Postharvest Fertilization – Q&A

Q. How much nitrogen should be applied in the postharvest period?

A. This depends.  This should be based upon the current tissue N levels detected from mid-July sampling. If within the prescribed ranges of leaf N (2.2-2.5%), 20% of the budget should be planned for application. If richer (>2.5%), slightly less can be added. If really high N leaf levels are observed (>3.0% in mid-July), postharvest fertigation may not be needed. 

Q. When should the N be applied? 

A. Nitrogen can be applied anytime after hullsplit up until a few weeks postharvest. In earlier harvested varieties and ‘Nonpareil,’ nitrogen can be applied shortly after harvest with the first post-harvest irrigation. With later varieties, such as ‘Monterey’ or ‘Fritz,’ the application can be made post-hullsplit prior to harvest. This timing matches bud development that tends to occur about 2 weeks after ‘Nonpareil’ harvest for most varieties (i.e. ‘Nonpareil,’ ‘Carmel,’ ‘Mission.’).  In other words, it appears that most almond trees, regardless of variety, will begin bud development around the same time. It is important to note that the bud development timing has not been studied for all varieties, and this is an assumption carried over from previous research.

Q. What about other nutrients, like potassium? Phosphorous?

A. Potassium applications can also begin in the post-harvest period. Uptake by the tree will be minimal since the almond hull is the primary sink for potassium (~3% by dry weight), so I wouldn’t go crazy. Applications made at this time are essentially rebuilding the soil reserves of K. This may be a reasonable strategy IF you are on a soil that is able to hold the potassium. In sandy soils, which are common in Merced, potassium can be leached out of the rootzone, which may create a situation of deficiency in the following year.

We dont know much about phosphorous. Almonds appear to use small amounts of P (~ 7 lbs/1000 kernel pounds) in relationship to the other major nutrients. Since it is exported from the system,  deficiency may occur, but it is rare. We think that enough P is being provided from the degradation of the parent material. Applications should be considered if leaf tissue values are approaching the minimum requirement of 0.1%.

Q. Boron?

A. Yes, postharvest is a great time for boron applications. Grab a bag of hulls and submit for analysis. based upon the analysis of the hulls, boron rates and application timings can be established. The current boron guidelines for hulls are as follows:

  • 80 ppm or lower = deficient
  • 80-150 ppm = adequate
  • Over 200 ppm = may be toxic

Please see this article for more information on rates for soil and foliar applications.

Q. Anything else?

A. It is also important to provide adequate water during this time. Extreme water stress in the post-harvest has been shown to reduce yields. Also, late fall applications of N will have reduced effectiveness due to lower rates of ET and therefore N uptake. the earlier, the better.

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8 thoughts on “Postharvest Fertilization – Q&A

    1. Yes, you can — it depends on the combination of the foliar nutrients. Some blends are tank compatible, some arent’. If unsure, run a bottle test before mixing in the sprayer. A bottle test is mixing the concentration expected to spray with the two products that you plan to mix in a bottle to see if a precipitate forms.

  1. This article advised applying nitrogen after harvesting Nonpareil and after hull split of later varieties (Fritz and Monterrey). What happens if you applied nitrogen after harvesting Nonpareils but before hull split of Monterrey and Fritz? Do the late varieties have a tendency to stick to the tree making their harvest even more late? Do the late varieties cling to the tree making them difficult to harvest?
    Thank You
    Andre Tolmachoff

    1. Andre,
      That is a good question. Even though we have little data in nitrogen timing studies, we are concerned that applying N too early before the nuts split may lead to increased vigor. This could lead to an increase in the time to maturation, meaning that hullsplit and harvest could be delayed. I think this is in alignment with your thoughts.

      Have you seen ‘Monterrey’ and ‘Fritz’ splitting after ‘Nonpareil’ harvest?


  2. No, I have not seen the late varieties split yet. Perhaps early September this year. We had an assumption that applying N too early may delay harvest of the late varieties. Thank you

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