MODELING NUTRIENT BALANCES IN THE RIO MANNU BASIN AND SCENARIO ANALYSIS OF THE IMPACT OF FERTILIZER REDUCTION

The Rio Mannu River Basin (Sardegna Island, Italy) is experiencing an intensification of agriculture, and correspondingly, irrigation areas are increasing. Like many Mediterranean areas, this basin is characterized by water shortage and diffuse pollution from agricultural sources. It is than important to design, evaluate and adopt adequate management policies to prevent further water quality impairment. The Soil and Water Assessment Tool (SWAT), a model for agricultural watersheds, was applied to simulate hydrological processes and evaluate current and future nutrient loads. An alternative scenario that assumes a reduction in fertilizer was simulated. This option was assessed by considering the effects on water balance, water quality, crop yields and economic benefits. The model was able to simulate the hydrologic cycle and water quality, notwithstanding an insufficient availability of measured data. This study suggests that a better use of fertilizers could substantially reduce the amount of nutrients flowing into surface waters, even though the effects of such a policy on crop yield and farm income are in some cases negative.