Q&A for Boron in Almond Orchards

Several articles have been posted on the importance of boron. These have highlighted the importance of boron for fruit set, reliance on hull sampling for tree boron status, and foliar applications.In regards to these posts, I have received several good questions that I thought I would share.Q. When should I apply boron to my field?A. The hull serves as a sink for boron. Applications made after the fruit is removed will be more effective in increasing boron levels within the tree. The nutrient will require transpiration in order to move throughout the tree, and therefore ground applications made in the dormant season will have minimal effect on the coming year's crop, but will impact the next, next year crop. In other words, an application made in January 2015 will provide the most benefit to the 2016 crop. I should add that an application in the 2015 dormant should increase boron applications in 2015 hull samples - it just will not be in the fruit bud of the tree until 2016.Q. What about foliar sprays, and do I need them?A.  A foliar spray made between post-harvest and pink bud has been shown to increase yields. This is an effective way to increase boron levels within the tree. Unless boron hull levels are over 150 PPM, foliar sprays are recommended. Low rates should be applied.Q. What about if my water or soil contains boron?A. Boron can be a toxic salt at too high of a level. If soil or water levels are too high, boron should not be applied. Again, hull analysis for boron should indicate if the tree is requiring boron. Boron levels within soil will eventually reduce if applications by irrigation water or fertilizer are eliminated.Q. Does boron leach?A. Yes. Boron will leach at different rates depending upon soil textures. Soils with lower exchange capacities should make smaller, more frequent soil applications (~10-15 lbs of solubor/acre), while soils with higher exchange capacities may suffice with larger applications (~15-20 lbs solubor) every other year.Q. How much boron is used by the tree?A. This is dependent upon hull concentration and crop load. Keep in mind that boron is in greatest concentration in the hull, and hull removal amounts are typically double that of kernel yields (e.g. a 2000 lb/acre crop removes 4000 lbs/acre of hulls). In regards to removal, the following table indicates rates of removal for 1000 kernel lbs for various hull boron levels:

Hull Boron Content (PPM)	Lbs of Boron Removed per 1000/kernel lbs
75	0.15
100	0.2
125	0.25
150	0.3
200	0.4
300*	0.6
500*	1

*These levels are considered toxic within almond.