emphasize applying nitrogen at the right rate, time, source and placement. In many orchards: • Post-harvest nitrogen should account for only a small portion of the annual nitrogen budget. • Orchards with July leaf nitrogen levels above sufficiency ranges often require little or no additional fall nitrogen. • Higher yielding orchards or orchards with lower- than-desired July tissue values may benefit from a modest post-harvest application. The goal should be replacing crop removal and supporting carbohydrate storage, not stimulating unnecessary vegetative growth. Modern nitrogen management programs focus on efficiency rather than total pounds applied. Potassium: Protecting Next Year’s Crop Potassium remains one of the most heavily utilized nutrients in almond production. Deficiencies can lead to: • Increased spur mortality • Reduced flower formation • Lower yields the following year • Poor tree vigor Recent UC research emphasizes maintaining adequate leaf potassium concentrations through July and using soil applications strategically to build long-term reserves. Potassium management should be viewed as maintaining both a checking account and a savings account. Tissue levels reflect the checking account, while soil reserves represent long-term savings. Banding potassium fertilizers within the active root zone remains a preferred strategy. Broadcast applications outside the wetted area are often inefficient, particularly in micro-irrigated orchards.
Fertilizer application in Stanislaus County. Photo credit: Austin Jackson, Blue Diamond Growers
Foliar Nutrient Applications Post-harvest foliar sprays containing nutrients such as boron and zinc products are valuable tools when applied before natural leaf senescence begins. The key is timing. Nutrients absorbed through healthy leaves can be relocated and stored before leaf drop. Applications made too late often provide little benefit because nutrient movement into storage tissues has already slowed. Hull analysis is the best tool for evaluating boron status since boron accumulates in the hull. Research and current recommendations continue to indicate: • Hull boron levels below 80 ppm are considered deficient. • Levels between 80 and 100 ppm often respond to supplementation. • Both soil and foliar applications can be effective when properly timed. Boron plays a direct role in bloom and fruit set, making it one of the most important micronutrients for almond production. Zinc sulfate should be used strategically. Historically, zinc sulfate was commonly used to accelerate leaf drop. Today, its most valuable use is often disease management. In healthy orchards without significant disease pressure, high rates of zinc sulfate can cause premature defoliation, reduce carbohydrate storage, and potentially affect next year’s bloom. There are plenty of foliar zinc products out there, so choose the one that fits your needs.
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