Soybean root water uptake in two soils

Abstract

Knowledge of root water uptake distributions patterns in soil profiles may help in developing better water management practices. Soil water content profiles in two loam soils under soybeans ( Glycine max L.) were monitored by the neutron attenuation method. Soil water potentials were determined from soil moisture retention curves. Soil water depletions calculated from volumetric water moisture data were equated to root water uptake. Root densities were obtained from the core-break method. Root water uptake was related to soil water potential, root density and uptake per unit root length. The results indicated that the uptake rate was primarily a function of soil water potential, but root density and uptake per unit root length were also important. The limiting soil water potential for maximum uptake rate varied with the soil type. With decreasing soil water potential uptake rates were maintained at a higher level through an increase in root density. Where the root density became sparse uptake rates were maintained near maximum through an increase in uptake per unit root length. In the soil with apparently good transmission characteristics, uptake as high as 1.0 mm d −1 (0.15 m) −1 depth of soil was observed at −1.5 MPa soil water potential. The suberized segments of roots appear to be more effective in uptake at low soil water potentials whereas the young roots were more effective at high soil water potential.