David Doll0 commentsApril 25, 2019Nutrient

Fertilizing First Year Almond Trees: Major Nutrients

Determining fertilizer needs for newly planted orchards is challenging. This is due to the desire to grow the trees as rapid as possible while considering the risk of uptake burn and irrigation system inefficiencies. To determine the optimal fertilizer plan, the amount and type of nitrogen and other nutrients need to be considered. Nitrogen: Rate studies conducted in California have found that tree growth seems to peak with 3-4 ounces of nitrogen application per tree. This is based on three different studies – one located near Arbuckle, CA and the other two in Merced County. Within the most recent studies in Merced County, applications were made every three weeks from April through July for a total of six applications. A total of 0, 1, 2, 4, and 6 ounces of actual nitrogen was applied during this period to replicated plots using a NPK blended fertilizer. The source of nitrogen did not create a difference in trunk caliper in the multiple studies within Merced County. Very simply stated, “nitrogen is nitrogen.” There are benefits, however, to the various nutrients that are within fertilizers. If soil levels of phosphorous or potassium are low, utilizing an NPK blend would provide an addition of these major nutrients. The same could be said about calcium-containing fertilizers. If these nutrients are at sufficient levels for plant growth, however, there is minimal benefit from adding additional amounts. Potassium and Phosphorous: Within California conditions, phosphorous (P) and potassium (K) do not appear to be the limiting factor with most soils. The two trial locations within Merced County were located on sandy soil and found no increase in growth from the inclusion of P and K within the fertilizer programs. This does not mean that these major nutrients are not important, rather that many soils contain adequate levels of

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David Doll0 commentsSeptember 13, 2018Nutrient

Postharvest Nitrogen Management 2018

Many operations often apply nitrogen postharvest. Application rates vary from orchard to orchard, but typically I hear applications between 30 and 50 lbs/acre. This nitrogen is used to rebuild the nitrogen reserves within the tree and help with a variety of tree processes. Being applied late in the season, however, it is susceptible to leaching from over-irrigation and early rains. While it is critical to make sure there is nitrogen available for the tree, postharvest nitrogen budgets should be evaluated to determine if they are too high or not needed. Work at UC Davis has indicated that 15-20% of the nitrogen demand occurs from harvest through the post-harvest period. This suggests that somewhere between 20-30 lbs of nitrogen is utilized during this period, which could be sourced from residual nitrate in the soil or post-harvest applications. A further breakdown of the uptake curve shows that less than 8% of the annual need occurs after September, suggesting the importance of timeliness in application (Figure 1). Applications can begin when the abscission layer begins to form on the later harvesting varieties, but consider lowering rates to reduce the risk of hullrot flare ups (e.g. apply 10-15 lbs/acre instead of 25-30 lbs/acre). Applications of nitrogen in the post-harvest tend to be relatively inefficient due to several factors, including tree defoliation, leaching by early rains or long irrigations, shorter days and lower water use. This suggests that more nitrogen may be needed to achieve a 20-30 lb uptake, but studies in Kern County failed to see a response from applications greater than 50 lbs/acre of nitrogen applied after Nonpareil harvest (mid-August). Rates should not exceed this amount and applications made in September and October should be significantly reduced. Mid-July leaf nitrogen and residual soil nitrate should be taken into consideration when determining the amount.

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David Doll4 CommentsOctober 17, 2017Irrigation, Nutrient

Almond Kernel Defects

It has been a challenging year in regards to kernel quality within almonds. Several issues have emerged including insects, diseases, and deficiencies. Samples of each of these have been brought to the office for identification. In doing so, I thought it would a good idea to share what we have found with the accompanying figure. Each of these problems seem to have a set of circumstances that led to an increased observance of the problem in 2017. They include: Leaf-footed plant bug. These large bugs damage the kernel by feeding. There was a larger over-wintering population in 2017 which is thought to be due to the milder winter and increased vegetation that occurred from the increased rain. Damage was reported on nearly all varieties, but was particularly bad on ‘Aldrich’ and ‘Fritz.’ If the feeding occurs early in the season it will kill the kernel. Later feeding occurring as the shell hardens and the embryo matures will not kill the nut but cause staining and sometimes gumming. The defining characteristic is a sunken black spot located on the kernel. Boron deficiency. This deficiency can occur in areas with clean surface water and low soil boron and is observed regularly on the east side of the central valley. Boron deficiency can lead to gum that crystallizes on the end of the kernel and is not in response to a feeding wound. A hull analysis should be conducted to determine boron levels as leaf levels are not indicative of tree boron status. A hull analysis under 80 ppm indicates deficiency and boron should be applied to the soil to bring the trees to sufficient levels. Insect damage. Navel orangeworm (NOW) was high this year with reports as high as 40% in late harvesting varieties. Lack of winter sanitation due to the rains

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David Doll0 commentsSeptember 19, 2017Nutrient

Almond Postharvest Management: Nitrogen Considerations

Written by David Doll (UCCE Merced) and Franz Niederholzer (UCCE Yuba-Sutter-Colusa) Applications of nitrogen in the postharvest period have been promoted as a good farming practice.* Trees utilize nitrogen at this time to rebuild nitrogen stores and provide nutrients for bud development. Research from the Kern County nitrogen trials found that trees can absorb approximately 15% of annual nitrogen demand in the 8 weeks after harvest (30-45 lbs/acre, excluding application inefficiencies). This work was done in a highly productive orchard (3000+ lbs/acre) and applications were applied as multiple fertigation events through the entire year. Fertilizer nitrogen applications should be made as soon as possible after harvest to allow the trees the most time to absorb fertilizer nitrogen before the leaves drop, when root nutrient uptake essentially stops. Whole almond tree nitrogen need after harvest is much less than in the spring (no shoot growth or crop), therefore fall fertilizer nitrogen needs are relatively minor compared with leaf out to hull split.  Fall nitrogen fertilization need is further reduced by remobilization of leaf nitrogen into woody tissue storage as trees prepare to drop their leaves in November (if they are not burned off with zinc sulfate.) Interestingly, recent research suggests that late postharvest fertilization (October) can be skipped if mid-July leaf nitrogen levels are adequate (over 2.5% nitrogen). This work by Franz Niederholzer conducted at the Nickels Soil Lab in Colusa County has found no negative impact on yields when skipping postharvest nitrogen applications within orchards over the past two years. In this trial, trees had mid-July leaf nitrogen values of 2.55% or greater. Trees receive 0 or 30 lbs/acre of postharvest nitrogen in mid October. Trees didn’t receive late zinc sulfate foliar spray and maintained leaves up to or through Thanksgiving. Over the past two years, there were no differences

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Franz Niederholzer4 CommentsOctober 11, 2016Nutrient

Fall Foliar Nutrients – Zinc and Boron Review

Symptoms of zinc deficiency of almond Written by Franz Niederholzer, UCCE Advisor, Colusa and Sutter/Yuba Counties Bloom is the most important time of the year for adequate boron (B) and zinc (Zn) levels in almonds.  Zinc is essential to many processes such as cell division, protein synthesis and auxin synthesis in growing points (flowers and shoots), and bloom is the time of the most growing points in a tree.  Boron is essential for cell wall synthesis and division. Boron fertilization has improved fruit or nut set compared to deficient plants in many crops, but only if applied in time to get B into buds at bloom.  Both Zn and B can be absorbed into leaves and translocated within almond trees. Check leaf symptoms, summer leaf analysis or hull analysis results to see if Zn and/or B fertilization is needed.  Zinc deficiency produces “little leaf” symptoms (see photo below), with trees showing summer leaf levels of 15 ppm Zn or less considered deficient.  Trees with hull B levels below 80 ppm B at harvest are thought to be deficient, but almond yield may benefit from B application if hull levels are below 120 ppm B.  Do not fertilizer with B if hull levels are 200 ppm B or greater, as excessive B is toxic to plants. A fall foliar nutrient spray is a cost effective way to get Zn or B into buds for the following year’s bloom.  The return on investment for a fall B spray can be significant.  Yield increases of 200-400 kernel pounds per acre have been measured from a foliar nutrient application the previous fall at Nickels Soil Lab of 0.6 lbs. of actual B (the equivalent of 3 lbs. Solubor®/acre applied in 400 gallons/acre). Fall Zn sprays should increase leaf Zn the following year and eliminate Zn
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David Doll2 CommentsSeptember 6, 2016Nutrient

Postharvest is a Good Time for Boron Foliar Sprays

Boron is a critical micronutrient for fruit set.  Work has shown that yield can be reduced when boron hull concentrations fall below 80 ppm. In order to determine deficiency, a hull analysis should be taken to determine tree boron status. Leaf tissue levels are not consistent in providing boron status. Applications of boron should occur to the ground if hull levels are below 80-100 ppm. Boron foliar applications, however, should be considered for nearly all orchards except ones approaching toxicity (hull boron greater than 200 ppm). Boron foliar applications have been shown in several studies to increase yields in orchards deemed boron sufficient. A study from 1999 compared the application of foliar boron at two locations – one in Fresno County and the other in Glenn County – for two years. The Fresno County location applied the foliar sprays either in September, December, or February at three rates (0 lbs/acre, 0.71 lbs/acre, and 1.5 lbs/acre of boron) using Solubor® (a 20.5% boron product). The Glenn County site applied the foliar spray either in August, September, or February at four rates (0 lbs/acre, 0.71 lbs/acre, 1.11 lbs/acre, 1.50 lbs/acre, and 1.91 lbs/acre of boron) using Borosol® (a 10% boron product). At the Fresno Location, the September application was the most effective in increasing tree boron levels, fruit set and yield. All rates out-performed the control. At the Glenn County location, the increasing rates increased tree boron tissue levels almost linearly for the August and February timings. February application timings at both sites increased initial fruit set, but the greatest increase in tissue concentration, nut set, and yield response came from the September timing. The increases observed are most likely is due to the increased efficiency in nutrient uptake from the active leaves. If a September application cannot be made, a February/early pink bud spray should be considered. Ground applied boron should

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David Doll3 CommentsMay 5, 2016Nutrient

Potassium and Almonds: Rates, Timings, Other Tips

I received a few questions on potassium applications in almonds. These include points on rate determination, application timing, and other considerations. Q. How much potassium is needed? Almonds remove about 72 lbs of elemental potassium (K) for every 1000 kernel pounds. This is equivalent to 92 lbs of potassium oxide (K2O), the unit which potassium fertilizers are measured. This means that for every 1000 pounds of kernels removed, 92 lbs of K2O must be available or applied to prevent future deficiency. This is equivalent to 184 lbs of potassium sulfate (50% K2O) or 368 lbs of potassium thiosulfate (25% K2O). The amount of potassium applied should take into account leaf tissue levels as well as soil analysis. If the soil analysis reveals K values greater than 150 ppm, the trees are less likely to respond to K applications. In these cases, applications should match removal. If high amounts of K are available in the soil (>250 ppm), K rates could be reduced to help reduce costs (applications should match ~80-85% of demand) until soil analysis begins to show a decrease in K values. If lower than 150 ppm, rates should be increased to help build reserves. please note that some soils-such as sands- can not hold this much potassium. Leaf tissue levels of K are variable. “Critical values” established at other times of the year have not been verified to production levels of trees through research. Therefore, mid-July leaf sampling is still recommended for determining K status of the tree. If trees have a leaf K percentage greater than 1.7%, minimal gains will be observed with increasing applications. Leaf tissue concentrations below 1.4% require increased applications. Q. How should potassium be applied? K fertilizers can be applied by granular applications or through the irrigation system. Ground applications are often made

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David Doll8 CommentsMarch 29, 2015Nutrient

Young Tree Nitrogen Fertilization

In attempts to incorporate varying media within the website, here is my first go at using Google Hangouts to LiveCast a presentation. The recorded presentation below provides nitrogen fertilization considerations for  newly planted and developing orchards. Total length is around 15 minutes. A quick overview of the presentation: Nitrogen is nitrogen. Several studies within CA have indicated that there is no benefit in using different types of nitrogen for fertilizing young almond trees. Some fertilizers, however, may influence soil pH as well as be more prone to leaching; Studies within Merced and Colusa COunty have indicated that newly planted trees will maximally grow with actual nitrogen applications between 3-4 ounces. This has to be adjusted for tree density and application efficiency; Developing trees have developing rootzones which leads to inefficient applications. If fertigating, the best irrigation system would deliver nitrogen directly to the rootzone of the tree (e.g. single line drip with punched emitters). If not possible, controlled release fertilizer has been shown to grow as well as conventional fertilizer and have a lower labor cost (one application and done for the season). The 120 day controlled release blend in this trial was supplied by Agrium Technologies; Do not apply more than one ounce of actual nitrogen per application per year of growth. This helps reduce lanky growth and nitrate uptake toxicity; Take into account residual soil nitrogen and nitrogen within the irrigation water if using a well. In some cases, these may provide sufficient nitrogen; Finally, don’t start too early. Give the trees time to grow and draw down some of the moisture within the rootzone. Around 6″ of growth should be visible prior to the first fertilization. Here is a link for a pdf copy of the presentation.

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