• Energy Research

The increasing shortage of water for crop irrigation in arid and semiarid regions is encouraging the use of non-conventional resources. In the last decade, seawater desalination has consolidated its position as an alternative source to increase the supply for agricultural irrigation in Spain and Israel, where the farmers’ acceptance is progressively rising, despite the supply price being much higher than that of other conventional water sources. This article describes the current situation of desalinated seawater production and supply to agriculture in the southeast of Spain, and analyzes key questions such as its role in regional water planning, the infrastructure needed for conveyance and distribution, the energy requirements, the production and distribution costs, and the final price to farmers. The study is based on descriptive and quantitative data collected from desalination plants and irrigation district managers through technical questionnaires and personal interviews. The results show how seawater desalination is effectively alleviating the regional constraints in the irrigated agriculture supply, and why it is becoming strategic to maintaining food production and socioeconomic development. However, the high-energy requirements and associated costs in comparison with other water sources limit a more widespread use for agriculture, and for this reason desalinated water still only plays a complementary role in most irrigation districts.

This study employs a methodological approach for estimating long-term series of monthly reference evapotranspiration (ETo) from historical data. To carry it out a regionally calibrated version of the Hargreaves equation was applied at old ordinary weather stations which only provide data of air temperature and precipitation. The proposed approach was based on the analysis of: (1) the Hargreaves coefficient obtained by local calibration from data of 66 modern automatic weather stations; (2) the regional characterization of the spatial variability of that coefficient by means of a “regional function”; and (3) the final application of this function to the old ordinary weather stations. This approach was assessed under the semiarid conditions of the Segura River Basin (south-eastern Spain) by comparing ETo estimates against those obtained with the Penman-Monteith method, which was used as reference. Spatial variability of the Hargreaves coefficient was well correlated with the annual and monthly means of daily temperature range, so they were selected as explanatory variables for the regionalization of the Hargreaves coefficient following two approaches: a global regional function and monthly regional functions. The regionally calibrated version of the Hargreaves equation by monthly functions clearly improved the performance of its original parameterization (average relative error decreased from 19.8% to 10.1%) although, as expected, estimates were not as good as those obtained with the local calibration (average relative error=7.7%).

Citrus fruit production is a major food business with global relevance in the agricultural sector. The surface area of citrus irrigated with desalinated seawater in Spain, the leading citrus producer of Europe, has increased dramatically in the last decade. Desalinated seawater has alleviated water scarcity, but is facing environmental and agronomical challenges due to its high energy consumption and high boron content. The latter particularly affects citrus production due to its sensitivity to boron, since additional water treatment may be required to prevent phytotoxicity damage. The objective of this work was twofold: to quantify and compare, for the first time, the life cycle environmental footprint of (i) organic and conventional grapefruit systems irrigated with desalinated seawater, and (ii) two on-farm boron reduction technologies, namely reverse osmosis and ion exchange resins. Life Cycle Assessment has been used to evaluate the grapefruit production systems and the two technologies. The systems compared had similar characteristics (cultivar and planting density), to enable a fair comparative assessment between organic and conventional woody crops. The results show that the organic grapefruit production had better environmental performance than the conventional system in all selected impact categories and both, land and mass, functional units. The comparison of deboronation technologies showed that ion exchange resins caused a much (one order of magnitude) lower environmental footprint than reverse osmosis. Overall, this study shows that the most environmentally friendly grapefruit system irrigated with desalinated seawater was organic production combined with the use of ion exchange resins for deboronation. This research was supported by the projects SEA4CROP (PID2020-118492RA-C22), funded by MCIN/AEI/10.13039/501100011033 (Spain), and Solution4Farming (PCI2021-122031-2A), funded by MCIN/AEI/10.13039/501100011033 (Spain) and the European Union's NextGenerationEU/PRTR, Horizon2020 Research & Innovation Programme, Joint Call of the Cofund ERA-Nets (grant agreements 696356, 771134, 862665 and 696231). Additional financial support was provided by the AGROALNEXT programme supported by MCIN with funding from European Union NextGenerationEU (PRTR-C17.I1) and by Fundación Séneca with funding from Comunidad Autónoma Región de Murcia (CARM) and the European program NextGenerationEU by the Science and Innovation Missions 2021, Recovery, Transformation and Resilience Plan, NextGenerationEU under the CDTI project SOS-AGUA-XXI" (MIG-20211026). B. Gallego-Elvira acknowledges the support from the Spanish Ministry of Universities (‘Beatriz Galindo’ Fellowship BEAGAL18/00081). Imbernón-Mulero acknowledges the financial support for his PhD work from the project SEA4CROP and the predoctoral program of the Technical University of Cartagena (RV- 484/21, UPCT, Spain).

Greenhouse cultivation in the Mediterranean region has undoubtedly enhanced the economic growth and has generated social benefits by making an efficient use of resources. However, these production systems caused undesirable environmental impacts. In order to move towards cleaner production in greenhouse areas, this study has assessed the potential environmental benefits and trade-offs of the integration of an on-farm reverse osmosis system powered by photovoltaic solar energy to recycle the drainage effluents from greenhouses. To that end, we compare the environmental footprint of a greenhouse tomato crop using this technology in a hydroponic system (HS), versus the conventional sanded soil 'enarenado' (CS) with free-drainage to soil. Additionally, for comparison, three independent irrigation sources (desalinated seawater with low electrical conductivity and two different mixes of underground and desalinated water, with moderate and high electrical conductivity, respectively) were evaluated. The use of desalinated seawater can help reduce the overexploitation of aquifers, although if the desalination process is not done with clean energy it also comes with a negative impact on the carbon footprint. Life Cycle Assessment (LCA) was used to analyse and evaluate six environmental impact indicators associated with these production systems and water treatments. In addition, a sensitivity analysis was conducted to explore the potential environmental benefits of increasing the use of renewable energy for desalinated water production, whilst also curbing the common over-fertilisation malpractice reported in the study area. Based on our findings, the HS with leachate treatment technology showed, compared to the CS system, a significant reduction in the eutrophication (72 %), although it did inevitably increase the depletion of fossil fuels (43 %) global warming (37 %) and acidification (32 %) impacts, due to the need for additional infrastructure and equipment. Among the inputs considered for the cultivation systems, the greenhouse structure, and the production of fertilisers and electricity for fertigation represented the highest environmental burdens. When comparing the three irrigation treatments, it was observed that the partial substitution of desalinated seawater by brackish groundwater substantially mitigated (27 %) the global warming footprint. The sensitivity analysis revealed that a significant reduction in the environmental impact is feasible.

Agroecological ecosystems produce significant carbon dioxide fluxes; however, the equilibrium of their carbon sequestration, as well as emission rates, faces considerable uncertainties. Therefore, sustainable cropping practices represent a unique opportunity for carbon sequestration, compensating greenhouse gas emissions. In this research, we evaluated the short-term effect of different management practices in alleys (tillage, no tillage, alley cropping with Rosmarinus officinalis and Thymus hyemalis on soil properties, carbon sequestration, and CO2 emissions in a grapefruit orchard under semiarid climate). For two years every four months, soil sampling campaigns were performed, soil CO2 emissions were measured, and rhizosphere soils were sampled at the end of the experimental period. The results show that alley cropping with Thymus and Rosmarinus contributed to improve soil fertility, increasing soil organic carbon (SOC), total nitrogen, cation exchange capacity, and nutrients. The CO2 emission rates followed the soil temperature/moisture pattern. Tillage did not contribute to higher overall CO2 emissions, and there were no decreased SOC contents. In contrast, alley crops increased CO2 emission rates, especially Rosmarinus; however, the bigger root system and biomass of Rosmarinus contributed to soil carbon sequestration at a greater rate than Thymus. Therefore, Rosmarinus is positioned as a better option than Thymus to be used as an alley crop, although long-term monitoring is required to evaluate if the reported short-term benefits are maintained over time.

Spain is the leading citrus producer in the European Union, with the Segura River Basin in southeastern Spain playing a crucial role in this industry. However, the impact of local agricultural production on water appropriation has been overlooked. This study assesses the water footprint (WF) of both conventional and organic citrus production using the Water Footprint Network approach, addressing beneficial practices aiming to reduce the water appropriation impact. Focusing on four citrus fields, the evaluation covers green, blue, and grey components of the WF, and secondary impacts from electricity and fossil fuel consumption, which are usually omitted from the WF assessments. The results indicate that the total WF for organic orange and lemon production is over 19% lower than for the conventional system. Notable differences are observed in the blue component, attributed to the use of vegetative mulches, and in the grey component due to the reduced impact of fertilizers in organic practices. The individual and total WF values are lower than those reported in other citrus studies, and are linked to efficient resource management in semi-arid regions that helps overcome water scarcity. Nevertheless, the sustainability analysis reveals major challenges for the citrus sector in the basin, highlighting the strain on resources given the limited water availability. The available water remaining (AWARE) indicator demonstrates extremely high potential water deprivation in the area. Overall, the study underscores the necessity of integrating WF analyses in agricultural planning to manage resource scarcity effectively. Future research should focus on developing precise methodologies and incorporating unconventional farming practices to enhance sustainability. This research provides valuable insights for stakeholders aiming to optimize water use in agriculture under scarce resource conditions.

The present study evaluated the effects of inoculation with arbuscular mycorrhizal fungi (AMF; Glomus iranicum var. tenuihypharum sp. nova) on the physiological performance and production of lettuce plants grown under greenhouse conditions and supplied with reclaimed water (RW; urban-treated wastewater with high electrical conductivity; 4.19 dS m(-1)). Four treatments, fresh water, fresh water plus AMF inoculation, RW and RW plus AMF inoculation, were applied and their effects, over time, analyzed. Root mycorrhizal colonization, plant biomass, leaf-ion content, stomatal conductance and net photosynthesis were assessed. Overall, our results highlight the significance of the AMF in alleviation of salt stress and their beneficial effects on plant growth and productivity. Inoculated plants increased the ability to acquire N, Ca, and K from both non-saline and saline media. Moreover, mycorrhization significantly reduced Na plant uptake. Under RW conditions, inoculated plants also showed a better performance of physiological parameters such as net photosynthesis, stomatal conductance and water-use efficiency than non-mycorrhizal plants. Additionally, the high concentration of nutrients already dissolved in reclaimed water suggested that adjustments in the calculation of the fertigation should be conducted by farmers. Finally, this experiment has proved that mycorrhization could be a suitable way to induce salt stress resistance in iceberg lettuce crops as plants supplied with reclaimed water satisfied minimum legal commercial size thresholds. Moreover, the maximum values of Escherichia coli in the reclaimed water were close to but never exceeded the international thresholds established (Spanish Royal Decree 1620/2007; Italian Decree, 2003) and hence lettuces were apt for sale.