Types of chemical fertilizers in agriculture

Any type of material that increases the yield of the product both qualitatively and quantitatively in order to strengthen the soil and increase its fertility is called fertilizer. Fertilizers are generally divided into three categories, which are: chemical fertilizers, fertilizer organic and biological fertilizer.

The production of this type of fertilizers brought about a revolution in agriculture and the increase in the production of crops. Over time, the production of these fertilizers has increased and since, in addition to the fact that these fertilizers increase the yield, it should also be kept in mind that these fertilizers cause a lot of damage to the soil, living organisms, and the ecosystem. The chemical composition and purity percentage of different fertilizers containing the same element are very different. These differences have a very important effect on the consumption, spreading method, fertilization time and effectiveness of fertilizers. Therefore, it is necessary to know enough about the types of chemical fertilizers before choosing or using them. Chemical fertilizers are divided into two categories, some of which are part of high-use plant elements (macroelement) and some are part of low-use plant elements (microelement). High consumption elements (macro) including: nitrogen-phosphorus-potassium-magnesium-calcium Low-consumption (micro) elements include: iron-zinc-copper-manganese-boron Chemical fertilizers are divided according to the type of element. For example, nitrogen, phosphorus and potassium fertilizers have one or two elements. If a fertilizer has all the elements together and proportionally, it is called complete fertilizer.

N2 is supplied from air and H2 from methane gas and CH4. That is, N2+3H2 is converted into NH3 (molecule) in the presence of suitable catalyst temperature and pressure. Ammonia produced during this reaction is a nitrogen fertilizer. Nitrogen fertilizer with 82% nitrogen is directly injected into the soil as fertilizer in many countries, and in Iran there are few facilities for its use. Ammonia as a raw material can be used to produce other nitrogen fertilizers. If we combine NH3 with O2 molecule, urea fertilizer is produced, which is one of the most widely used chemical fertilizers. If we combine NH3 with H2SO4 (sulfuric acid), ammonium phosphate fertilizer is produced, which is one of the best fertilizers for alkaline soil conditions, that is, it has acidic properties and is very desirable and suitable for Iran's soil conditions.

Nitrogen can be absorbed by plants in the form of nitrate, ammonium ion and urea. Ammonium nitrate has 33% nitrogen and both forms of nitrogen can be absorbed by plants. Because it has a negative charge, it is not absorbed by soil colloids and is subject to washing from the soil. But because it has a positive charge, it is absorbed by soil colloids. Urea is the most common nitrogen fertilizer in Iran. Urea is one of the organic compounds and can be absorbed by plants in this form. Urea solution is also used in foliar spraying of plants. Ammonium nitrate urea can be applied to the soil before planting the crop or as a solution after the plant has grown a little. Ammonium sulfate has 24% sulfur in addition to nitrogen. Ammonium hydrate, which is obtained by dissolving ammonia in water, is placed under layers of soil with special syringes before planting.

Calcium nitrate and potassium nitrate have a low percentage of nitrogen and are used less as a source of nitrogen fertilizer in the soil. These fertilizers are often used in nutrient solutions as sources of calcium or potassium.

One of the fertilizers used is urea. Urea fertilizer, which is also known as sugar fertilizer, is one of the most widely used and cheapest nitrogen chemical fertilizers in the world. Urea fertilizer has 46% nitrogen and its solubility in water is very good, and for this reason, it is used in the soil to prepare fertilizer solutions and foliar spraying on plants. In foliar spraying on the plant, it is possible that the urea fertilizer contains a certain amount of biourea, which should not exceed a certain amount. The problem with urea fertilizer is that due to its high solubility, it washes too much in the soil. That is, if the irrigation water or rainfall is high and the soil is sandy, this fertilizer is easily washed into the soil.

Another famous nitrogen fertilizer is urea fertilizer with sulfur coating. The solubility of urea fertilizer is high and it is possible to wash it, and the grains of urea fertilizer create a sulfur coating on it. This fertilizer is called slow dissolving. It means that SU fertilizer gradually releases its nitrogen, and washing and loss of fertilizer are much less, and from this point of view, it can be a suitable fertilizer, but it is more expensive than normal urea fertilizer, and for ornamental plants and for conditions where water washing is possible, or products that are The economic opinion is economical, it can be a suitable and useful fertilizer.

Choosing nitrogen fertilizer can depend on several parameters. One of these is the price of fertilizer. As we said, urea fertilizer is much cheaper than ammonium sulfate fertilizer. Fertilizer has 46% nitrogen and ammonium sulfate fertilizer has 21% nitrogen. Soil conditions can also be a determining factor for choosing fertilizer. If the soil is very alkaline and its pH is high, we will reduce the pH to some extent by using ammonium sulfate fertilizer.

1) Ammonium sulfate Ammonium sulfate fertilizer has 21% nitrogen and 23% sulfur. This acid-forming fertilizer is suitable for calcareous soils and is relatively expensive and slightly resistant to washing.

2) Urea fertilizer: contains 46% nitrogen. This fertilizer is not acid-forming and is suitable for most soils. It is the cheapest and most common Iranian nitrogen fertilizer.

3) Ammonium nitrate fertilizer: contains 26% nitrogen. This fertilizer is not acid-forming and is suitable for sugar beet and is relatively expensive and sensitive to washing.

4) Ammonium phosphate fertilizer: 17% nitrogen and 26% phosphoric acid. Ammonium phosphate fertilizer is relatively acid-forming and dual-purpose and has a reasonable price and is slightly resistant to washing.

5) Urea form fertilizer: contains 26% nitrogen. This fertilizer is relatively acidic and suitable for grass, it is expensive and very resistant to washing.

6) Urea fertilizer: with sulfur coating: 35% nitrogen. It is acidic and suitable for light and wash-resistant soils, and its price is reasonable.

Of the advantages of chemical fertilizers, cheap price, simple and easy application, short-term false income (regardless of the depreciation of the main capital i.e. soil and its organic matter). The spread of many diseases and pests, for example, the spread of pear fire in the pear orchards of Karaj and Qazvin, nematodes in tea fields and even citrus canker in the south of the country, are mainly the result of unbalanced use of fertilizers.

Often, the percentage of phosphorus in chemical fertilizers is mentioned as the percentage of phosphorus oxide. Phosphoric acid, which is obtained from the decomposition of soil organic matter, can be absorbed by plants, but it is not used as a chemical fertilizer. Most of the phosphorus fertilizers that are given to the soil. It is stabilized by calcium in alkaline soils and by iron and aluminum in acidic soils. Usually, up to the phosphorus fertilizer that is given to the soil remains absorbable by the plant in the first year, and a small part becomes absorbable by the plant in the following years. The above-mentioned amounts depend on the method of fertilizing, the texture and composition of the soil, the records of phosphorus fertilizer consumption in the soil, and the amount of phosphorus fertilizer that is consumed. Because the solubility and movement of phosphorus fertilizer in the soil is very limited, phosphorus fertilizers should be given to the soil before planting and placed directly in the root development area. The maximum amount of phosphorus solution is observed at pH 6 to 6.5. Therefore, bringing the pH of the soil to these limits can be effective in increasing the solubility and absorption of phosphorus. Changing soil pH can be done in acidic soils by adding lime and in alkaline soils by adding sulfur or acidic fertilizers. Using a lot of animal manure can also be useful in reducing soil pH. The solubility of phosphorus fertilizers is also variable.

Potassium deficiency is mostly seen in acidic soils and sandy soils, but its deficiency in other soils under irrigation conditions and harvesting a large amount of crops (especially alfalfa) is also observed. Most potassium fertilizers are soluble in water, and the way they are added to the soil does not play a big role in the effectiveness of the fertilizer. Chlorpotassium is the most abundant potassium compound in nature. Chlorpotassim has a large amount (60 to 62%), however, the use of chlorpotassim is not very desirable in cases where a large amount of potassium is needed, because there is a possibility of poisoning due to the abundance of chlorine, although a small amount of chlorine is used for products such as tobacco and cotton. It is necessary, but a lot of chlorine in the soil causes watery potato tubers and a decrease in the quality of tobacco. Potassium nitrate has 44% potassium oxide, but it is an expensive fertilizer. Potassium sulfate is the most common potassium fertilizer that is used in agriculture. Potassium is also added to the soil from the initial decomposition of plant residues, but soil humus is not considered as a significant source of potassium, because potassium is not stabilized by organic matter. Soils that have a large amount of vermiculite and illite clay stabilize potassium. The potassium in the soil solution is in balance and is considered as a soil potassium reserve. If the stabilization intensity is high, potassium should be placed in strips before planting.

Deficiency of sulfur is observed in soils that are heavily exposed to washing. In this case, sulfur should be added to the soil as fertilizer. The amount of sulfur in fertilizers is mentioned as the percentage of sulfur element (s). The choice of type of sulfur-containing fertilizer depends on the pH of the soil. In acidic soils, calcium sulfate or gypsum can be used as a source of sulfur. This composition contains 18% sulfur and 22% calcium. In addition to providing sulfur and calcium, gypsum also increases soil pH. Sulfur powder can also be used as sulfur fertilizer. As a result of the activity of oxidizing bacteria, the sulfur element becomes sulfuric acid and eventually becomes sulfates. The smaller the particles of sulfur element and the more uniform its distribution in the soil, the higher the rate of sulfur oxidation. Oxidation of the sulfur element has made the soil acidic, and for this reason, it is used as a solution for alkaline soils. It takes about 3 to 4 weeks for sulfur to oxidize in the right temperature and humidity. Some sulfur fertilizers (such as SO2 and polysulfides) are dissolved in irrigation water and added to the soil.

Calcium and magnesium are used less as fertilizers, because their deficiency is not seen in many soils (except the soils of humid areas). The soils of wet areas are acidic and calcium and magnesium are used to improve them. In acidic soils, a large amount of calcium carbonate, double calcium and magnesium carbonate, or calcium sulfate is used to improve acidic soils. As a result, the possible lack of calcium and magnesium is also removed. If changing the pH of acidic soils is not desired and the goal is only to supply the calcium required by the target plant, phosphorus fertilizers containing calcium can be used. Magnesium sulfate or double sulfate of magnesium and potassium is used to solve magnesium deficiency.

Nitrogen, phosphorus and potassium elements are used as fertilizers more than other elements. Sometimes commercial fertilizers are prepared as a mixture of the above elements. The percentage of elements in these fertilizers is usually low, and most of the volume is made up of other materials other than the above elements. The composition of such fertilizers is mentioned with the percentage of nitrogen (N), phosphorus oxide and potassium oxide and the same composition, for example, 10-10-20 fertilizer has 20% nitrogen, 10% phosphorus oxide and 10% potassium oxide, sometimes the percentage of sulfur (S ) is mentioned as the fourth number, such as 5-10-10-15, which has 5% sulfur. Mixed fertilizer may lack one of the three main elements. Such as 13-0-44, which does not contain phosphorus and is actually potassium nitrate, or diammonium phosphate, which can be expressed as 18-46.

Iron, copper, manganese and zinc deficiency is possible in the soils of dry areas and molybdenum, chlorine and boron deficiency in the soils of wet areas. Sometimes there is a large amount of chlorine and lead in the soil and irrigation water of dry areas and they can cause plant poisoning. The important point in the use of fertilizers of low consumption elements is that the border between the required amount and the limit of poisoning the plant is very narrow. In other words, excessive consumption of these fertilizers causes plant poisoning.