A Detailed Guide to Common Fertilizer Types and Application Methods
Fertilizer refers to a class of substances that provide one or more nutrient elements essential to plants, improve soil properties, and raise soil fertility levels; it is one of the material foundations of agricultural production.So what are the common types of fertilizer? What are their application methods?
1. Ammonium bicarbonate: molecular formula NH4HCO3, contains about 17% nitrogen. It is a white crystalline substance with unstable chemical properties, easily absorbs moisture and decomposes, and is volatile, with a strong pungent, eye-irritating ammonia odor. The greater the humidity and the higher the temperature, the faster it decomposes. It is easily soluble in water and shows an alkaline reaction (pH8.2-8.4).
Ammonium bicarbonate is an unstable compound and decomposes completely at normal pressure when the temperature reaches 70°C. At an air temperature of 20°C, the loss rates after open-air storage for 1 day, 5 days, and 10 days are 9%, 48%, and 74% respectively. In a humid environment it readily absorbs water, deliquesces, and cakes (caking itself is a manifestation of slow decomposition). During storage and application, corresponding measures should be taken to prevent volatilization losses.
It is suitable for all types of soil and crops, and is best applied as a base fertilizer; when used as a top dressing, care should be taken to apply it deeply and cover it with soil.
2. Urea: molecular formula (NH2)2CO, contains about 46% nitrogen. Ordinary urea is a white crystalline substance with strong hygroscopicity. Most urea currently produced is in the form of semi-transparent granules and has been treated to prevent moisture absorption. At an air temperature of 10-20°C, its hygroscopicity is weak; as the temperature rises and humidity increases, its hygroscopicity also strengthens.
Urea is a neutral fertilizer and has no side effects on soil when applied over the long term. After being applied to the soil, it is easily hydrolyzed into ammonium carbonate by the action of urease secreted by soil microorganisms and then absorbed and utilized by crops. Its hydrolysis process is: (NH2)2CO+2H2O→(NH4)2CO3. The hydrolysis speed is related to soil acidity, humidity, and temperature, and is also affected by factors such as soil type, degree of maturation, and fertilization depth. Under normal circumstances, the time required for urea to hydrolyze completely into ammonium carbonate is: about 10 days at an air temperature of 10°C, 4-5 days at 20°C, and about 2 days at 30°C. Therefore, urea has a relatively slow fertilizer effect, and when used as a top dressing it should be applied appropriately earlier.
Urea is suitable for all types of soil and crops, and can be used as a base fertilizer, top dressing, and foliar spray (spray concentration 1-2%).
3. Ammonium chloride: molecular formula NH4Cl, contains 24-25% nitrogen. It is a white crystalline substance, easily soluble in water, with low hygroscopicity, does not cake, has good physical properties, and is convenient to store. Ammonium chloride is acidic and is also a physiologically acidic fertilizer.
Ammonium chloride should not be applied to acidic soils, saline-alkali land, or chlorine-sensitive crops (fruit trees, tobacco, etc.). Chloride ions have a certain inhibitory effect on nitrifying bacteria, and after application to the soil, the nitrification and leaching loss of nitrogen is weaker than that of other nitrogen fertilizers. Therefore, ammonium chloride is a relatively good nitrogen fertilizer for paddy fields.
When applying ammonium chloride, it should be combined with watering, striving to leach chloride ions down to the lower soil layers to reduce their adverse effects on crops. Ammonium chloride is not suitable for use as a seed fertilizer.
4. Ammonium nitrate: molecular formula NH4NO3, contains 33-35% nitrogen. Ammonium nitrate comes in two forms, crystalline and granular; the former has very strong hygroscopicity, while the latter has slightly weaker hygroscopicity because its surface is coated with an anti-moisture agent. Ammonium nitrate is easily soluble in water and has a neutral pH.
Ammonium nitrate contains both ammonium nitrogen (NH4+-N), which has relatively low mobility in the soil, and nitrate nitrogen (NO3--N), which has relatively high mobility; both can be well absorbed and utilized by crops. Therefore, ammonium nitrate is a good nitrogen fertilizer that leaves no residue in the soil and is a physiologically neutral fertilizer.
Ammonium nitrate is suitable as a top dressing for dryland crops, and applying it in small amounts several times is more economical. It should not be applied to paddy fields, nor used as a base fertilizer or seed fertilizer.