RESPONSE OF INTERNAL TISSUE WATER-BALANCE OF PEANUT TO SOIL-WATER

Efficient water application for crop productivity requires knowledge of the plant/soil water balance. The objectives of this research were to determine how peanut (Arachis hypogaea L.) leaf water were to determine how peanut (Arachis hypogaea L.) leaf water content responds to soil water content and to examine the soil water content-phi-s relationship for predicting limiting levels of soil water relative to crop water status in the field. Few field data describing peanut internal water balance responses to soil water are available. In the present study, available soil water content is defined as water content minus water content at - 1.5 MPa divided by water content at - 0.01 MPa minus water content at - 1.5 MPa. This approach normalizes water content to the fraction available. It is analogous to leaf relative water content (LRWC) and is expressed as soil relative water content (SRWC). The objectives of this research were to: (i) define the relationship between SRWC and LRWC of peanut grown under rainfed and irrigated conditions, and (ii) use SRWC to predict limiting levels of soil water relative to crop water status. Plants were grown on a Teller loam soil (fine, mixed, thermic Udic Argiustoll). Weekly midday (1130 to 1300 apparent solar time) measurements of LRWC were made between 40 and 100 d after planting (DAP). Weekly SRWC values were interpolated to correspond to LRWC measurement days. Above 50% SRWC, the mean LRWC was about 85%, and appeared to be affected more by evaporative demand than by SRWC. Below 50% SRWC, LRWC was highly correlated with SRWC. The predicted SRWC when turgor pressure potentials approached zero was about 45%. This SRWC threshold occurred under rainfed conditions in the 3 yr studied at 59, 56, and 64 DAP during flowering and pod formation. It is concluded that the SRWC vs. soil water pressure potential curve of Teller soil may be useful for predicting limiting levels of soil water for peanut and that limiting levels of soil water may occur well above the classically defined lower limit of soil water availability.