Abstract
In Miyako Island, Okinawa, the actual situation of fertilizing sugarcane was examined in 1998 and 2000,and the concentrations of inorganic nitrogen in groundwater taken from the Nogusuku spring were surveyed from 1994 to 1999. The correlation between the fertilizing and the nitrate concentration was analyzed. The amount of fertilizer nitrogen for sugarcane cultivation was researched to be 203 kg ha^<-1> which was not much in comparison with the suggested amount (240 kg ha^<-1> by the prefecture. However, the fertilizing period was concentrated in a very short term in the beginning of the cultivation, i.e., from mid -October to late December. Most fertilizers used by the farmers were quick-acting. The concentration of nitrate in groundwater had the negative correlation with the amount of rainfall, and the tendency changed from downward to upward in October every research year. According to the results, it is showed that the concentrated fertilizing quickly influences the quality of groundwater and makes the concentration of nitrate higher just after the fertilizing period every year.
