The importance of an even application and the correct amount that should be applied to your forest crop.
I have been researching boron, and the results that various borates have on conifers, both in tree form and wood quality, for over 30 years.
Initially, in 1976, our first commercial boron application was a bit of a disaster .
The reason for this was that the boron we used was of a fast release only ( sodium borate), and was unevenly applied. Since then, we Discovered the range between Boron deficiency, Optimum levels and Boron Toxicity. We have also found the importance of having the product applied evenly.
This is achieved by having a variable distribution sized chip, capable of being evenly spread from a calibrated spinner bucket slung underneath a helicopter. The first product we used was imported from Turkey, (1980-89) because this had a relatively high specific gravity, (weight) and a chip distribution of 2-4 mm, it was ideal to give us an even spread. That is the larger chips being flung further than the smaller sizes. It is this understanding of granular distribution that gives the even spread.
Now that we are using Hydroboracite chip, which has a slightly different specific gravity to the Turkish ulexite chip, we have found that if we increase our granular distribution to 4 – 8 mm we get a more even application with a wider swath width, therefore making application cheaper.
Without this larger chip size, uneven application is quite common, especially in even slight wind conditions, and this problem is further compounded when the applicator has not got a properly calibrated bucket.
What usually occurs, if applied unevenly, is a toxicity effect which occurs immediately under the flight path of the aircraft, and because the chips do not get to the end of the 40 metre swath, deficiency occurs at this end. All this results in a striping effect which cannot be corrected.
Equally, as important, is the correct application rate for your site. In most cases this usually ranges between 8 to 10 Kg per Ha of elemental Boron. Because you want one application to supply enough Boron for the complete crop rotation, 8kg/Ha of elemental is my advised rate. If, for example you are applying a product with an active ingredient of 10%, then the minimum rate you should consider is 80kg/Ha of that product.
If on the other hand your site is low in organic matter, or is older than two years, or has a high weed content, increased application rates are advisable (and in most cases imperative). Make sure you get the correct advice on this.
Of all the factors that influence boron uptake, the amount and type of weeds growing within your stand, is the most critical, especially if your weeds are brushweed such as, legumes, gorse and broom. Not only do these weeds take up the boron faster than the trees, they will also dry out the site, creating moisture as well as boron deficiencies.
In many situations if a nutrient(s) is applied to a stand of trees without an accompanying herbicide regime. The applied nutrient can actually be detrimental to your trees simply because such weeds as gorse and broom can access the applied nutrient faster than the trees can, and therefore out grow and smother your crop.