Abstract
The mineralization pattern of organic nitrogen (N) in subsoil of paddy field in Shonai, Yamagata, was evaluated under field condition. It was computed using the double exponential model (kinetic method). No difference in mineralization rate constant (ka) was observed with values of 0.004/d. However, the ka value in subsoil was less than in topsoil with 0.01/d. Likewise, the mineralization potential (A) in subsoil was less than in topsoil. It was found that there was no relationship in apparent activation energy (Ea) between top- and subsoil. It was computed that the amount of absorbed N by rice plant was more than the amount of mineralized organic N in topsoil during late growth stage. This suggests the importance of the N-supplying potential of subsoil.
