Effect of high saline irrigation water on the sustainability of barley cultivated in a Mediterranean climate

The Mediterranean agrosystem 'Campo de Cartagena' (Murcia, Spain) faces a complex challenge, due to almost permanent water scarcity and high diffuse nitrate contamination of the groundwater. The electrical conductivity (EC) of groundwater can reach ≈6.5 dS m^-1 and ≈96 mg L^-1 of N (NO₃^-). In contrast, the EC of water from the Tajo-Segura water transfer is ≈1.5 dS m^-1 and contains <≈5 mg L^-1 of NO₃^-. Therefore, groundwater quality limits this resource only for tolerant or resistant crops, among them, barley is considered a salinity resistant crop with low nutritional requirements. Thus, the objective of our work was to evaluate the agronomic response of barley 'Shakira' (Hordeum vulgare L.) irrigated with saline water and with the incorporation of continuous monitoring sensors of soil water status and remote sensing. The crop was established during 2022 winter with a seeding rate of 200 kg ha^-1 and a drip irrigation system. A completely randomized block design was established with 3 treatments with three blocks and each experimental unit corresponded to 150 m². The treatments were: (i) "Control", irrigated with 100% water from the water transfer with an EC of 1.46 dS m^-1; (ii) "High salinity", irrigated with a mixture of 40% water from the water transfer and 60% groundwater to reach an EC of 4.5 dS m^-1, and (iii) "Very high salinity", irrigated with 100% groundwater with an EC of 6.5 dS m^-1 and with a total N input of 36.2 kg ha^-1 from irrigation water. In the rest of the treatments, fertilizer units were adjusted by proportional fertigation with ammonium-nitrate. Irrigation was scheduled to allow a 30% depletion of field capacity in the active root zone. At the end of the irrigation period, the soil EC_1:5 between 0.05 and 0.4 m was significantly higher in proportion to the groundwater treatments. However, no differences were detected in soil EC_1:5 or nitrate concentration up to 0.6 m depth. No differences were detected in the yield parameters, reaching an average of 3.5 t ha^-1, 16.6 grains per spike, and a 1000-grain weight of 52.2 g. Likewise, the caliber distribution was not affected and the proportion of grains larger than 2.8 mm reached an average of 89.4%. Regarding grain quality, germination capacity (>99%) and dry protein were not affected (10.4%). NDVI and GCI vegetation indices were calculated to evaluate the treatments effect on chlorophyll content and crop vigor, when plants reached 30 and 100% cover and pre-harvest. NDVI ranged from 0.3-0.71 and CGI from 1.5-3.37, both reaching maximum when the crop was fully covered, but no differences between treatments were detected. The results obtained validate the economic viability of barley cultivation irrigated with highly saline water and, from an environmental point of view, highlight the importance of incorporating quantitative and objective methods for irrigation scheduling to minimize water and nutrient leaching.

Acknowledgments: The authors would like to thank the ‘Estrella de Levante’ Foundation for funding this experiment through the agreement “6699/21IA-C” with the UPCT. In addition, we thank to Laura Soria-López for the technical support in the laboratory evaluations.