Optimization of deficit irrigation through monitoring the plant and soil water status in adult lemon trees

Agriculture located in arid-conditions is under high pressure for water resources, due to scarcity and poor quality of water resources to a large extent. Under these conditions, this sector may need up to 70% of the available water, and there is a high level of competition with other economic sectors. The Region of Murcia (Spain) is one of the main productive areas of the country and has the largest irrigated area in relation to its extension. The SE Spain is characterized by a robust hydraulic infrastructure, efficient irrigation systems and a high incorporation of technology for irrigation scheduling. Also, a significant decrease in water resources due to climate change is projected, so it is necessary to maximize irrigation water use efficiency (iWUE) to ensure the economic and environmental sustainability of the sector. Therefore, the main objective of the study was to increase the iWUE and nutrient use to maximize the sustainability of the lemon trees ‘Fino 95’ (Citrus limon L.) in Campo de Cartagena by monitoring the plant and soil water status, during two consecutive seasons. The orchard was established in a 6.5 × 4.5 m planting frame in 2010 with a drip irrigation. A randomized experimental design was established with 12 trees as an experimental unit. Two treatments with four replicates were tested: (i) a control (CTL) irrigated to satisfy the 110% of the crop evapotranspiration (ET_c) during the entire crop cycle according to FAO; and (ii) a precision irrigation treatment (PI), irrigated in both seasons as CTL until the start of the fruit-phase II in which the irrigation was reduced by 40%. Several multispectral vegetation indices over canopy were calculated monthly to evaluate the irrigation effect on chlorophyll content and crop vigor. NDVI ranged from 0.8-0.87 and CGI from 4.3-8.7, both reaching maximum values in December, but no differences between treatments were detected. The results confirm the possibility of applying regulated deficit irrigation strategies on lemon trees, achieving a 34% increase in iWUE, and a water saving of around 25% with respect to the CTL treatment. However, the water deficit period should be better delimited according to the trunk growth in this period, as has recently been proven in other citrus fruits, in order not to affect the earliness of the harvest and to obtain a higher percentage of irrigation water savings.

Acknowledgments: The authors would like to thank the ‘Sindicato Central de Regantes del Acueducto Tajo-Segura’ for funding this experiment through the agreement “6217/20IA-C” with the UPCT.