Water Flow in Soil in Presence of Soybean Root Sinks

Abstract

Water depletion patterns in the 10 to 70 cm soil depth in the root zones of two soybean varieties, 79.648 and Chippewa - 64, and in a bare soil were established on Waukegan loam. Soil hydraulic properties of the soil profile, suction-water content and hydraulic conductivity-suction relationships were determined in the laboratory and supported by field measurements. Following irrigation, proportional contribution of various soil layers to the total water loss showed a downward shift with the growth stage of soybeans. In general, 10-cm layers in the upper horizons contributed a major portion to the total water losses. The contribution of the 10 to 20-cm layer remained above 20 percent while that of the 50 to 60-cm layer accounted for less than 10 percent of the total water loss from the 10 to 70-cm profile. During the early stages of growth the evapotranspiration rate was .64 cm/day which agrees with the pan evaporation rate of .66 cm/day. Soil outside the 10 to 70-cm zone contributed about .2 cm/day towards evapotranspiration. About 55 percent of the soil volume showed root densities of 1.0 to 2.0 cm/cm(3). Generally, root density tended to be higher near the plant rows and between the 25 and 45-cm depths below the surface.