When is the optimum time for a boron application to be applied for maximum effectiveness to your forest crop?
If you haven't applied Boron to your trees by age three, you may start noticing typical Boron deficiency signs within your crop during the following Autumn period. It is during this stage of growth that the tree can show the typical deficiency signs.
This includes signs such as lack of apical growth, (the tree has no main leader and looks more like a bush as opposed to a tree) to sinuosity in the stem, branches, and then to the more severe signs such as complete dieback of the tip of the tree. When this happens the tree is saying: "Well I am stuffed, if you dont do something soon you must be keen to grow a plantation of low value chip as opposed to a high quality sawlog or clearwood regime"
Of course when you think of it, this is quite understandable. If the tree is not capable of growing a single main leader, it can not develop a suitable saw log. Depending upon what regime you are intending for your crop, between 65% to 80% of the value of a tree is in the butt log.
So if the butt has a kink, sweep or bend in it due to lack of Boron during its initial years of growth then the value of your crop has been at least halved .
Any forester worth his salt knows that the nutrient demand that a tree puts on its immediate environment starts at age two, and is maximised at age 7-8 at which time the demand slackens off slightly due to recycling. So it is important to realizes that it is at this time that a Boron supplement maybe required, this can be further accentuated by drought and weed invasion. Or if trees are growing in ex-pasture land, the most common reason for deficiency is due to "Boron Lockup". This occurs when excessive nutrients such as Nitrogen (Urea or animal waste) and Calcium (eg. Lime) have been applied to the site in the past. Excess Potash can also be responsible, this is common in areas where slash has been burnt to improve the planting access.
So when is the optimum time to be applying Boron?
In the 80's we use to apply Ulexite to our crop when they reached the age of around 3-4 years old. which is still the case for many, However as the genetic quality of our trees improved, so did its nutrient requirements in particular Boron, and our Hydroboracite has the ability to be applied at age 2.
In the early 90's a study was done on the possible advantages of applying Boron to P.radiata in the nursery. Prior to this the Boron levels within the foliage was dictated by the nurseryman. In most cases these guys do an excellent job in maintaining a suitable nutrient balance within their crop, so it was not surprising to see little difference in the appearance of the crop when various borate rates were applied, compared with the their normal crop.
However on lifting, the root mass of the P.radiata seedlings were significantly larger in the Boron treated seedlings.
A further advantage of the Boron treated seedlings was found once this stock had been planted out. All seedlings which had boron levels greater than 20ppm had significantly better survivals and growth in the initial year when compared with the untreated stock, especially when planted on harsh sites such as frost flats and/or drought prone areas.
At this stage we can only speculate at the reason for this, but it is thought it may have something to do with the improved root system of the plant, as well as cell structure, making it less prone to desiccate in frosts and a better scavenger of nutrients and moisture.