Nitrogen Leaching Behavior During the Chinese Yam Growing Period in a Large-Scale Upland Field in the Byobuzan Dune Area : Effect of the Microbe-Decomposable Type Slow-Release Fertilizer

Chinese yam production is prosperous in Aomori Prefecture, Japan, a cold, snowy region. Recently, the risk of nitrogen leaching in Chinese yam fields, composed of sandy soil, tends to be high because of increasing localized torrential rain due to global warming. In addition, the relationship between the type of fertilizer used for Chinese yam cultivation, the amount of N leaching, and the timing of leaching have not been revealed. This study aimed to investigate the behavior of nitrogen components of fast-acting and delayed-release fertilizers on conventional and excessive irrigation plots. Using an improved mathematical model and the spatiotemporal dynamics of inorganic nitrogen concentration in soil pore water, we evaluated the negative impact of nitrogen leaching on the groundwater environment. In cold, snowy regions, NO 3 -N remaining during the harvest season is leached at once by snow melting percolated water in early spring. The numerical analysis results revealed that the NO 3 -N concentration could be halved during the harvest season by the combined use of slow-release fertilizer (H-CDU) with mineralization properties. Therefore, this study revealed that the negative impact of nitrogen leaching on the groundwater environment can be reduced by cultivating Chinese yam under a fertilizer application system that includes the use of a slow-release fertilizer