Climate-normalized cotton leaf water potentials for irrigation scheduling

Pressure chamber measurements of leaf water potential ( ψ 1) provide a useful means to quantify plant responses in both research and managerial circumstances. However, day-to-day variation in climatic parameters affect transpiration rate and cause proportionate variability in ψ 1 values that can lead to significant errors in forcasting a needed irrigation. A procedure was developed from field studies in the San Joaquin Valley, California, U.S.A. that allows cotton ( Gossypium hirsutum L.) ψ l 's to be adjusted to common climatic evaporative demand conditions. The derived adjustment factors are sensitive to increased soil-plant flow resistances encountered during drying cycles between irrigations. Validation of the procedure was very successful for all climatic conditions and contrasting plant ages of an entire growing season.