Increasing agricultural output in a drier and warmer climate using membrane technology

Increasing agricultural output in drier and warmer climates will require resilient irrigation systems that can minimise evaporative water losses and operate on brackish water in lieu of reduced supplies of fresh water. In this paper we compare the performance of convential versus subsurface membrane irrigation. Germination percentage for Phaseolus vulgaris seeds was equivalent on membrane and conventional irrigation on variable salinity water (0.2 dS/m to 3.1 dS/m), however, membrane irrigation resulted in 52% less soil salt accumulation. Water demand during seedling establishment under both membrane and conventional irrigation was highly correlated to the Penman-Monteith model used to estimate crop water demand based on climate varialibity (r2 of 0.9). In dynamic field tests average yield with membrane irrigation achieve a maximum yield of 5.2 ton/ha at a plant water use efficiency of 14.6 kg/m3 as a result of direct plant water uptake across a thin film polyamide membrane cast on a woven support. In contrast, the average yield was 1.6 ton/ha for a thin film polyamide membrane cast on a composite structure consisting of ultrafiltration membrane with a non-woven polyester support. The observed differences in yield can be attributed to differences in the resistance imposed by the two membrane structures on water transport. More importantly, carbon (delta13C) and nitrogen (delta15N) content of green bean pods and leaves of plants grown on membrane irrigation were within the expected results for C3 plants. Results indicate that membrane irrigation may be a solution for improved water use efficiency in a drier and warmer climate and allow use of brackish water without exacerbating soil salinization.