Irrigation with novel membranes for improved water use efficiency
- School of Chemical Engineering, UNESCO Centre for Membrane Science and Technology, The University of New South Wales, Sydney 2052, Australia.
- School of Life and Environmental Sciences, Sydney Institute of Agriculture, University of Sydney, Australia.
We tested the potential of a novel subsurface membrane irrigation system to sustain the growth and productivity of crop plants. The membranes are commercially available and designed for use in reverse osmosis (RO) and forward osmosis (FO) applications, but when buried underground can react to changes in water-potential in the root zone, thereby supplying sufficient water for growth without the need of substantial positive water pressure on the supply side. Common bean plants (Phaseolus vulgaris) were grown in pots with RO and FO membranes and compared to conventional surface irrigation (control). We measured various physiological and agronomic parameters to assess productivity and stress, including assimilation rate (A), stomatal conductance (gs), the efficiency of photosystem II reaction centres (Fv/Fm), stable isotope composition of leaves and pods, as well as biomass and yield. A and gs was highest in the control, closely followed by the FO; in contrast, A and gs were significantly reduced in the RO due to the added resistance of this membrane to the water pathway. No difference was found between treatments for leaf internal carbon concentration (ci), Fv/Fm and carbon isotope composition, suggesting no significant effect of membrane irrigation on the production of photosynthates. Yield was significantly reduced for RO, but statistically equivalent between control and FO, with a 25% increase in plant water use efficiency for the latter. These results indicate that membrane irrigation may deliver a significantly improved water-use efficiency for crop growth without compromising yield.