have much leaching potential, except in sandy soils, so you want to place the material in a concentrated strip about 3–4 feet from the tree. In micro irrigation situations, you can use a diverted broadcast method to spread the material through the irrigation wetting zone for more contact with feeder roots. Drip irrigation makes things a little difficult when trying to soil apply potassium material in the irrigation wetting zone, so fertigation during the season will be needed to supplement any deficiency. As you can see in Figure 1 , this drip irrigation orchard has a sulfate of potash (SOP) application nowhere near the wetting zone, which will lead to, at best, an inefficient uptake. This is an example of how not to apply SOP. If tissue samples are low, a liquid
injection of K is recommended to get a quick response within the plant. I always thought of potassium in the soil as a savings account and potassium levels in tissue as a checking account. You can remove and add money to a checking account easily. However, if you deplete your savings account, it can take years to replenish it. 5. The last sample that should be taken this time of year is a hull sample. Hull samples give a better representation of Boron levels, since boron accumulates in the hull. According to the CDFA Fertilization Guidelines, a sample with less than 80ppm is considered deficient. A soil application of Boron in the dormant season can be made to raise levels in deficient orchards. Samples that are between 80ppm–120ppm would benefit from a post- harvest foliar application of boron. Always discuss boron applications with your PCA/ CCA, since over application can lead to toxicity. As I mentioned above, post-harvest foliar nutrient sprays can be beneficial. Applying them soon after harvest is finished allows the plant to utilize that energy
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SEPTEMBER–OCTOBER 2022
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