Almond Drought Management: 2021 Update

Drought conditions are forecasted to persist into 2021 for California. Although almonds are relatively tolerant to drought from a survival standpoint, yields are impacted when water applications are reduced. To minimize this impact, the water use strategy that accounts for available water resources must be developed and applied to the orchard operation. These resources include contributions from stored soil moisture, rainfall, wells, and surface water resources.  Impact of water stress on almonds. Reduced water applications affect both in-season and future yields. In-season water stress reduces gas exchange, affecting the amount of energy that can be directed into kernel development. This often leads to reduced kernel size and weight, an increase in shriveled kernels, and minimal growth. Typically, nut set is unaffected. Although not exactly clear, the relationship between in-season crop loss and water stress is around 1 to 0.7-1.0, meaning that for every percent of reduced water application leads to the same percentage of crop loss (i.e. a 10% water deficit leads to 7-10% crop loss). Please note that this relationship isn’t exactly defined, and these numbers are estimates. Moderate to severe deficits will also affect next season’s crop. This crop loss is due to the reduced spur positions from the lack of growth and the reduced carbohydrate reserves going into floral bud development. This leads to reduced nut set. Nut weight and size will only be affected if in-season curtailments continue. . Field observations suggest that water shortage in a given year will have a greater impact on crop yields the following year, where the relationship of water stress (from the previous season) and crop loss approaches 1:2. This means that for every percent of reduced water application in year one, year two’s crop will be reduced by about 2% (i.e. a 10% water deficit leads to 20% crop

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Drought Management for Almond 2015

Many farmers across the state will be impacted by this year’s drought. Within almonds, there has been a lot of research conducted to determine better strategies to apply water. A publication developed through UC ANR highlights the two more consistent, easier applied strategies. These strategies, along with the effects of water stress, are highlighted below. The strategy applied should be based on water available. If 15% or less than of the estimated full almond evapotranspiration (ETc) is available, Hull Split strategic deficit irrigation (SDI) could be considered. If the reduction is greater than 15%, the strategy of proportional deficit irrigation should be considered. An example of both strategies is given in figure 1. Hull split Strategic Deficit Irrigation:  Hull Split SDI maintains full irrigation until the completion of kernel fill. After kernel fill and until 90% hull-split, irrigation is applied only when trees reach SWP values of -14 to -18 bars (Shackel, et al, 2004). Field research has shown that this technique will decrease water use by as much as 34% during this period, reducing total seasonal water use by about 15%, while having minimal impacts on current and next season’s crop (Stewart, et al, 2011).  In practice, it can be difficult to fine-tune the irrigation schedule to this SWP threshold. Many growers will initially reduce water applications by 50% around mid-June and will adjust the amount of subsequent irrigations once stress levels increase and soil moisture depletion occurs. Water should be applied prior to harvest to improve hull-split and reduce hull tights (Prichard, et al, 1994). This strategy is a particularly effective method for reducing hull rot (Tetviotdale, et al, 2001), if that is a problem, but it also improves harvest-ability by reducing the force and time required for shaking, which can benefit the long term health of the orchard.

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