K Watanabe1, Y Kawamitsu2 and M Ueno2
1Faculty of Agriculture, Setsunan University, Osaka 573-0101, Japan
2NPO Subtropical Biomass Research Center, Okinawa 903-0213, Japan
In Japan, sugarcane crops are frequently exposed to drought after rainy season; thus, irrigation management during summer is essential to achieve high yields. To efficiently use limited water resource, we demonstrated smart irrigation systems that can be remotely controlled and determine irrigation requirement and timing using micro weather data. A field experiment was conducted on Minamidaito Island for 2 years. The field was divided into three blocks: Blocks A and B were both composed of no irrigation (NI), surface drip irrigation (SDI), and subsurface drip irrigation (SSDI), where irrigation was remotely performed before drought stress occurred based on evapotranspiration rate calculated from micro weather data. Block C was all irrigated through subsurface drip irrigation but under the management of the field owner (farmer-managed SSDI, FM-SSDI). In the 2022/23 season, sugarcane was subjected to moderate drought during July to October. The cumulative irrigation was 200 mm in SDI and SSDI and 300 mm in FM-SSDI. Plant height was higher in the irrigated plots, and yield at harvest increased by 8, 14, and 4% in SDI, SSDI, and FM-SSDI, respectively, as compared to NI. In the 2023/24 season, extremely severe drought occurred and the total precipitation was less than half of the average. As a result, the cumulative irrigation was 370 mm in SDI and SSDI and 440 mm in FM-SSDI. Greater differences than the previous season were observed in plant height, and yield increased over NI by 18, 23, and 19% in SDI, SSDI, and FM-SSDI, respectively. Although irrigation was similarly performed, SSDI showed better yield than SDI, suggesting improved water use efficiency. FM-SSDI received more water but recorded lesser yield than SSDI, indicating that farmers supply excessive water at wrong timings. Therefore, our smart irrigation systems combined with SSDI would be worthy for sugarcane production in Japan.