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,

July 28, 2012

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?

May 19, 2012

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

May 12, 2012

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

April 5, 2012

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

March 31, 2012

Tips for Maximizing Nitrogen Use Efficiency for Almond

Previously this week, I wrote an article discussing nitrogen needs within the almond orchard. Application of nitrogen, as briefly discussed, varies in efficiency based upon techniques of application and irrigation/fertigation systems. Below are some tips to maximize efficiency and reduce losses for many common fertilizer application strategies. Maximize Efficiency:1. Apply N only when leaves are present and the tree roots are active. Avoid dormant season applications.2. Efficiency can be increased by applying N in small doses more frequently than large doses less frequently.3. Apply a uniform irrigation that is adequate to carry the N into but not past the root zone.4. Because young fruit trees have a fairly constant N uptake, apply multiple applications of N throughout the growing season.5. Mature trees need most of the N in the spring, around 70-75% of the nitrogen budget.6. Late summer/postharvest applications, 25-30% of the budget,will help with flower bud differentiation and formation for next year’s crop.7. Fertigation has generally been very efficient in N applications.8. Analyze leaves in July each year to fine tune N level to the orchard. Maintain the level in the adequate range. Minimize Losses:1. If fertilizer is surface applied, disc or irrigate N into the root zone shortly after application.2. Fertilize the tree, not the covercrop. Evaluate how best to bypass the covercrop. This may be by applying the fertilizer to the herbicide sprayed strip, mowing, or cultivating the covercrop.3. Don’t over irrigate. Nitrogen is soluble and moves with water. Excessive runoff of tail water or leaching will remove N.

April 29, 2010

Nitrogen Content in a Gallon of UAN-32

I have been emailed a few questions in regards to calculating the amount of nitrogen in a gallon of Urea Ammonium Nitrate (UN-32 or UAN-32). Since UN-32 is widely used to fertilize/fertigate almonds, it is necessary to know how much is being applied per application. 1 gallon of UN-32 weighs 11.02 pounds. 32% of the weight is nitrogen – hence the “32.” This roughly equals 3.4 pounds of nitrogen per gallon, or 55 ounces. So, following the guidelines suggested by Brent Holtz (UCCE San Joaquin),when fertigating 2nd leaf trees with UN-32, at 110 trees/acre, no more than 4 gallons should be used in a single application. I hope this helps.

March 26, 2010

Using Mid-summer Leaf Samples to Guide Fertilizer Decisions: Part 2- Potassium

Potassium fertilizers have seen major increases in price over the past year. This is due to multiple factors, including increased demand, trade embargos with Belarus, and shipping constraints from Russian suppliers. Due to this price increase, many operations are trying to determine the appropriate amount of potassium needed for a specific orchard. Potassium fertility management is different than nitrogen. Potassium moves into the root through diffusion and mass flow. This means that it must be within the active rootzone to be utilized by the tree. Additionally, potassium is a cation (K+) and will respond differently based on the type of soil. High cation exchange capacity (CEC) soils have many charge sites, which can prevent potassium from being available to the plant. This can be further complicated by the presence of micas and other clay minerals. In low CEC soils, the opposite is true, the reduced number of charge sites in the soil mean higher potassium uptake for the plant. However, keep in mind that this higher availability in the soil can also lead to more potassium leaching below the rootzone, increasing costs, or reducing tree productivity. Potassium programs vary. Almonds use a significant amount of potassium, with 92 lbs of K2O needed for every 1000 lbs of kernels produced (92 kg of K2O/metric ton). Potassium is often applied as one of several products, including potassium sulfate, potassium chloride, potassium thiosulfate, and potassium nitrate. These materials may be applied blended with other fertilizers. For example, potassium chloride is commonly used within blends as it is easy to dissolve and stays in solution.  Other sources are available, but are often more expensive and, regardless of the sales pitch, equal in performance. The only exception is compost, which can be cheaper per unit depending on the source and the analysis. Due to the soil

August 21, 2022

Using Mid-Summer Leaf Samples to Guide Fertility Programs, Part 1

By this time, mid-July leaf tissue sample results should be available. These tissue results are critical for any nutrient management plan. They should be taken annually to determine if the nutrient program is adequate for the orchard, and the values should be used to tune the orchard´s nutrient program. Research has shown that once an orchard reaches sufficiency of a specific nutrient, increasing it further will not improve yields. This has been demonstrated several times, both within nitrogen and potassium. Second-guessing and adding more fertilizer beyond sufficient levels to address existing yield problems will not improve the situation. This fact is relatively unpopular as it is easier to add more fertilizer than it is to fix the problems that limit orchard production, or assure oneself during a period of second guessing.  More on that can be found here (slide 17) and here (slide 20), and this article will focus on nitrogen The typical nitrogen program often budgets for 20% of the nitrogen to be applied during the post-harvest period. Mid-summer leaf samples should be used to determine if the post-harvest fertility plan should be changed. Within nitrogen, leaf tissue samples that exceed 2.5% can reduce or even eliminate the need for postharvest nitrogen applications. This is based on: Many orchards with leaf levels above 2.5% often have high residual nitrogen within the soil that will meet post-harvest needs, The reduced transpiration rates of the postharvest period reduce uptake of nitrogen, There is significant canopy loss from the harvest process, reducing nitrogen uptake, Nitrogen remobilization back into perennial tissues is happening earlier than previously thought – probably sometime between hull-split and harvest (or maybe even earlier!). Additionally, a long-term study in Arbuckle found that postharvest nitrogen applications did not improve yields in a reasonably high producing almond orchard. Nitrogen levels within

August 1, 2022

Re-evaluating operational costs for a difficult year

2022 will be a difficult year. Increased input costs, including water, fuel, and fertilizer, and decrease crop pricing will impact the operational expenses and crop revenues significantly. Many operations will struggle to maintain cash flows through the year. Operational costs should be closely evaluated to determine if savings are possible. Some expenses may be reduced on a short-term basis until pricing improves. Others may be eliminated from the current and future budgets due to more efficient management. A list of things to consider in helping reduce costs for the coming year include: Balance nitrogen rates. Typically, nitrogen budgets utilize a nitrogen use efficiency factor of 70%. By integrating more frequent, smaller applications of nitrogen, it is possible to assume a much higher utilization ratio – maybe closer to 85-90%. This could reduce nitrogen needs by 15-30 lbs/acre without impacting tree performance. Mid-summer leaf samples can provide feedback to this process (target range 2.2-2.5%). Test groundwater and accounting for nitrogen content. Groundwater in many parts of the San Joaquin Valley contains nitrate-nitrogen. If groundwater is used to irrigate orchard and it contains nitrate, make sure to account for the nitrogen and reduce the nitrogen budget. Balance potassium applications with any compost usage. The amounts of potassium and phosphorus within compost contribute to the nutrient budget of the orchard. Testing compost and accounting for moisture percentage should provide an estimate of the nutrients applied. This can reduce the need for fertilizers containing potassium and phosphorus (as well as many micronutrients). Review annual soil samples to determine if certain nutrients are not needed to be applied. It is common to see very high phosphorus amounts within CA soil samples and additional P may not be needed. Additionally, many loamy to clay containing soils contain potassium reserves. If the amount of potassium is high

April 25, 2022