Yield and Water Productivity Responses to Irrigation Cut-off Strategies after Fruit Set Using Stem Water Potential Thresholds in a Super-High Density Olive Orchard

An increase in the land area dedicated to super-high density olive orchards has occurred in Chile in recent years. Such modern orchards have high irrigation requirements, and optimizing water use is a priority. Moreover, this region presents low water availability, which makes necessary to establish irrigation strategies to improve water productivity. An experiment was conducted during four consecutive growing seasons (2010-2011 to 2013-2014) to evaluate the responses of yield and water productivity to irrigation cut-off strategies. These strategies were applied after fruit set using midday stem water potential (9 stem) thresholds in a super-high density olive orchard (cv. Arbequina), located in the Pencahue Valley, Maule Region, Chile. The experimental design was completely randomized with four irrigation cut-off treatments based on the psi(stem) thresholds and four replicate plots per treatment (five trees per plot). Similar to commercial growing conditions in our region, the psi(stem) in the T-1 treatment was maintained between -1.4 and -2.2 MPa (100% of actual evapotranspiration), while T-2, T-3 and T-4 treatments did not receive irrigation from fruit set until they reached a psi(stem) threshold of approximately -3.5, -5.0, and -6.0 MPa, respectively. Once the specific thresholds were reached, irrigation was restored and maintained as T1 in all treatments until fruits were harvested. Yield and its components were not significantly different between T-1 and T-2, but fruit yield and total oil yield, fruit weight, and fruit diameter were decreased by the T-3 and T-4 treatments. Moreover, yield showed a linear response with water stress integral (S-psi), which was strongly influenced by fruit load. Total oil content (%) and pulp/stone ratio were not affected by the different irrigation strategies. Also, fruit and oil water productivities were significantly greater in T-1 and T-2 than in the T-3 and T-4. Moreover, the T-2, T-3, and T-4 treatments averaged 37, 51, and 72 days without irrigation which represented 75-83, 62-76, and 56-70% of applied water compared with T-1, respectively. These results suggest that using the T-2 irrigation cut-off strategy could be applied in a super-high density olive orchard (cv. Arbequina) because it maintained yields, saving 20% of the applied water.