What Types of Nitrogen Fertilizers Are There? A Detailed Guide to Application Methods
The nitrogen fertilizers commonly used in fruit tree production mainly include urea, ammonium bicarbonate, ammonium nitrate, ammonium sulfate, ammonium chloride and slow-release urea. Urea is an amide-form nitrogen fertilizer with a nitrogen content generally of 46%, and can be used as a base fertilizer, a top dressing and a foliar top dressing. Ammonium bicarbonate is an ammonium-form nitrogen fertilizer with a nitrogen content generally of 16.5%-16.8%, and can be used as a base fertilizer, ...
1. Rational application of nitrogen fertilizers 1. Fertilizing according to soil conditions:
(1) Organic matter content. When soil organic matter content is high, nitrogen content is also high; when the limited fertilizer is being allocated, nitrogen fertilizer can be applied sparingly or not at all.
(2) Soil texture. Light-textured soils have poor fertilizer retention capacity, so nitrogen fertilizer, especially nitrate nitrogen fertilizer, should be applied in small amounts several times to prevent nitrogen leaching; heavy clay soils can receive a large single application of nitrogen fertilizer.
(3) Soil pH. Apply physiologically acidic or chemically acidic fertilizers to alkaline soils; apply physiologically alkaline and chemically alkaline fertilizers to acidic soils, in order to adjust soil acidity.
(4) Saline soils. Do not apply fertilizers containing Cl- or Na+, to avoid increasing the salt content of the soil.
(5) Arid regions. Nitrate nitrogen fertilizers have a better effect, while in rainy seasons ammonium-form nitrogen fertilizers have a better effect.
2. Fertilizing according to the crop:
(1) Different crops have different nitrogen requirements and degrees of sensitivity. Leafy vegetables, mulberry, tea and similar crops need more nitrogen, while leguminous crops are given nitrogen fertilizer only in the early stage.
(2) Different crops respond to different degrees to the type of nitrogen
Paddy fields: the fertilizer effect of ammonium-form nitrogen fertilizer > nitrate nitrogen; dry land: ammonium-form nitrogen fertilizer = nitrate nitrogen fertilizer or slightly less.
For crops rich in carbohydrates, ammonium-form nitrogen fertilizer > nitrate nitrogen fertilizer; for sugar beet in the early stage, ammonium-form nitrogen fertilizer< 硝态氮，后期铵态氮肥 > nitrate nitrogen; for tobacco, ammonium nitrate is best.
(3) Do not apply fertilizers containing Cl- to chlorine-sensitive crops
(4) Nitrogen requirements differ at different growth stages
(5) Pay attention to fertilizing at the two key periods of crop nutrition
3. Fertilizing according to the nature of the fertilizer:
(1) Ammonium-form nitrogen fertilizers volatilize easily and should be applied deeply.
(2) Nitrate nitrogen fertilizers leach easily, so do not irrigate heavily; moreover, nitrate nitrogen fertilizers act quickly and are suitable as a top dressing.
(3) Fertilizers containing alkaline substances, volatile substances, toxic substances, salts, etc. are not suitable as a top dressing.
4. Fertilizing according to climatic conditions:
The fertilizer effect of nitrogen fertilizer is greatly affected by climatic conditions such as rainfall, temperature and light.
Generally, in arid regions or dry years, the fertilizer effect of nitrogen fertilizer is poorer, while in humid regions or wet years the fertilizer effect is better.
5. Emphasize balanced fertilization:
Advocate the combined application of nitrogen, phosphorus, potassium and organic fertilizer to achieve nutrient balance and improve the economic benefit of fertilizers
6. Fertilize in combination with agricultural technical measures:
(1) Adhere to the principle of "deep application with soil covering."
(2) Avoid the leaching loss and denitrification loss of nitrate nitrogen.
(3) Adopt rational integrated management of water and fertilizer.
The nutritional role of nitrogen fertilizer:
Because nitrogen nutrition plays a decisive role in the growth and development of crops and the formation of yield, and most farmland soils in our country are deficient in nitrogen. With rational application, each kilogram of standard nitrogen fertilizer (ammonium sulfate) can increase grain production by 3-5 kilograms, and the economic benefit is very significant. If applied improperly, the yield increase is not obvious, and it may even cause a reduction in yield. Rational application of nitrogen fertilizer is of great significance in agricultural production. Nitrogen is one of the main components of many important organic compounds in plants; proteins, chlorophyll, enzymes, nucleic acids, vitamins and alkaloids all contain nitrogen. Some people call it the "element of life." When nitrogen supply is sufficient, plants can synthesize more protein, promote cell division and growth, increase leaf area, and enrich chlorophyll, which is conducive to the accumulation of dry matter and the formation of yield, and can improve the quality of crop yield. A notable feature of nitrogen deficiency in crops is that the lower leaves first lose green and turn yellow, then gradually extend upward to the upper leaves, and the plant's growth process is delayed. At the seedling stage, plant growth is hindered and appears short and weak, with thin and small leaves; gramineous crops show fewer tillers and thin, elongated stems; dicotyledons show fewer branches; if nitrogen deficiency continues, gramineous crops show small heads, shriveled grains and premature aging. When nitrogen supply is excessive, plants become overly luxuriant, stay green and lodge, and are prone to disease, delaying maturity, and yield instead declines.
2. Types, properties and application methods of nitrogen fertilizers:
There are many types of nitrogen fertilizers, broadly divided into four types: ammonium-form, nitrate-form, amide-form and slow-release nitrogen fertilizers.
1. Ammonium-form nitrogen fertilizers: including liquid nitrogen (NH3), ammonia water (NH3.H2O), ammonium bicarbonate (NH4HCO3), ammonium sulfate [(NH4)2SO4] and ammonium chloride (NH4Cl). Their nitrogen exists in the forms of NH4+ and NO3-, and their common characteristics are:
(1) Easily soluble in water, they are quick-acting nutrients that crops can directly absorb and utilize, with a rapid fertilizer effect.
(2) NH4+ can undergo exchange reactions with various cations on soil colloids, forming exchangeable nutrients, so that NH4+ is not easily lost in the soil and its fertilizer effect lasts longer than that of NO3-. Ammonium-form nitrogen fertilizers can be used both as a base fertilizer and as a top dressing.
(3) When encountering alkaline substances, they decompose and release NH3; on calcareous soils, surface application of ammonium-form nitrogen fertilizers also causes volatilization loss of NH3. Deep application with soil covering can improve the fertilizer effect.
(4) In well-aerated soil, NH4+-N can be nitrified into NO3-. Although both are absorbed and utilized by crop roots, NO3- is prone to leaching loss and denitrification loss of nitrogen
2. Nitrate-form nitrogen fertilizers: including calcium nitrate [Ca(NO3)2], sodium nitrate (NaNO3), ammonium nitrate (NH4NO3) and potassium nitrate (KNO3), etc. Their nitrogen exists in the form of NO3-, and their common characteristics are:
(1) Easily soluble in water, with a rapid fertilizer effect, very high solubility and strong hygroscopicity, especially Ca(NO3)2 and NH4NO3, which can absorb moisture and dissolve themselves during humid rainy seasons, so they must be strictly protected from moisture during storage.
(2) NO3- is an ion with a negative charge. After being applied to the soil, it exists in the soil solution due to negative adsorption, has high mobility, and is prone to leaching loss under heavy rainfall or in paddy fields.
(3) Under anaerobic conditions, NO3- is acted upon by denitrifying bacteria to form gaseous substances such as N2 or N2O, resulting in nitrogen loss. Therefore, this fertilizer is not easily used in paddy fields, and NH4+-N fertilizer is used instead.
(4) When heated, nitrate-form nitrogen fertilizers can decompose and release oxygen, are extremely combustion-supporting, and can explode under strong impact, so they must be protected from both moisture and heat during storage. From the common characteristics of nitrate-form nitrogen fertilizers, it can be seen that they are not suitable as a base fertilizer or seed fertilizer, nor are they suitable for application in paddy fields, but they are most suitable as a top dressing in dry fields.
3. Amide-form nitrogen fertilizers: any fertilizer containing an amide group (-CONH2) or producing an amide group during decomposition belongs to this category, and urea [CO(NH2)2] is its representative. Urea is a neutral organic compound. After being applied to the soil, it exists in molecular form in the soil and undergoes hydrogen bonding adsorption with soil colloids, and its adsorption force is slightly less than charge adsorption. In the soil, urea is converted into ammonium carbonate under the action of urease, forming NH4+-N, and its fate is the same as that of NH4+-N fertilizer. Urea has strong hygroscopicity, is easily used as a base fertilizer and top dressing, and is not easily used as a seed fertilizer.
4. Slow-release nitrogen fertilizers: most commonly used nitrogen fertilizers are quick-acting fertilizers, which release quickly after being applied to the soil, have a short fertilizer effect period, and easily cause nutrient loss. New-type slow-release nitrogen fertilizers have the characteristics of slow nutrient release, a long fertilizer effect period and high fertilizer utilization rate, and a single application can meet the crop's nutrient needs throughout the entire growth period, without burning seedlings or poisoning crops. The main varieties include organically synthesized slow-release nitrogen fertilizers (such as urea-formaldehyde, urea-acetaldehyde, etc.) and coated fertilizers (such as sulfur-coated urea, polymer-coated urea, slow-release inorganic nitrogen fertilizers, slow-release ammonium bicarbonate, etc.).
The above four types of nitrogen fertilizers have their common features, which are the basis for rational fertilization, but they also have their individual characteristics, for example:
1. Ammonium sulfate and ammonium chloride are physiologically acidic nitrogen fertilizers. Long-term use of these fertilizers will cause soil acidification, which is unfavorable to crop growth.
2. Ammonia water, liquid ammonia and ammonium bicarbonate are all alkaline fertilizers with strong volatility, also known as volatile nitrogen fertilizers, but after being applied to the soil, they become NO3- through nitrification, and the alkalinity disappears. They leave no residue in the soil and will not bring adverse effects to the soil. Ammonium nitrate and urea also belong to the category of residue-free nitrogen fertilizers.
3. Although urea is extremely soluble in water, it cannot be absorbed and assimilated by the root system before it decomposes into ammonium carbonate. Therefore, it should be applied several days earlier than other nitrogen fertilizers.
4. Slow-release nitrogen fertilizers mostly provide insufficient nutrients in the early stage, and sometimes need to be combined with a small amount of quick-acting nitrogen fertilizer. In addition, organically synthesized or coated nitrogen fertilizers have a relatively high cost, and are often suitable for cash crops, ornamental plants, etc.