Nutrient losses from a paddy field plot in central Korea

The study was carried out to investigate the balance and losses of nutrients at a paddy field plot located at the southwest of central Korea from May 1, 1997 to September 30, 1999. The soil of experimental paddy field was in Jisan series (SiL: fine loamy, mixed mesic family of Fluventic Haplaguepts) and its area was 5,000 m² (100 m × 50 m). The water balance in experimental paddy field was measured as follows. They were 3,693 mm for precipitation, 2,449 mm for irrigation water, 3,081 mm for runoff water, 1,354 mm for evapotranspitration, and 1,683 mm for infiltration water. The input amounts of nitrogen and phosphorus into paddy field were measured as follows. They were 155-210 kg N ha^-1 yr^-1 and 30-52 kg P₂O₅ ha^-1 yr^-1 by chemical fertilizer, 30-39 kg N ha^-1 yr^-1 and 0.4-0.7 kg P ha^-1 yr^-1 by precipitation, and 22-30 kg N ha^-1 and 0.4-0.5 kg P ha^-1 by irrigation water, respectively. The output amounts of nitrogen and phosphorus from paddy field were measured as follows. They were 107-138 kg N ha^-1 yr^-1 and 3.4-4.6 kg P ha^-1 yr^-1 by runoff water, and 18-20 kg N ha^-1 and 0.14-0.16 kg ha^-1 by infiltration water. The runoff loading was the highest in June may be because of the higher concentrations of chemical components due to applied fertilizer. When the loss ratio of nutrient was calculated based on the amounts of applied chemical fertilizer, the nitrogen and phosphorus by runoff water and infiltration were found 57.0-65.7% and 8.8-9.4% and 9.7-12.4% and 0.3-0.5%, respectively.