Evaluation of soil water dynamics in the subsurface irrigation system OPSIS using lysimeter experiments.

In tropical and subtropical island regions, alterations in precipitation patterns due to climate change have led to an escala- tion in extreme weather conditions. Owing to the limited availability of irrigation infrastructure, agricultural practices in these areas predominantly rely on rainwater and groundwater. The Optimized Subsurface Irrigation System (OPSIS), a water-efficient subsurface irrigation technology developed in Japan, was engineered to irrigate upland crops by harnessing soil capillarity. This study aimed to investigate soil water dynamics under OPSIS in a subtropical island located in Japan. The water supply from OPSIS in a field devoid of vegetation exhibited considerable variability contingent upon rainfall events. This observation implies that the infiltration of wa- ter captured by the waterproof sheet prompted the cessation of water supply in the OPSIS. Following the initiation of irrigation, soil water content increased at depths of 35 and 55 cm, proximal to the 60 cm depth from the OPSIS installation point, and soil moisture levels remained elevated, except at depths of 5 and 15 cm. Therefore, the implementation of OPSIS at a depth of 60 cm can effective- ly irrigate sugarcane with substantial water-saving benefits, except in the period immediately following planting. Irrigation and deep drainage were higher at 60 cm than at 30 cm depth of PVC sheet installation. To operate OPSIS with optimal water savings in areas with more severe water use restrictions, such as arid and semi-arid lands, controlling the irrigation of perforated pipes according to the soil moisture conditions in the effective root zone is essential. [ABSTRACT FROM AUTHOR]