Abstract:In California, alfalfa is grown on a large area ranging between 325,000 and 410,000 hectares and ranks among the thirstiest crops. While the hay production industry is often scrutinized for the large usage of the state's agricultural water, alfalfa is a crucial feed-supplier for the livestock and dairy sectors, which rank among the most profitable commodity groups in the state. Sub-surface drip irrigation (SDI), although only practiced on approximately 2% of the alfalfa production area in California, is claimed to have the potential to significantly increase hay yield (HY) and water productivity (WP) compared with surface irrigation (SI). In 2014-2016 we interviewed a number of growers pioneering SDI for alfalfa production in Central and Southern California who reported that yield improvements in the order of 10-30% and water saving of about 20-30% are achievable in SDI-irrigated fields compared with SI, according to their records and perceptions collected over few years of experience. Results from our research on SDI at the University of California, Davis, revealed significantly smaller yield gain (~5%) and a slight increase of water use (~2-3%) that are similar to findings from earlier research studies. We found that most of the interviewed alfalfa producers are generally satisfied with their SDI systems, yet face some challenges that call for additional research and educational efforts. Key limitations of SDI include high investment costs, use of energy to pressurize water, the need for more advanced irrigation management skills, and better understanding of soil-water dynamics by farm personnel. SDI-irrigated fields also need accurate water monitoring and control, attentive prevention and repair of rodent damages, and careful salinity management in the root zone. In this paper we attempt to evaluate the viability of the SDI technology for alfalfa production on the basis of preliminary results of our research and extension activities, with focus on its water and energy footprints within the context of resource efficiency.

IntroductionIn the interest of sustainable development and the minimization of climate change impacts, national and international policies are prioritizing the improvement in the use of the natural resources. Water is an essential and limiting resource for private use, industry and agriculture that requires large amounts of energy for AbstractThe high energy requirements and the rising costs highlight the need to reduce the energy dependence of the irrigation sector. Alternative management strategies have been developed to reduce the energy consumption of the irrigated areas and to improve the efficiency in the water and energy use. In addition, the renewable energy sources are starting to be considered as an alternative to reduce energy costs with smaller environmental impacts. In this work, a new methodology, that combines sectoring as energy saving measure and solar energy, is developed. Thus, it reduces the energy requirements and the dependence on conventional energy resources. This methodology is applied to the irrigation district of Bembézar Margen Izquierda (Córdoba, Spain). The results show that organizing the network in two irrigation sectors, annual potential energy savings of 30.8% were achieved. Therefore, this measure reduces the annual energy bill in 30.4% without major investments. Then, a 2.1 MW photovoltaic would supply energy to the sector with higher energy consumption. However, conventional energy would be required (with an annual cost of € 33.6 ha -1 ) when solar energy is not available or it is not enough to supply the demanded flows. Both measures together would reduce the energy costs in 71.7% and the greenhouse gases emissions in 70.5%. The total investment would be Me 2.8 but with a payback period of 8 years. At present, solar energy is a technically and economically viable alternative, which offers both economic and environmental benefits.Additional key words: water management; renewable energy; solar PV; greenhouse gas emissions.* Corresponding author: g22carco@uco.es Received: 20-11-13. Accepted: 20-06-14.Abbreviations used: AC (alternating current); BMI (Bembézar Margen Izquierda); DC (direct current); GHG (greenhouse gases); IPS (intelligent power system), IRR (internal rate of return); MPPT (maximum power point tracker); NPV (net present value); OHPM (open hydrant probability matrix); PV (photovoltaic); RIS (annual relative irrigation supply); S1 (Sector 1); S2 (Sector 2); WEBSO (water and energy based sectoring operation). Glossary: E [daily energy demanded by the pumping station in the peak demand month (kWh)]; EF [emissions conversion factor (kg CO 2 eq kWh -1 )]; E mjl X P [energy demand at the pumping station in month (m), management scenario (j) and operating sector (l) (kWh)]; E T [annual energy consumption in the pumping station (kWh)]; G [global irradiation on the PV array plane for the peak energy demand day (kWh m

In recent years, energy consumption for irrigation has grown rapidly. Actually, nowadays energy represents a significant percentage on the total water costs in irrigation districts using energy to pressurize water. With the aim of improving energy efficiency in the Fuente Palmera irrigation district, was applied the protocol for conducting energy audits in irrigation districts developed by Spanish Institute for Diversification and Energy Savings (IDAE). The irrigated area organized in two independent sectors according to a homogeneous elevation criterion is analyzed and simulated. The potential energy savings derived from this measure was evaluated. For this purpose, a model based on the hydraulic simulator EPANET has been carried out. Its energy demand was estimated in 1,360 kWh ha -1 and its overall energy efficiency in 56%. The district was globally classified in group C (normal). Results show potential energy savings of up to 12% were obtained when the network was divided in sectors and farmers organized in two irrigation shifts. Further energy savings could be achieved by improving the hydraulic structures, such as the pumping station or the network layout and dimensions.Additional key words: energy efficiency; pressurised irrigation networks; water management; water supply systems. ResumenLa importancia de las auditorías energéticas en zonas regables. El caso de la zona regable de Fuente Palmera (España)En los últimos años, el consumo de energía en el regadío ha crecido de forma significativa. De hecho, hoy en día la energía representa un importante porcentaje de los costes totales del agua en las comunidades de regantes que usan energía para presurizar el agua. Con el objetivo de mejorar la eficiencia en el uso de la energía en la Comunidad de Regantes de Fuente Palmera, se ha aplicado el protocolo para la realización de auditorías energéticas, elaborado por el Instituto para la Diversificación y Ahorro de Energía (IDAE). Se ha analizado y simulado los ahorros potenciales de energía alcanzados si se reorganiza la demanda en turnos de riego, sectorizando la red en grupos de cota homogénea. Esta medida ha sido evaluada mediante el simulador hidráulico EPANET. Su demanda de energía se estimó en 1.360 kWh ha -1 y su eficiencia energética global en el 56%. De esta forma se clasificó la comunidad dentro del grupo C (normal). Los resultados muestran ahorros potenciales de energía hasta el 12% mediante la sectorización de la red y la organización de los regantes en dos turnos. Medidas alternativas de mejora en las estructuras hidráulicas, tales como en la estación de bombeo o en el diseño de la red alcanzarían relevantes ahorros energéticos.Palabras clave adicionales: eficiencia energética; gestión del agua; redes de riego a presión; sistemas de suministro de agua. * Corresponding author: jarodriguez@uco.es Received: 26-02-10; Accepted: 18-06-10.Abbreviations used: ECI (energy charge index), EDR (energy dependence rate), ER (energy required), ESE (energy supply efficiency), IDAE (Instituto para la Diversi...