Root distribution and water uptake by irrigated soybeans on a duplex soil

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Abstract
Water uptake by plants is described in relation to the root system configuration for an irrigated soybean crop on a duplex soil in northern Victoria. Measurements are described for three irrigation cycles as the crop grew to maximum ground cover and advanced physiological development. Few roots penetrated below 0.7 m, and the total root length beneath unit area of ground surface was lower than soybean root systems measured elsewhere. Water uptake patterns reflected this as uptake took place mainly from the depth interval 0.15-0.5 m. 'Crop water use' decreased below maximum values, even though water was placed in the profile at potentials higher than c. -90 kPa. In this situation, it is suggested that low root numbers at depth and low hydraulic conductivity in the subsoil were limiting water uptake. Practical consequences for irrigation management of soybeans are discussed.