Water Balance and Crop Coefficient Estimation of SRI Rice under Subsurface Evapotranspiration Irrigation

¹ Department of Agricultural Technology, Faculty of Agriculture, Sriwijaya University
² Department of Civil and Environmental Engineering, Faculty of Agricultural Technology, IPB University
³ Department of Agricultural and Biosystems Engineering, Faculty of Agricultural Technology, IPB University

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Precise irrigation scheduling is needed to improve water productivity in rice systems that avoid continuous flooding. This study quantified water balance components, crop evapotranspiration (ETc), crop coefficient (Kc), growth response, grain yield, and water productivity of System of Rice Intensification (SRI) rice under automated subsurface evapotranspiration irrigation. A pot-based hydraulic prototype was evaluated using a connected control tank and planting pots that supplied water in response to water-level decline. Rainfall, irrigation inflow, runoff, infiltrated rainfall, drainage outflow, water depth, soil water content, plant growth, dry grain yield, and water productivity were monitored during the SRI growth period. The selected system maintained an average water depth of 8.6 cm, with total water storage ranging from 84.14 to 101 L. During 149 days after transplanting (DAT), irrigation inflow reached 1738 L, total rainfall was 9154 L, infiltrated rainfall was 3366 L, and runoff was 5789 L, indicating that only 37% of rainfall contributed to effective water availability. ETc was 2302 L, while potential evapotranspiration was 1770 L. The optimized Kc varied by growth stage, with approximate mean values of 0.73 in the initial stage, 1.02 in the vegetative stage, 1.27 in the reproductive stage, and 0.92 in the maturity stage. Grain yield reached 4.7 t ha-1, and water productivity based on irrigation inflow was 1.21 g L-1. These findings indicate that subsurface evapotranspiration irrigation can support empirical ETc and stage-specific Kc estimation for precision irrigation in water-saving SRI rice, although field-scale validation is still required.