Nitrogen load and river water chemistry in a fruit-rich watershed were estimated by numerical simulation. The study area was the Zakurogawa River Watershed. The proposed method could calculate monthly emission factor of nitrogen in orchard. Therefore, seasonal variation of TN load from the watershed and TN concentration in the river could be simulated. The TN load from orchard occupied about 79% of the total and the monthly loads were larger from autumn to spring. These would depend on the amounts of fertilizer and precipitation. Consequently, it was revealed that the TN concentration in the river was controlled by seasonal variation of the TN load from orchard.
