Leaching characteristics of nitrate nitrogen in an apple orchard andosol under significant snow accumulation

The purpose of this study was to clarify nitrogen (N) leaching behavior as affected by snowmelt percolation in an Andosol soil planted with an established apple orchard, with the aim of supporting fertilization management that preserves the soil environment while maximizing apple production. Simultaneous measurements of electrical conductivity (EC), pH, NO3-N, and NH4-N (inorganic-N concentration) of the apple orchard soil pore water were taken. The adsorption nature of NO3-N and NH4-N were also monitored using Langmuir type and Logistic type adsorption isotherms. Numerical analysis relevant to the spatiotemporal dynamics of inorganic-N in soil pore water was also conducted during the growing and non-growing period for apples. The level of soil pore water EC resulting from fertilizer application was characteristically altered by downward leaching over time. Regarding the NO3-N concentration of soil pore water in the investigated area with heavy snow accumulation, the bulk of the fertilizer applied from January to July 2016 was leached down to z = 100 cm within 5 to 6 months. In the apple orchard during and after snowfall, the numerical results revealed that when NO3-N < 100 mg L− 1, NO3-N was leached without being adsorbed by the soil. In addition, since the NO3-N concentration in soil water after the disappearance of snow was very low, it is necessary to apply N fertilizer in early April (initial growth stage of current shoots and anthogenesis) in order to maximize apple tree growth. Extreme N-leaching due to percolated snowmelt in early spring (a 35-cm movement within 0.5 months) was observed in the apple orchard planted on Andosol soil. Therefore, it was inferred that concentrations of inorganic-N in the soil during April were reset to zero, and that N supplementation in the apple orchard is necessary for maximizing apple production.