Monitoring and modeling of nitrogen leaching caused by nitrogen fertilizer application to green tea fields in Japan

Yuhei Hirono1, Shigekazu Nakamura2, Tomohito Sano3, Kunihiko Nonaka3

1 National Agriculture and Food Research Organization, 2769, Kanaya-Shishidoi, Shimada, Shizuoka, 428-8501, Japan, E-mail: [email protected]

2 Shizuoka Prefectural Research Institute of Agriculture and Forestry, Mobata, Shimizu, Shizuoka, 424-0101, Japan

3 National Agriculture and Food Research Organization, 2769, Kanaya-Shishidoi, Shimada, Shizuoka, 428-8501, Japan

Abstract

Large amounts of nitrogen fertilizer are required in the cultivation of tea (Camellia sinensis (L.)), relative to other crops, resulting in nitrate contamination of surrounding water systems and high rates of nitrous oxide emissions. In response to these problems, the amount of nitrogen fertilizer applied to tea fields in Japan has been decreased by the improvement of fertilizer application methods in recent years. In this study, we aimed to assess the changes in water quality due to the reduction of nitrogen input and determine the environmental response to improved fertilizer application methods in tea fields. First, we analyzed 21-year water quality monitoring data in an intensive tea-growing area in Japan. We found nitrate concentrations significantly decreased at most studied sites in water systems in the tea-growing area, indicating that water quality was improved by reducing nitrogen fertilizer application in tea fields. Second, we modeled nitrogen leaching from tea field soil based on the data obtained by lysimeter experiments. This showed that the calculated amounts of water and nitrogen leachate agreed well with the observed results.