Irrigation targeting deep soil water storage for mitigating water supply uncertainity in orchards

The Mediterranean climate in general and particularly in Israel, has a typical unsynchronized water supply, with rain during the winter and almost no precipitation during the hot summers. Orchards require extensive water resources, in order to meet the high demand, even at peak transpiration times during summer. While Israeli farming relies on pressurized irrigation with treated wastewater, these reserves deplete during summer, and orchards face critical water shortage, which can become extreme under drought conditions.
Trees can mitigate seasonal water shortages by abiotic resiliency and the capacity to grow roots to deeper soil water horizons. However, on the one hand, the sporadic rain evens in recent years, with their higher intensity and shortening periods, cause for lower infiltration and more water loss via runoff. Therefore, there is less soil water in the spring. On the other hand, current irrigation practices do not utilize tree temporal and spatial hydraulic capabilities that could spare such valuable resources.
We search for irrigation strategies that could mitigate climatic effects by harnessing tree resiliencies and the soil-water storage capacity. We hypothesize that additional water dose during the dormant tree period in winter could sustain trees through spring and summer without waterlogging risks. Therefore, we proposed to fill the root-zone soil profile during winter, by utilizing the drip irrigation system with treated effluent water that are highly available in winter but not in summer.
We present a comparative analysis of soil water status and tree physiology acquired from multiple sensing platforms in the soil-tree-atmosphere system under three irrigation approaches: (i) hydrated, irrigated to match potential ET during summer; (ii) deficit, irrigated about half of the hydrated treatment; and (iii) winter irrigated, filling the top 2 m soil profile and deficit-irrigating trees in summer. We found that the winter irrigation mitigated the effect of water shortage from April through June. Moreover, winter-irrigated trees managed to tap into the deep profile for water uptake until August. Later, trees depleted the soil water and experienced drought stress. 
With improved hydration in spring and possible deep soil water use in summer, winter-irrigated trees increased yields by 30% after two years. Thus, winter watering orchards has the potential to sustain farming during climate shifts, and there is need to continue to investigate and improve this application.