A study on the effect of different irrigation water (TSE, groundwater and RO water) on lettuce and soil

Abstract

Water scarcity, mainly in agriculture has been an issue for these last years in the Maltese Islands. In the near future the aquifer capacity is expected to decrease due to effects from global climate change and an increase in the population through its effect on agricultural products demand. The reuse of Treated Sewage Effluent (TSE) is not something new for many countries around the world. With good research and a set of policies it can be exploited for many different reuses. In Malta agriculture irrigation demand is high when compared to groundwater availability and farmers use groundwater directly from source. This is wrong for two reasons: the first is that the water is not being analysed and the second is that groundwater is a limited resource in that it is constrained in quality and quantity. On the other hand if TSE is used for agricultural purposes it will be treated accordingly and monitored all the time. Reusing TSE for agriculture is something sustainable as it is a recycled source, and less impact is inflicted on the natural resource. In this project 6 different water sources were used to irrigate lettuce and the yield was compared. The irrigation waters included TSE's, RO water and groundwater. No artificial fertilisers were used. During the growing period the length of the crop was measured on a weekly basis, and the mass, % dry matter, sap K and sap N03 -were measured after harvest. The soil was also analysed for conductivity and % SOM before planting and after harvesting. It was shown that crops irrigated with TSE have higher yield in terms of mass and % dry matter, and that low conductivity irrigation water makes the crop grow longer. Regards sap K and sap N03- the result was directly proportional to the concentration of these ions in the irrigation water. Soil conductivity was also altered according to the conductivity of the irrigation water. SOM was slightly changed with TSE irrigation, and decreased with low conductivity irrigation water. No effect of crop storage shelf life was observed. Although the results obtained are conclusive, more research is required on the use of TSE on large scale irrigation under varying scenarios.