Root Water Uptake and Root Nitrogen Mass of Winter Wheat and Their Simulations

In this study, winter wheat (Triticum aestivum L.) was grown in nutrient solution (Exp. 1) and soil columns (Exp. 2) under controlled environmental conditions to investigate the relationship between root water uptake (RWU) and root N mass (RNM). In Exp. 1, 15 treatments were designed to examine the influence of NO3 concentrations (0.007-0.42 kg m(-3)) and illumination conditions (free water surface evaporation rates of 0.25-0.47 cm d(-1)) on root N content (RNC) and RWU Measurements included transpiration, dry weight, N content, and root length. In Exp. 2, RNC and RWU of wheat were measured at two NO3 levels (0.011 and 0.105 kg m(-3)) and low and high (80% field water capacity) soil water contents. The distributions of soil water content, NO3 concentration, RNM density, root length density, and sod temperature were observed. Results showed that the potential transpiration was proportional to RNM of wheat (R-2 = 0.99), and the maximum RWU rate, S-max, which changed from 0 to 0.023 m(3) m(-3) d(-1), was also linearly related to the RNM density (R-2 = 0.78). The ratio between potential transpiration and RNM, namely the potential RWU coefficient per unit RNM, was independent of environmental NO3 level and wheat maturity, but changed linearly with the free water surface evaporation rate (R-2 = 0.88). The relationship between RWU and RNM was applied to simulate the distributions of soil water content, sod NO3 concentration, and RNM density in Exp. 2. The simulated results compared well with the measured data, and the maximum RMSEs were 0.0085 m(3) m(-3), 0.0283 kg m(-3), and 0.0009 kg m(-3), respectively.