Abstract
Sugarcane has been cultivated across large areas of Negros Island, the Philippines. Clean groundwater is essential for island residents, yet high concentrations of nitrate nitrogen have sometimes been observed. Thus, it is important to implement the appropriate management of nitrogen fertilizers by farmers to reduce the nitrogen load to groundwater from sugarcane production. In particular, nitrogen applied during the early growth stage of sugarcane is considered to be only slightly absorbed by the plant, and a large portion of the nitrogen is leached into groundwater. It is necessary to clarify the actual state of nitrogen fertilizer application to develop appropriate fertilizer application management. In this study, therefore, a survey of farmers was conducted to clarify the actual state of nitrogen application. The results showed that (1) many farmers applied more nitrogen than the standard nitrogen application rate developed in the Philippines, and a relationship between the nitrogen application rate during the cultivation period and the sugarcane yield in new planting was not observed; (2) the frequency of fertilization, the timing of the first nitrogen application, and the application rate differed by farmer; (3) many farmers applied a large amount of nitrogen during the early growth stage of sugarcane, and a relationship between the nitrogen application rate during that stage and the yield was not observed. To reduce nitrogen load to groundwater from sugarcane cultivation, it is imperative to clarify the appropriate timing of nitrogen applications and the application rate of each timing and to disseminate this information to sugarcane farmers.
