Measurement of Water Potential Using in Situ Thermocouple Hygrometers

Publisher Summary This chapter discusses some of the problems associated with the field use of in situ hygrometers for the nondestructive measurement of soil and plant water potential, including measurement techniques associated with psychrometric and dewpoint methods. Water potential gradients are used to predict the direction of water movement in the soil, plant, or atmosphere. If the liquid and vapor conductivities in this system are known, rates of water movement can be predicted and vice versa. Water stress of plants is inferred from measurements of water potential, as this thermodynamic quantity appears to be most closely related to the physiological and biochemical processes that control plant growth. Other methods of determining plant water stress involve soil water potential measurements or rate of evapotranspiration. Water relations are affected by and affect many agricultural practices and occurrences—for example, influences of water on microbial decomposition of crop residues, the effect of fire and the fire regime on grassland plant water relations, and drought responses of crops. One of the major problems associated with soil water potential measurement appears to be the condensation or drying out of soil water in the vicinity of the hygrometer and in the presence of temperature gradients.

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