David Doll7 CommentsApril 3, 2021Irrigation

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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David Doll0 commentsMarch 7, 2021Horticulture, Irrigation

Drought and Almonds: Spring Considerations

The current drought conditions faced by California will impact the agricultural industry. Annual precipitation, snowpack, and reservoir conditions are well below average for this time of the year. Although there is some rain in the forecast, future rain and snowfall amounts are hard to predict. Furthermore, spring storms tend to come in warmer temperatures, leading to more rain but less snow at lower elevations. Although we cannot control the weather, there are things we can do to improve the use of water resources. These practices will improve the use efficiency of on-farm water resources. They also include strategies to help capture more water from spring rain events. Lastly, implementing practices now will provide on-farm data for future mitigation strategies as the Sustainable Groundwater Management Act (SGMA) comes into full enforcement. Start timing. Most farm operations begin to irrigate too early. This occurs even in low rainfall years. Stem water potential (SWP) or other plant-based monitoring systems are strongly recommended to help determine start timings in the spring. With SWP, recommendations are to wait to at least 2 bars more negative than baseline (remember, SWP is read in negative numbers). This will most likely lead to an irrigation timing around early- to mid-April, depending on leaf-out date. A study demonstrating this method was established in a ‘Butte’/’Padre’ located near Delhi, CA in a very sandy soil. The trial was established in the drought year of 2014-2015 and continued through 2017. Within this study, the delayed start to the irrigation did not impact yield in comparison to the grower standard. The dates for the first irrigation were between April 22nd – 26th, for all three years. Since ‘Butte’ and ‘Padre’ are later leafing cultivars, I suspect that ‘Nonpareil’ and other earlier leafing cultivars will be 1-2 weeks earlier. This delay saved between

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David Doll5 CommentsMarch 7, 2015Irrigation

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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David Doll5 CommentsJune 7, 2014Horticulture, Irrigation

Water Stress, Early Hullsplit, and Kernel Size

I have been getting a few reports of hull-split in almonds from varying points across the state. We were expecting an earlier than normal hull-split, but many would agree that this is earlier than expected. Much of the splitting trees are in the more stressed areas of the fields, or in orchards with reduced water allocations. Although I haven’t observed this until this season, early hullsplit induced by spring-time water stress has been described in the literature.

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David Doll5 CommentsFebruary 14, 2014Irrigation

Determining Orchard Water Needs With Yields

In delivering workshops on irrigation (and drought) management, there are always a few questions on how to estimate canopy coverage without the use of special equipment. Not being content with the typical answer of “Use your best guess,” I began to review the research, and found that an estimate of photosynthetically active radiation (PAR) (also known as mid-day light interception) can be calculated from orchard yields. This question was asked because in a water short year, the available water needs to be spread out evenly as the respective % of evapotranspiration. This following will help determine how much water your trees are using.

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David Doll8 CommentsJanuary 16, 2014Irrigation

Severe Drought Management Recommendations for Almond

UC researchers have urged growers not to take aggressive actions in reducing tree size or crop load in response to the West side water shortages this year. Severe pruning will increase new growth which would increase the leaf surface and evapo-transpiration rates (ETc) of the tree. Crop thinning has a similar effect and is also not recommended. By reducing crop load, the source/sink ratio of the tree is disturbed, causing the tree to put nutrients into vegetative growth instead of the nuts.

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