David Doll4 CommentsJuly 19, 2020Irrigation

Regulated Deficit Irrigation: Is it appropriate for your operation?

Regulated deficit irrigation is the practice of reducing irrigation to obtain some type of desired stress level. This practice is often used during the initiation of the hull-split period to reduce hull-rot strikes. It also has been utilized during periods of water shortages to save 5-15% of the seasonal water use of almond. Due to the limited effect on yield, as well as the benefits, it has been advocated for application within orchards by the University and industry (including myself!). This practice, however, can have negative impacts when applied incorrectly and should only be used if deemed appropriate. In theory, this practice is easy to apply. Water application rates should be cut to achieve -15 bars stem water potential for two weeks preceding the onset of hullsplit (e.g. Blank split). This stress should be maintained at this level for this period. At the end of the two weeks, regular irrigation resumes and the orchard prepares for harvest. The difficulty in application has everything to do with accurately monitoring plant stress. Every orchard and orchard practice creates a different approach in application. For example, assuming similar irrigation levels, stress levels achieved in a mature orchard planted on sandy soil will occur in a shorter time frame than an orchard on a heavier clay loam. Every orchard site requires careful monitoring to determine when to cut and resume full irrigation. I have observed numerous orchardists apply tree stress only to see a reduction in kernel yield. This is due to ongoing gains in nut weight that occur between the onset of hull-split and harvest. If the tree is significantly stressed during this period, the conversion of carbon to fats is reduced, impacting the final crack out percentage. One closely monitored orchard in which I worked, demonstrated a 10-15% reduction in kernel weights

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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 Doll3 CommentsDecember 15, 2017Irrigation

Is Winter Irrigation Needed?

The reduced late fall rains have led to relatively dry conditions throughout the State. Within the San Joaquin Valley, limited amounts of rain have fallen, with recorded precipitation around one inch in Merced. The lack of rain has led to a series of questions about winter irrigation requirements in which answers are included. Question (Q). Do I need to irrigate now? Answer (A). Evapotranspiration rates are very low and almond water use is even lower. A table has been included that has utilized the real-time evapotranspiration data (ETo), the corresponding crop coefficients (Kc), almond evapotranspiration (ETc) and rainfall for the MERCED CIMIS station. The need to irrigate should be based on almond water use, the amount of water that has been applied in the Late October through early December period, and rainfall. Week Starting: ETo Kc ETc (in) Rain (in) Nov 5th 0.48 0.69 0.3312   Nov 12th 0.38 0.69 0.2622 0.71 Nov 19th 0.34 0.6 0.204   Nov 26th 0.32 0.6 0.192 0.27 Dec 3rd 0.3 0.4 0.12   Total: 1.82   1.1094 0.98 Based on this example, ETc for the month of November and first week of December has been 1.11” with roughly 0.98” of rainfall. This suggests that an irrigation may be needed. If, however, any irrigation was applied in late October or November, most likely the water needs have been met. Water demands and rainfall are site specific. Determining the situation for the orchard location will be needed to determine localized water needs. When in doubt, checking soil moisture status may assist with the decision making. Q. I didn’t irrigate in Late October – December and rainfall has been limited, how do I apply the water? A. Irrigation sets should be shorter than 24 hours to reduce saturated soil conditions and the risk of Phytophthora. If

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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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David Doll6 CommentsMarch 14, 2016Diseases, Horticulture

Yellow Trees and Saturated Soils

Annually, several calls regarding poor tree growth and “pale trees” are received. This is often due to saturated soils. Too wet of soils reduces the movement of oxygen into the soil, killing fine feeder roots. This impacts the ability for the tree to uptake water and nutrients, leading to micro-nutrient deficiencies, impacting nut set and tree growth. Later-season effects are also observed and include a limited rootzone, leading to severe water stress during hull-split and harvest. The problem is often compounded by farm practices. Too early of fertigations before the tree begins to “suck” water from the soil can lead to an increase in saturated conditions. Spring rains, cool temperatures, and heavy soils compound the problem. Once the symptoms appear, the reaction is to fertigate or chemigate in attempts to manage the symptoms of stunted growth and yellow leaves. Symptoms continue to worsen. Recovery is not always possible. If conditions are prolonged, the symptoms will worsen. Trees may eventually die or shed leaves and crop. In some cases, the roots and crown may become infested with Phytophthora. In many cases, Phytophthora is serving as a secondary problem, infecting only after the tree has been weakened by the saturated soils. The problem can be alleviated by warmer temperatures which increase the transpiration rate of the tree or reduced irrigation until the tree recovers. Recovery is dependent on severity, and may take several months. Optimally, it is best to do what is possible to prevent the symptoms from occurring. Prior to the first irrigation, moisture levels in the soil should be dropping. This can be determined with the use of a shovel or auger, pressure chamber, or soil moisture sensors. If using the pressure chamber, irrigation should be considered if trees are 1-2 bars more negative than baseline. More on using the pressure bomb to

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Allan Fulton2 CommentsMay 16, 2015Irrigation, Salinity

Q&A: Evaluating a Water Supply for Suitability to Irrigate Nut Crops

After receiving the results of a water analysis, there are several components that need to be reviewed to determine suitability of the water for the planted crop. If the water does not meet the expected suitability range, it may require ammendments (e.g. gypsum or acid) or mixing with other water sources to prevent crop loss. Below are five questions that are usually asked when reviewing a water sample as well as some other information regarding a water analysis and conversions. Does the salt concentration (ECw) pose a potential problem (osmotic effects)?  Crop  Unit Degree of growth or yield reduction None Increasing Severe Almond and Walnut dS/m <1.1 1.1 -3.2 >3.2 Pistachio dS/m <4.0 4.0 – 8.0 >8.0 Are there specific elements (B, Cl, and Na) that could accumulate to potentially toxic levels?  Element  Unit  Crop Degree of growth or yield reduction None Increasing Severe B (boron) mg/l (ppm) Almond and Walnut <0.5 0.5 – 3.0 >3.0 Pistachio <4.0 4.0 – 10 >10.0 Cl (chloride) meq/l Almond and Walnut <4.0 4.0 – 10 >10.0 Pistachio <20.0 20 – 40 >40.0 Na (sodium) SAR(none) Almond and Walnut <3.0 3.0 – 9.0 >9.0 Pistachio <5.0 5.0 – 10 >10.0 Na (sodium) meq/l Almond and Walnut <4.0 4.0 – 7.0 >7.0 Pistachio <20.0 20 – 40 >40.0 Could the water chemistry contribute to unstable surface soil structure and lower water infiltration rates?  Lab Information  Unit Potential of Water Infiltration Problems Developing Unlikely Increasing Likelihood Likely Ratio of SAR/ECw ratio <5.0 5.0 – 10.0 >10 Ratio Ca/Mg ratio >2.0 2.0 – 1.0 <1.0 Could the water chemistry be prone to plugging drip emitters, microsprinklers, or filters?  Lab Information  Unit Potential for Water Infiltration Problems Developing Unlikely Increasing Likelihood Likely ECw dS/m <0.8 0.8 to 3.0 >3.0 HCO3+CO3 meq/l <2.0 2.0 – 4.0 >4.0 Mn (manganese) mg/l <0.1 0.1

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