Impact of sprinkler irrigation management on the Del Reguero river (Spain). I: Water balance and irrigation performance

Abstract

Irrigated agriculture notably increases crop productivity, but the generated irrigation return flows may induce surface water pollution by nutrients if irrigation water and fertilization management are inadequate. In this study, the Del Reguero watershed (Huesca, Spain) was characterized, and irrigation performance was assessed to identify sprinkler irrigation water management impact on surface and subsurface water losses during the 2008 and 2009 hydrological years. Farmers were interviewed, and soil and water use surveys were performed. The main water inputs and outputs of the system were measured (irrigation, precipitation, filter cleaning, and outflow surface drainage) or estimated (municipal waste waters, actual evapotranspiration, wind drift losses, and evaporation losses) and the evaluation of the irrigation performance was performed using various water management indexes. Thirty-two percent of the area contained platform soils or cambisols characterized by a small depth, high stoniness, and limited value of total available water. The main cultivated crops were corn, barley, alfalfa, and sunflower, occupying more than 83% of the irrigated area. The annual average water inputs were 3.1% higher than water outputs. However, the error balance is considered acceptable and its resulted inputs and outputs parameters values can be used to calculate nutrients mass balance. The annual average irrigation efficiency was low (72%), due to the fact that alfalfa and corn were inadequately irrigated. The average annual consumptive water use efficiency was high (91%), indicating that a high percentage of available water was destined for crop evapotranspiration. However, irrigation management was inadequate because there was an annual average water deficit of 9%, indicating that not all the water requirements of crops were met. This high deficit was justified by the reduced irrigation allocation received by sunflower and barley. These two crops were under-irrigated by 90 and 168 mm below their respective net irrigation requirements. At a watershed scale, the average annual seasonal irrigation performance index (SIPI) was 87%, which could indicate that all crops were water satisfied. However, the calculation of SIPI at field scale, revealed that alfalfa and corn were water satisfied (SIPI = 81% and 78%, respectively) and that barley and sunflower were water stressed (SIPI = 132% and 200%, respectively).