Integrated analysis of key parameters in the design of a gravity-fed subsurface drip irrigation system under low pressure for predominantly sandy soil

Gravity-fed subsurface drip irrigation (GSDI) supplies water directly to the root zone without the need for pumping, which makes it particularly suitable for areas with limited energy access. In areas where food scarcity and insecurity remain major problems, GSDI offers a promising opportunity to boost agricultural production. This study assessed the design and performance of the GSDI system for growing mungbean in predominantly sandy soils through field trials, laboratory tests and analytical modelling. The maximum irrigation depth for the mungbean was 5.94 mm, corresponding to 90 litres per 15.12 m2 of wetted area per 2.5-day irrigation cycle. When scaled to 0.25 ha, the system requires an average daily irrigation volume of approximately 3.62 m³ , applied over about 63 % of the cultivated area. This corresponds to an irrigation interval of 2.58 days and an average irrigation duration of approximately 1.5 h day⁻¹ under gravity-fed operating conditions. Performance indicators confirmed satisfactory results: the uniformity coefficient (CU) ranged from 0.9 to 0.94, the emission uniformity (EU) from 0.88 to 0.91 and the distribution uniformity (DU) from 0.88 to 0.91, reflecting a uniform distribution of water with minimal friction losses and an adequate pressure head. The rate of soil infiltration (365 mm per hour) was consistently higher than the application rate (1.6 mm per hour), indicating a negligible risk of surface runoff or deep percolation. Overall, GSDI has a strong potential as a cost-effective, efficient and appropriate solution for smallholder farmers in water-limited environments.