Abstract
Development of a simulation model to estimate quantitative nitrogen discharge from a field has a difficult problems due to an impossibility of measuring the absolute contents of several nitrogen forms in the field. The objectives of this study were to develop a simulation model of nitrogen transformations in a barley field making reference to our examination on the field and many investigations for nitrogen transformations in soils that have been done in the past, and to estimate nitrogen discharges from the field. The unique features of this model are;(i) nitrogen contained in a field exists as six forms: stable organic N, unstable organic N, exchangeable ammonium N, soluble ammonium N, nitrate N and urea N, (ii) various transformation processes: nitrification, denitrification, mineralization, immobilization, urea hydrolysis and ion exchange were assumed to obey-first-order kinetics, (iii) Arrhenius' law was applied to the temperature dependence of transformation rates, and (iv) a nitrogen concentration of the field drainage is assumed to have direct proportion to nitrate nitrogen content in the field. It is possible to trace the observed data of nitrogen discharge from underdrain observed for two periods of barley field. This model can be contribute to predicting of a nitrogen discharge from a field linking to a field drainage model.
