Performance of two commercial membranes to configure a membrane-based subsurface irrigation system for germinating bean seeds
V Lima, P Le-Clech, G Leslie, B Sutton
Publication Date (Web): 4 July 2016

The use of water with a high presence of total dissolved solids (TDS) can cause deleterious effects on both plant growth and soil quality. In order to mitigate these impacts, the removal of salts from water prior to irrigation is required, which can be achieved through conventional desalination processes. However, due to their complexity and high costs, their full-scale application for irrigation is often limited.

An alternative strategy to desalination using membranes for irrigation applications necessitates a system of reduced mechanical complexity and energy consumption, but that is able to supply water that matches crop demand during various stages of growth. The concept of a new subsurface irrigation method where irrigation pipes are fashioned from polymeric membrane material has been demonstrated. The system allows brackish water to be treated and delivered directly to the soil-plant interface due to a negative potential generated by both soil-matric potential and plant demand, thus reducing damage of soil structure and yield decrease. Additionally, delivery of the water through a sub-surface irrigation system would retain water in the soil and eliminate evaporative losses.

This study aims to access the performance of two commercially available membranes, reverse osmosis (RO) and forward osmosis (FO), operated under the proposed membrane-based subsurface irrigation system. The system was used for the germination of bean seeds in a silty clay loam soil on a range of saline solutions. The best membrane performance was evaluated in terms of final germination, seedling growth parameters and electrical conductivity of soil. Plants grown under the proposed irrigation system presented germination similar to hand-watered plants, while salt accumulation in the soil was minimised. A better performance was observed for the RO membrane, as the flux remained higher than the estimated plant demand over the examined salinity range. Hence, the proposed irrigation method based on membrane technology has demonstrated the ability to respond to crop water demand during germination and mitigate soil salinisation for feedwater salinity ranging between 0.21 and 3.1 dS/m (Sydney tap water and 2,500 mg/L, respectively).

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