Cameron Zuber0 commentsMarch 14, 2021Irrigation

Field Note: Irrigating and Deep Soil Moisture After Rainy Season

The rainy season this year in the San Joaquin Valley has been fairly dry and has probably got many growers thinking about how much water they should start applying. In orchards, one consideration to add to the list is the soil moisture at deeper depths. As an example, let us look at information from a wetter rainy season in 2018. In the beginning of that year, soil moisture measurements were collected every month at a research site in Parlier, CA. While not extensive, it does show something interesting. Overall, the soil moisture increased at all depth month to month (i.e., green line to orange then to grey). By March, the soil moisture above 1½ feet reached the maximum wetness the soil could hold, called the field capacity (e.g., red box in image). However, no matter how much it rained, the soil moisture at and below 2½ feet consistently stayed below the field capacity. The trees at this location were planted in 2009 with a rootzone well past a five-foot depth and were beginning to leaf-out by the middle of March. While trees typically transpire much of its water needs from the upper portion of the rootzone, a decent amount is still absorbed from the lower portion. At this site, the soil moisture at and below the 2½ feet may not be enough to supply the water needs of the trees even with appropriate moisture in the topsoil. When scheduling your first few irrigations realize that you may have different soil moisture at different depths. A few minutes with an auger and using the “feel” test or looking at sensor data can give an idea of the soil moisture profile across all depths. Think about the size of your tree’s rootzone, the soil types in your field, and how wet the

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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 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 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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