Farida Dechmi

Analysis of an irrigation district in northeastern Spain: II. Irrigation evaluation, simulation and scheduling

In the first paper of this series, the Loma de Quinto Irrigation District (LQD) was characterised, and water use was assessed. In this work, the analysis of the LQD is completed with field irrigation evaluations, solid-set sprinkler irrigation simulations and irrigation scheduling for optimal crop yield. The results of the irrigation evaluations indicated that the average Christiansen coefficient of uniformity (CU) for solid-sets, centre-pivots and linear-moves was 68.0, 75.5, and 80.0%, respectively. In solid-sets CU was severely reduced by wind speed. However, in centre-pivots and linear-moves CU was higher in evaluations with wind speeds between 2 and 6 m s-1 than under calm conditions. The evaluation data set was used to validate a ballistic solid-set sprinkler irrigation simulation model. The performance variables used for model validation were CU and the potential application efficiency of the low quarter (PAElq). Both variables were adequately predicted in the range of the observed values. The model was used to extend the evaluation results to all the solid-set plots in the LQD. CU maps were produced for different wind speeds and operating pressures. These maps can be used to identify plots with low irrigation performance. The effect of irrigation scheduling on crop yield and net benefit was analysed using the CropWat simulation model. Simulations of the 1997 irrigation practices performed on a limited number of plots detected a 12% decrease in crop yield due to deficit irrigation and/or large irrigation intervals. The introduction of an optimal irrigation schedule (avoiding yield reductions) would imply increasing the alfalfa seasonal irrigation depth by 101 mm, and applying light, frequent irrigation events. Due to labour scarcity in the LQD, the implementation of the optimal schedule would require a high degree of irrigation automation, which is currently unavailable. Taking into consideration the value of the additional yield and the costs of the extra irrigation water depth and the automation devices, the resulting net benefit would be 50 ha-1. The purpose of this analysis of the LQD is to contribute to the diagnostic analysis phase of an incipient Management Improvement Program at the LQD. In order to complete this phase, an interdisciplinary committee will perform a study not just on irrigation but on a wide scope of irrigated agriculture in the LQD. Author Keywords: Sprinkler irrigation; Irrigation uniformity; Simulation model

Evaluation Of BMPs Scenarios For Minimizing Phosphorus And Sediments Transport In Sprinkler Irrigation System

Simulation models are useful tools to quantify the effects of best management practices (BMPs). After SWAT (Soil and Water Assessment Tool) adaptation and calibration for intensive irrigated watershed, it has been used to evaluate the impact of several (BMPs) on water yield (WYLD), total suspended sediment (TSS), organic P (ORG_P), soluble P (SOL_P), and total P (TP) at the outlet of the Del Reguero stream watershed (Spain). Economic impacts of the BMPs on crop gross margin were also evaluated. In total, 6 individual scenarios and 14 combinations of various management practices including tillage (conservation and no-tillage), fertilizer (incorporated, recommended, and zero), and irrigation (adjusted to crop needs) were been tested. Results indicate that the best individuals BMPs (adjusted irrigation water use BMP) reduced WYLD to 31.4%, TSS loads 33.5%, and TP loads to 12.8%, in comparison of the initial conditions. When individual BMPs were combined, the percentage reductions of losses were increased. The BMPs combination between optimum irrigation application, conservation tillage and reduced P fertilizer dose was the best analysed one with a TP loads reduction about 22.6%. For corn and alfalfa, the best BMP scenario was the combination between conservation tillage and reduced P fertilizer dose, reaching an increase of gross margin by 309 € ha-1and 188 € ha-1, respectively. While for sunflower and barley, the best scenario was the combination between irrigation adjustment, conservation tillage and reduced P fertilizer dose. The increase of gross margin under this BMP was about 171 € ha-1and 307 € ha-1, respectively.