Nitrogen Leaching and Nitrogen Balance under Differing Nitrogen Fertilization for Sugarcane Cultivation on a Subtropical Island

Fertilizer application during sugarcane cultivation is a main source of nitrogen (N) loads to groundwater on small islands in southwestern Japan. The aim of this study was to quantify the effect of reducing the N fertilizer application rate on sugarcane yield, N leaching, and N balance. We conducted a sugarcane cultivation experiment with drainage lysimeters and different N application rates in three cropping seasons (three years). N loads were reduced by reducing the first N application rate in all cropping seasons. The sugarcane yields of the treatment to which the first N application was halved (T2 = 195 kg ha(-1) N) were slightly lower than those of the conventional application (T1 = 230 kg ha(-1) N) in the first and third seasons (T1 = 91 or 93 tons ha(-1), T2 = 89 or 87 tons ha(-1)). N uptake in T1 and T2 was almost the same in seasons 1 (186-188 kg ha(-1)) and 3 (147-151 kg ha(-1)). Based on the responses of sugarcane yield and N uptake to fertilizer reduction in two of the three years, T2 is considered to represent a feasible fertilization practice for farmers. The reduction of the first N fertilizer application reduced the underground amounts of N loads (0-19 kg ha(-1)). However, application of 0 N in the first fertilization would lead to a substantial reduction in yield in all seasons. Reducing the amount of N in the first application (i.e., replacing T1 with T2) improved N recovery by 9.7-11.9% and reduced N leaching by 13 kg ha(-1). These results suggest that halving the amount of N used in the first application can improve N fertilizer use efficiency and reduce N loss to groundwater.

Automated summary

The study shows that reducing nitrogen fertilizer application in sugarcane cultivation can decrease nitrogen loads and improve nitrogen use efficiency. Although reducing the amount of nitrogen in the first application leads to a decrease in yield, it still maintains relative stability in the first and third seasons.