Water status, gas exchange and crop performance in a super high density olive orchard under deficit irrigation scheduled from leaf turgor measurements

We evaluated the suitability of scheduling a regulated deficit irrigation strategy in a hedgerow olive orchard with high plant density from leaf turgor related measurements. Measurements were made for two consecutive years at an olive orchard with 1667 'Arbequina' trees per hectare where we had two deficit irrigation treatments, 45RDICC and 45RDITP, plus a full irrigation as a control. The two 45RDI treatments consisted on applying the same regulated deficit irrigation strategy, aimed to supply a total of 45% of the irrigation needs. The 45RDICC treatment however, was scheduled with the crop coefficient approach, while the 45RDITP treatment was scheduled with an irrigation scheduling approach based on leaf turgor related measurements, first suggested by Padilla-Díaz et al. (2016, Agric. Water Manage. 164:28-37). They worked at the orchard in 2014, and made a preliminary evaluation of the irrigation scheduling approach by comparing 45RDITP versus 45RDICC in terms of irrigation dose and frequency, predawn and midday stem water potential (Ψstem), and the fruit yields of each treatment. In this work, we considered the same variables as well as maximum daily values of stomatal conductance and CO2 net assimilation, the seasonal courses of the number of internodes in current-year shoots, leaf area and oil accumulation in the fruits, and total fruit and oil yields. All those variables were monitored both in 2014 and 2015, and we found no differences between the 45RDITP and the 45RDICC treatments, for any of them. The irrigation amounts applied to each treatment differed occasionally, but the total water supplies were similar to both 45RDI treatments. Our results, therefore, confirm the suitability of the irrigation scheduling approach proposed by Padilla-Díaz et al. (2016) to apply regulated deficit irrigation in commercial hedgerow olive orchards. We found additional evidence for the 15% changes on the irrigation amount recommended by the irrigation scheduling approach as being suitable for the orchard conditions. Caution must be taken when applying this approach to other olive orchards, since the relations between the tree water status and the shape of the daily curves recorded with the ZIM probes may depend on the cultivar and orchard conditions.