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

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Major Nutrient Fertilizers: Thoughts to Reduce Operational Costs without Impacting Productivity

Increasing input prices are being observed across the farming sector. Fertilizer prices have increased due to demand, government regulations, weather, trade issues, and energy prices. Prices are some of the highest in a decade, with nitrogen and phosphate fertilizer prices nearly double what they were in 2020. Within almonds, maintaining the proper fertilizer status within the tree is important to maintain yields. Research projects have determined how much of each major nutrient is needed for the tree to maximally produce. These studies first occurred in the early 1990’s and were re-done between 2008-2013. In summary, the projects concluded that for every 1000 lbs of almond kernels harvested, 68 lbs of nitrogen, 92 lbs of K2O, and ~12 lbs of P2O5 are removed from the orchard. These nutrients need to be re-applied to maintain yields. Leaf tissue, soil samples and other in-season assays and monitoring can be used to determine if optimal levels have been achieved. If optimal levels are present, input levels should only match crop demand, while if excess amounts are present, applications can be reduced. These adjustments will help reduce waste, run-off, and leaching.   More on this here and here. Nitrogen (N) usage and uptake occurs when there are leaves on the tree. As such, N applications should only occur in-season. When applying N, more than 68 lbs/1000 kernel pounds of production is applied – typically around 85 lbs/1000 kernel pounds of production. This inefficiency of about 20-30% considers the N lost to NOx conversion, run-off, and leaching. Fortunately, I have observed many orchards much more efficient than this. These orchards have been able to reduce N amounts applied based on the observation of high N within leaf samples.  They have found that maintaining N levels at 2.5% in mid-July allow for the maintenance of high yields (>3000

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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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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!).

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