Ahorro de agua y energía en redes colectivas de riego presurizado mediante mejoras en el manejo del riego en parcela

Climate change, the growing limitations in the supply of irrigation water and the continuous increase of the world population present a great challenge to guarantee the world's food. It is necessary, among other things, to increase the arable land, intensify the crops and modernize the irrigation systems in a sustainable manner. The design and management of modernized areas should be oriented to increase production and optimize the efficiency of water and energy resources otherwise the systems will not be economically or environmentally viable. In this thesis, the capabilities of the ADOR-simulation software of irrigable areas have been increased, taking into account the characteristics of the physical environment, the economic aspects of agricultural production of irrigation, as well as the design and management of hydraulic irrigation infrastructures. The capacities of on-farm irrigation modules have been increased, incorporating, in addition to sprinkler solid-set irrigation system, the center pivot irrigation system (ADOR-Pivot) and the drip irrigation system (ADOR-Goteo). The ADOR-Crop module has been updated including more types of crops and double crops (double harvest). Finally, the response to the following on-farm irrigation management guidelines has been incorporated: low pressure irrigation, irrigation frequency and irrigation time (day and night irrigation). In a first phase of the work, the new parameters implemented in the tool have been adjusted and validated. To this end, five variants of a theoretical case study have been simulated in which the operation of the different on-farm irrigation systems, types of crops (simple crops, double crops) and alternative management patterns have been compared. The operation of a zone working at standard pressure in nozzle, 300 kPa, or at low pressure, 200 kPa has been analyzed. The comparison is made on irrigation quality, agronomic, economic and environmental variables. Once the changes implemented in the program were checked and validated, the irrigation area of Bardenas XI, of 931 hectares, was analyzed in a second phase of the work. The study of this area has been carried out for the current design in which the area is irrigated with natural pressure. This design results in different pressures between hydrants that limit the on-farm irrigation system that can be installed. The physical properties (available water holding capacity (AWC) and depth) of the soils of the area were characterized by field sampling and its subsequent processing in the laboratory. The spatial distribution of the soils, crops and the on-farm irrigation system was done using the Geographical Information System tool QGIS and taking into account the design premises of the irrigable area. The effect of meteorological variability was analyzed in the series 2004-2018 of the SIAR station of Ejea de los Caballeros on the hydrological, irrigation quality, agronomic, economic and environmental variables. Finally, two operating scenarios of the Bardenas XI irrigable zone were analyzed comparatively: 1) Assuming that there is natural pressure for the entire area to irrigate by sprinkler solid-set at 200 kPa in nozzle or 2) by installing a pumping station that increases the natural pressure so that all the parcels can irrigate by sprinkling solid-set at a standard pressure of 300 kPa in nozzle. The comparison was made on irrigation quality, agronomic, economic and environmental variables. The improvements made in the tool, which simulates the operation of alternative designs and management of an irrigable area, respond correctly to the results included in the scientific literature. Sprinkler solid-set irrigation systems need to apply greater volume of water to achieve the same production as the rest of the on-farm irrigation systems analyzed (center pivot machines and drip irrigation). The biggest losses of these systems, especially wind drift and evaporation losses (WDEL), are the ones that explain these differences. This is true for both simple crops and double crops. The hydraulic design of the network imposes limitations on the management of irrigation when the level of intensification of crops exceeds that which was raised in its design. The reduction in the nozzle working pressure in sprinkler irrigation systems (from 300 kPa to 200 kPa) does not have a significant effect on irrigation quality, irrigation volumes or crop production. However, the reduction in working pressure decreases the electrical needs (in the case studied, the electric bill is reduced by 28 per cent, Euros 58 ha-1), which increases the net profit of irrigated farms (4 per cent). The effect of irrigation duration on the hydrological and economic variables of irrigation depends on the type of soil. Thus, for soils with medium AWC, the two-hour irrigations are the most adequate, while when we have a soil with high AWC, the risks of two or more hours give rise to the same results. In the case studied, and for both types of soil, very frequent and short-term irrigations (one hour) are not the most appropriate, since they present lower yields, higher interception losses and lower net income. Regarding the management of irrigation in the area studied, the strategy of forcing the irrigation of corn to start at night is not profitable compared to an irrigation demand, especially when we have moderate-quality soils (medium AWC). The results indicate that the best irrigation management strategy depends on the conditions of the physical environment and the design of local infrastructures. In the analysis of the current design of the irrigable area of Bardenas XI, it is concluded that the factors that most affect the quality of irrigation are the on-farm irrigation system and the soils. The plots with sprinkler solid-set irrigation system are the ones that lower distribution uniformity (DU) and efficiency of application presented. This is because adverse weather affects these systems, more importantly increasing WDEL and reducing DU, which in turn results in lower efficiency. The plots with lowest percolation losses coincide in general with the plots that have the best soils from the hydraulic point of view (very deep soils with a high or very high AWC). Irrigation needs are also affected by the crop, by the weather and by the quality of irrigation. ix Regarding the comparison of Bardenas XI in the two operating scenarios of nozzle pressure, 300 kPa or 200 kPa, it is concluded that this decrease in pressure has a small effect on the variables that define the quality of irrigation, being uniformity and irrigation efficiency slightly lower in the low pressure treatments, 5 per cent and 2 per cent, respectively. However, these differences do not affect crop yields. On the other hand, the reduction of the operating pressure achieves an average saving of the electric cost of € 72 ha-1 year-1, which translates into an increase in the net benefit of 6 per cent on average.