SW-Soil and Water: Nitrogen and Phosphorus Losses due to Soil Erosion during a Typhoon, Japan

The objectives of this study are to observe soil, nitrogen and phosphorus losses under different amounts of fertilizer during the typhoon of 20 June 1997, and to evaluate the effects of soil and nutrient losses associated with the typhoon on the annual loads. Cumulative rainfall of 143·5 mm was recorded during the typhoon of 20 June 1997. At the onset of surface runoff, the concentration of ammonium nitrogen was dominant among inorganic nitrogen, and gradually decreased with cumulative surface discharge. After 4 h of surface runoff, nitrate nitrogen concentration became higher than that of ammonium nitrogen. According to the loads of nutrient losses, it became clear that the total nitrogen and phosphorus losses in the most fertilized plot (6285 kg ha-1), were the highest among plots. Additionally, total nitrogen and phosphorus loads during the typhoon ranged from 20 to 49% and from 35 to 45% of the annual loads, respectively. It was concluded that the typhoon largely affected the annual nutrient losses.