Good agricultural practices to minimize nitrate leaching when irrigating with saline water

Abstract

Practices through which the leaching of nitrates can be minimized when irrigating with saline water were identified in this study. This was achieved by studying the factors that contribute to the process of leaching and by proposing good practices to control them. This was mainly done through analysis of the reviewed data and literature. The study revealed that the root of the problem lies in the lack of good quality water for irrigation in Malta. This is the result of over-abstraction of groundwater, lack of rainwater harvesting and problems in the supply and quality of sewage to the treatment plant. The average electrical conductivity of water from the mean sea level aquifer is around 3.7dS/m while that of the sewage treated effluent presently stands at around 9.0dS/m. The effects of salt on the soil and plants were studied, and hence the importance of salt leaching for salinity management in agriculture was well understood. Ways through which the crop yields are not affected by salinity, but at the same time the leaching is avoided, had to be found out. Understanding the way the salt is distributed in the soil under different irrigation methods, made it clear why drip irrigation can be a very good tool to reduce the leaching of nitrates. Additionally, good management of the irrigation water is needed. Irrigation scheduling can help the farmer to achieve this by giving him information on the amount of water needed by the particular crop being grown, and when to irrigate. The economic feasibility of utilizing good quality water by using rainwater and desalinated water was analysed and discussed. The study also revealed that the solution for the problem of nitrate leaching has to be complimented by good management of nitrogen in the soil. On one hand, literature on crop nutrient requirements highlighted the importance of nitrogen for plant growth. On the other hand, the sourced data revealed that the nitrate levels in the groundwater of the Maltese Islands are rather high. This creates problems for supplying this water for potable use due to the health hazards associated with the presence of this compound. The reasons for the high vulnerability of nitrate leaching were studied in detail. It was then possible to identify the best ways by which the losses of nitrogen from the soil caused by over-irrigation can be reduced. This can mainly be achieved by using a fertilizer plan for the supply of nutrients to the plants at the correct rates, in the best manner, and at the right time. Techniques that prevent any unused nitrogen in the soil from being leached can also be very useful.