DIFFERENCES IN WATER UPTAKE RATES OF SOYBEAN ROOTS ASSOCIATED WITH TIME AND DEPTH

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Abstract
A model of water uptake by soybean root systems was developed. The model incorporated soil, root-soil contact, and radial and axial resistances to water flow. Parameters for the model were developed from field experiments conducted during the 1979 growing season on Ida silt loam, a loess soil, at Castana, Iowa [USA]. The specific H2O uptake rate decreased from 0.23 to 1 .times. 10-4 cm3 H2O cm-1 root per day as the soil H2O became depleted in a particular layer. The average conductivity of the soil-root system decreased linearly with age of plant. The water potential decrease along the vertical axis at the 20-cm depth was 0.0615 bar cm-1 when the transpiration rate was 1 cm day-1. A simulation of water uptake, based on a solution of the water flow equation with a sink term and performed with the aid of a differential equation solver DGEAR, tracks the seasonal withdrawal of water in a reasonably accurate manner.

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