WATER TRANSFER FROM SOIL TO THE ATMOSPHERE AS RELATED TO SOIL PROPERTIES, PLANT CHARACTERISTICS AND WEATHER
Annual research rept., Jul 1965-Jun 1966
AGRICULTURAL RESEARCH SERVICE RIVERSIDECA SALINITY LAB
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Psychrometers that essentially eliminate the requirement for precise temperature control were used to instrument a soil-plant system, and preliminary data on the influence of soil-water potential on transpiration rate were collected. A single pepper plant was grown in each of two soil columns 30 cm in diameter and 260 cm deep. A water table was set up in column A and the amount of water taken up from the water table was monitored daily. Column A received an amount of water approximately equal to 85 of that transpired since the previous irrigation. Column B received water equal to about 115 of the amount transpired. Soil water suction measurements were made daily with tensiometers placed at 50-cm depth intervals and at the 25-cm depth in the columns. Transpiration from the columns was determined daily by means of a load cell weighing system. Mathematical analysis of the data has not been completed, but an outline of the approach is given. It is apparent that attempts to estimate transpiration by means of soil moisture measurements will be in error if no way is provided to account for the flux of water into or out of the root zone. The report includes the following chapter topics plant-soil-water energy relations water movement in the soil and uptake by plant roots and further tests of the salinity sensor. Appendixes deal with psychrometric measurement of soil water potential without precise temperature control design criteria for Peltier-effect thermocouple psychrometers effect of soil salinity on water potentials and transpiration in pepper and apparatus for weighing the long soil columns.