EVALUATION OF ROOT DEPTH-EVAPOTRANSPIRATION RELATIONSHIP

Abstract

The present study is concerned with the prediction and field verification of the moisture extraction pattern in the crop root zone. Different root water uptake models assume the moisture extraction pattern from the crop root zone to follow different patterns i.e. constant, linear, non-linear, logarithmic and exponential. Reason for the wider applicability of the constant rate•(Feddes, 1978), and linear rate (Molz and Remson, 1970, Prasad 1988) models is that they involve parameters. Ojha and Rai (1996) non-linear root water uptake model termed as O-R model has versatile applicability. To check the field applicability of the crop specific non- linearity on root uptake pattern, Lysimeter and field crop experiments performed on wheat under controlled conditions. Various crop parameters i.e. root depth variation, leaf area index, plant height and soil parameters i.e. bulk density, particle density, saturated hydraulic conductivity is determined using standard procedures. Soil moisture measurement sensors embedded at different depths in the crop root zone and TDR soil moisture meter. The suitability of reference evapotranspiration estimation model in computing crop evapotranspiration for the local agro-climate has been investigated. Hargreaves —Samani method is used to compute reference evapotranspiration from the available meteorological data. The FAO recommended crop coefficients for crop is used to compute crop evapotranspiration. The daily crop evapotranspiration is partitioned into evaporation and transpiration on basis of observed leaf area index. Field observed moisture depletion values are compared with model predicted values to verify the relation i.e. ratio of root depth and evapotranspiration is remain constant throughout crop period using O-R model.