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Features, Classification, and Environmental Aspects of Mineral Fertilizers
First, let’s define what we mean by Mineral Fertilizers in this article: these are chemical industry products, various compounds (salts), which contain the components needed for the growth of agricultural plants and proper nutrition. Fertilizers are applied to the soil or delivered to the plant by other means (for example, drip irrigation) in order to increase yield.
They can also be called artificial or chemical fertilizers.
Classification of Mineral Fertilizers
There are three main characteristics by which classification can be made.
1. By physical state — liquid and solid. The distinction is somewhat conditional, since solid fertilizers can be diluted with water before application. Liquid fertilizers, in turn, can be divided into liquids proper, aqueous solutions, and suspensions.
Also by the properties of the fertilizers themselves:
- water solubility;
- flowability;
- caking during storage and transportation, for which an anti-caking additive is added to many types;
- hygroscopicity — the ability to absorb moisture from the surrounding air. For this, sealed packaging can be used, for example, bags with an additional polyethylene liner, since when absorbing moisture the fertilizer can begin to decompose into its constituent elements even during storage;
- the rate of leaching after application to the soil and being blown away by wind.
The properties listed above are more characteristic of coarse-crystalline fertilizers (for example, Ammonium sulfate) and granulated ones (for example, Carbamide).
2. The second classification method — by agricultural purpose:
- direct purpose — the components applied are themselves nutrients for plants. Direct fertilizers can in turn be divided into single-component and multi-component (two or more) — containing one or more types of nutrients (this partially overlaps with classification method 3);
- indirect purpose — these substances improve the soil, including its biological composition, change its acidity or alkalinity, etc. A clear example would be liming fertilizers, which reduce soil acidity.
3. The next classification method is by the number of main nutrients. There are three main elements — nitrogen, phosphorus, and potassium. Fertilizers are divided according to them.
- single or simple — contain only one of the main elements;
- complex — contain two or three main elements. Accordingly, they are called double or complete (triple);
- micro-fertilizers — contain only substances that stimulate growth and/or ripening. These substances themselves are called trace elements. Such substances include Zinc, Copper, and others. Such elements are typically applied in small quantities — micro-doses. Hence the name — micro-fertilizer.
Complex fertilizers, in turn, are divided into:
- compound — which during production already contain several main nutrients within a single compound, for example, Di-ammonium phosphate;
- mixed — which are mixed by a simple mechanical method, for example, bulk blends. In these, the main substances are contained in different chemical compounds, but mixed and pressed together, for example, into granules;
- compound-mixed — a combination of the first two types of fertilizers.
By the amount of additional substances, for example, various additives for better storage. Fertilizers with few additives and a lot of the main substance are called concentrated (for example, Ammonia water).
Compound and combined fertilizers usually contain a small amount of additional substances. This reduces their cost due to the absence of unnecessary production and delivery expenses.
Complex Mineral Fertilizers
The main types are represented as follows:
- Nitrogen-phosphorus;
- Phosphorus-potassium;
- Triple compound.
Nitrogen Fertilizers
The main active substance is nitrogen. Externally, they look like granules or small white crystals. They are highly soluble in water.
They are produced mainly from Ammonia and Nitric acid. Nitrogen, when applied to a plant, significantly accelerates growth and overall build-up of “green mass.”
Carbamide (urea) is one of the most widely used fertilizers. It contains 46% nitrogen. It is excellently soluble in water and in soil. It is very well absorbed. Among the relative drawbacks are high hygroscopicity and, as a result, increased caking. To eliminate this drawback, it is produced in granule form and often with an anti-caking additive.
A second feature is a tendency to acidify the soil, so it is recommended to neutralize it with lime at a ratio of 1 to 0.8.
Ammonium nitrate is the second most widely used nitrogen fertilizer. But this type is more complex to store — it is even more hygroscopic, and also explosive.
The advantages of ammonium nitrate include nitrogen content in two different phases — the ammonium phase is absorbed through the soil, while the nitrate phase is more mobile.
Ammonia water (aqueous ammonia) accounts for about 10% of all nitrogen fertilizers produced. Drawbacks include increased ammonia loss through evaporation during transportation and storage, and especially during application. For this reason, it is recommended to apply it 10-20cm deep into the soil, depending on soil type.
Ammonium sulfate is another nitrogen fertilizer, which in the chemical industry is a by-product. This type is considered one of the best for irrigated soils.
Ammoniated solutions — nitrogen fertilizers dissolved in ammonia. Quite effective, but difficult to transport and with increased losses during soil application.
Nitrogen-containing by-products (waste) of certain industrial cycles — sodium and calcium nitrate, etc.
Phosphorus Fertilizers
Simple forms are obtained from the reaction of sulfuric acid with natural phosphates.
Produced types:
- single superphosphate — obtained from natural phosphates. In granule form. To reduce acidity, it is treated with Ammonia; such simple phosphate is called ammoniated;
- double superphosphate — produced the same way as the simple form, but treated with Phosphoric acid. In granule form.
It is not recommended to apply these to acidic soils, because the main substance transitions into forms practically unavailable to plants. The same happens in calcareous soils.
Phosphate rock flour is also widely used — this is a simple natural phosphate, mechanically ground. But this fertilizer dissolves very poorly in water and is difficult for plants to access. However, in soil, microorganisms and acidity gradually convert it into accessible forms. This happens over the course of several years.
It is also recommended to add phosphate rock flour to compost.
Potassium Fertilizers
Contain potassium, produced from natural ore. During production, various impurities and Sodium chloride are separated out.
Potassium chloride is the most common type. More than 90 percent of all potassium fertilizers. It dissolves well in water.
By-products of other industries are also used:
In agriculture, Potassium chloride should be applied with sufficient care, since it contains chlorine compounds in addition to potassium.
Chlorine negatively affects:
- the quality of grapes;
- the amount of starch in potatoes;
- the properties of tobacco;
- the yield of buckwheat.
Environmental Aspects of Fertilizers
In nature, in its normal state, everything is in balance. But when fertilizers are applied, this balance shifts.
It should be taken into account that recently the environment has been affected by the extraction and production of fertilizers, as well as their subsequent use, which is only increasing every year.
Norms for applying substances to soil have been developed for agriculture, and components that combat pests and weeds are also taken into account. All of this still leads to an uncontrolled, gradual shift of the fragile balance.
As at least some kind of positive alternative, one can highlight the breeding of varieties resistant to diseases and/or certain pests. Also, in recent years, bacterial and viral methods of pest control have been actively developed, as well as various biological supplements, etc.
Attempts are also being made to propagate natural enemies of pests, and to apply hormones and anti-hormones. These affect the biochemical systems of certain insect species. It is very difficult, if possible at all, to predict what this will lead to in the future.
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