Root Water Uptake Distribution Based on Change of Soil Water Contents.

Root water uptake of plants plays an important role to estimate water dynamics in soils. Typically used root water uptake model determines local root water uptake rates by potential transpirations, stress response functions, and root densities. In this study, we conducted pot experiments with soybeans and determined root water uptake distribution of each depths. Ten 1/2000 are pots were filled with a loamy soil, and soybean seeds were sowed in each pots. Four TDT soil moisture sensors and four tensiometers were installed at each depths in one of the pots to monitor water contents and soil water pressure heads, respectively. The surface of the pot was covered with a mulch to prevent surface water evaporation. By locating the pot on a scale, transpiration rates associated with root water uptake were monitored. Plant roots were sampled every 5 cm depth at each growing stage, and root distributions were obtained by an image analysis. Numerical simulation including root water uptake using HYDRUS-1D were conducted to compare simulated and observed water contents. The root densities in each growing stage were determined as simulated results agree well with observed ones, and compared with measured root distributions.