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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Cameron Zuber2 CommentsSeptember 16, 2018Field Notes, General, Irrigation

Field Note: Securing Irrigation Tubing

While conducting surveys across Merced County, I have noticed diverse ways growers secure the ends of irrigation tubing.  Many are attached using some type of stake made of wood or PVC in which the tubing is tied. Other orchards have the lines wrapped around a tree and used as an anchor for the line. Finally, some of them are staked directly into the ground. Irrigation tubing moves because of expansion and contraction of the plastic caused by temperature changes, as well as, from the water and air moving through the irrigation system. Securing the tubing creates tension that helps prevent the tubing from moving. These keeps the emitters and microsprinkers in place which helps maintain good irrigation efficiency. There are a few problems with securing the tubes. The first is the added cost and time to first secure the tubing and then maintain how the tubing was secured. Secondly, the lines may contract after fixing, which can pull them off the riser. Finally, the lines, if wrapped too tight, can cut into and girdle the tree. All of these are preventable. If you do choose to secure the end of your irrigation tubing, below are some considerations to take into account: Leave some slack in the tubing: Due to changes in temperature, plastic tubing expands and contracts. When tightly secured tubing contracts, coupling points may become undone (e.g., at the riser) or may cause the plastic in the tubing to stretch, creating weak points that may eventually break. Be wary of using trees to secure tubing: While this may cut down on supply costs, make sure it does not begin to girdle the tree. Do it right: Since you are taking the time (and money) to secure your tubing, be sure to do it right. There is a lot of power

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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 Doll0 commentsSeptember 9, 2017Horticulture, Irrigation

Almond Postharvest Management: Water Demands

After the hustle of harvest, it is easy to think that the orchard work is nearly wrapped up for the year. With almonds, this isn’t the case. Research over the past 30 years has identified the postharvest period as the primary development period that impacts next year’s crop. Not surprisingly, much of this work has shown proper irrigation practices during this period being the major factor. For this article, the post-harvest period will be defined as mid-August through early November. During this period, the trees can demand an estimated 12-15″ of water based on location and weather. Roughly 70% this demand is from the six weeks immediately after harvest – when the days are hot and longer (see included table). Shorting trees of water during this period of high water use (mid-August through September) has been shown to significantly reduce next year’s yield. In fact, research by David Goldhamer and Elias Fereras have found that the first 8″ of water applied during the postharvest period is the MOST CRITICAL water applied to maintain orchard yields. Why is this?  Almond floral bud differentiation, unlike other Prunus spp.,  begins in mid- to late-August and continues through early September. Water shortages during this time reduces carbohydrate development, leading to less energy being able to be directed towards the creation of next year’s flowers, affecting both flower quality and quantity. This, in-turn, leads to an overall reduction in fruit load. Practices should be employed to keep leaves on the tree through the postharvest period (early November).  Reducing tree stress through the harvesting process is the first step in maintaining highly productive trees. This includes being timely with shaking so trees are stressed for a minimal amount of time and understanding the amount of soil moisture and the rate of use – which includes taking

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David Doll0 commentsOctober 5, 2016Irrigation

WUE Part 2: Kernel Yield per Inch of Water

Water use efficiency (WUE) within agriculture has became a bit of a buzz word over the past few years. This is mostly due to the heightened awareness of the public due to the drought. This has placed a lot of emphasis on water usage within agriculture, in which many are demanding that water should be used at the highest efficiency. Almonds are no exception to this. WUE is essentially how much crop we can produce with a given amount of water. This is not an easy value to determine due to the complexity of many farming systems. Once determined, however, it provides an insight into determining issues affecting productivity. Within almonds, there have been attempts to determine optimal WUE. Monitoring of yields in several orchards over the last 10 years has determined a theoretical WUE of 83 lbs of crop for every inch of water use (essentially 1000 kernel lbs of crop for every acre foot of water use). Previous work within a production almond orchard from a single site in California found it to be around 70-72 lbs per acre inch of water use. This range was supported by research work in Australia. Interestingly, anecdotal evidence from water cuts experienced during the drought suggests a similar range, with many farmers experiencing yield losses around 800-1000 lbs/acre for every acre foot of water reductions. To further explore this concept and expand the findings across may locations, three trials were established across California. These trials are located in Kern, Merced, and Tehama Counties and are studying the effects of varying water use amounts on yield. Results from a previous year have been written about earlier. As shown in table 1, our results from the Merced County trial found an average of 73 kernel lbs per acre inch of water use. This

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