Agroanaliz Georgia


If we fertilize we must do it right

Everybody use fertilizers today. Organic, mineral, simle, complicated, special, it all depends the production technology, the thickness of the purse and the agronomist’s competence. Demand for supply is growing, agricultural business is becoming more cost-effective and manufacturers are willing to invest in technology, including the mineral nutrition.

The maximum effect is achieved not at maximum, but at optimal dose of fertilizer

For all the merits of organic fertilizers they simply may not be enough to ensure continued growth in production, and so, professional manufacturers mainly work with mineral fertilizers. So, we’ll talk about them.

And first we heed to define the notion of ” providing the needs of plants in mineral nutrition”. What is it?

There are many definitions of the notion. But the essence of all of them is reduced to one: in order to properly ensure the plant with nutrients. It’s necessary to find answers to four questions: 1- how many nutrition elements? 2- which types or fertilizers? 3- when to introduce? 4- how to introduce?

Let’s start with the first question. Nutrition elements can be devided into macro- , meso- and microelements (based on their content in plants). This doesn’t include such important components for the plant nutrition as carbon, hydrogen, oxygen, because a plant assimilates them from the atmosphere and soil on their own, and (with rare exception in greenhouse technolgies) we don’t talk about their introduction as additional elements of supply. But the rest must be supplied, as a rule, in a form of fertilizer.

So, in order to plan the introduction, we need to decide how much of each element do our plants need?

All these decisions are taken in different ways.

The first reason: “Everything and more!”. Such an approach was very popular in the time of cheap fertilizer, and it is also still there in the farms, which are permanently financially supported by the state or investors. This approach is as simple as it is erroneous. In order to properly provide the plants needs in nutrients, it is necessary to give them these elements as much as they need. Many years ago the scientists have formulated the 5 basic rules of agriculture. One of them is the optimum law: “The highest harvest is achieved not at the maximum value of any of the factors, but at the optimum one”.

Рисунок 2. Картограмма обеспеченности почвы

The cartogram availability of soil potassium exchange

In order to demonstrate it we conducted a simple experiment- we have grown cabbage seedlings in peat substrate at 5 backgrounds of mineral nutrition: 1- without fertilizer. 2- with the 50% introduction of the calculated dose of fertilizer for this technology. 3- 100%. 4- 150% and 5- with the 300% introduction of the calculated dose.

The optimal dose has been calculated according to the analysis of the substrate, taking into account the needs of the crop by the suttlement normative method. The picture shows clearly that at the beginning the increasing of fertilizer dose leads to faster growth and cultivation of the crop. After reaching the optimal level, the further increase in dose of the fertilizer doesn’t give a positive effect, and even higher doses cause an inhibition of plant growth and toxicosis.

Agronomists, who worked at the end of Soviet times have frequently an opportunity to observe this effect. In those years fertilisers “have been stored” directly on the field in bulk, in heaps and the next years the “storages” were visible on the field- as lifeless patches of bare ground, where nothing grew for a few years! Because the excess of nutritives is as bad as the lack of them.

So, the method “everything and more” will not work!

There is also the second version: “As it is written in the book”. In the books they write. Especially precise figures of recommended doses of fertilizer are indicated in books, which are written by people, who are far from the agrotechnical science. The specialists know good that there isn’t and there won’t be the uniform optimal dose of fertilization for all fields, all climatic zones and all technologies. At first, because the need in nutrition strongly depends on the size of the planned harvest. Just as in animal husbandry, and so as in catering, the more mouths we have to feed, the more products we need to stock up. At second, because the soil, fortunately, isn’t fruitless, it contains all the nutrition elements in a particular amount. And, for our disadvantage every field is provided with every element in different amount.

The cartogram figures clearly show how do the fields differ in the provision of the exchangeable potassium even in the same farm. Every agronomist should have such cartograms, at least, for each microelement. Of course, the need for additional application of these elements for different fields cannot be the same.

So, the introduction “as it is written in the book”- is also wrong. And for the same reason, while visiting The Field Days and watching a truly outstanding harvests, made by professionals, it’s no sense to write down in a notebook how much and what kind of fertilizer have they introducted. As a rule, such a high harvest is achieved by people, who didn’t copy the others experience blindfold, and who found their own solutions, which are optimal for their field.

The third version: “We’ll orient on external signs”. Followers of such an approach recklessly collect albums with the external signs of the plant starvation in various nutrition elements, analyzing carefully the differences between the interveinal and the mosaic yellowing. This activity is just as exciting as it is useless in practice. At first, because the external signs of deficiency in various nutritives may be similar and also look like the manifestations of fungal, bacterial and virus deseases. And, at second, because the external signs appears when the deficiency became critical.

Let’s take, for example, a very characteristic feature of the calcium starvation symptom on tomato – the apical rot. Really, it is possible to accurately determine, that the plants don’t have enough calcium. But, when our tomatoes have already covered with such spots, it is late to introduct calcium- the harvest is irretrievably lost.

A similar situation with deficiency of boron on sugar beet – wait for rotting of the kernel, what is characteristic for this problem, and boron fertilization will not be needed.

So, the method “we’ll orient on external signs” is unacceptable for professionals.

One of the variation on a theme ” Everything And More” is an approach “let’s take the content of nutrients in soil as zero and introduct the maximum fertilizer”. This approach is categorically unacceptable. Annually, examining hundreds and thousands of hectares of fields in Russia, Ukraine and Moldova, we repeatedly face the cases where the content of nutrients in soil is not only sufficient to achieve a planned crop, but even exessive. The notion “overphosphating” of the soil, unfortunately, began to meet as an explanations for crop losses as the habitual notion “salinization”. And both of these notions are often directly related to the immoderate application of mineral fertilizers.

In contrast to cylindrical drill a triangular shape shovel distorts sampling

So, if is no use of standard silutions or attempts to solve the problem, after it has already accured, don’t lead to success, one thing remains – to accurately calculate, what amount of each nutrition element does our crop need for new harvest formation.

How to calculate? Calculation methods of nutrients needs are developed by the world science since the mass application of mineral fertilizers began.
There are a lot of them for today, but the most adequate of them are always based on three primary constituents: the value of the planned harvest, the difference in the assimilable ability of various crops, the soil provision with the given nutrition element. And again, we should understand each norm.

It’s possible to calculate in detail the need un nutrition only for a particular planned harvest. The more harvest we want to obtain, the more nutrition’ll be required. But, unfortunately, no matter how simple is this idea, there are still a lot of consultants and, occasionally, even consulting companies, which obstinately don’t understand it. And which calcutation logic is the principle:” the phosphorus content in soil is 12, the optimal phosphorus content in soil is 18, it means that it’s necessary to introduct…”

It is agronomically senseless talk about the optimal level of the phosphorus content in soil, for example, for wheat, because for the harvest formation of 25 c/ha is required phosphorus amount and for 70 c/ha it is quite another.

It is also necessary to take into account such an important factor as determining the valibility of any sattlement, as the feature of the nutrients assimilation by the given crop. The assimilating ability of the root system of different plants varies. Therefore, the content of phosporus in the same field may be sufficient to obtain maximum yield of one crop and critically insufficient for another. It is possible to ascertain it not only from the literature, but simply observing plants in the field. Thus, for example, in spring furing cold snaps, the flow of phosphorus in tomatoes harshly low down. This crop, with a very low assimilating ability of roots, clearly demonstrates the purple underside of the leaf blade- a characteristic feature of phosphorus feficiency. That’s why each calculating method should be based on taking this speciality of the plant into account.

And, at last, the content of a nutrient in soil. The fact that it must be measured and taken into account in the calculation of mineral nutrition needs is certainly understandable. The devil is, as usual, in details and, it is necessary to talk apart about these details. At first, it’ absolutely not interesting for good agronomist how much phosphorus(or any other element) is there in the soil, it is important for him to know the content of available forms of elements to plants (mobile phosphorus, exchangeable potassium..,). It is no difference between available and unavailable forms for all devices, which measure the element content (by the photocolorimeter to the spectrometer). To select from a sample of soil not all the phosphorus, but only the available for plants part, they prepare an extract by special reagents. That’s why, we’d like to clarify agronomists, that the dreams of rapid tests with the miracle devices (put the probe and see- how much and what kinds of elements are there un the soil) will remain the pipe ones. And the more “expression” is there in the analysis the lower is its accuracy. And the accuracy here determines the success of the case.

The composition if the reagents for the extract preparation is varied depending on the type of soil. Each type of soil in each region has its own method of amalysis (by Chirikov, by Machighin, by Kirsanov etc.). And, therefore it is as absurdly to carry out analysis of our soil in Germany or Austria, as also to take their soil samples for analysis to the laboratory in Russia or Ukraine. It won’t be correct anyway. There ara no appropriate chemicals, no knowledge of appropriate techniques. Is everybody agree? No, not everybody. People, living by the principle “there is no prophet in his own country”. It’s so prestigious to have on your table the analysis on the form of the european laboratory. In this case we’d like to advise to do the analysis twice: the first – for “prestige”, and the second – to make an accurate calculation.

And there is also a category of people, who sincerely dislike Machighin, Chirikov and other authors of techniques accepted for our soils. They are some excessively venturous dealers of fertilizers. They are much closer to Olsen method, which is absolutely inadequate for our soils, but it shows much lower supply of soil with nutrients, than GOST methods (and it means a higher need in fertilizers). If the fellow Olsen were alive he’d personally rebel against such manipulation, that in fact discredits the good name of the great chemist.

And, therefore, read the analysis conclusion attentively, pay attention to lines, where the holding methods are listed and don’t trust the conclusions where such information is not mentioned.

Talking about problems of correctness in soil analysis, it is worth to note – the exact analysis begins with the correct sample selection. And for today there is no order in the matter. We won’t pause at the elementary sloppiness, when the director charged the agronomist, agronomist charged the foreman and the foreman consigned a worker, who went to the woodland belt and digged up two buckets of soil and made two tens of bags with so-called “sol samples”. Knowing the price issue, the most managers (directors) don’t admit such cases. Let’s examine examples of systematic violation of the samples selection rules.

The first violation is selection by shovels. The shovel has a form, close to the triangle and that’s why, while selecting it leads to uneven representation of lower and upper lands in the sample.
Therefore, for sample selection, it should be used a special drill, which allows to take samples to an adjusted depth evenly of all lands.

The second violationis the depth of the selection. For analysis it should be selected the soil from the area with the most developed root system. For classical technologies of cultivation the field and vegetable crops- it ‘s the topsoil (25-35 cm, depending on the depth of plowing). But, for example, while the No-Till technology application, the root system forms in more topsoil, and the selection is made from the depth of 15 cm.
For orchards and vineyards, conversely, the selection is applied from the depth of 100 and even 150 cm. This drill allows to trench a well and to take samples of soil by layers (0-20, 20-40, 40-60 and so on).

The third is the violation of standard land area for selection of composite samples. Everytime plunging a drill into the ground and taking it from there, we receive not a sol specimen, but a sample. The sample shouldn’t be analysed, because it may be not the same for all the area. That’s why, several samples are selected from each piece. They are mixed, averaged, generating accordingly the averaged sample. But even an averaged sample is generated not only from the field. The field is a relative concept: in Belgium even 20 hectares are considered to be a field, and in Astrakhan region it happened to work in the field of 1500 hectares.
The agronomists developed the guidelines of areas dimension and the number of samples for generating an averaged sample. For field crops on flat terrain one averaged sample is selected from 30 hectares, and for cross- country individually are selected samples in depressions and on the slopes, for irrigated crops the selection rate is one sample from 10 hectares, for vegetables with drip irrigation- from 2,5 to 3 hectares. These standards are directly connected with the error price for crops of different intensity degree. The shortage of 10% vegetable harvest with drip irrigation will lead to loss of money, exceeding thousandfold the cost of analysis of extra ten samples. And therefore, if we can undertand those, who want to get reinsured and select the samples more than it is recommended, it’s very difficult to understand those, who bring to laboratory only one sample from 200- hectare field and ask to calculate the mineral nutrition for 3 crops at once.

The forth violation is untimely sampling. In the analytical work practice we face such problem very often. And thereby, we’d like to distinguish the degree of roughness of such violations.

1 – Sampling a week before proposed fertilization. This is the least of violations. Because in this case a laboratory is still can correctly carry the analysis, make recommendations on the use of fertilizers, but the farm will have very little time to fulfill the recommendations (the fertilizers must be bought, delivered to the farm etc.). Therefore, it is better not to delay this issue and take samples immediately after the predecessor.

2 – sampling after plowing. It’s more unpleasant situation. The soil analysis in this case is easy to carry, but the calculation of mineral nutrition is more difficult to do. For the most classic technologies of agricultural crops cultivation the adding of major amounts of phosphorus and potassium may be carried foremost out plowing. And it’s very difficult to look for ways of their introduction at high needs of crops in these elements, when the plowing has been already done.

3 – sampling after application of mineral and organic fertilizers. It is really bad. In this case the undissolved particles of fertilizer fall into the selected soil, and which may distort the analysis results, and also the calculation of needs in fertilizers. In such cases it’s not worth to carry the analysis at all.

So, let’s arrange once again: the optimum time for sampling is immediately after the predecessor. Before or after disking, but it’s very desirable to do it before plowing, because a part of fertilizers is introducted exactly before plowing (except for cultivation with drip irrigation, where the major amounts of nutrients are introducted while watering).

So, the samples are taken correctly, the precise analysis us carried out by the appropriate method for this soil, the calculation of the need in each nutrient (in macroelements) is performed and thus is received a reply of “how much?”. And we already know full surely, that for our planned harvest in this field this year we have to introduct, for example, 150 kg/ha of phosphorus in the active substance.

There are still three questions: in the form of what fertilizers, when and how to introduct this phosphorus? Answers to these questions are strictly interdependent. Let’s consider it all taking as an example the same phosphorus.

Phosphorus belongs to elements the less mobile in soil. To demonstrate this fact the universities always show a simple experience, un which a solution of phosphoric acid in admixture with the indicator (methylene blue) is passed through a bed of soil in 10 cm only, and all the phosphorus instantly communicates with the soil absorbing complex, what can be clearly seen by the colorless filtrate. Unfortunately, many students, evidently, have truanted these classes, because there are a lot of stupid talks about random potassium introduction on the surface of the field. Phosphorus must be introducted at that depth, where it is the main mass of roots. On dry land this is the topsoil, the top 5-7 cm of which give phosphorus except at the beginning of the growing season, and in summer, at the drying of the upper layers, the plant will absorb phosphorus from the aquifer 7-30 cm.

Therefore, phosphorus on the dry land is substantially introducted at plowing with conduction on the depth of 25-30 cm. For this purpose are usually used superphosphate, ammophos, and in acidic soils is used even phosphate fertilizer.

That’s the answer for the questions “what fertilizers to choose, when and how to introduct them?” But there are some nuances.

In the first days after seed germination, immediately after the transition to the root nutrition, a small plant has difficulties in the nutrients assimilation from the soil. It is due with the weak root system development at this stage. Therefore, returning to the issue of our phosphorus, we’ll plan to introduct a part of it together with seeding, putting the fertilizer near the seed to provide the need in this element in the first days of a plant life. If a method of introduction is changed so change the terms of its introduction, accordingly will change also a form of fertilizer. Since a plant is in need of nutrients complex at this stage, so as a fertilizer it is best to choose, for example, the nitrophosca, which contains, besides phosphorus, also nitrogen and potassium.

Have we finally determined with terms, methods of introduction and forms of mineral fertilizers?

Of course, no. Because sensibly analyzed the climatic conditions of the region, the expected terms of sowing and knowing the strict dependence of phosphorus assimilation by roots on the temperature, we may confidently predict that in spring, when the soil isn’t yet warmed sufficiently, we’ll get the problem of phosphorus starvation on sensitive to phosphorus crops (corn, for example) even at good soil provision. Because at low temperatures roots of certain crops slowly absorb even available forms of soil phosphorus, especially when the root system is still insufficiently developped. In this case the foliar feeding,the top-dressing reftilization will be the most effective to help. With superphosphate? Ammophos? Nitrophosca? No, of course not, these fertilizers are not suitable for such application. Foliar feedings are carried with monopotassium phosphate, or with the special chelate complex water-soluble fertilizers.

A next change of term entails changing of introduction method and forms of applyed fertilizers.

And also, when choosing forms fertilizers it is necessary to consider the soil acidity, a chloride concentration in soil solution, sulphate- and carbonate- ions, salt index of various types of fertilizers and presence of attendant ballast elements and compounds in them.

Thus, for example for trucker of South Ukraine, the most important type of phosphorus fertilizer can be the orthophosphoric acid, which is applied in small doses with watering. It doesn’t deliver only phosphorus to plant, but also reduces pH of the soil solution (which is often too high in this region) and as well clears the drips of sediments of other fertilizers applied earlier in the same manner.

The nitrogen, potassium, calcium nutrition are also can be analogically examplified.

So, it’s not easy, but only such approaches allow to arrange the program of the mineral nutrition competently and in accordance with crops needs. These calculations are complex and scale and they also must be carried quickly and accurately. Of course, in the age of information technologies this should be done not on a calculator.

It’s surely not worth to put all these calculations on the agronomist’s shoulders. It is the task of the consulting structure, which is due not only to carry analyzes of the soil and to compose charts of provision, but also to the detailed plan for the use of fertilizers in crop rotation. And agronoms must clearly know and consider all the basic rules and principles of such calculations, on the one hand, to control the level of consultants competence, and on the othe hand, to accurately and correctly carry out these plans and recommendations.

Our laboratory use the computer program “Agroanalizon-line” for several years. This program is created by Ukrainian company “Agrosoft” and allows to conduct the calculations by the amendments method, balance and the estimated-normative. The algorithms of data processing is focused on all methods of the GOST soil analysis on territory of the former Soviet Union (by Machighin, by Kirsanov, by Karpinskiy etc.).

This program doesn’t only calculate a crop need in nutrients, but it also automatically recalculate this need to optimal forms of mineral fertilizers for each crop considering the characteristics of the soil, way of calculation, period of introduction and many other factors. The final document, generated by this program, is the plan of a mineral fertilizers application (use), in which all the fertilizers are calculated in physical weight, casted in stages of introduction indicating, the ways of introduction. This is the final result, instruction for agronomist, for manager. Only such document represent the real value to the farm, ordered the soil analysis, and only this level of work should be provided by consulting companies.

Vadim Dudka,
general director of AgroAnaliz company,
Kahovka city, Ukraine