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What are fertilizers and what are the differences between a large number of different types of fertilizers? What is the difference between mineral and organic fertilizers, granular and liquid? Do waterborne fertilizers have an advantage over those that decompose more slowly in the soil? What are the time-controlled fertilizers? These are the questions that, in plain language, are answered in this article.
The fertilizers may be organic (for example compost), or the product of the chemical industry, inorganic or mineral fertilizers. But, those fertilizers are broken down into different types depending on their origin, feeding time, nutrient type, aggregate state, and more, and all the explanations can be found in the rest of the text.
Fertilizer is a mixture of a substance used in agriculture or gardening to improve plant growth. Usually applied to agricultural land.
Fertilizers contain mainly in different proportions, three major biogenic elements (nitrogen, phosphorus, potassium), and secondary biogenic elements (calcium, sulfur, magnesium), and sometimes trace elements, which are useful for fertilization: boron, chlorine, manganese. iron, zinc, copper, and molybdenum.
How do we distinguish fertilizer types?
The following types of fertilizer are distinguished by origin:
Mineral fertilizers (“synthetic”, “artificial”, chemical) are mostly mineral salts, although this group usually includes urea, which is an organic compound, but is transformed into the soil by the action of microorganisms in the soil. Other mineral fertilizers may contain carbon, but synthetic products are, unlike natural, easily water-soluble, often 100%. It should be emphasized that the urea molecule can be adopted by the plant both root and foliar.
- Organic fertilizers (natural) contain nutrients mainly in the form of organic compounds and are most often of natural origin (sometimes called natural organic), eg manure, peat, straw, etc.
- Organomineral fertilizers are a mixture of organic and mineral.
- Bacterial fertilizers contain cultures of bacteria that have the ability to transform inaccessible forms of nutrients into bioavailable ones.
By input time fertilizers are divided by:
- Basic fertilizers applied under the furrow
- Initial fertilizers to be introduced immediately before or during sowing
- Fertilizers for added feeding are added during the growing season
According to the type of nutrient the fertilizers are nitrogen, phosphorus, potassium, magnesium, boron, etc.
The basic forms of nitrogen fertilizers are:
- Ammonia (ammonium salts, eg sulfates, chlorides, carbonates)
- Nitric (calcium, sodium and other nitric acid salts)
- Ammonium nitrate
- Amide fertilizers
Phosphorus fertilizers are salts of orthophosphate (but also metaphosphate, pyrophosphate, and polyphosphate), while potassium is in the form of chloride, sulfate, carbonate, etc.
According to agrochemical significance, the true mineral fertilizers contain the necessary biogenic elements, and the intermediate fertilizers mobilize them from soil reserves, either by improving the physical properties of the soil or by chemical and biological changes that cause it in the soil. These include calcareous fertilizers, use of gypsum and the like.
Mineral fertilizers may contain one or more nutrients and are therefore divided into:
- Individual mineral fertilizers
- Complex mineral fertilizers
For example, sodium nitrate (NaNO3) and magnesium nitrate (Mg (NO3) 2) are individual mineral fertilizers, although magnesium and sodium are also used by plants, while potassium nitrate (KNO3) and MAP (NH4H2PO4) are complex mineral fertilizers containing, in addition to nitrogen, phosphorus, resp. potassium. Thus, the division is based on three basic or major nutrients N, P and K. Depending on the number of major elements, compound fertilizers are double or triple (complete). Fertilizers containing a small amount of filler are called concentrated, whereby the filler adapts to the required nutrient concentration. If the filler is a product of a chemical reaction in the production of mineral fertilizers, it is also called ballast.
Thus, individual mineral fertilizers contain only one of the major nutrients (N, P, or K). They are mixed with individual fertilizers (whether they are only physically mixed or pelleted), while they are a complex product of chemical reactions and contain multiple nutrients in several forms. The division into complex and mixed fertilizers is somewhat conditional since mixed fertilizers with longer storage also lead to different chemical reactions that can lead to deterioration of physical (eg hygroscopicity and decomposition of granules) or chemical properties (eg loss of some nutrient or its transformation into less available chemical forms) of mineral fertilizers.
The nutrient content and ratio of fertilizer may vary. Fertilizers that have a nutrient ratio adapted to the needs of a particular plant species or the content of available nutrients in the soil are called adapted. If all the components are for plant nutrition, then they are non-filler fertilizers (non-ballast), and this group includes salts whose cation and anion plants use, eg KNO3, NH4NO3, etc.
Depending on the aggregate condition, fertilizers are:
Solid fertilizers can be powdered, pelleted (powder compressed into granules or sticks that may contain pesticides, hormones, etc.), granulated (by drying a viscous mass in a stream of warm air), trionized (eg vermiculite granules with NPK), etc. Liquid fertilizers are divided into real solutions (no precipitate) and suspensions, while gaseous are of such aggregate state at normal atmospheric pressure (eg liquefied ammonia). Liquid fertilizers, lately, offer more formulations for different needs, which in addition to NPK, often contain other macro and microelements (Ca, Mg, Fe, Cu, Mn, Zn and B).
Fertilizers that contain exclusively or the highest concentration of microelements from the biogenic elements are also called micro-fertilizers because they are used in small quantities (up to 500 g ha-1 active substances). Due to the difficulty of evenly distributing such small amounts, they are usually added to conventional fertilizers in the production process, used as a liquid that can be mixed with individual repellents, applied to irrigation systems, or dipped into low concentrated solutions of such fertilizers before sowing (sometimes added to the pelleted seed wrap).
Granular mineral fertilizers are solid granules (grains 2-5 mm in diameter) and liquid fertilizers are made of water-soluble substances or powders (concentrates) that are mixed with water to obtain liquid fertilizer before use. Plants absorb nutrients from liquid fertilizer very quickly, while granular fertilizers take some time to dissolve or decompose the granule before the plants can absorb the nutrients. Slower dissolution of granular fertilizers prevents the movement of nutrients with water and their action is significantly longer than liquid fertilizers that are easily flushed out of the root zone. Thus, granular fertilizers are introduced into the soil, less often by surface (bugs) and their effect is estimated to be 1-9 months, depending on the type of fertilizer, method of application and agroecological conditions.
Slow-acting mineral fertilizers have prolonged effects, that is, their effect is throughout the vegetation, or even longer (1-24 months). Such fertilizers are obtained by the synthesis of slow-decomposing chemical compounds in the soil, or the granules are coated with a layer of a substance that does not allow rapid transfer of nutrients from the granules to the soil. Often, in warm regions, but also in temperate climates, irrigation, and light soils, nitrification inhibitors are used, which significantly reduces nitrogen losses by leaching or denitrification.
Mineral fertilizers (synthetic or chemical) are divided by origin, purpose, composition, method, and type of production, and by the function, they are divided into:
- Direct or true mineral fertilizers that, in the soil, under the influence of the aqueous phase of the soil, decompose very quickly to substances that can be directly absorbed by the plants. They contain nutrients in the form of mineral salts that can be directly absorbed after dissolution (hydrolysis).
- Indirect fertilizers contain biogenic elements (essential for plant life), but in a chemical form that cannot be readily absorbed by plants (eg: hummus, lime, etc.) and affect or act indirectly (eg, stimulate microbial activity, neutralize acidity and allow better uptake of certain elements of nutrition, acting through the improvement of soil structure, etc.) or directly after microbiological or chemical transformation.
- Complete fertilizers (often referred to as complete, complex or NPK fertilizers) provide all the essentials plant growth ingredients so no additional fertilizers are needed.
- Incomplete fertilizers contain only one or two of the three major nutrients (N, P, K, NP, NK, or PK), eg: DAP or diammonium phosphate: (NH4) 2HPO4, potassium nitrate: KNO3, etc.
- Mixed fertilizers are obtained by mixing an appropriate amount of individual fertilizers.
- Pelleted mineral fertilizers or compound fertilizers are actually agglomerated mixed fertilizers (formed into granules or pellets by compression with a binder or at certain moisture)
- Synthetic organic fertilizers (urea, calcium-carbide, etc. containing carbon) which may be granular
Organic fertilizers originate from organic sources such as solid manure or slurry and plant and animal residues. The efficiency of organic fertilizers depends on the microbiological activity in the soil, ie at what rate they are degraded into and transformed into nutrients suitable for adoption. It should be emphasized that organic fertilizers more strongly stimulate the activity of soil microbes, fungi, and other “destroyers” of organic matter than mineral fertilizers, and introduce much less salt and acid into the soil. Unfortunately, microbes are poorly active under 50 °F, and it is considered that each of the following 50 °F doubles the activity. Therefore, caution should be exercised when applying organic fertilizers (dose, route and time of application) because, for example, too much organic fertilizer can strongly stimulate its microbial activity, resulting in more nutrients than plants can absorb from the soil.
Organic fertilizers are, by their composition and properties, a very diverse group comprising mainly different wastes of plant and animal origin
Organic fertilizers, with or without the addition of mineral fertilizers, are divided into several groups:
- Fertilizers based on peat (or substances of similar stability): peat, composted tree bark, lignite, etc., minimum concentrations nutrients 1.0% N, 0.5% P, 0.8% K and 30% organic matter
- Waste of animal origin such as horns, bone meal, blood meal (9-13% N), feathers, etc.
- Fertilizers based on waste materials of plant or industrial origin: beer pulp, soybean oil cake, oilseed rape, olive or sunflower, wine pulp, etc.
- Municipal waste-based fertilizers, eg sewage sludges, biogenic and garden composts, commercial composts, etc., which must be used to ensure that they do not exceed the permissible concentration of heavy metals, especially Pb, Cd, Cr, Cu, Ni, Hg, and Zn. Otherwise, they should not be used in food production but only for parks, sports grounds, flower growing, etc
It is typical for the application of organic fertilizer to be applied once a year, or once in several years, as a rule, in the coldest part of the year, in order to avoid “overloading” the soil with nutrients. Also, organic fertilizers have a much longer degradation time, so their effect (nutritional, but also on the repair of the chemical-physical properties of the soil), extends over many years, that is, has a pronounced prolonging effect.
The use of organic fertilizers, but only during its regular application, increases the amount of humus in the soil. The effect is less noticeable when using liquid organic fertilizers. It is important to emphasize that the application of organic fertilizers improves soil properties, in particular the structure resulting in better water-air ratio, higher water retention, greater availability of all nutrients, and greater erosion resistance on sloping surfaces. Also, the application of organic fertilizers when the soil is vegetation-free or when plants do not need nutrient uptake can cause environmental problems (eg nitrate leaching, in lighter terrain and potassium, phosphorus buildup in the erosion-prone upper layer, etc.).
Liquid fertilizers can be purchased or prepared by dissolving them before use (eg urea, crystalline, etc.). Often these are colored substances to help identify the type of liquid fertilizer. These fertilizers require the use of special application devices such as sprinklers or fixed irrigation systems.
The efficiency of liquid fertilizers is high, but they are short-lived, usually only 7-14 days, and need to be applied frequently. Also, a low concentration of the active substance must be applied when spraying, so use a lot of water to avoid burns and other damage to the plants, all of which have a higher application cost than granular ones.
The advantage of liquid fertilizers is that they are easily and quickly adopted, which is very suitable as a “starter solution” for a quick boost during the growing season. Therefore, liquid fertilizers are useful as a grain supplement, when the need arises.