Sustainability and environmental assessment of fertigation in an intensive olive grove under Mediterranean conditions

Abstract

Water and nitrogen surpluses are major concern for the new intensive olive groves in South of Portugal. In this study, field measurements were integrated with a system model, Root Zone Water Quality Model (RZWQM2) to assess the sustainability and environmental impact of fertigation in an intensive olive grove (Olea europaea L. var. Arbequina). The model provided acceptable predictions of evapotranspiration, soil moisture and nitrate contents. Based on model simulations, under current fertigation practices, 57% of the irrigation applied was lost via drainage, while 71% and 5% of fertilizer N inputs were lost through leaching and denitrification, respectively. The non-fertilizer N input from soil organic matter (OM) satisfied 64% of the crop N needs. The tested model was used to predict the impacts of a full irrigation (FIFC) and two regulated deficit irrigation schemes (RDI75, RDI50) on drainage and N leaching. In FIFC the atmospheric demand was met while the application frequency maintained the water storage below the soil field capacity. In RDI75 and RDI50 the irrigation application amount between stone hardening and onset of ripening was 75 and 50% of FIFC respectively.Compared with the current practice, the FIFC decreased drainage and N leaching by 47% and 90% respectively, while maintaining the actual evapotranspiration (ETa). The RDI75 seems to be the most adequate for the studied agro-system since, in relation to the FIFC, it saved 13% of irrigation water with only 5% decrease in ETa. Furthermore, the 15% reduction in leaching, together with the 19% increase in soil OM mineralization optimized the trees N uptake. The study of three different N application rates for each irrigation scenario indicated that, to minimize residual storage, N should be applied according to plant needs, by using a real-time indicator based upon foliar analysis or the chlorophyll meter measurements.