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 Doll0 commentsAugust 6, 2020Technology

Technology Corner: Q&A w/Tule Technologies

EDITOR’S NOTE: This entry is part of a series to highlight a new technology related to almond and tree nut production. The question/answer format is set to focus more on the technical aspects and application of the technology. In many articles, I discuss the importance of irrigation. With that in mind, I though I would reach out to a company that assists with irrigation scheduling based on site-specific data: Tule Technologies. Thanks to Valerie Bednarski for taking the time to answer my questions. Tule is an irrigation technology that determines site specific water use for a specific crop. How does this technology work? Tule measures the actual evapotranspiration (ET) of your orchard. We are able to do this using the Surface Renewal Method that was developed at the University of California at Davis (Paw U et al. 1995; Snyder et al. 1996; Shapland et al. 2012a and 2012b; Shapland et al. 2014). ET is the process of evaporation from plant and soil surfaces and from within plant tissues (i.e., water movement through stomata). In most modern agricultural systems, ET is the dominant process of water loss from a field. (Editor’s note: more info on ET here) What equipment is installed, and resources are used to determine water use? The Tule Sensor is installed in the orchard and is positioned above the canopy. The sensor is able to measure the amount of evapotranspiration from the orchard based on air movement.  As the wind moves over your orchard, it picks up the water that transpires from the trees and carries it to our sensor. This is how we are able to measure the crop water use over a broad area. An installed pressure switch is fitted to the irrigation system. This provides a direct measurement of irrigation durations. Using site specific irrigation specifications,

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David Doll1 CommentMay 31, 2020Irrigation

Almond Irrigation Scheduling: Sourcing ETo

When determining plant water demand, the current environmental conditions must be taken into consideration. These factors, which include temperature, solar radiation, wind speed, humidity, and percentage of soil cover, influence both the rate of evaporation from the soil and the rate of transpiration from the plant (also known as evapotranspiration). By knowing these variables, we can calculate the evapotranspiration of the plant of interest. Research over the past 50+ years has refined the ways we estimate evapotranspiration. Initial estimates used to be performed using evaporation pans (Epan). Epan filled with water would be manually monitored for water evaporation on a daily basis. Water evaporation was then correlated with water use by fully irrigated grass (ETo) through the use of lysimeters. Fast forward a few years, with the development of more precise electronics, weather stations demonstrated the ability provide accurate measurements of the required variables. Using these data, a correlation between measured weather variables and ETo was developed. This equation, known as the Penman-Monteith equation, or some variation, is now used by nearly every weather station to estimate ETo. Having the ability to identify the rate of ETo is the foundation of irrigation scheduling. Although it is variable due to day-to-day environmental fluctuations, it is accessible through multiple sources. Within California, State funded weather stations placed throughout California measures the required water variables. These values are reported on the CIMIS web-site and are available free of charge. Within other almond growing areas, similar programs also exist, but are not as thorough. Thankfully, many weather stations can provide an estimation of ETo – as long as they have the ability to measure the required variables. Furthermore, ETo information is often made available in many publications, including trade newspapers, websites, and extension offices. Regardless of where the ETo information is sourced, it is

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David Doll1 CommentMarch 26, 2020Irrigation

Almond Irrigation Scheduling: Deciding on a Crop Coefficient

Crop coefficients for almond have been studied for nearly 50 years. These values indicate the ratio of water use of almonds in comparison to fully irrigated grass (ETo). Values less than one indicates that almonds are using less water than grass at that period while values greater than one indicate a higher water use. This ratio needs to be multiplied by the daily ETo, whether actual or estimated, to determine the water usage for almonds. The crop coefficients provided below are research derived. Differing techniques have been used to develop the coefficients. Some rely on a “water-balance” method in which soil moisture levels are monitored and maintained to match water use. This method has been utilized by many researchers across the world and has formed the foundation of most irrigation research. A more exact method of this technique involves the use of a weighing lysimeter, which is a giant scale that measures the amount of water used by the tree. Due to a minimal number of lysimeters in the world, studies have not been performed until recently and the results for mature almond water use has yet to be published. Outside of the “water-balance” method, there are newer technologies that have been used to develop crop coefficients. These techniques utilize fluctuations of canopy temperature that occur from transpiration loss.  These measurements, when taking into account solar radiation, wind, and ambient air temperature and humidity, can be used to back-calculate the water loss. This method is known as “eddy covariance.” When reviewing the differing crop coefficients, it will be clear that the general trend is greater water use. Some of the upward trend is due to a change in irrigation practices and orchard canopy densities – the switch from surface/flood irrigation methods to pressurized drip and microsprinkler orchards as well as

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David Doll0 commentsJune 15, 2018Irrigation

Summer Irrigation: Considerations for Deficit Irrigation

Summer irrigation is challenging. Water use of mature almond trees is the highest of the season, with an average evapotranspiration being around 2.00 acre inches of water use per week during June and July for most of the San Joaquin valley. This doesn’t consider distribution uniformity problems as well as any high heat events that may occur, which may require increased water applications. During this period, it is common to see stressed trees. This is frequently due to the lack of or improper calculation of evapotranspiration (ETc) leading to under-irrigation. It may also be due to an under-performing irrigation system leading to poor distribution uniformity, in which some areas are getting over-irrigated while others are under-irrigated. Lastly, and sometimes surprisingly, poorly designed systems are commonly observed which aren’t able to meet the tree’s demand for the water in the summer.  This is due to miscalculation or variable well/pump flows, too low of application which requires long pump times, or general poor design that limits water flows (i.e. reduced pipe sizes to save money). Some stress during this period is okay. Mild water stress that occurs at the onset of hull-split has been shown to increase the uniformity (or ‘evenness’) of hull-split. Sometimes, especially in fine textured soils with high water holding capacities, this application of deficit irrigation can be applied earlier in June to draw down levels of stored soil moisture. In these cases, careful monitoring of tree stress through the use of a pressure chamber should occur. Water reductions should start in range of a 10-20% reduction. When trees reach a mid-day stem water potential (SWP) of 2-3 bars more negative than baseline, near-to-full irrigation should resume to reduce tree stress. As hull-split begins (~1% hullsplit, or when blanks split) AND there is a desire to reduce hull-rot, water

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David Doll3 CommentsApril 10, 2017Irrigation

Yellow Trees from Being Too Wet

It is very common to see yellow trees in the spring. The lack of color is often due to saturated soils which reduces the movement of oxygen into the soil, killing fine feeder roots. This impacts the ability for the tree to take in water and nutrients, leading to micro-nutrient deficiencies, impacting nut set and tree growth. In severe cases, especially with younger trees, the symptoms are similar to glyphosate drift or zinc deficiency. Later-season carry-over effects are also observed and include a limited rootzone, which leads to severe water stress during hull-split and harvest. Most of the time, this problem is caused by the orchard being irrigated too soon. Many operations apply water because it is perceived as needed or they are wanting to apply fertilizer. The need to apply water, however, is usually very low in the spring due to the cooler conditions and crop stage. Based on the 30-year average almond evapotranspirational values across California, water use from Mid-February (bloom) through the first week of April for almonds across the State ranges from 3.6″ to about 4.25.” This demand is often met by rain and the tree accessing stored moisture within the soil. To determine when to start applying water, plant stress or soil moisture levels should be monitored. The soil profile should be starting to dry at the two to three feet zone and can be checked with with the use of a shovel, auger, or soil moisture sensors. If using the pressure chamber to monitor plant stress, irrigation should be considered when trees are 1.5-2 bars more negative than baseline. For more information on the use of a pressure chamber in perennial crops, please see this document. If wanting to apply nitrogen, applications should occur by ground application or the shortest fertigation set as possible. These practices will help to properly time the first

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David Doll0 commentsMay 24, 2016Irrigation

Water Use Efficiency: Irrigating for the Highest Crop per Drop

Written by David Doll (UCCE Merced County) and Allan Fulton (UCCE Tehama County) This past week I presented on our preliminary findings of the water production function trials underway across the state. Highlights included the release of some newer crop coefficients that were determined using eddy-covariance stations placed in the North and South, discussion on water needs, and the impact of water stress on crop growth. Of most interest was the crop coefficients, which were higher than what most operations use, and led to the questions of the need for that much water. Crop coefficients (Kc) are derived to estimate ET for various crops as they develop over the course of a season.  Kc’s are developed under conditions where soil moisture is not limited and the crop is not stressed at all.    So, they represent maximum ET or water use.  . In the case of almonds, there have been several recent efforts to determine these values (see below). Various methods have been used ranging from simpler soil-water balance to more advanced biometeorologic eddy-covariance measurements. All of these have led to significantly higher calculated Kc’s and crop ET, with one set suggesting that around 60″ of water was needed in Bakersfield conditions. It is important to keep in mind that ET does not equal irrigation need.  The two will be more similar in almond growing areas with lower rainfall and more different in higher rainfall areas.  Water holding capacity of orchard soils and root depth will also influence the relationship between ET and irrigation need.   Even increases in production do not necessarily correspond with higher ET and more irrigation. There is increasing evidence that when given the conditions, “luxury consumption” of water will occur. In other words, the water demand is present, but crop load does not increase. This highlights the value of

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David Doll0 commentsApril 8, 2016General

2016 Mid-Spring Update

The crop is developing nicely in many areas across the areas of the San Joaquin Valley in which I observed. Crop loads vary, depending on last season’s stress or crop-load, but generally look good. Looking forward to this week, there area few pointers to keep in mind. Rain is forecasted for this weekend with chances through next week. This will have minimal impacts on the physiological development of the crop. It will, however, impact the amount rates of evapotranspiration and soil moisture. This variance should be accounted for by either using soil moisture monitors or plant based measurements. If possible, rain gauges (or other measurement tool) should be placed at the various farms as rainfalls can be variable. Last year, for example, a thunder cell dropped around 3/4″ of rain in a farmer’s field on the North side of Livingston, while his block on the south side received less than 1/4.” Accounting for these differences can prevent the “stalling-out” of growth from over-irrigation. Even though it warmed up this week, it might be wise to question the start of the irrigation season. Only two out of four plots in which we are measuring stem water potential have indicated the need to irrigate. The other two are still reading around baseline…one is even in a Delhi sand. Plant based measurements should be used to help determine the need to irrigate. Remember: the tree is essentially a giant tensiometer with a lot larger volume of soil impacting the result. Disease update: Multiple days of rain are predicted. This could mean conditions suitable for Bacterial Spot (especially on ‘Fritz’ and ‘Padre’), Anthracnose (for ‘Monterey’), Scab, and Shot-hole. Lingering infections of green fruit rot may also progress. If a treatment is warranted, check the fungicide efficacy table. Remember to rotate away from the last spray

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David Doll1 CommentJuly 10, 2015Irrigation, Soil

Soil Moisture Sensors

Soil moisture sensors are great tools to aid in irrigation management. They provide feedback on the movement and depth of moisture within the soil, providing the ability to identify the proper duration of irrigation. Proper use relies on a thorough understanding of the soil characteristics of the orchard, which include soil type, water holding capacity, and salinity level. Sensors can be used to help schedule irrigation. Timing of irrigation usually occurs when moisture levels drop below certain trigger points at varying depths. These points are different for every soil and sensor type and require in-field calibration to help reduce unwanted plant stress. Calibration can occur by comparing sensors readings to plant stress responses (e.g. Pressure chamber readings) or to a “feel” test to determine how much water is still available to the plant. Several factors need to be considered when planning to install the sensors. Sensor locations should be placed to account for varying soil types of the orchard. If only a few locations are planned, the predominant soil types should be selected. If possible, sensors should be installed at varying depths to provide moisture levels in the middle, bottom edge, and below the active rootzone. A common 3 sensor installation pattern is 12-18″, 30-42″, and 48-60.” Work by the University of California has compared many soil moisture monitoring systems. Neutron probe data, dielectric, tensiometers, and electrical resistance blocks have all been found to respond to water applications similarly. Essentially, if sensors are properly installed and maintained, and time is taken to understand and interpret the data, they can provide similar information. The table below highlights some of the varying aspects of these systems. Each system has strengths and weaknesses. Please note that the sensors types are linked and when clicked will direct to further information. “Feel” Tensiometers Dielectric Sensors

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David Doll2 CommentsJuly 1, 2015Irrigation

Using the Pressure Chamber to Schedule Irrigation in Almonds

Written by Matt Jones, Staff Research Associate, UCCE Merced County Determining the appropriate time to irrigate is among the most critical tasks facing growers and farm managers. Traditionally, growers have relied on orchard water budgets using ET and CIMIS stations, and monitoring soil moisture levels to develop irrigation schedules. For in-depth explanations of these methods, consult the UC ANR Almond Production Manual. However, these methods only indirectly measure water status of trees in an orchard. To directly and quantitatively measure tree water status requires the use of a pressure chamber. One of the quantities a pressure chamber can measure is stem water potential (SWP), or the amount of tension in the water column as it is pulled from the soil and through the plant. For a complete guide on pressure chamber use and plant-water relations, see UC ANR Publication# 8503. But what do these numbers mean, and how can they be used in irrigation management? Interpreting these numbers depends on temperature, relative humidity, and the degree and type of water stress you are trying to manage with an irrigation set. Knowing temperature and relative humidity will establish what normal or ‘baseline’ pressure chamber values (in bars) would be for an orchard that is fully irrigated. Baseline values can be  precisely determined by looking at table 14 in ANR Pub 8503. However, a rough estimate baseline (in almond) is to divide temperature by ten. For example, if it is 100 F, then your baseline value is -10 bars. The values measured in the field and how they deviate from baseline will determine the degree of tree water stress, and irrigation timing. If aiming for a fully irrigated, mature orchard, then irrigate when the measured SWP values are 4 bars lower (more negative) than the baseline. For example, if the baseline value

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