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

April 3, 2021

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

March 7, 2021

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.

March 7, 2015

Q&A Drought Management for Almond

A few lingering questions from the various presentations on almond drought management over the past few weeks. I thought I would address some in a quick Q and A. Q. How should I plan to irrigate my trees?

March 18, 2014

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.

January 16, 2014

Podcast: Irrigation Management for Almonds in a Drought Year

Owen Taylor (from AG Fax) and I created a podcast to discuss irrigation strategies for a drought year. Topics covered within the podcast include: How much water do almonds need? What happens if they do not receive the correct amount of water?  How do almonds manage reduction in water applications? Tools to help with managing irrigations. Managing irrigations with varying water availability. (85-100% of ETc, 65-85% of ETc, >65% of ETc) Using groundwater to subsidize water use. This is my first podcast, so I hope you find it educational as well as useful. Click here. It is 20 minutes in length, but one can jump to their topic of interest. More information can be found at UC Drought Management Website.

March 24, 2013

Reduced Kernel Size – 2021 Harvest

There have been several reports of smaller than expected nut size for the 2021 harvest. Nonpareil sizes have been reported to be in the range of 28-30/ounce rather than the typical 24/25 nuts per ounce. Many have suggested that this is due to drought induced water shortages, but this has occurred even on fully irrigated orchards. Water stress has played a role, but earlier conditions of the season should also be considered. Nut weight is influenced by a few different factors. These include: Reduced number of cells; Reduced cell size; Reduced cell weight. Cell number is mostly impacted by temperatures that occur during cell division, which occurs early in the season, typically within 6-8 weeks following fertilization. Cell enlargement is influenced by plant stress. It begins in April and continues through May. Lastly, weight accumulation begins in May and continues until early August. It is influenced by plant stress, which reduces the production of carbohydrates. To maximize nut size, carbohydrates (sugars) must be available during these periods for cell building processes. Carbohydrate availability is influenced by the rates of photosynthesis and respiration. These two processes are heavily influenced by plant temperature, which are influenced by ambient air temperature and water availability. Temperature influences photosynthesis and respiration. Both processes increase rapidly as temperatures warm, and begin to drop as temperatures increase above a certain point. The peaks, however, are different, with 86F and 103F for photosynthesis and respiration, respectively (figure 1). Since these peaks are different, there is a net gain of carbohydrates when temperatures are below 86F, but a net loss as temperatures increase above this point. Furthermore, as temperatures warm towards 86F, there is more energy being directed towards respiration, which reduces availability to be used for other processes, like nut development and plant growth. Internal plant temperature is

September 26, 2021

Post-harvest Leaching Fractions to Manage Soil Salinity

Drought years are tough. Limited water supplies create several challenges that impact the current and future year’s crop. Several articles have been constructed to help manage almond orchards with limited water supplies, but as harvest starts, focus needs to shift to post-harvest management of the orchards. Many orchards relied on groundwater at some point through this year. This may have been sourced directly from a well on the property, or from wells within an irrigation district. Groundwater often contains elevated levels of salt, in particular sodium and chloride. These salts accumulate in the soil from the irrigations that occur during the season. Due to almond roots generally excluding salts, salt levels within the soil could climb as high as 10-15 times the concentration of the irrigation water within a single season. These higher levels of salt will impact growth and productivity as well as lead to tissue toxicity and leaf loss. To manage these salts, they need to be removed from the active rootzone of the tree. Salinity management for various soil types have been described previously for sandy and finer texture soils. These programs rely on winter leaching to reduce the salinity levels within the active rootzone of the tree. This process, however, can be improved by taking actions in the post-harvest to increase soil moisture levels. At this time of year, a leaching fraction should be added to each water applications to increase soil moisture levels. An increase of 15-20% of the irrigation duration should be sufficient. This additional water will refill the soil profile during this period, increasing the effectiveness of leaching by winter rains. The value of applying a leaching fraction in the post-harvest is greater than leaching fractions applied earlier in the season. This is due to the irrigation practices associated with harvest – a

August 16, 2021

Almond’s Water Use Efficiency

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May 16, 2021