Nitrogen uptake by wheat in relation to water regime and depth of N placement in a loamy sand soil: measurement and model simulation*

Nitrate-N distribution in soil, root-length, rate of water uptake and flux of nitrate-N to wheat roots as influenced by moisture regime and depth of nitrogen placement were studied in 60 cm diameter by 180 cm deep metal columns filled with loamy sand soil. The contribution of the different soil depths in the root zone towards total N uptake was calculated employing a convective-diffusion model and compared with the experimentally measured N uptake by wheat plants. Under non-irrigated conditions with surface-mixing of N(N_s) concentrations of nitrate, root-lengths and water uptake rates were high only in the upper soil layers. With deep placement of N(N_d), the lower layers also contributed significantly towards total N uptake and total N uptake was greater with N_d than with N_s. In spite of many simplifying assumptions and certain estimates the predicted values of N uptake were quite close to those measured experimentally.