Water Utilization Pattern by Cowpea Fodder Crop as Affected by the Sodicity

Effect of exchangeable sodium on the rate and pattern of water withdrawal from the soil profile by cowpea (Vigna sinensis L) grown for fodder was studied in a field experiment. Root water extraction was measured by monitoring the changes in water content and flux divergence with time in soil profile. Flux divergence was calculated from the knowledge of hydraulic conductivity vs water content relations established for different ESP soils and the hydraulic gradients obtained in situ during the crop growth. Both the rate (R_z) and the pattern of water withdrawal were significantly affected by the degree of sodicity in the soil profile. In high ESP soil 96% of R_z (0.78 cm/day) came from the 0–15 cm layer whereas in low ESP soil the layers below 15 cm contributed about 32% of R_z(1.00 cm/day). Water use efficiency linearly decreased with increasing ESP and was 750 kg/cm/ha at ESP 8 and 200 kg/cm/ha at ESP 40.