In situ Studies on the Water Balance of Rainfed Cereal and Legume Root Zones in a Typic Haplustult -II. Estimates of Percolation Amounts

Amounts of rain water percolation were estimated below the root zones of rice, ragi ((Eleusine coracana), black gram and groundnut growing in 4 x 3m fieldplots in a lateritic soil, making use of mercury-water tensiometers and in situ measured K(θ) relationships. The mean daily percolation rates were measured to be 0.54 for rice, and 0.67cm for ragi and the mean recharge rates were + 0.08 for black gram and + 0,33cm for groundnut during 30 to 70 days of cropgrowth. Around 30 days of growth during a 5-day long dry spell, nearly the entire amount of rainfall (19.4mm) received seemed to be lost by percolation from the root zones of cereals whereas, on an average, only 30% of it is lost by this means in the case of the legumes. On the other hand, during the second 5-day long dry spell (60 days of crop growth) nearly 30% of the rainfall (34.7mm) is lost from the root zones of cereals while the legumes not only did not allow percolation but also caused waterflow upward from the lower layers. Ragi seemed to gain waur from layers below 120cm depth whereas rice did not appear to possess such capability.