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 commentsAugust 22, 2015Diseases, Irrigation

Irrigation Rates and Hull Rot

Written by Andrew Ray, Staff Research Associate for Univ of CA Cooperative Extension, Merced County Our water production function (WPF) project within almond has given us an opportunity to look at how irrigation rates can impact the amount of hull rot that develops.  The goal of the WPF is to be able to calculate the impact that water applied has on yield.  This plot is replicated in three different places across the Central Valley. In the Merced WPF plot, there are five different treatments of water applied at the rates of 110%, 100%, 90%, 80% and 70% of the evapotranspiration rate (ETc).  There are 3 blocks of these treatments within an 80 acre orchard.  Irrigation rates stayed constant with their established relationship to ET through hull split, and reduced deficit irrigation was not applied. During mid August hull rot occurrence was estimated in the Merced WPF plot on two trees in each treatment within each block.  Twenty five branches were counted on each quarter of the tree, totaling 100 branches per tree, and the number of incidents of hull rot was recorded. There were two ratings performed by two different people and the estimated percentages were averaged. Table 1 shows the averages by treatment of all the trees rated.  Included in the table is the average stem water potential (SWP) for each tree and leaf nitrogen percentage.  The SWP measurements were taken with a pressure chamber on three separate occasions during hull split in early July.  Baseline SWP during that time was -9 bars.  Leaf tissue samples were taken in mid July and the average percentage of nitrogen for each treatment. Table 1: Average hull rot percentage observed in each irrigation treatment, along with average SWP during hull split, and leaf tissue nitrogen percentage. %ET % Hull Rot SWP (bars) %N

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David Doll1 CommentJuly 25, 2015Diseases

2015: Lower Limb Dieback Returns

I have received several calls and comments regarding the severity of lower limb dieback (LLDB) in almonds this year. This topic has been discussed to a greater extent here, but I thought I would highlight a few points and some updates to keep in mind if you are observing these symptoms in your orchard. LLDB is used to describe branch death that occurs in the lower half of the canopy. The limbs tend to start the year off normally, but at some point – usually after a hot spell- the leaves on the affected limbs begin to yellow, and eventually the whole branch collapses. Observation of symptoms usually occurs between late May through late July, with symptoms delayed in years with mild springs. LLDB is very common on the ‘Padre’ variety. So what causes LLDB? The “jury” is still out, but there are a few hypothesis. The current thought is that over-irrigation in the spring followed by under-irrigation during the summer months can worsen or cause LLDB. Over-application of water often occurs in the spring time due to the variable weather conditions (e.g. unexpected cool spells and rain). When it cools off, it is easy to over-apply water especially if the irrigation scheduling is based on the 30 year average. A good example was this past May, in which we experienced an estimated 5.68″ of almond water use (ETc) and had rainfall events that dropped as much as 0.25-1.0 inches of rain in Merced. The 30 year average estimates that we would need to apply 6.44″ of water to match ETc, and if followed, over-irrigation with an inch or more water may have occurred. Furthermore, many orchard operators tend to begin too early with the first fertigation, often beginning before transpiration levels of the tree draw down soil moisture, which keeps the soil

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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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Franz Niederholzer3 CommentsAugust 30, 2014Irrigation

After a tough year, make key irrigation maintenance a priority.

Written By: Franz Niederholzer, UCCE Farm Advisor, Colusa/Sutter/Yuba Counties Despite strong nut pricing, the drought is making 2014 a very tough year for growers, their trees, and in many cases, their irrigation systems.  Low quality irrigation water, potentially stressing trees and irrigation systems, was/is applied to many orchards this year that normally received higher quality water.  Irrigation system maintenance, especially cleaning drip lines to ensure uniform and adequate water flow, should be high on the do-to list this fall.  The following is a quick review of key practices to keep drip emitters from clogging.  For more complete information, see the sources listed at the end of the post.

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Franz Niederholzer5 CommentsJune 22, 2013Irrigation, Soil

Gyp in June

Written by: Franz Niederholzer, UC Farm Advisor, Colusa/Sutter/Yuba Counties,  Allan Fulton, UC Farm Advisor, Tehama/Shasta/Glenn/Colusa Counties It’s June – the best time to apply gypsum to the soil surface in orchards with flood or wide coverage sprinklers.  Why now? But first, what does gypsum do and not do?  Adding gypsum to the soil can significantly increase the rate of irrigation water infiltration when using 1) very clean (usually canal/surface) irrigation water (EC < 0.5 dS/m); 2) when the soil surface sodium adsorption ration (SAR) is 5 to 10x that of the irrigation water EC; or 3) when calcium to magnesium ratios in the water are not at least 1:1.  Adding gypsum also provides additional calcium and sulfate for nutrition, if needed.  Gypsum, calcium sulfate, is a neutral salt so it affects soil pH very slowly causing it to seek neutral soil pH (7.0).  It won’t break up hard pans or soil layers with distinctly different soil textures or compaction that impede water infiltration.  Gypsum stabilizes the soil.  It reduces dispersion of larger soil aggregates when a dry soil is irrigated.  In turn this reduces the formation of soil crusts and helps maintain more soil porosity and higher water intake rates. How much gypsum is recommended to improve irrigation water infiltration for the conditions described above? Injecting 500 to 1000 lbs finely ground gypsum per acre foot of water should increase irrigation water EC by 0.15-0.3 dS/m, enough to improve infiltration of very clean water or reduce the effects of sodium and magnesium. If not using micro-irrigation, broadcast up to one ton/acre of finely ground gypsum onto the soil surface and do not till it into the soil.  It will dissolve in the water as irrigations are applied and improve the water quality.  The best time to apply gypsum on the

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David Doll4 CommentsMarch 24, 2013Irrigation

Podcast: Irrigation Management for Almonds in a Drought Year

Owen Taylor (from AG Fax) and I created a podcast to discuss irrigation strategies for a drought year. Topics covered within the podcast include: How much water do almonds need? What happens if they do not receive the correct amount of water?  How do almonds manage reduction in water applications? Tools to help with managing irrigations. Managing irrigations with varying water availability. (85-100% of ETc, 65-85% of ETc, >65% of ETc) Using groundwater to subsidize water use. This is my first podcast, so I hope you find it educational as well as useful. Click here. It is 20 minutes in length, but one can jump to their topic of interest. More information can be found at UC Drought Management Website.

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