Seasonal runoff estimation of N and P in a paddy field of central Korea

The present study was carried out during a period of one year (from May 1, 1997 to April 30, 1998) to quantify seasonal runoff of N and P in a rice field with an area of 5,000 m². The total amount of runoff water was 1,043 mm during the cropping season and 281 mm during the non-cropping season. Nutrient concentrations in runoff water increased significantly during the period of fertilizer application and then decreased. During the non-irrigation period after harvest, however, the concentrations of total-N were 3 to 4 mg 1^-1. The annual runoff loading of total-N and total-P was 157.9 and 4.5 kg ha yr^-1. The runoff loading was 109.9 kg ha^-1 for total-N and 3.5 kg ha^-1 for total-P during the fertilizer application period (from May 13 to August 3, 1997). During the rainy season (from June 20 to July 20, 1997), the runoff loading was 66.1 kg ha^-1 for total-N and 1.9 kg ha^-1 for total-P. The runoff loading was 5.6 kg ha^-1 for total-N and 0.2 kg ha^-1 for total-P during the fallow stage (from October 1, 1997 to March 20, 1998) while it was 6.7 kg ha^-1 and 0.4 kg ha^-1 for each nutrient during the plowing stage (March 20 to May 10, 1998). The loss of total-N and total-P was 68.2% and 63.9% of annual runoff loading during the fertilizer application stage, respectively. During the non-cropping season after harvest, however, the loss was 30.4% of total-N and 22.3% of total-P. In summary, intensive long-term studies on various sites of nutrient management planning during the fertilizer application and rainy seasons are needed.