Sugarcane fertilisation management in island regions of Japan and its impact on production: a case study of Kitadaito Island.

OKINAWA Prefecture, located in the northern limit of the Tropics, consists of a large number of small islands. Sugarcane is grown as the major crop and, as land suitable for cultivation is limited, production can only be increased by increasing the yield. However, production and area under cultivation have both tended to decrease year after year. To compensate for the decrease in area under cultivation, there is an urgent need to increase yield. The main reason for the current low yield is believed to be inappropriate fertilisation management. Kitadaito Island was chosen for a case study to verify this hypothesis and to identify methods to improve the current situation. The average area under cultivation for each grower on Kitadaito Island is about 4 ha, and is larger than that on other islands in Okinawa Prefecture. The study was carried out for the benefit of growers, sugar factories and agricultural co-operatives. The validity of fertilisation management on each farm was evaluated on the basis of farm production. The cause of low unit crop production became clear when the appropriateness of fertilisation management was examined. The means by which each grower could improve the management were then established. Farmers on Kitadaito are willing to improve fertilisation management to increase yields. This motivation should be harnessed to speed up the application of new cultivation techniques. Introduction Okinawa Prefecture is located in the subtropical southernmost end of the Japanese archipelago. The Prefecture consists of 160 or more islands, some as small as 0.01 km in area. The islands are spread over an ocean area measuring 1000 km (east-west) by 400 km (north–south). Fifty of these islands are inhabited. As sugarcane represents a significant component of the regional economy, the recent decrease in sugarcane production is having a serious impact on the Okinawan economy. Furthermore, as the islands are quite isolated, individual island economies, such as those of Kitadaito and Minamidaito Islands, are dependent on sugarcane. Studies have previously been undertaken to investigate the management styles of agricultural production in island regions (Fukunaka et al., 1999 and Kikuchi, 2005) and to clarify management changes in response to mechanisation (Arai and Nagata, 2002). In this study, we focused on Kitadaito Village where farm management is under severe strain due to decreased profits resulting from the low and unstable production, and where large-scale completely mechanised operation systems have been introduced. In Okinawa Prefecture, the ageing of the farm labour force has made the introduction of a mechanised continuous operation system of utmost importance. In order to make a profit, we need to evaluate whether the present