Franz Niederholzer14 CommentsMarch 14, 2013Nutrient

Nitrogen Management in Mature Almonds, Part 1

Nitrogen is the most important mineral nutrient in almond production.  It is absorbed as nitrate or ammonium by active roots.  Mature almond trees use 80% of their total annual N requirement between March (full leaf out) and mid-May – June (kernel fill).    If the N isn’t available in this key application window, yield can be lost. To maximize yield (income) while minimizing N losses from the root zone ($ losses) that hurt growers wallets and may harm the environment attention to the four R’s – Right Rate, Right Time, Right Place, and Right Material — is needed in all orchard fertility programs.  Different nutrients are needed at different times and amounts by almond trees.  Spring is a key time for almond orchard nutrient management and the key time for nitrogen inputs.

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David Doll7 CommentsJanuary 24, 2013Nutrient

Nutrient Removal for Almond

I have received a few inquiries about the nutrients removed for almond. Based on Dr. Patrick Brown’s group’s work (Sebastian Saa Silva and others), the amount of NPK removed with every 1000 kernel pounds of almond is: Nitrogen – 65 lbs, Phosphorous – 8 lbs, and Potassium – 76 lbs. This includes the nutrients removed will all of the materials exported out of the orchard in a typical pick-up operation – hulls, sticks, leaves, shells, and kernels. Keep in mind that more than the above amounts may be needed to compensate for the inefficiencies of application and uptake (i.e. nitrogen uptake efficiency is somewhere between 75-85%, condition dependent — so to have 65 lbs of uptake, 76-85 lbs of N must be applied). As noted in the comments below, potassium and phosphorous must be converted to oxides. This can be done as follows: Almond removal 8lbs of P = 18.4lb of P2O5 76 lbs of K = 91.2 lbs of K2O For Phosphorus o Lbs. P x 2.3 = lbs. P2O5 o Lbs. P2O5 x 0.43 = lbs. P   For Potash o Lbs. K x 1.2 = lbs. K20 o Lbs. K20 x 0.83 = lbs. K

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Franz Niederholzer8 CommentsNovember 20, 2012Nutrient, Salinity, Soil

Broadcasting compost within Orchards

Compost spreaders are working in almond orchards in this area.  The addition of composted organic matter – often composted yard waste — to soil should generally benefit soil physical and chemical properties.  However, it isn’t a source of short-term plant available nitrogen.  Research by UC Davis specialists Tim Hartz and Jeff Mitchell has shown that composted yard waste, when mixed with sand and held under constant, optimum moisture and temperature (the optimum conditions for mineralization of organic nitrogen) produces a very little plant available nitrogen (2% of total nitrogen in the compost) in the short run (12-24 weeks).  When compost is broadcast on the soil surface and not incorporated, plant available nitrogen should be even less.  Dr. Hartz did conclude that manures and composts had value in long-term soil building in vegetable crop production, where those materials are incorporated into the soil.  [Untreated/uncomposted manure use in almonds is a food quality risk and not supported by the almond industry.] Why bring up compost use? Growers are willing to pay for it and seem happy with the results.  Here’s why.  If California agriculture ends up in a regulatory situation where nutrient budgets are required of growers, it should be recognized that the short term nitrogen benefits from composted yard waste are almost non-existent and the long term benefits are unknown. Previous entries on compost applications can be found here and here.

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David Doll3 CommentsOctober 17, 2012Nutrient

High Boron Hull and Leaf Values…

There have been a few questions regarding high boron levels in hull and leaf tissue sampled from this past year. The general consensus is that it is “just one of those odd things that occur every year.” Never-the-less, that prompted me to give Dr. Patrick Brown (UC Davis) a ring and inquirer about environmental influences on boron.

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Franz Niederholzer8 CommentsSeptember 19, 2012Nutrient

Fall Foliar Fertilizers: Targeted v/s General Approach

A PCA asking me the other day what I thought of a general micronutrient (iron + molybdenum + zinc + copper + manganese + boron +?) compared to a standard zinc + boron spray program that is common in postharvest almonds in the areas where I work. This question got me thinking about a review of fall fertilizer programs in general, with a focus on foliar nutrients. There are more than a dozen mineral nutrients essential for plant growth. However, only a handful of those nutrients have been shown to be important – in general — to profitable almond production. These

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David Doll0 commentsSeptember 6, 2012Nutrient

Post Harvest Nitrogen: How Much?

Generally, we recommend 20-25% of the season’s nitrogen budget to be applied in the post harvest period. This is based upon having a Mid-July leaf nitrogen value within the range of 2.2-2.5%.  This nitrogen is used for the post-harvest growth processes, which includes both vegetative and fruit bud development and some vegetative growth. When making this application, the sooner, the better, as it will help reduce tree stress.  Studies have shown that ‘Nonpareil’s’ fruit bud differentiates about 7-14 days after harvest, while other varieties, such as ‘Carmel’, the majority of fruit buds differentiate prior to ‘Carmel’ harvest. This timing will be delayed in cool, mild years. Tree stressed imposed during this period will reduce fruit bud set, and the buds will remain vegetative (leaf buds). In the cases of above recommended mid-July leaf nitrogen levels, nitrogen should still be applied, but the amount should be reduced. For example, if leaf nitrogen values are around 2.8%, apply 15-20% of the total seasonal nitrogen budget. If over 3%, reduce that application further to 10-15% of the total nitrogen budget. Nitrogen should be applied with caution in the post-harvest period as early rains may leach nitrate in sandier soils. Late fall (Late September, early October) nitrogen applications should also be reduced; the trees ability to pick up nitrogen is decreased due to lower levels of transpiration.

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Roger Duncan10 CommentsAugust 23, 2012Nutrient

Hull Analysis for Boron – Why?

Harvest is here. This is a good time to pull a a bag of almond hulls for a boron analysis. In making this recommendation, there are questions that are consistently asked. I already know my leaf tissue levels, so why do I need to perform a hull analysis for boron? Leaf sampling is not effective in determining the levels of boron as there are no obvious foliar symptoms of moderate boron deficiency. Furthermore, leaf levels may appear adequate while the actual levels within the tree are too low or high. Since the hull of the almond is a “sink” for boron, the analysis of mature almond hulls is a better indicator of boron status. When should I collect samples for a hull analysis? Boron will continue to accumulate in the hull until harvest. The best time to collect a hull sample is anytime after shaking the nuts. Varieties within the orchard may have differing boron levels due to different yields; it may be useful to pull a sample from the other varieties. How do I interpret the results? Trees with hull boron levels of less than 120 ppm may benefit from a postharvest boron spray (1-2 lb of a 21% B product in 100 gallons of water per acre). This will help with pollen germ tube growth in the flowers next spring but will not improve overall boron status of the tree. Boron applied earlier in the season as foliar spray is not a substitute for this timing because it is sequestered into the hull and is unavailable for the developing fruit bud. Hull boron of less than 80 ppm indicates the need for a ground application.  Fertilize with 2-4 pounds of actual boron per acre.  This is equivalent to 10-20 pounds of a 21% soluble boron product (i.e. Solubor). Boron can be applied through the irrigation system, broadcast or

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David Doll3 CommentsJuly 28, 2012Horticulture, Nutrient

Nitrogen and Potassium Leaf Content: Is There Such Thing as Too Much?

I have received a few questions regarding results of mid-July leaf tissue analysis. In many cases, when reviewing the leaf samples, I have noticed that levels of nitrogen and potassium are often much higher than the recommended mid-July levels. Having leaf nutrient contents well above adequate levels does not necessarily increase yield, but can increase fertilizer costs and hull rot incidence. Rationale for “pumping” up the trees above the adequate value is to address the “silent hunger” that may be taking place within the field. In other words, by overfeeding some trees, we are assuring that we are maintaining trees that may be borderline above the level of sufficiency. Performing this action may increase yields as some trees that are deficient will perform better; however, too much fertilizer will lead to waste. Assuming that the leaf samples were collected properly, the UC-established mid-July leaf values should be used for comparison.With nitrogen, leaves with 2.2-2.5% leaf nitrogen content indicate that the sampled trees are receiving enough nitrogen. Being a few tenths of a percent over this value (3.0%) is a good indication of over-fertilization, increasing the risk for hull rot. Regarding potassium, the sample is considered sufficient if it is above 1.4%. Most growers attempt to maintain their potassium leaf levels around 1.8-1.9% within their samples, buffering for the tree use and compensating for the spatial variability of potassium within the tree. I have seen several leaf analysis with potassium levels greater than 2% and have heard from growers that trees need to be above 2% to maintain production. This is not true. Research by Roger Duncan (Farm Advisor, Stanislaus County) found that orchards with potassium leaf levels greater than 2% did not have greater yields than orchards with leaf levels above 1.4%. If leaf samples are well above the sufficient levels, plan to reduce,

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Franz Niederholzer0 commentsJuly 18, 2012Nutrient

Summer leaf sampling is serious business

It’s July. Among key orchard activities as harvest approaches, it’s time to sample almond leaves for nutrient analysis. The lab analysis report for a leaf sample serves as part of the “report card” for your fertility program for this growing season for a particular variety in a particular block. A previous post from “The Almond Doctor” covers the practice of summer leaf sampling and shows the University of California critical nutrient levels for almond leaves sampled in July. This post will talk about several additional steps to orchard nutrition assessment in summer and to stress the importance of these practices to the commercial success of an orchard. Take separate leaf samples for each variety in a block. Crop load is the key factor determining mature almond tree nitrogen (N) and potassium (K) use. Different almond varieties in the same block can produce different yields and nutrient demand based on their genetic potential and conditions at bloom. If you don’t already, consider taking leaf samples for nutrient analysis from each variety. Use the lab reports and crop yield reports from each variety in the block from this year as background information when it comes time to apply N and/or K fertilizer for next year. If you applied the same amount of N and K fertilizer this season to all trees in an orchard, yet the Non-pareil yield was off and the Monterey yield was high, can you see that reflected in the leaf analysis reports? Variety specific leaf analysis and cropload data can help you understand how different varieties use expensive nutrients and how you might possibly fine tune your fertilizer delivery to optimize yield without wasting money.  Look up between leaf samples. Adequate tree vigor (growth) is key to good production. Adequate leaf nutrient levels and little to no growth

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David Doll0 commentsMay 19, 2012Nutrient

Estimating Nitrogen Needs = Estimating Your Crop

Research by Dr. Patrick Brown’s group at UC Davis has been reviewing nitrogen use efficiency of almonds. In their studies they have shown that almonds, when properly fertilized (i.e. not over/under-fertilized),  export between 60-65 pounds of N from the orchard for every 1000 kernel pounds harvested. This number includes all green weight removed to achieve the 1000 kernel pound yield – roughly 4000 pounds of hulls, shells, leaves, debris, and kernels. Interestingly enough, they also have found that orchards that are under-fertilized will export less N (65 lbs). Knowing this, is it possible to determine the nitrogen needs of the trees for the season? Simply stated, “Yes,” but only if an accurate estimate of crop can be made. The ability to accurately estimate a crop is gained through experience and the taking of careful notes from the early season to allow comparison with the sheets provided at harvest. Once a crop estimate is determined, the estimated kernel yield/acre can be multiplied by 60 pounds to determine the total amount of N required/acre for that year. Since almond goes through a period of several drops and weather events (i.e. frost, hail, etc), this adjustment can be modified in season to account for the change. Never-the-less, applying only 60 pounds of N for every 1000 kernel pounds will not meet the trees need because the application efficiency of nitrogen is not 100%. Further work within the study demonstrated that almonds are much more efficient than previously thought, with roughly 70-75% of the nitrogen applied through a micro-irrigation system making its way into the tree. Taking this use efficiency into account, we need to multiply the pounds required by crop demand by 1.4, giving a number of 84 pounds of N for every 1000 kernel pounds. So how does all of this relate to nitrogen leaf sampling?

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