Agroanaliz Georgia


Foliar feeding: fundamental delusions and mistakes

The level of agronomists training of specialized enterprises increases each year. But also the development of technological agricultural equipment doesn’t stand still. One of the main constituents of intensive technologies of cultivation, which provides a high yield, is the use of fertilizers. Volumes of the fertilizers use per hectare of arable land grow, and also appear new, more and more varied methods for their use.

Even during the financial crisis, when many farms were experiencing shortages of working capital, they found money for fertilizers, because all of them understood that they wouldn’t get a high yield without fertilizers.
Even experienced professionals make mistakes in views on both, on the system of the plant nutrition itself and so on issues of its practical implementation. And the most often they concerns a new method of the mineral fertilizers introduction- foliar feeding. We offer consistently understand the essence of these delusions.

The first delusion: foliar feeding does not need. Even in 1770 Bolotov A.T. presented a theory of mineral plants nutrition, and later U. Libikh cogently proved that the mineral nutrition is implemented mainly through the root system.
Since that time agronomists fertilize the soil systematically, and they began doing it since Aristotle. This is areliable way, which is proven for centuries of argonomic practices. Thet’s why there are many agronomists, who are convinced that animals feed by mouth and plants feed by roots. So, the fertilizers should be implemented only in the soil. The question arises: why fertilizers should be applied on leaves?

The first reason: the modern development of energy-saving technologies. The minimum tillage and even more, a zero cultivation technology of crops significally reduce the choice possibility of the fertilizers implementation method in comparison with classical agrotechnical technologies (watch table 1).

Thus, the less available methods of fertilizer application we have with a new technology introduction, the more important is their clever use.

The second reason: the intensity of assimilation of some plant nutrition elements from soil by the roots depends on many factors, in particular on temperature, humidity, aeration of the soil, pH and salt composition of the soil, root development of the crop.
So, there is often a situation when this or that element presents in soil in sufficient quantities, but the roots absorb it poorly because of low temperature. Therefore the plant suffers from the shortage of nutrition elements. In this case the optimal solution is foliar feeding. So, when making small quantities of the correct fertilizers applied on leaves, you can get a quick result, that is to significally improve the condition of the plants.

The third reason: the foliar feedings are advisable to apply when the activity of the root system expires. Good example: the classical foliar feeding method of crops with carbamide for higher gluten content in grains.

The fourth reason: you may carry the foliar feeding of plants when the inter-row cultivation is technologically impossible, for example when the plants have reached a height, which doesn,t allow to carry a cultivation with feeding.

The fifth reason: the economy of nutrition elements. While fertilisation on leaves (especially if the vegetative plant unit is already well developed) all its introduction losses are practically excluded, practically all the fertilizer enters the plant. So, if the foliar feedings are do important and favourable, then, may be it is worth to use only them?

The second delusion: Foliar feedings only!
It’s attractive, but, unfortunately, is impossible. First of all, because the plants needs in nutrition elements are more in dozens of times than it is possible to give them with fertilization on leaves. Let’s compare reference data (watch table 2) on the removal of the nutrition elements by plants from 1 hectare of the land with the number of elements, which plant can get by foliar nutrition. To simplify, we took only one element- phosphorus, and as a fertilizer we took the most concentrated with phosphorus monopotassium (52% P2O5).

So, how much foliar feeding do you need to carry to set up all needs of plants in soils with low level of phosphorus? About thirty! And it’s just for phosphorus!
And there are also nitrogen, calcium, sulfur and a numberof other nutrition elements.
There is hardly an agronomist, who would seriously consider such a ” plan of fertilizers use”. There is only one reasonable solution of this problem- to correclty combine the root and foliar nutrition in accordance with needs of the plant, soil supply and features of the chosen cultivation technology.

Therefore, there are no universal recipes. The mineral nutrition planning is very reasonable and difficult calculation, that should be done by specialists on the soil analysis basis individually for each farm and each field.

Thus, it’s important to calculate accurately the necessary amount of fertilizer, to choose correctly their forms, methods and terms of introduction. But that’s not all. It is important to keep in mind that for foliar nutrition are used highly concentrated solutions of chemical compounds, which have an active effect on plants. Any mistake can lead to a violation of physiological processes, occuring in plants, this may cause the leaf burn, and may cause a loss of yield. We just don’t have the right to such mistakes.

The first mistake: exceeding the allowable concentration of working solution.
Increasing the flow of the working fluid at 1 hectare while spraying leads to excessive fuel consumption, to the violation of the optimal timing of treatment, delaying the timing of the operations. To prevent it, we are forced to use solutions with extremely high concentration, but this may cause the leaf burn. How to avoid it? Read the label! The professional fertilizer producers write on the package not only the recommended doses for leaf feeding on 1 hectare, but also the concentration of the solution or working fluid flow for 1 hectare. If it’s not written, you may find it in the manuals or ask the professional consultant. Don’t work at random! It is also necessary to take into account the time of processing and the weather, because the leaf surface resistance of many crops to burns depends on the thickness of wax coating and, it is the maximum during the heat and the minimum after rains.

The second mistake: mixing with other drugs.

The temptation is great- to save money, not ti make extra passes by sprayer on the field to conduct a fertilizer in the form of tank mixes with plant protection products. The reasonable solution, but not always. Unfortunately, there are exceptions. One of examples is on picture 1. The tube A is the solution with fertilizer for foliar feeding (blue color gives the copper contained in the solution). The tube B- the solution with fungicide with active ingredient, the fosetyl aluminum. This solution is also transparent and homogeneous. And in the tube C- the mixture of these substances. It’s in this tube can be seen the formation of large conglomerates, in fact, the new compounds, absolutely unwanted neither for plants nor for sprayer. At the picture there is a result of adding drugs for foliar application to herbicides solutions. The burn. The selectivity of the action of herbicides dues to very delicate balancing of doses and concentrations not to burn the plants and withal to get rid of weeds. Sometimes, even a little adding of herbicides to solution disturbes this balance. And, then it’s not worth to bring claims to manufacturers of these chemicals. Just, while making decision on mixing drugs, it is necessary to scrutinize compatibility tables. As a rule, these tables can be obtained from the manufacturers or professional consulting companies.

The third mistake: importer distribution of the working fluid over the surface of the leaves. The fact that different nutrition elements behave differently inside the plant. Many experiments proved that all the essential nutrition elements can be absorbed in varying degrees through the leaf apparatus. The processes of absorption and distribution of nutrients inside the leaf, and also its transportation to other organs of the plant depend on mobility degree of nutrients.
Transportable elements (nitrogen, phosphorus, potassium, magnesium) move from top to bottom from the point of absorption. They can move to those organs where they’re most needed. These are mainly the young leaves, buds and growing roots. The elements with low mobility (copper, iron, magnese, boron and calcium) will be distributed only to the top from the point of getting up on a leaf (acropetally). That’s why, when spraying, the lower leaves of the plant are not covered with a solution, certain elements won’t fall for them.

The forth mistake: incorrect calculation of the dose by the band application. This question is becoming increasingly important with the growing popularity of the band spraying. The band application of fertilizer (spraying rows only with young plants without losses of fertilizer between rows) saves drugs for soil cultivation, especially in the early staged of plants growth, when they’re still small. But we must carefully calculate the dose and number of the working fluid. If the belt sprayer covers, for example, only a third of the working solution width of the middle row, the drug consumption and the solution also must be reduced three times. In this case, a mistake will lead to serious consequences. We often heard from farmers, whose plants have suffered from burns, how did it happen, because the fertilizers have been introduced how it was recommended- 3 kg per hectare. Correct, but it is necessary to consider, that in fact not a hectare will be cultivated, but only one-third of a hectare- for net area sown.

The fifth mistake: the wrong determination of application terms. Each plant has its appropriate dynamics of nutrients consumption. We can’t supply a plant with elements in store while foliar nutrition, how it’s usually done by the soil application, because all the applicated by leaves gets quickly into the plant. That’s why, it’s very important to understand and take into consideration, while application on leaves, when the plant mostly needs nitrogen, when phosphorus and when the critical periods of application with microelements have arrived.

The sixth mistake: “the cocktail of nutritives”, or what fertilizers should be used? The modern store of fertilizers for foliar feeding is huge. The foliar feeding preparations differs very much by compounds, form of active agent and price. And, besides, the most expensive isn’t always the most qualitative. All the diversity of these preparations is classified at table 3.

While choosing a mineral leave fertilizer, first of all you must pay attention to its composition. The simple fertilizers have quite poor chemical composition, low level of purity, bad solubility and wettability of the leaf surface. Besides that, the salt haze may appear on leaves after their use. Their application is justified only for extensive types of crops, when you can’t count on getting a great harvest, but whatever, the plants must be provided with the appropriate nutrients.

It is equally important to know in which form does the acting agent submitted. One of the most effective is the chelate form, which ensures the stability of the solution and its high level of absorption by plants. But it’s significally reflected in the price of such a solution. Sometimes the cheaper form of chelating agents (complex of organic acids) are used instead of chelates. Such compounds are less stable and worth assimilated, but in man cases they can help to correct the plant nutrition. The modern development are the polymeric chelates. They practically don’t loose the efficiency while application at very low and very high temperatures. Besides that, the high purity of compounds ensures their effectiveness. But, how to make the right decision? When, how much and what kind of fertilizers should be applied on leaves? Only the agronomical analysis of the plant tissues can give the answer on this question. Frequently, such an analysis is carried out by the wet ashing method- by the burning the organic matter with the sulfuric acid concentration (watch picture 2) followed by chemical analysis for each element.The results of analysis are compared with reference data by the levels of the plant provision and then, the recommendations on the selection of fertilizers for nutrition, based on this comparison can be done.

This work requires sophisticated equipment and the high level of specialists training, but there is no alternative. It is wrong, just to introduce all and a lot, it’s very expensive for the economy and dangerous to plants.

Vadim Dudka,
General Director of the “AgroAnaliz” company,
Ukraine, Kakhovka City