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 22^nd – 26^th, 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 4-6” of water from the grower’s standard program, and it provides the ability to increase the effectiveness of spring rains. It should be noted that this practice mirrors what Allan Fulton and colleagues have found within walnuts.

Delaying the start timing can impact fertility programs. To manage the timing, fertigation can occur, but frequency should be kept to a minimum to prevent root saturation. Try to decrease the duration of the irrigation run-time as much as possible while still maintaining good fertigation practices.

This strategy is useful if the orchard’s irrigation system has the capacity to meet the orchard’s water use. If the system has been under-engineered, maintaining some levels of soil moisture should be considered. This reserve of soil moisture will help reduce stress through the higher temperature occurring days of the spring. Moisture levels, however, should be reduced from field capacity in the top 2-3’ (60-90 cm) before irrigation is started.

Strategies to capture spring rainfall. In the past, drought years often have a larger number of intense spring rain events. These events can have precipitation rates that exceed the infiltration rate of the soil, leading to run-off of water. In preparation for these events, some different strategies should be considered to capture the water on the farm.  Essentially, these strategies slow and spread the water, leading to a greater amount of water infiltrating the soil. Planting of cover crops will help slow the rate of water movement through the field, and increase soil infiltration rates and storage. Strategies of fall planting and late spring termination have been shown to be beneficial in recent studies in California. Soil amendments should be applied to stabilize soil aggregates. These include calcium-containing products and composted materials. Use of a subsoiler could also be considered. This tool, pulled just to the side of the herbicide strip but still within the middle of the aisle, will open the soil to allow water to enter. A 12-24” shank would be sufficient for this practice. Depending on the soil, the shank trace could be sealed after the rainy season with the use of a roller to reduce issues at harvest. Lastly, if the farm has terrain changes, cross-cutting berms will allow the water to move across the field more naturally, preventing channeling, soil erosion, and water run-off.

Improving the orchard’s irrigation performance. Improving irrigation performance is a must when trying to improve water use efficiency. An appropriate design, constant maintenance, and occasional evaluation is required to have a high water use efficiency. Evaluations of micro-irrigation systems in the Sacramento Valley by Allan Fulton and colleagues found that micro-irrigation systems quickly lose their performance if proper maintenance is not performed. There are a lot of great materials on improving distribution uniformity, including this site and this article. Take the time to find where the “extra” water is going, and then use this information to direct that water appropriately.

It is also important to be comfortable scheduling and monitoring irrigation and water applications. There are multiple places of information demonstrating how to calculate almond water use and irrigation needs. Including determining ETo, crop coefficients, and scheduling (Part 1, Part 2, and Part 3). There are also useful online scheduling tools, such as Farm Water Advisor which eases the scheduling process.  

Drought Management for Individual blocks. If facing limited water supplies, the amount of water available for the year should be applied through the season as a percentage of water demand. For clarification purposes, this means that if total water supplies are 50% of the orchard’s annual water demand, then every water application should meet 50% of the tree’s use during the period. This proportional deficit irrigation strategy has been shown to be the easiest drought management strategy to apply while mitigating most kernel and tree quality effects. More on this strategy can be found here.

This season will not be the last drought of California. Typically, droughts tend to last for 3-4 years, with declining water supplies occurring as the drought intensifies. The practices mentioned above have been researched and demonstrated within almond producing areas world-wide to improve almond water use efficiency. Taking the time to learn how to apply the appropriate measures will help improve the viability of your farm operation.

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