Abstract |
Water depletion patterns in the ten 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 state of soybeans. In general, ten-cm layers in the upper horizons contributed a major portion to the total water losses. The contribution of the ten to 20-cm layer remained above 20% while that of the 50 to 60-cm layer accounted for less than 10% of the total water loss from the ten to 70-cm profile. During the early stages of growth the evapotranspiration rate was 0.64 cm/day which agrees with the pan evaporation rate of 0.66 cm/day. Soil outside the ten to 70-cm zone contributed about 0.2 cm/day towards evapotranspiration. About 55% of the soil volume showed root densities of one to two cm/cu cm. Generally, root density tended to be higher near the plant rows and between the 25 and 45-cm depths below the surface. |