Hull Analysis for Boron – Why?

Harvest is here. This is a good time to pull a a bag of almond hulls for a boron analysis. In making this recommendation, there are questions that are consistently asked.

I already know my leaf tissue levels, so why do I need to perform a hull analysis for boron?
Leaf sampling is not effective in determining the levels of boron as there are no obvious foliar symptoms of moderate boron deficiency. Furthermore, leaf levels may appear adequate while the actual levels within the tree are too low or high. Since the hull of the almond is a “sink” for boron, the analysis of mature almond hulls is a better indicator of boron status.

When should I collect samples for a hull analysis?
Boron will continue to accumulate in the hull until harvest. The best time to collect a hull sample is anytime after shaking the nuts. Varieties within the orchard may have differing boron levels due to different yields; it may be useful to pull a sample from the other varieties.

How do I interpret the results?
Trees with hull boron levels of less than 120 ppm may benefit from a postharvest boron spray (1-2 lb of a 21% B product in 100 gallons of water per acre). This will help with pollen germ tube growth in the flowers next spring but will not improve overall boron status of the tree. Boron applied earlier in the season as foliar spray is not a substitute for this timing because it is sequestered into the hull and is unavailable for the developing fruit bud.

Hull boron of less than 80 ppm indicates the need for a ground application.  Fertilize with 2-4 pounds of actual boron per acre.  This is equivalent to 10-20 pounds of a 21% soluble boron product (i.e. Solubor). Boron can be applied through the irrigation system, broadcast or sprayed on the ground, or included in a herbicide spray.  Herbicide sprays containing glyphosate may need to be buffered to prevent reduction of
herbicidal activity.

If hull levels are over 200 PPM indicate excessive boron. In these cases, it is important to perform soil and water analysis to determine strategies for boron management.

More information on boron application and timing can be found here.

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8 thoughts on “Hull Analysis for Boron – Why?

  1. I assuming that you are asking about the amount of water needed for a foliar spray application. Is this correct? If so, data suggests that the rate (amount of boron per 100 gallons), not amount of boron per acre, is important. In other words, you still put 5-10 lb. of a 20% B product in your 500 gallon spray rig whether you plan to spray 50 gallons, 100 gallons or 200 gallons of solution per acre. I would apply somewhere between 50-100 gallon per acre.

  2. For soil applications, it is the opposite of foliar applications…Its about delivering the prescribed amount of boron per acre. Regardless of volume applied per acre, apply 10-20 pounds/acre of a 21% boron product. A water carrier of 10-40 gallons should suffice using a broadcast weed sprayer.

  3. Have you ever heard of analyzing actual almond blossoms for boron content? If so, what value do you find in this data that can not be found in a hull analysis?

    1. Chad – I have not heard of analyzing flowers for boron. I will ask around and see what I can find. My best guess is that it becomes a bit of a moot point – if the flowers are deficient, the results won’t be received till after bloom. Even if they are received, data suggests that a boron application made at full bloom may actually decrease yield, making a recovery treatment unlikely. I would also suspect that the level of boron within flowers would be quite low, making it difficult to detect consistently.

      I will see what I can dig up regarding this question.

    2. Chad,
      I believe that a private company has advocated testing blossoms (at pink bud?) for calcium and boron to determine whether bloom sprays will help with fruit set. I have no idea what the critical level of boron should be at bloom or if there would be substantial variation among varieties. As David suggested, turnaround time would be very tight and full bloom applications of boron have shown a decrease in set.

  4. Pingback: Importance of Hull Sampling for Boron - The Almond Doctor

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