Farmers have been using foliar fertilisers since the 1950's. They knew it worked but were told by 'experts' it shouldn't, but kept using them anyway.
There are some, who would say that foliar fertilisers are a waste of time and money because they do not have elements in sufficient quantity to do anything.
There are others who say that plants do not take up nutrients through their leaves, so applying a foliar fertiliser is wasting money.
There are still others who say that foliars is all you need, and the way to go.
Some advocate using foliars in conjunction with soil applied fertilisers.
No doubt there are many others, but lets look at these in a little more detail.
Some believe this to be the case, but shows a lack of basic understanding, because as referred to already, this assumes, all that is needed are the 3 major NPK elements.
It is true that these 3 elements are needed in the largest quantity, but are only 3 of 16-17 needed by plants, and counting those elements needed by animals and found in plants are only 3 of at least 20.
If your farm has a serious copper or cobalt problem, all the NPK in the World will not fix it.
Foliar fertilisation is by far the most effective way to apply micro nutrients or trace elements, and supplement the major elements. The readily-available nutrients are more easily utilised, because they do not have to be dissolved by moisture and go into the soil solution.
This does not mean that the application of foliar fertiliser replaces the soil applied fertiliser, but increases their uptake.
The important thing to remember is that a small amount of fertiliser used, actually increases the uptake in terms of total uptake by several fold over the small amount of fertiliser applied.
In fact, where isotopes showed that it was 8-10 times more effective to foliar feed a plant as far as the amount of nutrients required and the speed with which those nutrients were utilized. Other authorities showed the effectiveness to be between 12 and 100 times more effective.
This research was applied to not only the trace elements Zinc, Iron and Magnesium, but to phosphorous ( P) as well, which showed an effectiveness of 20:1
The trace elements used were in sulphate form. Chelation has shown to increase absorption by 3 - 10 times, over the sulphate form depending on the element used.
The question is. 'How do herbicides work'?
If you consider that as little as 2 litres/hectare of glyphosate will kill all vegetation, it would appear likely that it is taken up by the leaves, particularly as it is totally inactivated by soil contact.
How could it be root absorbed?
If 2 litres/hectare is sufficient to kill all vegetation, it is conceivable that several litres/hectare of a soluble nutrient would also have an effect?
In the early 50's Michigan State University ran a series of tests using radio-active tagged nutrients and discovered that leaves of plants as well as bark take up nutrients.
Plants also contain growth hormones, produced by the plant itself.
Growth hormones participate in the control of growth. They may be either growth inhibitors or promoters depending on the site of action and concentration of the substance.
There are 5 major types of plant hormones: auxins, cytokinins, gibberellins, abscisic acid and ethylene.
Auxins are growth hormones produced in all higher plants.
Commercially synthetic auxins are used to initiate adventitious roots from plant cuttings in nurseries.
Weed control by another synthetic auxin, 2, 4-dichlorophenoxyacetic acid (2,4-D), is widespread as a selective herbicide against broadleaf weeds.
Used at some 2 litres / hectare for thistles, this is just over 1 litre of active ingredient / hectare (520 grams active / litre) which equates to 1/10th of 1 ml / square metre. One teaspoon is sufficient for 50 square meters.
How much herbicide does each thistle and other broadleaf weeds in a square metre receive?
Where 24D works by altering the hormonal balance in the plant, the absorption of nutrients by the plant through the use of Foliar fertiliser on the other hand increases photosynthesis