Water Transfer from Soil to the Atmosphere as Related to Soil Properties, Plant Characteristics and Weather

摘要

A laboratory technique is described for independent measurement of the total soil water potential and its components, based on the principles of the soil psychrometer and the porous plate apparatus. Only a negligible quantity of soil water is displaced. Such data are used to study interactions of the water potential New plant growth chambers are being built at Riverside to study the transport of water from the soil to the atmosphere through plants. The sunlit plastic-enclosed chambers have provisions for control of temperature, humidity, CO2 concentration, light intensity, and air velocity. Each chamber will be 20 feet high, with nearly 10 feet below the soil surface level to accommodate deep soil columns. A pepper plant was grown through three irrigation cycles in a soil column 130 cm deep; soil water potential was measured with tensiometers and a thermocouple psychrometer; plant water potential was inferred from a calibrated beta gauge; transpiration was measured by weighing the soil-plant system. Water movement in the transpiration stream was in the direction of the water potential gradient. Regardless of the distribution of water in the soil, transpiration was unaffected by declining soil water until it reached a level corresponding to about -8 bars soil water potential. Beyond this, transpiration decreased linearly with soil water content to a soil water potential of -37 bars, at which time the plant water potential was below -50 bars and transpiration was essentially zero. After irrigation, the plant regained full turgor. (Author)