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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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

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