WATER RELATIONSHIPS OF HONEY MESQUITE (PROSOPIS GLANDULOSA TORR. VAR. GLANDULOSA) SAMMY JOE EASTER, B.S. A THESIS IN RANGE SCIENCE Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Approved Accepted Díealh of tl^ Gradukte School May. 1973 AC 80 S T3 1573 ACKNOWLEDGMENTS My sincere appreciation is extended to Dr, Ronald E. Sosebee for his unselfish expenditure of time, dedicated guidance, and continuous support throughout the study. Also, I would like to thank Dr, Billie E« Dahl, Dr. Russell D. Pettit, and Dr. Joe R. Goodin for their helpful comments and timely suggestions. Special appreciation is extended to Dr. Ray Brovm for his help and suggestions on the calibration techniques of the thermocouple psychrometers and porometer and Elaine Holmes for her help on the illustrations. A very special thanks goes to my wife, Sara, and my family for their patience and support; without their help and encouragement this would not have been possible. 11 TABLE OF CONTENTS ACKNOWLEDGMENTS ii LIST OF TABLES V LIST OP FIGURES vi I. INTRODUCTION 1 II. LITERATURE REVIEW . 3 III. METHODS 11 IV. RESULTS AND DISCUSSION 19 Soil Water Relationships. 19 Plant Water Relationships 22 Atmospheric Water Relations and Transpiration. • • . 29 V. SUMMARY AND CONCLUSIONS 35 LITERATURE CITED 38 APPENDIX 42 A. MODAL DESCRIPTION OF THE AMARILLO FINE SANDY LOAM SOIL SERIES 43 B. CALIBRATION INSTRUCTIONS FOR THERMOCOUPLE PSYCHROMETERS 44 C. CALIBRATION INSTRUCTIONS FOR THE LAMBDA POROMETER 4? D. RELATIONSHIP OF ATMOSPHERIC WATER POTENTIAL AND TRANSPIRATION RATES FROM HONEY MESQUITE TREES GROWING UNDER IRRIGATION 52 iii E. RELATIONSHIP OF ATMOSPHERIC WATER FCTENTIAL AND TRANSPIRATION RATES PRCN' HOiiEY KESQUIT" TREES GRÛWING UNDER NON-IRRIGATIO: 53 F. DAILY ENVIRÛNMÎNT. PLANT WATiR PÛTENTIALS. AND TRANSPIRATION THAT EXISTED CN THE IRRIGATED SITE Or ThE STUDY OP Y^SiUITE WATER RELATIONSHIPS 54 G. DAILY ENVIRONMENT. PLANT WATr^R POTENTIALS, AND TRANSPIRATION THAT EXISTED ÛN ThE NON- IRRIGATED SITE OF ThE STUDY ÛF MES^UIT-^ WATER RELATIÛNSHIPS 56 H. NAME OF EQUIPMENT USED AND ADDRESSES FROM WHICH THEY WERE OBTAINED 58 iv LIST OF TABLES Table 1. Average water potentials of the gradient from the soil through the plant into the atmosphere throughout the day on the irrigated site of the study of soil«plant water relationships of honey mesquite. •..«.•.....••• 24 2» Average water potentials of the gradient from the soil through the plant into the atmosphere throughout the day on the non-irrigated site of the study of soil-plant water relationships of honey mesquite^ . .••••••• 25 LIST OF FIGURES Figure !• Diagrara of a double-junction Spanner thermocouple psychrometer used in the study of soil-plant water relationships of honey mesquite •••••• 13 2^ Installations of thermocouple psychrometers at three different positions in each tree for plant water potential determinations on the irrigated and non-irrigated site of the study of soil-plant water relationships of honey mesquite. • • • • 14 3^ Measurement of soil water potential with the Spanner thermocouple psychrometers and the S-B Systems microvolt meter ........•••••• 16 4^ Measurement of plant water potential with the Spanner thermocouple psychrometers and the S-B Systems microvolt meter •••••••••••••• 1? 5» Diffusion porometer used to measure transpiration rates in honey mesquite • • • 18 6. Average soil water potential at various depths for the irrigated and non- irrigated site June 1 through August 28, 1972, in the study of soil-plant water relationships of honey mesquite^ ...••••••••••• 20 7, Average soil water content at various depths for the irrigated and non- irrigated site June 1 through August 28, 1972, in the study of soil-plant water relationships of honey mesquite^ ••...••••••••• 21 vi 8. The relationship of soil water potential (bars) to soil water content (^) at four depths on the non-irrigated site in the study of soil-plant water relationships of honey mesquite 23 9t Correlation of time of day and water potential at three positior.s in honey mesquite trees growing under irrigated conditions 27 10. Correlation of time of day and water potential at three positions in honey mesquite trees growing under non-irrigated conditions 28 11. Relationship of time of day and transpiration rates of trees growing on the irrigated and non-irrigated site in the study of soil-plant water relationships 32 12. Honey mesquite trees on the irrigated site showing a large number of leaves per tree 34 13. Honey raesquite trees on the non- irrigated site showing fewer leaves per tree 34 14. Thermocouple psychrometer calibration chamber ..... 45 15. Thermocouple psychrometer calibration chamber illustrating position of the moistened filter paper 45 16. Transit time (A t) required per chane^e in microaonperes for various standard diffusion pathleneths (L) of resistance at different teraperatures. ... 48 17. Teraperature dependence of resistance meter sensitivity (S) and of the water vapor diffusivity (D) 50 18. Relationship of leaf resistance (R^) and transit tirae ( A t) 51 vii IE^M>««l CHAPTER I INTRODUCTION Honey mesquite (Prosopis glandulosa Torr. var. glandulosa) has infested about 22 million hectares of Texas rangeland to varying degrees. More than I3 million hec- tares of Texas rangeland are covered by moderate to heavy infestations^(Smith and Rechenthin, 1964). Mesquite varies in growth form from large single stem plants to small multiple stem shrubs. Mesquite generally has a well developed root system which may spread about 22 m laterally and extend to a depth of 53 ra (Phillips, 1963). >/parker and Martin (1952) reported that velvet mesquite (ProsoT)is velutina) can eliminate available soil moisture from an area with a radius of 15 m and 60 cm deep for as long as 73 days during the summer in Arizona and thus prevent development of desirable perennial grasses. Mesquite has been reported to use water inefficiently. McGinnies and Arnold (1930) reported that velvet mesquite required 1725 kg of water in the summer to produce a kg of dry matter, whereas perennial grasses such as blue grama (Bouteloua gracilis) and sideoats grama (Bouteloua curtipendula) required only 387 and 550 kg respectively. When water is available. raesquite uses it extravagar.tly (Wendt, 1966). Yet it is able to survive during lor.g periods of drought and in areas characterized ty less than 15 cm annual rainfall. Thus mesquite must be adapted to a broad raxige of available soil water. A need exists for fundaraental knowledge of plant-soil water relationships in mesquite growing under field condi- tions. Most past work was with seedlings, while the water relationships of mature trees is yet to te establishei, The objectives of this study were (1) to determine the potential for use of psychrometry to study soil-plant water relationships in honey mesquite, (2) to compare soil water potentials with the soil water content of ain area. (3) to measure diurnal water potential gradients in mature mesquite trees, (4) to compare water relationships in mesquite grown under natural (non-irrigated) environmental conditions to mesquite grown on an area that was irrirated throughout the growing season, and (5) to compare differ- ences in transpiration rates of trees grown in both areas. "^^ftilSH.''-'. CHAPTER II LITERATURE REVIEW Mesquite water stress is most often reported to be correlated with percent soil water (Wendt, Hass, and Runkles, I968; Degarmo, I9661 Shimshi, I963). However, an alternate method based on determinations of free energy of water offers many advantages. One advantage of the latter method is that of expressing soil water in terms of the energy required for removal of a unit of water from the soil by plants (Brown, 1970). This energy status has been termed water potential and may be used to describe the state of water in any part of a soil-plant-atmosphere system (Slatyer and Taylor, I960). Stanhill (1957) stated that since plants respond much more closely to the water potential than to the water content of a soil, it is more desirable to know the potential of water than the amount of water in the soil. Soil water characteristic curves for loam soils indi- cate that approximately 50% of total available water is held at approximately -2 bars, while in sandy soils 7Q% of the total available water is held at tensions less than -2 bars (Woodhams and Kozlowski, 195^)« Thus the available water in the sandy soil is extracted much more quickly through evapotranspiration during periods of high potential evapotranspiration. There has been some disagreement about the degree of availability of water to plants in drying soil over the range from field capacity to permanent wilting percentage. Some workers have reported that water is equally available to plants over the entire range (Magness, Degman, and Furr, 1935í Veihmeyer and Hendrickson, 1950). Others have reported water release curves which strongly suggest an exponential or curvilinear depletion of water as a result of increasing soil-water tension (Zahner and Stage, I966). According to Kramer (1949)» disagreement over the degree of availability of water in drying soil exists partially because of differences in water tension-water content relations for different textural grades of soils. In coarse textural soils water tension changes relatively little from field capacity almost to the wilting percent- age. At that point water tension changes sharply to permanent wilting percentage. The water release curves for fine textured soils do not exhibit this shgarp break, indicating that water is withheld from plants with appreciably greater energy. Taylor (I965) stated that the status of soil water potential nearly always differs among soils of different texture, Measurements of soil water energy have merit because they are more directly comparable among different textural classes (Brown, 1970). Beckett and Dunshee (1932) and Kozlowski (19^9) observed that plant processes are markedly influenced by decreasing soil water. Seasonal growth responses of forest trees and most other woody vegetation are more sensitive to fluctuations in soil water than to any other environmental factor (Kramer and Kozlowski, I960).