Water use of irrigated almond trees when subjected to water deficits

Recently planted intensive almond plantations may have access to limited water supply due to water scarcity thus, information on almond water use under limited irrigation is needed. Here, the soil water balance was used to assess the consumptive use (ET) of full irrigated, moderately stressed and severely stressed almond trees over a three-year study, as well as the relation between applied water and ET. Sap flow measurements in eight experimental trees were used to obtain independent transpiration (T) measurements. Evaporation from soil (ES) was modelled to estimate tree T from the water balance. Relative consumptive use in the deficit irrigation (DI) treatments largely exceeded the relative applied water, highlighting the need to measure ET in stressed treatments for hydrologic purposes. The moderately stressed treatments (irrigated at 65.5% of full irrigation) consumed 79.0% of maximum evapotranspiration (ET of 897 mm), while the severely stressed treatment consumed 63.6% of ETc (ET of 722 mm) when applied water was only 39.6% of control. On average, almond ETc approached 1200 mm, Seasonal evolution of the transpiration coefficient yielded maximum peak values ranging from 0.99 to 1.08, and minimum peak values of 0.33 attained with a severe deficit irrigation strategy. Transpiration measured by Compensated Heat Pulse-Calibrated Average Gradient sap-flow (x), was compared to water balance T estimates (y), and yielded a very good relation over the three years of study (y = 0.90x + 4.23, r2 = 0.81). The sap flow measurements proved to be useful to overcome the limitations of the soil water balance technique, revealing that almond trees were able to extract water from below the monitored depths and suggesting that deep percolation event must have occurred in spring and autumn.