Common potassium fertilizers are potassium chloride (muriate of potash), potassium sulphate (sulphate of potash), and potassium magnesium sulphate.
POTASSIUM CHLORIDE [KCl]
Potassium chloride contains about 60% potash (K2O).
Potassium chloride is a crystalline white salt, but the colour of fertilizer grade potassium chloride ranges from white to red depending on the amount of impurities in the potash minerals. The colour does not affect the fertilizer effect.
The crystallized potassium chloride is free-flowing and does not pose any problems in handling and storing. Formally, the fertilizer used to cake up, but this problem can be removed by mixing anti-caking agents.
The potassium chloride salt is 100% soluble in water. When applied to soil, the potassium ion is adsorbed and retained by soil colloids, so there is little possibility of leaching. Plant roots take up the ionic form of the nutrient.
Potassium chloride is neutral in nature and does not produce acidity or alkalinity in the soil.
The chlorine content of potassium chloride is about 47 per cent.
Although potassium chloride is suitable for most crops and soils, potassium sulfate is preferred for crops such as tobacco and potatoes, where excess chloride affects quality.
一般的、 the entire potassium requirement can be applied as a basal dose, but in sandy soils, high rainfall areas, and wetland rice, a split application is preferred.
POTASSIUM SULPHATE [K2S04]
The most common potassium fertilizer is potassium chloride, but potassium sulphate is used to a lesser extent for specific crops.
In nature, potassium sulphate occurs as langbeinite, a double salt with magnesium (K2SO4.2MgSO4), but it can also be manufactured by the action of sulfuric acid on potassium chloride.
White crystalline salt, potassium sulphate is free-flowing and contains 48 to 52 per cent potash (K2O) and 18 per cent sulfur. Normally, handling and storing crystalline potassium sulfate does not pose any problems.
Potassium sulphate is soluble in water, and when applied to the soil, the potassium ions are retained by soil colloids and do not easily leach out.
It is an excellent fertilizer that can be applied to all soil types and crops.しかし、 since it is more expensive, it is usually used only in cultivating chloride-sensitive crops.
Potassium sulphate is soluble in water, and when applied to the soil, the potassium ions are retained by soil colloids and do not easily leach out. It is an excellent fertilizer that can be applied to all soil types and crops.
Due to its sulphur content, it is a two-nutrient fertilizer. It can be used for tobacco, ポテト、 fruits and vegetables.
さらに、 it may be a good choice for saline soils as well as in poly house where chloride accumulation can be a problem.
POTASSIUM MAGNESIUM SULPHATES
There are several fertilizers that contain both potassium and magnesium in the sulphate form, such as the above-mentioned langbeinite or schoenite (K2S04.MgSO4.6H20).
Potassium magnesium sulphate is commercially produced in Europe and the United States.
Potassium magnesium sulphate has 22-30 per cent K2O, 10-19 per cent MgO, 16-23 per cent Sulphur.
The use of potassium magnesium sulphate is especially recommended for acidic soils and soils deficient in magnesium.さらに、 it is recommended for crops with high magnesium requirements, such as potatoes, fruits, vegetables, and forest trees.
KAINITE
Kainite is a naturally occurring mineral.
Pure kainite has the chemical composition kcl.MgSO4.3H2O, but in nature, it rarely occurs as such.
Kainite, a commercially available product, is largely composed of potassium chloride, magnesium sulphate, and magnesium and sodium chlorides.
Kainite contains 14-22 percent K2O.
It is alkaline in nature and contains 46 per cent chlorine.
Unlike most other potassic fertilizers, it may cake in storage and need to be broken up before use.
It can be beneficial for crops that use sodium, such as sugarbeet.
Complex fertilizers
As a result of the high nutrient content of complex fertilizers, the cost of packing, handling, and transport per unit of nutrient is lower than that of many straight fertilizers.
Complex fertilizers are available in granular form and are free-flowing, making them easy to handle and apply.
Complex fertilizers have the advantage of ensuring balanced fertilization of crops, especially in developing countries. The production and use of complex fertilizers is therefore on the rise and accounts for a considerable proportion of world fertilizer consumption.
Classification of complex fertilizers
Complex fertilizers can broadly be classified into (I) ammonium phosphates, (II) nitrophosphates and (III) NPK fertilizers.
Examples of complex fertilizers
I. Ammonium Phosphates
一般に、 ammonium phosphates are satisfactory for all crops and soils. It exhibits the characteristics of nitrogen fertilizers containing ammonium as well as highly water-soluble phosphate.
It is possible that, in some circumstances, nitrogen from urea ammonium phosphate will be less effective.
Crops are not immediately able to utilize the polyphosphate in ammonium polyphosphates, しかし、 it is quickly transformed to the available orthophosphate form in soil.
Due to its high phosphorus content, DAP is used more extensively and in crops where the phosphate requirement is relatively high;一方で、 MAP is usually mixed with additional nitrogen and potassium intermediates due to its wide N:P205 ratio.
(i) Monoammonium phosphate (MAP)
Monoammonium phosphate (MAP) is a high-analysis fertilizer that is almost completely soluble in water. It contains 52 to 55 per cent P2O5 and 11 to 12 per cent nitrogen.
Because it is non-hygroscopic and compatible with most other fertilizer materials, it is widely used in the manufacture of multi-nutrient fertilizers. Produced by reacting ammonia with wet phosphoric acid at a concentration of 45-52%, maintaining an NH3:H3PO4 ratio of 1:1.
Spray-drying of the concentrated MAP solution yields powdered material which is later granulated for application in the fields.
(ii) Diammonium Phosphate
DAP (diammonium phosphate) is produced in large quantities. Commercial DAP is mostly water-soluble, free flowing and granular and contains 18 per cent nitrogen and 46 per cent P2O5.
The manufacturing process of diammonium phosphate requires a mole ratio of 2:1 between NH3 and H3PO4, which involves an additional step of ammoniation.
The slurry thus produced is granulated, dried, screened, cooled and conditioned by a coating agent.
(iii) Ammonium Phosphate Sulphate
Approximately 60% of ammonium phosphate sulphate is ammonium phosphate, while 40% is ammonium sulphate. It contains 16 percent nitrogen and about 20% P2O5.
Nitrogen content can be increased by adding urea, and a variety of N:P2O5 analysis products can be obtained.
Ammonium phosphate sulphate is a free-flowing substance that is usually not difficult to handle and store.
(iv) Urea Ammonium Phosphate
The chemical reaction between ammonia and phosphoric acid produces urea ammonium phosphate (UAP).
In the granulator, additional ammonia and urea are added to the ammonium phosphate slurry. A coating agent is applied to prevent caking after the material has been dried, screened and cooled.
There are various N:P2O5 analyses available.また、 it is possible to produce liquid (solution) UAP directly, thereby avoiding drying costs.
Almost all the phosphorus is water-soluble, while some nitrogen is in the form of ammoniacal and some in the form of urea.
Free-flowing granules and good physical properties make the fertilizer an excellent choice for soil, although it may cake when humid.
(v) Ammonium Polyphosphates
By reacting ammonia with superphosphoric acid, ammonium polyphosphates (APP) are produced. Both liquids and solids are made of them.
The typical APP solutions in the USA have analyses of 11-33-0, 10-34-0, 12-40-0, and 8-27-0;しかし、 granular products can be produced with nutrient contents of up to 15-61-0, depending on the acid purity used. APP is completely soluble in water.
In APP, nitrogen is entirely in the form of ammoniacal nitrogen, and phosphate is present as monoammonium phosphate (NH4H2PO4) and orthoammonium polyphosphates.
In addition to their high analysis, APP solutions allow for the addition of large quantities of micronutrients without precipitation. Ammonium polyphosphates are mainly manufactured and used in the United States.
II。 Nitrophosphates
Nitrophosphates are fertilizers made by nitrifying phosphate rock with nitric acid or a mixture of nitric and sulphuric acids, followed by ammoniating the resulting slurry. Afterwards, the slurry is granulated or prilled. Additional nitrogen can then be added, in the form of ammonium nitrate, along with potassium chloride or sulphate, to achieve the desired NPK analysis.
Granulation characteristics of nitrogen phosphates are good, and they are coated to minimize moisture absorption. When properly packaged and stored, cakes do not form.
Solubility of the phosphate determines the agronomic performance of nitrophosphates. Most phosphate is citrate-soluble, しかし、 its solubility in water varies (0-80%) based on the ammoniation process.
一般に、 all crops and soils are suitable for nitrophosphates containing 60 per cent or more water-soluble phosphate.しかし、 low water-solubility phosphates are suitable only for long duration crops such as sugarcane or grassland, and for acid soils.
Short duration crops like cereals and potatoes are less suitable for Nitrophosphates.
III。 NPK Complex Fertilizers
Nitrogen, phosphorus, and potassium are contained in varying proportions in solid NPK fertilizers.一般的、 they are easy to handle and apply, free flowing and granular in structure. Various grades are produced and marketed depending on soil and crop needs.
They can be prepared either by the ammonium phosphate or nitrophosphate routes by adding potassium. The production process used determines the ratio of ammonium, nitrate and urea nitrogen. The production process also determines the the content of water-soluble and citrate-soluble phosphorus.
The best way to apply them is as a basal dressing. In spite of the extensively wide range of available NPK analyses, most factories limit their output to a few products for operational reasons.
The main benefit of NPK complex fertilizers is their ease of use, including ease of handling and application of all three nutrients in just one operation.さらに、 they can include calcium, マグネシウム、 phosphorus, and micronutrients.
There may, しかし、 be some situations where the farmer might need to apply additional amounts of these nutrients separately, as the available grades of NPK might not always meet those requirements.
Compound fertilizers
Compound fertilizers, also known as mixed fertilizers, differ from complex fertilizers primarily in their method of preparation.
(i) single nutrient or two-nutrient intermediates granulated together
(ii) Using straight fertilizers or intermediates mixed together to form a blend, each granule maintaining its original composition
(iii) A mixture of powders
Compound fertilizers perform essentially the same as their components.
The physical characteristics, storage, handling, and application characteristics of granular compound fertilizers are influenced by the manufacturing process.それにもかかわらず、 compound fertilizers are generally safe to use as long as the coating, packaging, and storage conditions are good.
It’s also critical that the components of granular mixtures are homogenous in size and shape to avoid segregation.
Compared to granulated fertilizers, powdered fertilizers have poor storage properties and are difficult to apply uniformly. Distributors are limited in their ability to apply them.
Examples of Compound fertilizers
Granular Compound Fertilizers
Compound fertilizers are usually produced in factories using straight nitrate, phosphorus and potassium fertilizers, sometimes using two-nutrient intermediate fertilizers such as MAP.
The intermediates are usually in powder form or are slurries that are fed into a granulating plant, typically a large rotating drum.
Water or steam is added as needed, and rotation causes the formation of granules which are dried, screened for size, and bagged or bulk stored. The composition of granular compound fertilizers depends mainly on their agronomic suitability and availability. Using urea and superphosphate together can cause the phosphorus to lose water solubility and hence it is not preferred to mix such substances to make compound fertilizers.
Powdered Mixed Fertilizers
Multinutrient fertilizers are made by mixing powdered (or crystalline) straight fertilizers together on the farm, thereby reducing the number of fertilizer applications needed per field.
It is possible to formulate powder mixtures with a wide range of nutrient ratios by combining and adjusting ingredients.例えば、 an 8-8-8 fertilizer can be prepared by mixing Ammonium sulphate, 20.6% N + SSP, 16.5% P205 + Potassium chloride, 60% K2O ( 39% + 48% + 14% =100%) 。
Compared to granular compound fertilizers, powder compound fertilizers are more affordable.しかし、 it has some disadvantages such as:it has short term storage capabilities, the application is more time consuming and less uniform and some of the more concentrated intermediates such as ammonium nitrate and urea cannot easily be used.
Bulk Blends
By mixing or blending granular intermediates such as CAN, MAP, and potassium chloride, the cost of re-granulation can be avoided. Bulk blending involves blending granular intermediates with compatible properties. The compatible properties such as granule size, surface properties, and density should match so that there is no segregation during storage, handling and application.
Bulk blending eliminates bagging costs, and since bulk-blended fertilizer is prepared and sold immediately before application, storage factors are no longer relevant.
The bulk blending of fertilizer is primarily developed in the United States. It is typically applied by the suppliers on contract basis, したがって、 the farmer’s operations are simplified as large capacity equipment belonging to the contractor can be used for application.
Fluid Mixed Fertilizers
There are two types of liquid mixed fertilizers:clear liquids and suspension fertilizers.
Clear liquids are solutions in water that contain primary nutrients and are designed to not precipitate or salt out at prevailing temperatures since such deposits are hard to remove.
Ammonium nitrate, urea, ammonium phosphate or phosphoric acid, and potassium chloride are the most common nutrient sources. Concentrations achievable are considerably lower than with solid fertilizers, for example about 9-9-9 compared with 17-17-17.
Suspension fertilizers contain a small quantity of special clay, which delays the settling from the suspension of any salts that crystallize out.したがって、 it is possible to achieve a higher level of concentration than clear liquids, but not as high as solids, and even high-quality ingredients are not required.しかし、 suspension fertilizers require continuous agitation in storage and specialized application equipment.
Over solid fertilizers, fluid mix fertilizers have several advantages, namely reduced labor requirements, contract application options, and the ability to combine herbicides with fertilizers.
Secondary major nutrient fertilizers
The secondary major nutrients are calcium (Ca), sulphur(S) and magnesium(Mg). Although the uptake of calcium, sulphur, and magnesium by plants is quite substantial, it is rarely as large as those of nitrogen, phosphorus, and potassium.
Calcium Fertilizers
In soils, plants, and liming materials, calcium content may be expressed as calcium oxide (CaO) or as elemental calcium, with a factor of 0.72 between the two.
Total calcium content in soils varies greatly depending on the parent material and can be substantial in soils formed from limestones, igneous rocks such as granites, syenites, diorites, gneisses and schists.
In contrast to this, soils derived from sandstones and shales that are noncalcareous in humid areas may contain little calcium.
A liberal application of sodium nitrate over time or repeated applications of irrigation water with a high sodium chloride content may produce an alkaline soil in which sodium is the dominant cation instead of calcium.
Regardless of the total amount of calcium in the soil, the calcium present in the soil’s base exchange complex provides readily available calcium to plants. The lower the pH value (i.e. the higher the acidity) and the lower the exchange capacity value, the less calcium is exchangeable. Calcium deficiency is particularly harmful to fruits and vegetables.
CALCIUM CHLORIDE [CaCl2 6H2O]
It is almost completely water soluble and contains 15% calcium. Because of its highly water soluble nature, it is a good candidate for foliar nutrient application.
CALCIUM NITRATE [Ca(NO 3 ） 2 ]
Calcium nitrate, also knon as Norgessalpeter 、 is also a highly water soluble calcium ferltilizer. It contains 26.5% calcium in the form of calcium oxide and 15.5% Nitrogen.
Magnesium Fertilizers
The magnesium content in soil, plants, or materials containing magnesium is usually expressed either as magnesium oxide (MgO) or as elemental magnesium, with a conversion factor of 0.61.
The soil magnesium content ranges from a trace to as much as 1 per cent. Magnesium is well supplied to arid areas or soils with high clay content, while sandy soils in high rainfall areas tend to have a low magnesium content because leaching removes it. Excessive potassium application can worsen magnesium deficiency. The soil exchange complex normally provides magnesium to the crop.
As compared with potassium and calcium, magnesium uptake by crops is much lower. Up until the last two decades, magnesium deficiency was rare, but now it is readily apparent in many crops, particularly potatoes, sugarbeets, brassicas, and maize.
It is best to correct magnesium deficiencies before plant establishment, using a variety of soil application treatments such as dolomitic limestone, kieserite, and various potassium magnesium fertilizers. Magnesium-containing NPK fertilizers are also available.
Considering economic factors and whether liming is needed determines the choice of magnesium fertilizer. Magnesium deficiency being observed during crop growth may be alleviated with foliar sprays of magnesium sulfate (Epsom salts) 。
DOLOMITIC LIMESTONE (Ca and Mg carbonate)
This magnesium fertilizer contains 5-20% magnesium in the form of MgO (magnesium oxide). It also contains 20-45% calcium oxide (CaO)
MAGNESIUM SULFATE (Epson Salt) [MgSO4.7H20]
This contains 16% MgO and 13% Sulphur
NITROMAGNESIA
This contains 7% MgO and 20% Nitrogen and 15% Sulphur
GROUND BURNT MAGNESIUM LIME [Ca and Mg oxide]
This contains 9-33% MgO and 26-58% calcium oxide (CaO)
SULPHATE OF POTASH MAGNESIA [K2SO4 , MgSO4]
This contains 10-18% MgO, 22-30% potassium oxide (K2O) and 16-22% sulphur(S)
MAGNESIUM CHLORIDE [MgCl2.6H2O]
This contains 20% MgO
KIESERITE [MgSO4.H2O]
This contains 27% MgO and 22% sulphur
MAGNESIUM SULPHATE ANHYDROUS [MgSO4]
This contains 33% MgO and 26.5% sulphur
MAGNESITE [MgCO3]
This contains 45% MgO
Sulphur Fertilizers
Sulphur is a highly mobilized element in soils. When soil biomass breaks down, it is mineralized into the sulfate form that crops can absorb. It is very easy for sulphate to leach from soil. Sulfur is dissolved in rainfall and deposited in soil by dry deposition but amounts vary depending on rainfall and fossil-fuel burning.
Precipitation amounts range from a few kilograms per hectare per year to over 100 kilograms. Sulphur deficiency may occur at the lower end of this spectrum.
Among brassica crops and legumes, sulphur uptake can reach 40-60 kg/ha. There is a prevalence of sulphur deficiency among these crops on every continent.
The following methods can be used to correct sulphur deficiency:
Using sulphur-containing fertilizers like ammonium sulfate or superphosphate
Gypsum, which is a calcium source and an ameliorant that corrects alkalinity
By applying elemental sulphur, though this should only be used on very alkaline soils because of its soil acidifying effect; in some soils oxidation of the applied sulphur may be slow.
Magnesium sulphate anhydrous (MgSO4), Ammonium sulphate (NH4)2SO4, Kieserite (MgSO4.H2O), Sulphate of potash magnesia (K2SO4. MgSO4), Potassium sulphate (K2SO4), Gypsum (CaSO4.2H2O), Superphosphate (Ca(H2PO4)2.2CaSO4 ), Ammonium sulphate nitrate (2NH4NO3. (NH4)2SO4), Epsom salts (MgSO4.7H2O) can be used as sulphur suplimentation fertilizers depending on the needs and circumstances.
Micronutrient Fertilizers
Micronutrients, such as iron, zinc, 銅、 マンガン、 boron, molybdenum, and chlorine, are used by plants in very small amounts, usually in terms of grams per hectare.しかし、 even a few grams can mean the difference between high yields and crop failure.
Some elements are beneficial but not essential for crop growth, including cobalt, selenium, vanadium, nickel, lithium, silicon, and aluminum. These elements are not mentioned here.
Plants with micronutrient deficiencies display characteristic symptoms, but corrective measures may be too late once the symptoms appear, since the damage has already been done. When micronutrients are applied at this stage, they may not fully compensate for earlier deficiencies, resulting in a lower yield.
In order to ensure proper growth and development of the crop, it is necessary to determine whether the soil which the crop will be grown on contains sufficient micronutrients or if it is deficient in one or more micronutrients, and then to take corrective measures accordingly. Micronutrients should not be recommended as a blanket treatment in all soils and cropping situations; such an approach might actually cause more harm than good because of toxicity.
The amount or level of nutrients required for optimum growth of the plant is called the critical level 。 Different soils, different species, and even different varieties will have different critical levels of nutrition requirement.
