Up to 20% of the total seasonal demand for nitrogen in almonds can be applied post-harvest. Post-harvest nitrogen will help maintain leaf area and extend the time for photosynthesis to keep producing carbohydrates in the trees. Post-harvest N will also ensure that reserves are replenished and early shoot growth and leaf out will be strong in the spring. It is important to take in-season tissue samples into consideration when determining how much nitrogen to apply. Any soil-applied nitrogen in the nitrate form that is not taken up by the roots will be subject to leaching from rainfall and irrigations. Foliar-applied nitrogen is also a good choice for post-harvest applications. It is common to use a fast-acting nitrogen source in this situation, such as urea-based products.
The amount of phosphorous used by trees is much less compared to the demand for nitrogen and potassium. However, this does not mean it is less important for optimal growth and yields. A post-harvest application of phosphorous will promote healthy fall and spring root flushes, as well as ensure the trees have a good energy source when dormancy breaks in the spring. Choosing a phosphorous fertilizer that is protected from tie up from cations in the soil is important and will ensure that it is free and available for the plant to uptake as needed.
Potassium demand in almonds is even higher than that of nitrogen. A post-harvest application of potassium is essential in order to restore reserves, even more so if your yields were above average this season. If potassium reserves are deficient when dormancy breaks in the spring, new fruiting spurs will develop at a slower pace or even die prematurely as compared to a tree that has optimal potassium reserves. Root uptake is minimal at this point, so a soil application of potassium will serve to replenish K reserves in the soil. A post-harvest foliar application of potassium is a way to ensure you get the potassium into the trees and vines to replenish those reserves. Choosing a K product that is free of chlorides and hydroxides, as well as effective at penetrating the leaf cuticle and easily translocated once in the leaf will provide the greatest return on your fertilizer investment.
Zinc is an important micronutrient that plays a major role in synthesizing auxins. These auxins ensure a uniform bud break in the spring. Almonds are commonly zinc deficient. This is due to a number of reasons, including certain rootstocks that are not adequate at taking up zinc from the soil. Zinc deficiencies are also common in areas with alkaline soils. Zinc is fairly immobile in the soil so post-harvest foliar applications are most effective at correcting deficiencies and restoring reserves.
Collecting hull samples to send off for boron analysis should be a staple in your post-harvest game plan. Hull samples are the most effective indicator of boron levels in almonds. Boron is critical for development of flowers, specifically pollen development and viability. If the hull analysis shows less than 80 parts per million boron, the trees are deficient and are most likely losing yield potential. Post-harvest foliar applications of boron are an effective way to correct deficiencies and restore boron levels in the tree.
With a good post-harvest fertility program, your crop will be off to a great start come spring and you’ll be well on your way to improving yields and quality year after year.