Post-harvest fertility and irrigation management are critical in order to ensure tree health through the harvest period until dormancy. Utilize in-season soil and tissue analysis to determine your post-harvest fertilizer and amendment requirements. Remember Liebig’s Law of the Minimum – The nutrient in least supply affects the crop more than the nutrient in the greatest supply. With this in mind, let’s look at some of the elements. While the elements listed below are typically most critical for post-harvest, it is important to review the samples, understand the value of each nutrient, and prioritize applications based on the expected return value.
Nitrogen is needed for rebuilding plant vigor and maintaining late seasons growth. Research supports that 20% of your annual nitrogen budget be applied as soon as possible after harvest. Nitrate based products are immediately available in the soil and are utilized efficiently by the tree. As an example, if you yield 3000 lbs/ac and anticipate a 3000 lbs/ac crop next season, then you should apply roughly 60 pounds of nitrogen now. This is based on the nutrient removal by the crop, as well as the trees use and the efficiency of the entire root-tree-soil system.
Phosphorus is essential for the energy relations in the tree, as well as production and mobilization of nutrients for carbohydrate storage. Phosphorus applied on the leaves and through the soil will support balanced growth throughout the season.
Potassium is important for plant metabolic processes, carbohydrate production and storage. Leaf tissue analysis for almonds should be above 1.4% in a July sample. Post-harvest is the time to feed the soil potassium bank account.
Calcium supports soil structure and balanced nutrient availability in the root zone. Soluble calcium is critical for root growth and nutrient uptake. Calcium will moderate high soil sodium conditions where present. Calcium also balances high soil magnesium conditions.
Magnesium in the leaf is the basis of chlorophyll and photosynthesis. It’s needed to replenish leaves from harvest stresses. Generally, foliar applications are suggested.
Zinc is needed for production of the plant hormone auxin, which contributes to healthy cell division of all tissue: leaves, shoots, spurs, fruits and roots. Fall applications support good spring bloom, set, and size.
Boron is critical for pollen tube development during both bloom and flowering. Boron, along with calcium, is also critical in cell wall integrity during cell division and cell expansion in the spring. Post-harvest soil and foliar applications are required. Hull analysis should be taken annually. Levels need to be above 80 through 120 ppm. Leaf tissue analysis is not a good indicator of boron accumulation.
A comprehensive post-harvest fertility program will not only help your trees recover from harvest stress, but it will also set your trees up for a successful bloom.