Continuous Measurement of Nitrogen Runoff Loads During Long Term and Nitrogen Balance in a Tea Field Zone

The aim of this study was to estimate the nitrogen balance of the tea field zone. The study area was located in the Makinohara tea field zone, Shizuoka, Japan. The water quality and discharge were measured daily from June 2001 to May 2003 and the authors discussed runoff loads. The average concentration of T-N was 28mg·l-1and the pH value was 4.9. Therefore, this case is rare in Japanese fields. Annual T-N runoff loads were estimated to be 496.5kg·ha-1·y-1in the first year and 485.8kg·ha-1·y-1in the second year. The average load for both years was 491.2kg·ha-1·y-1. The reaching rate was 83% of the applied amount of nitrogen fertilizer. The T-N concentration was very high after strong rains during the rainy and typhoon seasons. The annual absorbed nitrogen flux was 31.3% of the applied fertilizer in the first year, and it increased to 32.4% in the second year. The average nitrogen balance ratio (input/output) was 0.97. Therefore, the tea plants absorbed a significant amount of accumulated nitrogen fertilizer in the soil.