Nutrient monitoring of sewage water irrigation: Impacts for soil quality and crop nutrition

Abstract

Agriculture in the Middle East region, specifically crop production (mainly cereals and food and forage legumes), is invariably limited by low rainfall and thus soil moisture. Although irrigation is contributing to increased yields, its potential is also limited because of few surface-water sources (rivers, lakes) and declining groundwater tables. The only source of water that is increasing is urban wastewater. Such waters are rarely treated in the Middle East but are nonetheless used for irrigation in perimeters of urban areas. Despite the potential health hazards of using such waters, crop benefits are evident to farmers. This study involved monitoring of the Quake River, south of Aleppo, Syria, where it irrigates about 10,000 ha of mixed crops (e.g., cotton, cereals, oil crops, and vegetables). The water was sampled at various points along the river in winter and summer (1997-98) and again 6 years later (2003) and analyzed for nitrate, ammonium, phosphate, potassium (K), micronutrients, salinity, and pH. A similar suite of analyses, plus organic matter, was done on soil profiles along the river and progressively away from it. The river water was rich in major and micronutrients and, with normal irrigation amounts, was sufficient to supply the needs of most crops, thus avoiding fertilizer use. These nutrients increased in the soil profiles with time. The nutrient value of such untreated wastewater, as well as being a source of irrigation water, re-enforces the argument for treatment plants to promote the safe use of this valuable resource in a drought-prone and nutrient-deficient region.