Effects of chlorides in effluents used for irrigation on the irrigated crops

摘要

Chloride is an essential micronutrient as a cofactor in the oxidation of water in photosynthesis and as an activator of enzymes. It is readily taken up by plants. Chloride also serves in the plant as a charge balance during cation transport, and contributes to cell hydration and turgor maintenance. In the soil, chloride balances the positive charge of the soluble cations Na, Ca, Mg, and potassium. Treated effluent water, which is increasingly used for agricultural irrigation, contains higher chloridelevels then the potable water from which it is derived. High concentrations of chloride in the irrigation water or the soil are toxic to plants and may affect plant function and reduce productivity. Despite the voluminous literature on saline soils, itis difficult to answer the question: how long can water containing high chloride levels safely be used for agricultural purposes under given conditions before damage to soil and plants is observed. The answer to this question must take into considerationsoil clay content and clay type, irrigation methods, evaporation conditions, and plant type and composition. The chloride anion is very stable and will not leave the soil system unless it is leached by an excess of good quality irrigation water, or removed from the soil by exported vegetative plant parts. Continuous long-term utilization of recycled water for irrigation may therefore increase the chloride content of the soil, and without proper leaching it will deteriorate soil fertility, and under extreme conditions may render the soil unproductive.