. 20-30 inches: dark brown clay loam: same structure than 821t: 1% pebbles. 823t. 30-38 inches: dark yellowish brown: sandy loam with clay films: medium acid. IIB31. 38-60 inches: dark yellowish brown: loamy coarse sand: massive friable: medium acid. Ap. 0-10 inches: dark brown loamy sand: weak fine granular structure: very friable: slightly acid. A21. 10-16 inches: dark yellowish brown: loamy sand: weak coarse subangular blocky structure, friable, slightly acid. A22. 16-28 inches: yellowish brown loamy sand: very friable: 3% pebbles: neutral. A88. 20-86 inches: yellowish brown sand single grained: massive very friable: 1% pebbles: neutral 121 Appendix 2. Weather data for the 1988 growing season at the Kellogg Biological Station. Air High Air Low Air Mean Solar Day of Temp. Temp. Temp. Radiation Year Mo. Day (°C) (°C) (°C) (MJ m“) 112 April 21 9.78 -3.92 2.93 21.27 113 April 22 15.71 0.33 7.30 22.95 114 April 23 14.97 1.84 5.60 6.97 115 April 24 10.98 1.58 5.18 20.57 116 April 25 16.63 -3.41 7.93 23.79 117 April 26 16.95 5.34 10.90 16.47 118 April 27 10.25 2.50 4.53 4.56 119 April 28 13.60 2.22 6.91 22.50 120 April 29 17.28 1.13 8.48 25.33 121 April 30 20.44 2.46 11.35 27.28 122 May 1 22.40 1.05 12.61 27.81 123 May 2 23.38 4.02 14.58 28.15 124 May 3 18.99 4.31 11.63 20.44 125 May 4 19.39 1.75 10.70 23.08 126 May 5 22.01 4.35 13.17 21.77 127 May 6 26.31 5.43 16.47 28.21 128 May 7 25.64 6.58 16.55 23.26 129 May 8 27.50 13.13 18.94 19.68 130 May 9 18.14 11.43 13.67 13.38 131 May 10 15.04 7.98 12.31 9.16 132 May 11 20.78 1.47 11.58 28.87 133 May 12 24.02 8.49 16.23 20.68 134 May 13 19.43 8.61 15.45 28.46 135 May 14 23.87 4.16 14.04 28.51 136 May 15 26.82 11.57 16.97 12.89 137 May 16 18.88 9.92 14.11 26.37 138 May 17 21.49 8.33 13.37 25.18 139 May 18 24.84 5.96 15.27 28.88 140 May 19 24.81 7.43 16.16 21.59 141 May 20 26.16 13.20 18.47 20.75 142 May .21 27.68 13.85 19.77 18.43 143 May 22 31.64 11.99 22.31 25.61 144 May 23 20.75 16.15 17.56 5.26 145 May 24 21.18 5.96 14.83 28.00 146 May 25 18.81 1.41 9.53 30.21 147 May 26 24.11 2.36 14.52 29.82 148 May 27 27.50 11.51 19.74 29.09 122 123 Appendix 2 (cont.) Air High Air Low Air Mean Solar Day of Temp. Temp. Temp.- Radiation Year Mo . Day (°C) (°C) (°C) (MJ m'z) 149 May 28 29.83 10.77 20.63 22.92 150 May 29 31.06 14.59 22.74 28.17 151 May 30 31.58 12.31 22.56 27.83 152 May 3;. 34.03 12.50 22.77 28.83 153 June""1 32.45 14.55 23.69 27.96 154 June 2 20.42 9.38 13.25 11.31 155 June 3 22.26 5.77 13.73 28.89 156 June 4 24.42 4.44 15.22 30.32 157 June 5 29.28 10.80 20.35 28.94 158 June 6 31.70 16.33 23.51 28.89 159 June 7 31.77 16.07 23.87 29.53 160 June 8 24.58 7.74 16.29 26.63 161 June 9 20.65 4.00 12.11 30.21 162 June 10 22.73 4.35 14.22 30.52 163 June 11 26468 4.54 17.00 29.17 164 June 12 30.33 11.08 21.81 30.15 165 June 13 33.45 15.02 24.25 29.27 166 June 14 34.12 19.18 26.48 27.69 167 June 15 32.41 20.28 25.56 26.72 168 June 16 29.46 14.55 21.18 26.55 169 June 17 30.33 11.62 20.66 25.42 170 June 18 32.93 11.10 22.27 30.30 171 June 19 32.65 17.76 25.13 25.96 172 June 20 32.85 19.57 25.75 24.73 173 June 21 35.85 16.06 26.22 27.23 174 June 22 33.67 21.18 26.64 15.19 175 June 23 29.28 13.21 21.42 30.77 176 June 24 29.16 13.70 21.63 24.97 177 June 25 35.82 22.04 28.29 27.62 178 June 26 25.89 13.18 18.65 24.30 179 June 27 29.06 10.08 19.15 29.85 180 June 28 24.13 12.49 16.82 8.47 181 June 29 25.27 11.06 18.02 31.46 182 June 30 25.37 7.38 17.06 28.69 183 July 1 25.63 6.82:5 17.12 26.93 184 July 2 28.99 7.57 18.69 29.28 185 July 3 31.82 7.82 20.78 28.75 186 July 4 34.62 ,10.71 23.71 28.36 187 July 5 37.74 14.43 26.37 26.23‘ 188 July 6 38.58 15.89 27.27 25.73 189 July 7 37.89 17.65 27.46 21.88 190 July 8 35.65 18.75 27.04 25.09 191 July 9 35.09 17.21 26.53 24.07 192 July 10 29.01 20.08 22.71 12.54 193 July 11 29.73 17.12 22.93 26.57 194 July 12 30.43 11.67 21.47 26.91 124 Appendix 2 (cont.) Air High Air Low Air Mean Solar Day of Temp. Temp. Temp. Radiation Year Mo. Day (°C) (°C) (°C) (MJ m“) 195 July 13 32.16 11.85 23.15 25.55 196 July 14 33.30 20.48 27.22 28.39 197 July 15 37.13 14.98 23.33 17.37 198 July 16 34.98 20.65 26.64 17.61 199 July 17 32.66 20.04 24.77 25.29 200 July 18 24.61 18.72 21.48 4.46 201 July 19 31.07 18.43 23.71 21.97 202 July 20 24.57 16.48 20.09 8.91 203 July 21 28.14 15.79 21.14 20.74 204 July 22 29.84 15.90 19.67 16.12 205 July 23 30.09 14.04 19.62 20.70 206 July 24 28.88 13.45 21.05 26.87 207 July 25 27.91 17.26 21.42 17.53 208 July 26 28.40 14.44 20.81 24.61 209 July 27 29.64 13.40 21.60 23.94 210 July 28 33.07 19.59 25.85 26.92 211 July 29 32.24 19.90 26.08 25.72 212 July 30 30.27 20.67 24.91 17.59 213 July 31 31.21 15.27 23.27 23.97 214 Aug. 1 36.76 20.63 28.07 25.94 215 Aug. 2 35.51 23.16 29.18 24.53 216 Aug. 3 35.94 22.17 27.55 19.66 217 Aug. 4 34.40 21.67 27.86 20.76 218 Aug. 5 31.77 21.26 24.53 10.39 219 Aug. 6 29.21 18.30 23.67 26.34 220 Aug. 7 32.56 15.58 23.92 26.74 221 Aug. 8 31.93 18.10 25.01 21.74 222 Aug. 9 28.84 21.62 24.34 11.17 223 Aug. 10 29.98 19.75 23.67 11.84 224 Aug. 11 30.81 19.57 24.71 19.39 225 Aug. 12 32.82 20.87 26.65 20.61 226 Aug. 13 31.90 22.35 26.66 20.50 227 Aug. 14 32.32 18.47 27.60 21.23 228 Aug. 15 31.43 18.78 24.79 24.46 229 Aug. 16 32.85 15.68 24.33 21.54 230 Aug. 17 34.03 22.83 28.69 23.76 231 Aug. 18 22.79 15.44 20.29 5.48 232 Aug. 19 23.05 14.73 17.98 7.51 233 Aug. 20 27.26 13.83 20.19 24.39 234 Aug. 21 27.51 12.16 19.18 23.71 235 Aug. 22 24.58 11.05 17.65 18.01 236 Aug. 23 25.02 14.31 18.44 13.20 237 Aug. 24 24.24 15.73 19.17 19.76 238 Aug. 25 23.53 15.00 18.81 22.98 239 Aug. 26 23.35 10.83 17.25 22.30 240 Aug. 27 20.96 9.14 14.32 6.09 Appendix 3. Weather data for the 1989 growing season at the Kellogg Biological Station. Air High Air Low Air Mean Solar Day of Temp. Temp. Temp. Radiation Year Mo. Day (°C) (°C) (°C) (MJ m’z) 91 April 1 6.9 -3.0 2.1 17.2 92 April 2 11.1 5.1 6.8 6.7 93 April 3 10.3 5.4 7.5 5.4 94 April 4 16.8 4.3 9.5 19.0 95 April 5 5.1 0.8 3.7 4.6 96 April 6 9.5 -o.2 3.9 16.0 97 April 7 8.5 ‘-2.4 2.5 15.7 98 April 8 _9.4 -2.2 1.8 11.4 99 April 9 -0.7 -6.5 -3.4 11.0 100 April 10 0.8 -9.5 -3.9 13.8 102 April 12 6.6 -1.0 2.4 9.2 103 April 13 9.9 -3.1 p 2.8 24.7 104 April 14 13.2 1.0 7.3 7.9 105 April 15 17.1 0.7 8.6 22.0 106 April 16 20.2 -1.0 10.2 23.4 107 April 17 16.4 3.2 10.8 8.8 108 April 18 8.0 -0.5 3.0 9.8 109 April 19 13.5 -0.9 5.5 25.3 110 April 20 19.4 0.7 9.9 20.9 111 April 21 18.3 6.0 10.3 16.6 112 April 22 16.4 5.4 9.7 16.2 113 April 23 16.7 -0.9 7.6 25.9 114 April 24 20.9 0.0 10.6 24.3 115 April 25 27.4 9.2 16.9 21.3 116 April 26 24.0 11.6 17.1 24.1 117 April 27 22.7 9.7 14.6 18.3 118 April 28 11.1 6.7 9.1 4.4 119 April 29 17.6 6.4 10.0 10.8 120 April 30 14.5 5.2 9.4 24.5 121 May 1 16.6 2.1 9.2 23.0 122 May 2 8.4 2.7 5.9 7.6 123 May 3 16.9 1.9 8.9 27.0 124 May 4 19.5 6.1 12.0 21.8 125 May 5 16.3 5.3 11.4 20.8 126 May 6 6.8 -2.3 2.4 12.3 127 May 7 8.6 -4.1 2.4 25.1 125 126 Appendix 3 (cont.) Air High Air Low Air Mean Solar Day of Temp. Temp. Temp. Radiation Year Mo. Day (°C) (°C) (°C) (MJ m") 128 May 8 16.5 -0.4 8.0 17.8 129 May 9 16.9 6.6 11.7 21.0 130 May 10 18.5 0.9 10.3 27.7 131 May 11 17.3 2.7 9.4 29.1 132 May 12 15.5 6.1 9.7 8.9 133 May 13 16.3 6.6 9.5 9.3 134 May 14 18.4 5.8 11.2 15.2 135 May 15 16.9 8.2 11.7 12.9 136 May 16 24.9 5.1 14.3 23.5 137 May 17 27.3 5.7 17.1 26.4 138 May 18 24.1 10.1 18.3 14.9 139 May 19 20.5 15.3 17.7 5.0 140 May 20 21.2 11.1 16.7 9.8 141 May 21 24.6 8.9 16.5 29.1 142 May -22 27.2 7.1 17.0 21.1 143 May 23 26.8 11.1 18.6 29.8 144 May 24 26.3 10.3 18.7 19.8 145 May 25 23.7 14.4 19.2 13.9 146 May 26 22.7 11.2 18.1 29.1 147 May 27 17.4 8.2 12.4 27.3 148 May 28 21.4 2.3 12.9 28.2 149 May 29 21.3 8.2 15.1 15.1 150 May 30 27.5 17.1 20.9 15.6 151 May 31 27.8 17.3 20.7 10.9 152 June 1 24.5 17.2 19.1 12.4 153 June 2 25.2 14.2 19.7 29.9 154 June 3 20.7 13.8 16.9 7.7 155 June 4 22.8 10.3 16.5 29.2 156 June 5 24.2 10.7 17.1 20.9 157 June 6 27.6 10.0 19.7 28.3 158 June 7 29.6 15.5 22.3 26.7 159 June 8 28.1 15.8 21.6 20.2 160 June 9 23.3 11.5 17.4 21.9 161 June 10 19.8 10.1 13.5 19.8 162 June 11 25.6 5.0 15.9 29.9 163 June 12 17.0 14.8 15.6 5.5 164 June 13 22.2 14.5 17.5 10.6 165 June 14 24.1 13.7 16.9 14.9 166 June 15 19.1 10.7 15.0 12.5 167 June 16 313.8 10.0 11.6 6.9 168 June 17 23.1 10.0 16.7 24.8 169 June 18 25.9 14.3 20.1 26.8 170 June 19 21.9 16.8 19.4 7.4 171 June 20 25.9 15.9 19.2 17.7 172 June 21 28.4 13.7 19.7 21.5 173 June 22 28.2 16.0 21.2 12.7 127 Appendix 3 (cont.) Air High Air Low Air Mean Solar Day of Temp. Temp. Temp. Radiation Year Mo. Day (°C) (°C) (°C) (MJ m”) 174 June 23 32.2 18.1 23.3 21.1 175 June 24 30.8 18.2 24.0 27.0 176 June 25 33.9 17.5 24.4 26.7 177 June 26 32.0 19.0 23.7 19.8 178 June 27 24.2 18.2 20.7 8.3 179 June 28 24.5 15.0 19.9 29.1 180 June 29 24.5 7.8 16.4 30.4 181 June 30 27.4 8.5 18.1 30.0 182 July 1 29.8 10.9 20.7 28.9 183 July 2 30.9 15.4 22.1 22.1 184 July 3 28.5 17.8 22.7 23.8 185 July 4 31.7 17.0 23.9 24.0 186 July 5 30.4 17.5 23.8 25.7 187 July 6 32.5 18.1 25.0 26.7 . 188 July 7 29.9 - 17.9 24.1 27.0 189 July 8 28.7 14.3 22.1 22.0 190 July 9 31.0 19.6 25.1 22.5 191 July 10 31.5 24.3 27.7 25.2 192 July 11 31.1 18.5 23.5 18.4 193 July 12 24.5 15.5 19.8 12.1 194 July 13 26.1 15.1 19.3 14.7 195 July 14 26.6 11.8 18.7 28.1 196 July 15 27.2 11.5 18.7 21.8 197 July 16 28.2 11.4 19.9 21.9 198 July 17 28.5 12.4 20.7 26.6 199 July 18 28.9 13.1 21.0 20.0 200 July 19 22.7 17.2 19.0 7.6 201 July 20 19.9 15.9 17.7 5.1 202 July 21 25.4 16.3 19.8 11.2 203 July 22 30.5 16.7 22.9 22.5 204 July 23 31.4 17.1 24.0 25.9 205 July 24 32.5 18.9 25.1 18.0 206 July 25 30.7 20.2 24.0 14.9 207 July 26 31.0 20.0 25.1 22.8 208 July 27 29.1 18.8 24.0 17.0 209 July 28 26.0 14.4 20.2 19.8 210 July 29 25.8 9.1 17.7 21.5 211 July 30 19.6 15.4. 17.6 5.8 212 July 31 28.7 13.2 20.5 22.8 213 Aug. 1 29.8 14.5 22.0 23.5 214 Aug. 2 28.6 15.3 22.0 24.7 215 Aug. 3 31.6 17.4 24.6 21.3 216 Aug. 4 29.4 21.7 25.1 16.6 217 Aug. 5 29.3 18.7 23.9 24.1 218 Aug. 6 24.0 10.0 18.2 15.6 219 Aug. 7 19.8 7.7 12.7 23.3 .128 Appendix 3 (cont.) Air High Air Low Air Mean Solar Day of Temp. Temp. Temp. Radiation Year Mo. Day (°C) (°C) (°C) (MJ m'z) 220 Aug. 8 24.0 5.7 15.1 22.0 221 Aug. 9 26.0 11.0 18.5 20.8 222 Aug. 10 27.8 12.6 18.6 15.8 223 Aug. 11 29.4 12.4 19.9 18.2 224 Aug. 12 27.4 13.7 19.6 14.3 225 Aug. 13 27.6 13.4 20.3 22.0 226 Aug. 14 27.4 15.4 20.1 16.1 227 Aug. 15 25.6 15.9 19.9 15.4 228 Aug. 16 24.1 12.7 17.6 18.5 229 Aug. 17 27.2 10.6 18.6 24.3 230 Aug. 18 25.8 10.0 17.5 20.5 231 Aug. 19 27.5 10.2 18.4 21.5 232 Aug. 20 27.2 16.9 20.9 15.0 233 Aug. 21 28.0 17.1 22.0 24.0 234 Aug. 22» 27.4 16.9 21.9 13.8 235 Aug. 23 22.7 17.3 20.5 9.7 236 Aug. 24 25.9 13.3 18.8 20.2 237 Aug. 25 27.0 9.2 17.7 21.9 238 Aug. 26 28.8 11.2 19.5 22.5 239 Aug. 27 29.8 16.4 21.9 17.5 240 Aug. 28 25.2 16.4 20.7 6.0 241 Aug. 29 26.4 19.8 22.2 8.0 242 Aug. 30 25.2 15.1 19.5 23.0 243 Aug. 31 27.0 12.5 19.5 17.1 244 Sept. 1 25.2 17.3 20.4 13.7 245 Sept. 2 23.9 9.9 16.7 20.0 246 Sept. 3 25.7 8.9 16.4 20.7 247 Sept. 4 24.1 10.0 16.9 19.0 248 Sept. 5 27.6 15.4 20.4 15.4 249 Sept. 6 23.7 18.1 20.7 5.2 250 Sept. 7 28.8 18.3 22.1 13.2 251 Sept. 8 29.0 19.8 22.2 9.8 252 Sept. 9 27.0 17.7 21.3 10.7 253 Sept. 10 23.7 13.3 17.7 14.3 254 Sept. 11 24.2 10.7 16.7 11.6 255 Sept. 12 20.6 11.3 15.6 19.6 256 Sept. 13 11.2 8.9 10.1 1.9 257 Sept. 14 12.4 8.7 10.7 -2.4 258 Sept. 15 21.7 4.8 12.6 20.8 259 Sept. 16 14.1 8.8 11.7 3.7 260 Sept. 17 23.9 6.1 14.7 18.9 261 Sept. 18 25.1 6.4 15.1 19.0 262 Sept. 19 25.5 6.9 15.6 18.3 263 Sept. 20 26.1 7.5 15.8 17.3 264 Sept. 21 26.2 8.1 16.7 15.0 265 Sept. 22 23.6 9.3 18.3 8.7