Analysis of an irrigation district in northeastern Spain I.: Characterisation and water use assessment

In this work, the Loma de Quinto irrigation district, located in Zaragoza (Spain) was characterised, and water use (WU) was assessed. The study was performed to contribute to the diagnostic analysis phase of an incipient management improvement process, in this sprinkler-irrigated district. The objectives of this first paper of the series include: (1) characterising the irrigation systems, soil types and crops; (2) evaluating irrigation performance through the relationship between on-farm WU and net irrigation requirements (NIR); (3) identifying factors affecting on-farm WU. In order to accomplish these objectives, statistical analyses of field data, district records on WU and farmers' interviews were performed. Technical deficiencies were detected in solid-sets, centre-pivots and linear-moves. A seasonal irrigation performance index (SIPI), defined as the percentage of NIR to seasonal water billing, was determined at each plot and for each of the three study years. The average inter-annual SIPI amounted to 127%, indicating that crops in the district were consistently water stressed. An analysis of the SIPI for the main crops in the district revealed that water stress was more intense in drought resistant and/or heavily subsidised crops (SIPI for sunflower was 142%). The average irrigation interval (12.3 days) and irrigation depth (44 mm) were too high for some of the soils in the district. Farmers adjusted the irrigation interval to meet the seasonal change in irrigation requirements. The irrigation depth was reduced in windy days. In two of the three study years, large plots used less water than small plots, at a rate of about -5 mm ha(-1). The high cost of irrigation water in relation to crop revenues, the technical deficiencies of the irrigation systems, and the limitations imposed by climate and soils appeared to be major causes of local water management problems. In a companion paper, irrigation evaluations and simulations are presented, and irrigation schedules for optimal crop yield are proposed and evaluated via simulation. (C) 2003 Elsevier Science B.V. All rights reserved.