Abstract
Reports on the annual effects of deficit irrigation regimes on olive trees are critical in shedding light on their impacts on water use, yield, and water productivity in distinct olive growing climate regions of the world. From the account of a four-year experiment, the aim of this work is to add insight into such effects on olive growing in southern Portugal. We worked with trees in an intensive ‘Cobrançosa’ orchard (300 trees ha−1) under full irrigation (FI) treatment and two regulated deficit irrigation (DI) treatments designed to replace around 70% and 50% of the FI water supply, respectively. Crop transpiration (T), irrigation water use (IWU), total water use (TWU), irrigation water use efficiency (IWUE), yield (Ya), and water productivity (WP) obtained from all treatments were analyzed, as well as their crop coefficients (Kc), simulated with the SIMDualKc software application for root zone and soil water balance based on the FAO dual crop coefficients. As expected, IWUE of the 50DI treatment was the highest among treatments, with 70DI being slightly lower. Ya showed alternate bearing with an “on-off” year sequence and was consistently higher for the 70DI treatment. WP (the ratio of Ya to IWU) values for the 70DI treatment were also consistently the highest among all treatments and years. The mean simulated Kc act values for 70DI and 50DI for the initial, mid-, and end-season compared well to the FAO56 Kc for olive crops. In general, to rank the irrigation treatments, 70DI presented the highest conversion efficiency among all treatments and years, providing a suitable DI alternative for our ‘Cobrançosa’ orchard. The 50DI treatment may be an attractive DI regime to undertake under scarce farm water resources or the expansion of olive hectares under water constraints.
Highlights
Alentejo is the region in Portugal with the largest area devoted to olive growing, making up approximately 52% of all olive growing areas, and it is where the economic impact of olive growing is most significant [1]
An average of 417 mm of irrigation water use (IWU) was supplied to full irrigation (FI), for an average of 267 and 186 mm supplied to 70% deficit irrigation (70DI) and 50% deficit irrigation (50DI), respectively, in the same period
Deficit irrigation (50DI) regimes applied to olive orchards from 2011 to 2014
Summary
Alentejo is the region in Portugal with the largest area devoted to olive growing, making up approximately 52% of all olive growing areas, and it is where the economic impact of olive growing is most significant [1]. In 2010, olive groves occupied approximately 162,834 hectares in Alentejo [2], and projections estimate that the olive oil national production will be of around 100,000 Mg by 2020 [3]. Such an expansion requires from farmers an acute and careful irrigation water management of their orchards, as this is a region of scarce water resources, where water plays a decisive role in agricultural development. The dual crop coefficient approach using a density factor to simulate the evapotranspiration of a peach orchard: SIMDualKc model versus eddy covariance measurements.
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