In situ Studies on the Water Balance of Rainfed Cereal and Legume Root Zones in a Typic Haplustult—III. Estimates of the Components of Water Balance

In situ daily water balance for important rainfed crops viz, rice, ragi, black gram and groundnut grown in 4x3 m field plots was determined during two five-day long dry spells coinciding with the early vegetative and reproductive stages and also around every tenth day during 30–70 days of the growing season. The various components of water balance viz, soil water storage change, percolation, evapotrans-piration (ET) and minimum root sink were estimated and compared in the light of soil hydraulic properties based on daily (8 a.m. and 8 p.m.) readings of mecury-water tensio-meters. The mean daily ET rates observed during 30 to 70 days after sowing of thest crops happen, respectively, to be 0.84 cm for rice, 0.75 cm for ragi, 1.28 cm for black gram and 1.86 cm for groundnut. ET rates derived from lysimeter records were comparable with those derived from tensometric method of measurement in respect of ragi in this soil. Crop coefficient values derived from measured ET and ET (Penman: 0.47 mm/d) based on Doorenbos and Pruitt modification of Penman model turn out to be more than unity for all the crops.