Study of Nitrogen Transport around Rice Root by Numerical Model

Abstract

The root growth and the nitrogen uptake of paddy rice were measured in medium textured grey lowland soil (Fluvisol), and the nitrogen supply and the distribution of nitrogen around the absorbing rice root were estimated using numerical model assuming steady state condition. The results are as follows : Mass-flow seemed to have minor role in nitrogen supply to the root of paddy rice. Dispersion coefficient in paddy field was estimated to be far smaller than diffusion coefficient. BARBER-CUSHMAN's non-steady numerical model was applied also. The results showed the assumption of steady state condition could be regarded to be competent. Nitrogen concentration at root surface was estimated with the model and compared with that of bulk soil solution. For during early growth days, the difference of nitrogen concentration remained to be small compared with the nitrogen concentration of bulk soil solution, and was considered to be negligible. At the days after 60 days after transplanting, the concentration at root surface was estimated to be considerably smaller than that of bulk soil solution. The nitrogen supply by mineralization of soil organic nitrogen, that was not included in the model, was considered to have rate-limiting role at this stage of growth.