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

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

May 5, 2016

Potassium Webinar Q&A

At the end of February, David Doll and I presented a webinar on potassium nutrition of almond orchards hosted by Western Farm Press with support from Compass Minerals.  During the webinar, listeners asked questions and we tried to answer them at the end of the webinar.  We could only get through a few.  In this post, we try to answer at least a few of those questions asked (another link to the webinar…click here!).

April 11, 2014

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

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

May 28, 2011

Late Fall, A Time for Potassium Soil Applications

Maintaining adequate potassium (K) nutrition is especially critical for almond trees and fall is an excellent time to address K deficiency through soil potassium applications.    Potassium is found in one of three forms in the soil:  fixed K, exchangeable K, and K in solution.  Fixed K is tightly held within soil particles or is part of potassium-bearing minerals and may only be very slowly released through weathering.  Exchangeable K is attached by electrostatic charges to soil particles and is in flux with potassium ions in the soil solution.  Soluble K consists of ions moving freely within the soil solution constituting a readily available form of K.  At any given time, a soil will contain a unique balance of fixed, exchangeable, and soluble potassium characteristic of that soil type. Potassium is thus in equilibrium and moves back and forth between these states as the supply of K+ and other cations varies. Potassium ions (K+) have a one plus charge and are readily adsorbed by negatively charged soil clay particles becoming unavailable to the tree.  Avoid any type of application that broadcasts potassium over a large soil area because more of the K becomes fixed. UC research showed that four years of broadcast applications only moved K 6 inches down into the soil while banded treatments penetrated 2 feet.  Banded treatments have worked well under non-tillage but if you cultivate, shank the band in to get the material closer to the root zone.  Applying a gypsum (calcium sulfate) band overtop of previous potassium bands can help free up more potassium.  The calcium ions (Ca ++) in gypsum have a plus two charge and will displace potassium ions on the clay particles thus freeing up more potassium to remain in the soil solution while moving it deeper into the root zone.  Gypsum

November 1, 2010

Potassium Applications in Almonds

Having a major role in many plant processes, potassium promotes root growth, increases kernel/fruit size, and provides key metabolic features that include the formation of starch, translocation of sugars, stomata regulation, and the formation of xylem vessels. In general, plants deficient in potassium tend to have slow growth, with small, pale leaves. Trees that are severely deficient may have necrotic tips and margins. In many cases, the leaf tip curls upwards in a common symptom that is named the “Vikings Prow” (Figure 1). 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 above this value do not increase yields. Recent field studies by Roger Duncan (UCCE Stanislaus) have demonstrated that leaf potassium levels in excess of the 1.4-1.6% range did not increase yield. Through the study, leaf levels between 1.4-1.6% gave the best yield results, with yield decreasing when potassium levels were below this level. Leaf potassium levels higher than this range did not increase yield, and may actually reduce yields if applied in excess. Potassium usage by the almond crop is high. Upon harvesting the hulls and kernals, potassium is removed from the orchard. Studies by Dr. Patrick Brown (UC Davis), have shown that 76 pounds of potassium (92 lbs of K2O) are removed from the orchard for every 1000 pounds of kernals 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. Even though a large amount of potassium is used by the almond crop, it doesn’t always mean that large applications of potassium are needed

December 7, 2009

Potassium thiosulfate toxicity on almond

During periods of high heat and the corresponding high evapo-transpiration, several unique orchard problems can occur. Most of these are due to fertigation methods which have been widely adopted to increase fertilizer application efficiency. The benefits of fertigation greatly outweigh most negative impacts, but caution must be used as a simple mis-calculation can cause orchard damage. A field call from a grower in late June demonstrated the potential problems that can occur with fertigation. Observations of yellowing leaves, leaf drop, and death of lower limbs raised concerns by the grower and pest control advisor (PCA), prompting an orchard visit. Initial Observations: Upon arriving to the 11th leaf Sonorra/Nonpareil/Carmel (all on Nemaguard) orchard I noticed excessive leaf drop across all varieties (Picture 1). Most of these leaves were coming from the interior of the canopy, suggesting the possibility of drought stress from improper irrigation scheduling. Lower leaves found on the interior of the canopy were burnt back, with a crispy texture. Leaves closest to the trunk that were completely yellow were beginning to abscise, while leaves on the tips of the branches remained green (Picture 2). This is in contrast to lower limb dieback, which causes soft yellow leaves found on the ends of interior branches. Picture 1: Leaf drop associated with the over-application of potassium thiosulfate. Picture 2: Leaf wilting and “dieback” associated with the over-application of potassium thiosulfate. Note how the interior branches are more affected than the branches on the outside edge of the canopy. Up-Close Observations: Close inspection of the leaves revealed a necrotic tip, or burnt region of the leaf. This leaf was surrounded by a yellow halo (Picture 3). Typically, a yellow halo around a necrotic area would suggest the possibility of almond leaf scorch, but due to the widespread occurrence of the problem, this

July 20, 2009

Flooding and Almond Tree Survival

When periods of high amounts of rain occur, orchards can become saturated and flooded. During these periods, tree loss may occur, but this is dependent on the duration of soil saturation, the timing of year, and rootstock. Soil saturation reduces the ability for oxygen to infiltrate into the rootzone. Roots require oxygen to respire, and long periods of saturation can lead to root loss by asphyxiation. Fine feeder roots are often the first affected, with larger secondary roots affected during periods of extended saturation or flooding. Tree survival is dependent on how many roots survive and can regrow before periods of high transpiration occur. The sensitivity of almond roots to saturation is dependent on the timing and duration of the flood event. During dormancy, trees are reasonably tolerant due to lower soil temperatures and low rates of respiration. Flood events that are shorter than 7 days will not have any affect on tree performance. Extending beyond this, however, some root loss will occur, and poor spring tree growth may occur. With extended periods – beyond 10 days – tree loss may occur. After the trees have leafed out, the period of tolerance is much shorter. Standing water within an orchard for 5 days will kill mature trees. This is due to the higher activity of the root system due to warmer soil temperatures, and overall tree activity. In these cases, efforts to drain as much water as possible should occur to reduce the impact of the flooding event. If water is moving through an almond orchard, the effect of soil saturation/flooding is reduced. Since moving water carries oxygen, some movement of oxygen into the soil can occur. This will extend the period before negative impacts are seen by several days. For example, an orchard near the Merced River was flooded

January 15, 2023