David Doll5 CommentsMay 12, 2012Nutrient

Regional Considerations for Nitrogen Timing

Over the past few weeks, I have attended a few events that discussed the application timings of nitrogen. The results that were discussed at these events were based on an extensive five year study conducted by the University of California at a trial located in Kern County.One of the many findings of this study included the development of a nitrogen application schedule that maintains crop productivity. From this trial, the researchers have determined that 80% of the nitrogen should be applied before the completion of kernel fill (mid-June), while the remaining 20% should be applied in the post harvest. In the study, the researchers applied the spring nitrogen doses beginning in mid-February prior to bloom, and continued monthly until mid-May. They roughly followed a 10%-25%-25%-20% application schedule. The question remaining, especially with impending groundwater and nitrate regulations, is this applicable to all parts of California? The short answer is “Of course not,” as differing climates and soils create different challenges for growing almond efficiently. For example, in Merced County, we receive an average of 10-12 inches of rain and have some areas of very sandy soils. This is in contrast to the trial’s location in Kern County, which receives 6 inches of annual rainfall and is located on a sandy loam soil. Practices of nitrogen application, therefore, will vary by location – especially the timing of the first application. In a previous entry, I wrote about the movement of nitrate and the rationale for applying after leaf out. Although this is still the most efficient timing to apply nitrogen, I have since learned that there is some level of root uptake of nitrogen during the period of delayed-dormancy (bud-swell). This occurs due to nitrate, being found in a greater concentration outside of the root moves into the root to establish equilibrium. The higher

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David Doll0 commentsApril 5, 2012Nutrient

Nitrogen within the soil: The Nitrogen Cycle

Figure 1: The various forms of nitrogen and processes within the nitrogen cycle. Sourced from wikipedia.org. Written by Dr. Larry Oldham (Mississippi State Extension Service) and David Doll. Nitrogen is in organic and inorganic forms in soils. Over 90 percent of soil N is associated with soil organic matter. Nitrogen is in compounds identifiable as part of the original organic material such as proteins, amino acids, or amino sugars, or in very complex unidentified substances in advanced stages of decomposition. Plants may use either ammonium (NH4+), or nitrate (NO3-) which behave quite differently in soils. Positively charged NH4+ is attracted to negatively charged sites on soil particles as are other cations. It is available to plants, but the electrostatic attraction protects it from leaching. Conversely, negatively charged NO3- does not react with the predominately negatively charged soil particles, so it remains in the soil solution, moves with the soil water, and is susceptible to leaching. Nitrogen transformations in soils/Nitrogen Cycle: Nitrogen conversions depend on soil moisture conditions, soil acidity, temperature, and microbial activity. Ammonium is absorbed on the cation exchange complex or taken up by plants without transformation, but most likely it is converted to NH4+ soon after its formation or addition as fertilizer. This nitrification is a two step process involving two different groups of soil bacteria. First Nitrosomas bacteria produce nitrite (NO2-). Nitrobacter species then convert NO2- to NO3- soon after its formation. The carbon used by these bacteria is derived solely from atmospheric CO2. a) 2NH4+ + 3O2 = 2NO2- + 2H2O + 4H+ + energy b) 2NO2- + O2 = 2NO3- + energy Two things to note: 1) NH4+ has a short residence time in soils before conversion to the more mobile NO3- form; and 2) hydrogen ions are produced which lower the soil pH. Mineralization is

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David Doll3 CommentsMarch 31, 2012Nutrient

Nitrogen applications after leaf-out….Why?

Sourced from AccessScience topic of soil chemistry. Water moves within plant-soil system from wettest to driest. This gradient is termed water potential, and explains why irrigation works. Basically, the water potential gradient between the soil and the plant, from wettest to driest, would be wet soil, dryer soil, root, stem/trunk, branch, leaf, and finally, air. Water, when applied through irrigation or rain, will follow that path, moving through the soil, into and up the tree, and out the leaves through the stomata.The final destination for the water molecule is the driest environment, which is air. As an analogy, think of the plant as a wick of an oil lamp, as the oil is burned, oil moves up the wick out of the reservoir to the point of being burned, keeping the lamp lit. For more information, please follow the links for water potential and the process of mass flow. Since nitrate, the only form of nitrogen that is used by plants, is a water-soluble negatively charged particle (anion), it does not bind with most soils, and therefore remains in the water solution within soils. Once in solution, it moves with the water. As water moves into the plant’s roots and up into the plant, nitrate enters the root and plant as well. If there is no or low water demand by the plant due to conditions of dormancy, very little of the nitrate-water solution will move into the plant. Only when the process of transpiration begins does nitrate move into the growing tips of the plant, providing nitrogen, an essential element for plant anabolism. Since leaves are needed on the tree in order for transpiration of water to occur, applications of nitrogen before leaf-out are at risk for loss due to leaching from the root-zone. For example, lets say that

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David Doll1 CommentNovember 6, 2011Nutrient

Compost Applications for the Almond Orchard

Compost is applied by many growers as a supplement to their nutrient management program. Composts may contain nitrogen, phosphorous, potassium, and other micro-nutrients. Applications of compost also add organic matter, and the associated organic acids, which has been shown to increase soil tilth in cropping systems.  Since all composts vary in nutrient content due to the variability in source material, nutrient benefits can only be determined through analysis. Nitrogen from Compost. To understand the effect of nitrogen from compost, we must first understand the nitrogen cycle. Organic matter contains nitrogen that is bound to various chemical compounds within the plant material. Termed organic nitrogen, it is unavailable to the plant. It can only be made available to the plant upon mineralization and conversion to nitrate through the process of nitrification. These processes are mediated by the soil microbial community. Once converted to nitrate, the nitrogen is available for plant use. Synthetic fertilizers go through similar processes depending upon their starting point (i.e. ammonium, nitrate, etc.). Figure source: www.physicalgeography.net/fundamentals/9s.html Most finished composts vary from 0.5-2.5% total nitrogen. Since most of the nitrogen is held within plant compounds (organic form), not all of the nitrogen will be mineralized and available upon application. Research by Dr. Tim Hartz, UC Davis, has shown that most composts only release about 5-10% of the nitrogen in the nitrate form. Composts that have a lower carbon to nitrogen ratio release nitrate on the higher end of this range. Higher nitrogen containing composts (> 3% nitrogen) may release more than 10% of the nitrogen. Nitrogen benefits from compost also appear to be reduced in the following growing seasons, with very little mineralization occurring. At this point, it appears that the compost is simply organic matter. Phosphorus from Compost. Phosphorous (P) content within compost can be significant. Since exportation of

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David Doll0 commentsNovember 5, 2011Nutrient

Compost Quality: What the Analysis Reveals

Compost is applied by many growers as a supplement to their nutrient management program. Adding organic matter and the associated organic acids, has been shown to increase soil tilth in cropping systems. All composts vary in nutrient content, which is heavily dependent upon the source material of the compost. Since sources vary, it is important to have an analysis in order to determine nutrient content. To understand how compost works, we must first understand the nitrogen cycle. Organic matter contains nitrogen that is bound to various chemical compounds within the plant material. Termed organic nitrogen, it is unavailable to the plant. It can only be made available to the plant upon mineralization and conversion to nitrate through the process of nitrification. These processes are mediated by the soil microbial community. Once converted to nitrate, the nitrogen is available for plant use. Synthetic fertilizers go through similar processes depending upon their starting point (i.e. ammonium, nitrate, etc.). Nitrogen from Compost.Most finish composts vary from 0.5-2.5% total nitrogen. Since most of the nitrogen is held within plant compounds (organic form), not all of the nitrogen will be available upon application. Research by Dr. Tim Hartz, UC Davis, has shown that most composts only release about 5-10% of the nitrogen. Composts that have a lower carbon to nitrogen ration release on the higher end of this range.Higher nitrogen containing composts (>3% nitrogen) may release more than 10% of the nitrogen.. Nitrogen benefits from compost also appear to be reduced in the following growing seasons, with very little mineralization occurring. At this point, it appears that the compost is simply organic matter. Phosphorous from Compost.Phosphorous (P) content within compost can be significant. Since exportation of P from the almond orchard is low (7 lbs/1000 kernel lbs), attention should paid to prevent over application of P. P is

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David Doll14 CommentsOctober 21, 2011Nutrient

Post Harvest Foliar Sprays

After harvest is a good time to apply a few different foliar nutrients to the trees before the leaves fall. Nutrient uptake occurs through wood and leaf tissues. Applying when leaves are still green and active increases the sprayed surface area, thus increasing the efficiency of the spray and uptake of the nutrients. Applications can be made when leaves are off the tree, but the reduced surface area leads to a reduced nutrient uptake.  Below are considerations to make in regards to a few commonly applied foliar nutrients. Boron. Studies have shown that a foliar spray of boron can increase crop set regardless of boron hull content. If the tree is deficient in boron, the resulting “yield bump” is greater than in sufficient trees, but the “yield bump” is still observed in sufficient orchards.  Two pounds of Solubor (20% Boron) applied with 100 gallons of water/acre is commonly used. This article detailing boron foliar sprays highlights the specifics. Urea/Nitrogen. Fall foliar applications of lo-biuret urea are thought to reduce the incidence of bacterial canker and bud drop within almond. It is thought that this reduction is due to an increase of tissue nitrogen content which may increase overall tissue health making it more resistant to bacterial infection. Fall Urea applied for bacterial canker prevention should be applied later in the season (i.e. first week of November) and at a rate of 100 lbs/acre. Studies have also shown that fall applied lo-biuret urea can increase yield. Although studies have not shown the yield increase to be significant, it has been observed in two trials. Both yield increases were observed with the lower end of urea use, between 10-25 lbs/acre. Higher applications of urea did not produce as much of an effect and in some cases led to foliage burn and leaf

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David Doll11 CommentsMay 28, 2011Nutrient

Almond Potassium Fertilization: Where did My Potassium Go?

A common question received from growers after they see their leaf sampling results is “How come my potassium levels dropped significantly from last year?” The short answer is that it was removed with last year’s harvest, but there are many complicating factors that should be taken in consideration. Potassium Removal from the Orchard System. Studies by UC Davis have shown that 76 pounds of potassium are removed from the orchard for every 1000 pounds of kernels harvested. From nutrient analysis of the fruit parts, 70-80% of the potassium removed by the harvest is within the hull, while the rest is within the shell and kernel. Potassium loss from the orchard can also occur through leaching. Leaching of potassium is reduced in soils with high exchange capacities, which includes loams, clays, and silts. Sands and loamy sands have a relatively low exchange capacity, lower amounts will bind to the soil particles. Furthermore, this bond is not as strong within acidic soils which can lead to leaching in areas that are over irrigated or received excessive rainfall. Since potassium and sodium have the same charge strength, strategies used to move sodium out of the rooting zone will also move potassium as well. These include applications of gypsum or other strongly charged cations to “flush” the system. Excessive applications of water applied as a leaching coefficient may also leach potassium. Proper Leaf Levels of Potassium. Since Potassium plays a large role in tree health, it is important to maintain proper levels of the nutrient within the tree. A critical leaf value of 1.4% has been established by the University of California and current research has suggested that levels excessively above this value do not increase yields. Recent field studies by Roger Duncan (UCCE Stanislaus) have demonstrated that leaf potassium levels in excess of

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Franz Niederholzer7 CommentsApril 13, 2011Nutrient

Using Urea Efficiently

Summary: Soil applied fertilizer is intended for root absorption by plants. Manage fertilizer nitrogen (N) to keep as much of it as possible in the root zone to maximize crop N uptake, crop yield, and protect the environment. To keep urea fertilizer N in the root zone 1) incorporate urea into the soil with water or cultivation within a day or two of application and 2) don’t over irrigate when incorporating urea using water. Inject liquid fertilizers containing urea (for example, UAN32) into irrigation systems in the middle third of the irrigation set. This delivers urea N evenly through the root zone, avoiding leaching that can occur when urea is injected too early in the set and limited root zone distribution when injected too late in the set. Background: Urea is the most commonly used dry nitrogen (N) fertilizer in the U.S. It provides half of the nitrogen in UAN (Urea Ammonium Nitrate) 28 or 32 liquid fertilizers. Dry and liquid fertilizers that contain urea have several advantages — relatively high N content (28-46% N), ease of handling and reasonable price relative to other N sources. However, nitrogen from applied urea can be lost from the root zone when used improperly, wasting money, reducing plant available N, and risking reduced crop growth and yield. The lost N can also be an environmental contaminant. Growers and PCAs should be aware of how to avoid N losses and get the most from urea fertilizer dollar. Within days of application, urea N can be lost from the crop root zone in two ways – through ammonia volatilization or urea leaching. This article will briefly describe how these losses can occur and how to manage urea to avoid them. The uncharged urea molecule (H2N-CO-NH2) breaks down in or on the soil into two ammonium molecules

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David Doll24 CommentsMarch 25, 2011Nutrient

Fertilizing Young Almond Trees – A Few Tips

A few questions come up every year in regards to fertilizing first, second, and third leaf trees. Since these trees are rapid growing, and in some cases, producing crop, adequate fertilization is crucial for growth. First leaf trees: As a guideline, I generally recommend no more than one ounce of elemental nitrogen per tree per application. Three to four (or more) applications using a general blend (i.e. 12-12-12 NPK) fertilizer per year will produce a nice result. Using a triple 12, this totals about 8 ounces of actual fertilizer applied per tree.  Applications should begin upon leaf out and continue about every 4-6 weeks.  To prevent any nitrogen burn, the first applications of the year should be less than one ounce while later applications should not be greater than one ounce. Although I know some growers are successful, I have observed enough tree damage to caution against using liquid based fertigation products for first leaf trees. It is easy to overdose the trees with nitrogen, especially in hot weather, causing tree die-back. I agree that using granular fertilizers is a conservative approach, but one that has been tested and used extensively over the years. Second leaf trees: The rootzone of 2nd leaf trees can be quite extensive, but is still limited in comparison to mature trees. Even if the grower is able to fertigate, I usually still like to see the first application to be granular. Why? In many cases adequate potassium and phosphate have not been applied in the previous dormant season, thus applying a 12-12-12 fertilizer will ensure at least some level of these nutrients as the tree begins the rapid growth period of April and May. Later applications can be made through the fertigation system. Again, follow the rule of one ounce per tree per year of growth. So,

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David Doll0 commentsMarch 8, 2011Diseases, Nutrient

Some Early Season Thoughts

I have been in a few orchards this past week and thought I would relay on some thoughts.1). Bloom. In comparison to last year, bloom seemed to last much longer. Some orchards I have been working next to are now entering petal fall. Their first blossoms opened up about 20 days ago. It appears that the trees hit full bloom in our area during the nice weather that we had last week. Hopefully this will aid in pollination and nut set. 2). Frost Damage.  Frost damage appeared to be pretty minimal (1-5%) in the 15 or so orchards I checked around Merced County. I have heard mumblings that damaged pistils and stamen from the extreme temperature may lead to poor pollination and nut set. At this time, it is hard to predict if this occurred and to what extent. Most likely this type of damage will become apparent during the flower drop and nut drop periods. Keep in mind that other weather issues may contribute to these drops making it hard to determine what caused what. 3). Fungicide Sprays. The threat of Brown Rot is still pretty high, especially with Butte/Padre orchards. This weekend we saw great weather for Brown Rot – over 60F and raining. The winds today have aided in the reduction of leaf wetness, thus reducing brown rot risk. If Sat/Sun/Monday’s rain event fell in the 10 day window from your last spray, it looks like you may be able to get through this week without too much worry – unless the weather changes! You have at least 10-12 days of protection after a fungicide spray. As petal fall approaches and we move into leaf out and nutlet formation, keep an eye out for shot-hole, jacket rot, anthracnose, and scab. Of these four diseases, scab requires the latest treatment

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