Our Insights | Plant Nutrition
July 29, 2019

Post-Harvest Nutrition for Tree Nuts

With almond harvest getting underway, and pistachios and walnuts soon to follow, it’s time to consider post-harvest nutrition programs for tree nuts. With the removal of this season’s crop, it’s a great time to start replacing those lost nutrients and building for next season. 

 

All three tree nuts lose large amounts of potassium when the crop is removed. Conventional practice is to band high rates of sulfate of potash in the late fall to build soil levels for the next season. It may also be worth considering fertigating a highly soluble potassium source like BRANDT Reaction® K LS in the first irrigation after harvest. Rather than feeding the soil reserves with a late fall application, an earlier application will take advantage of the late summer root flush most tree nuts develop and start replacing what the tree lost. BRANDT Reaction K LS is a low salt index, low pH source of Potassium that is highly available to the plant and is ideally suited for fertigation. This will be especially beneficial if your mid-July tissue sample results were around or below 1.0% in walnuts, 1.25% in almonds, and 1.5% in pistachios (See Table 1).

 

Another consideration for post-harvest is making a foliar micronutrient application. Manni-Plex® Zn at 1-2 qt/ac and BRANDT® Smart B at 1 pt/ac are a good combination for this application. Both Zinc and Boron are needed in next year’s bloom in order to get adequate pollination and nut set. Foliar applications allow these micronutrients to directly penetrate next year’s fruiting buds. The Manni-Plex and BRANDT Smart System®  delivery systems improve foliar uptake and facilitate phloem mobility and translocation.  There were many almond orchards that did not get a pre-bloom micronutrient application this spring because of all the wet weather. Applying these materials post-harvest may be a good solution to avoid potential weather issues next year. Foliar nutrient sprays also benefit from including a good surfactant like BRANDT® Super Wetter.  This is especially true late in the season when the leaf cuticles are thicker.

 

 

Table 1

Crop Pounds K2O Removed per 1,000 lb Nuts (Includes hulls) Suggested Potassium Concentration in Mid-July Leaf Analysis
Almond 85-95 lb/1,000 lb nut meat >1.4% 
Pistachio 29 lb/1,000 lb marketable yield 1.8-2.0%
Walnut 27.5-32.5 lb/1,000 lb in shell >1.2%

Source: California Fertilization Guidelines: 
https://apps1.cdfa.ca.gov/FertilizerResearch/docs/Guidelines.html