Understanding NPK Compound Fertilizers: Composition, Production, Application, and Environmental Impact

Introduction to NPK Compound Fertilizers:

NPK compound fertilizer is a chemical fertilizer containing two or more nutrient elements. Through a specific granulation production process, it mixes or combines multiple nutrients in a 15-15-15 or 18-18-18 proportion to provide plants with a comprehensive and balanced nutrient supply. NPK compound fertilizer can simultaneously meet the needs of plants for multiple nutrients at different growth stages, help improve the yield and quality of crops, and enhance the ability of plants to resist diseases and pests and adapt to environmental changes. Compared with single fertilizers, compound fertilizers have the advantages of high nutrient content, few by-products, and good physical properties. They are more convenient and efficient to use, can reduce the number of fertilizations and labor costs, and have been widely used in agricultural production in the United States. Common compound fertilizers include nitrogen, phosphorus and potassium compound fertilizers, diammonium phosphate, potassium nitrate, etc.

Composition of NPK Compound Fertilizers:

 Understanding N-P-K Ratios

N - P - K Ratios are usually expressed in the form of three numbers, such as 10 - 10 - 10 or 20 - 10 - 5. These three numbers represent the percentage content of nitrogen, phosphorus and potassium in the fertilizer. Taking 10 - 10 - 10 as an example, it means that the fertilizer contains 10% nitrogen (N), 10% phosphorus (calculated as phosphorus pentoxide P₂O₅) and 10% potassium (calculated as potassium oxide K₂O).

Different effects on plants

• Nitrogen (N): It is one of the macroelements required for plant growth. Its main function is to promote the growth of plant stems and leaves, making the leaves lush and green. Adequate nitrogen can make plants flourish, improve the efficiency of photosynthesis, and thus increase the biomass of plants. However, if there is too much nitrogen, it may cause plants to grow too tall, stems to be thin and weak, delay flowering and fruiting, and reduce the ability to resist diseases and insect pests.
• Phosphorus (P): It is essential for the root development, flowering and fruiting, and seed formation of plants. Phosphorus can promote the growth and development of plant roots, make the root system more developed, and enhance the plant's ability to absorb water and nutrients. At the same time, phosphorus can also promote the differentiation of plant flower buds, increase the fruit setting rate, help plants mature early, and improve the quality of agricultural products. When phosphorus is deficient, plants grow slowly, leaves become smaller and purple, and root development is poor.
• Potassium (K): It can enhance the stress resistance of plants, making them more resistant to adverse environmental conditions such as drought, cold, diseases and insect pests. Potassium participates in many physiological processes in plants, such as photosynthesis and respiration, which helps improve the photosynthesis efficiency of plants, promotes the synthesis and transportation of carbohydrates, makes plant stems strong, and improves the lodging resistance of plants. When potassium is deficient, the edges of plant leaves will turn yellow and scorch, and the stems will become weak and easy to fall.

NPK requirements for different plants and growth stages

• Different plants have different requirements for N-P-K Ratios. For example, leafy vegetables such as cabbage and spinach require more nitrogen to promote leaf growth, and their suitable N-P-K ratio may be around 2:1:1; while for fruit trees, such as apple trees and peach trees, more phosphorus and potassium are required during the flower bud differentiation period and fruit expansion period, and their suitable N-P-K ratio may be 1:2:2 or 1:3:2, etc.
• The same plant's demand for N-P-K also changes at different growth stages. In the seedling stage of the plant, an appropriate amount of nitrogen and phosphorus are usually required to promote the growth of the root system and stems and leaves; in the vigorous growth period, the demand for nitrogen, phosphorus and potassium is relatively large; and in the flowering and fruiting period, the ratio of phosphorus and potassium needs to be appropriately increased to promote flowering and fruiting and fruit development.

What are the types of NPK Fertilizers?

Classification by nutrient content and ratio

• General NPK compound fertilizer: usually contains balanced nitrogen, phosphorus and potassium nutrients, such as 15-15-15, 16-16-16 and other ratios. This type of fertilizer is suitable for a variety of crops and different soil conditions, and can provide plants with comprehensive basic nutrients to meet the general needs of plants for various nutrients in the early and middle stages of growth.
• High nitrogen NPK compound fertilizer: The nitrogen content is relatively high, such as 20-10-10, 25-5-10 and other ratios. It is suitable for crops such as leafy vegetables and forage grasses that mainly focus on stem and leaf growth, and can promote the growth of plants and improve the growth rate and quality of leaves.
• High phosphorus NPK compound fertilizer: The phosphorus element accounts for a large proportion, such as 10-20-10, 12-24-12 and other ratios. It is mainly used for fruit trees, flowers and other crops that need to promote flower bud differentiation, flowering and fruiting, and root development. Used during the critical period of crop growth, such as before flowering, it helps to improve fruit setting rate and fruit quality.
• High potassium NPK compound fertilizer: The potassium content is prominent, such as 10-10-20, 15-5-20 and other ratios. Suitable for root crops, such as potatoes, sweet potatoes, etc., and fruit trees in the fruit expansion period. Potassium can promote the transportation and accumulation of carbohydrates, make the fruit plump, and improve the crop's resistance to lodging and pests and diseases.

Classification according to production process

• Chemical compound fertilizer: It is a compound fertilizer made by chemical reaction, with uniform composition, high nutrient content and good physical properties, such as diammonium phosphate, potassium nitrate, etc. Diammonium phosphate contains 18% nitrogen and 46% phosphorus (P₂O₅). It is a high-concentration, fast-acting nitrogen-phosphorus compound fertilizer mainly based on phosphorus, suitable for various crops and soils. Potassium nitrate contains 13.5% nitrogen and 46% potassium (K₂O). It is a chlorine-free potassium and nitrogen compound fertilizer with good water solubility. It is suitable for crops that avoid chlorine and crops with high potassium and nitrogen requirements.
• Compound fertilizer: A fertilizer made by mixing several single fertilizers or chemical compound fertilizers in a certain proportion, also known as compound fertilizer. Its advantage is that it can flexibly adjust the nutrient ratio according to the soil fertility conditions and crop needs in different regions to produce special fertilizers suitable for the local area. For example, urea, monoammonium phosphate, potassium sulfate, etc. are mixed in a certain proportion to make a special compound fertilizer suitable for local rice growth.
• Mixed compound fertilizer: During the production process, various raw materials are mixed and granulated under certain process conditions. The nutrient distribution of this fertilizer is relatively uniform, the particle size is consistent, and it has good physical properties and chemical stability. Some large compound fertilizer manufacturers usually use advanced mixing processes to produce compound fertilizers to ensure product quality and nutrient effects.

Classification by special functions or added ingredients

• Slow-release/controlled-release NPK compound fertilizer: Through special coating technology or adding slow-release agents, the nutrients in the fertilizer are slowly released to extend the fertilizer effect period. This fertilizer can reduce the number of fertilizations, reduce fertilizer loss and volatilization, and improve fertilizer utilization. It is especially suitable for long-term crops such as trees and lawns. For example, sulfur-coated urea is a common slow-release nitrogen fertilizer. In the soil, the sulfur coating will gradually be decomposed by microorganisms, causing the urea to be slowly released.
• NPK compound fertilizer containing trace elements: In addition to the three main nutrients of nitrogen, phosphorus and potassium, trace elements such as iron, zinc, manganese, boron and molybdenum are also added. Although these trace elements are less required by plants, they play an important role in the growth and development, physiological metabolism and other processes of plants. For example, when growing rapeseed in some boron-deficient soils, the use of boron-containing NPK compound fertilizers can effectively prevent the phenomenon of rapeseed "flowering but not fruiting" and improve the yield and quality of rapeseed.
• Organic-inorganic compound NPK fertilizer: It combines organic fertilizer and inorganic fertilizer. It has the advantages of organic fertilizer, such as improving soil structure, increasing soil organic matter content, and improving soil water and fertilizer retention capacity, and it also has the quick-acting effect of inorganic fertilizer, which can provide nutrients to plants in a timely manner. This fertilizer is suitable for crops that have high requirements for soil fertility and agricultural product quality, such as organic vegetables and fruits. For example, organic fertilizers such as chicken manure and pig manure are fermented and mixed with inorganic fertilizers such as urea, superphosphate, and potassium sulfate to make organic-inorganic compound fertilizers. It can be used for fertilizing orchards to improve the taste and flavor of fruits.

What are the Importance of balanced nutrient ratios in NPK fertilizers?

Promote overall plant growth

Role of nitrogen (N):

Nitrogen is an important component of plant proteins, nucleic acids and chlorophyll. Adequate nitrogen can promote luxuriant branches and leaves of plants. For example, in the early growth of rice, an appropriate amount of nitrogen supply can increase the tillering of rice plants. Generally, applying 100-150 kg of pure nitrogen per hectare can significantly increase the number of effective tillers of rice, thus laying the foundation for high yields in the later stage. When nitrogen is deficient, plants grow slowly, leaves turn yellow, and photosynthesis weakens.

Role of phosphorus (P):

Phosphorus is essential for plant root development, flowering and fruiting, and energy metabolism. It can promote the growth of plant roots and the division of root cells. In vegetable cultivation, for crops such as tomatoes, it is more appropriate to apply NPK fertilizers with a high phosphorus content from transplanting to flowering, and the ratio of phosphorus (measured in P₂O₅) to nitrogen (measured in N) is 1:2-1:3. This helps the tomato roots to take root deeper and better absorb water and nutrients from the soil. It can also promote flower bud differentiation and increase fruit setting rate. According to research, reasonable phosphorus application can increase the fruit setting rate of tomatoes by 10% - 15%.

The role of potassium (K):

Potassium can enhance the resistance of plants to stress, such as drought resistance, cold resistance, disease and pest resistance, and lodging resistance. In wheat planting, increasing the application of potassium fertilizer (measured in K₂O) from the booting stage to the filling stage can make the wheat stems tough and enhance the lodging resistance. When the available potassium content in the soil is 100-150 mg/kg, combined with appropriate amounts of nitrogen and phosphorus, the wheat yield and quality are the best. At this time, the N-P-K ratio is roughly 1:0.5:0.8. Potassium also participates in photosynthesis and the transportation of carbohydrates in plants, which can make the fruit plump and bright in color, and improve the quality of agricultural products.

Improve fertilizer utilization

When the nutrient ratio of NPK fertilizer is balanced, plants absorb various nutrients more efficiently. For example, in corn planting, if only nitrogen fertilizer is applied and phosphorus and potassium are ignored, the utilization rate of nitrogen fertilizer may be only 30% - 35%. However, when the ratio is reasonably adjusted according to the demand for NPK in different growth stages of corn, such as the ratio of N-P-K in the seedling stage is 1:1:0.5, and the ratio from the big bell stage to the tassel stage is 1:0.5:1, the comprehensive utilization rate of fertilizer can be increased to 40% - 45%. This is because there is a synergistic effect between nitrogen, phosphorus and potassium. A reasonable ratio can promote the absorption of nutrients by plant roots and their operation in the plant body, avoiding waste due to too much or too little of a certain nutrient.

Improve soil fertility

Long-term use of NPK fertilizers with balanced nutrient ratios helps maintain the acid-base balance and nutrient balance of the soil. For example, in acidic soil, the appropriate application of alkaline phosphorus fertilizers (such as calcium magnesium phosphate fertilizers) can neutralize soil acidity and supplement phosphorus. In some areas with low soil fertility, by rationally applying NPK fertilizers, the content of nitrogen, phosphorus and potassium in the soil can be adjusted to a range suitable for crop growth, which can gradually improve soil structure and increase soil organic matter content. Studies have shown that soils that have been rationally applied with NPK fertilizers for 5 consecutive years can increase their organic matter content by 0.1% - 0.3%, reduce soil bulk density by 0.1 - 0.2 g / cubic centimeter, and increase soil porosity by 5% - 10%, thereby improving the soil's ability to retain water and fertilizer, which is beneficial to crop growth.

Ensure crop yield and quality

In fruit planting, such as apples, a reasonable NPK nutrient ratio has a significant impact on the yield and quality of the fruit. In the early stage of apple growth, nitrogen fertilizer is mainly used, with appropriate amounts of phosphorus and potassium, and the N-P-K ratio is about 2:1:1, which can promote the nutritional growth of fruit trees and form sufficient branches and leaves. During the fruit expansion period, increasing the proportion of potassium and adjusting the N-P-K ratio to 1:0.5:2 can promote the accumulation of sugar in the fruit and improve the sweetness and color of the fruit. According to experiments, the orchards that adopt a reasonable NPK fertilization program can increase the apple yield by 15%-20% compared with the orchards that do not fertilize scientifically, the soluble solids content of the fruit can be increased by 1-2 percentage points, the fruit firmness can be increased, and the storage resistance can be enhanced, thereby improving the competitiveness of apples in the market.

What is the Production Processes of NPK Compound Fertilizers?

Overview of Manufacturing Methods

• Steam Drum Granulation method: Mix nitrogen, phosphorus, potassium and other raw materials in a rotary drum granulation machine, add an appropriate amount of water or steam, and agglomerate the materials into particles through mechanical force in the granulation equipment. The compound fertilizer particles produced by this process have high strength and regular shape, relatively simple production process, low investment cost, but the particle uniformity may be slightly poor.
• Slurry method: First, make part or all of the raw materials into slurry, and then spray the slurry into the granulator to contact with the return material or other solid materials, and make compound fertilizer through drying, granulation and other processes. This process can produce high-concentration compound fertilizer, the product particles are round, high in strength, and good in nutrient uniformity, but the production process is long, the equipment investment is large, and the operation control requirements are high.
• Melt granulation method: Heat the raw materials to a molten state, then spray them into the granulation tower, cool and solidify them into particles in the air. The compound fertilizer particles produced by this process have high nutrient content and good physical properties, the particle surface is smooth and round, not easy to agglomerate, and no drying equipment is required during the production process, and the energy consumption is relatively low. However, this process has high requirements for raw materials and is difficult to operate.
• Blending method: Mechanically blend nitrogen, phosphorus, potassium single fertilizer or compound fertilizer particles of different particle sizes in a certain proportion. This method has a simple production process and high flexibility. The product formula can be quickly adjusted according to market demand and soil nutrient conditions, and the production cost is low. However, the particle uniformity and stability of the product are relatively poor, and stratification may occur during storage and transportation.

Detailed NPK Fertilizer Production Method Comparison Table:

Granulation Method	Raw Material Processing	Mixing Method	Granulation Method	Post-Processing
Agglomeration Method	Raw materials are crushed to achieve suitable particle size	Fully stirred in a mixer	Granulation in a drum or disc granulator, where mechanical force, water, or steam helps materials agglomerate	Drying, screening, crushing oversized particles, regranulating undersized particles, cooling, and applying anti-caking agent
Slurry Method	Phosphate rock and other materials require pre-treatment, such as acid dissolution, to form a nutrient-rich slurry	Slurry is mixed with recycled materials in a drum granulator	Slurry is sprayed into a drum granulator, binding with recycled or solid materials to form granules	Drying, screening, reprocessing unqualified particles, cooling, and coating with anti-caking agent
Melt Granulation Method	Raw materials undergo high-temperature reactions to form a melt, eliminating complex pre-treatment	Mixing occurs during the reaction process	Melt is sprayed into a granulation tower, where it solidifies upon contact with cold air	Screening to remove unqualified granules
Blending Method	Raw material particles are screened to ensure uniform particle size	Stirred in blending equipment	No granulation process, direct mixing	Direct packaging

Steam drum granulation method:

Slurry spraying granulation method

• Raw material pretreatment: For some complex raw materials, such as phosphate rock, acid hydrolysis and other pretreatment are required. Phosphate rock is reacted with sulfuric acid or phosphoric acid in a reaction tank to generate products such as phosphoric acid and calcium sulfate. The reaction temperature is generally controlled at 80-120℃, and the reaction time is 2-4 hours. At the same time, other raw materials are crushed, screened, etc. to meet production requirements.
• Slurry preparation: Various pretreated raw materials are added to the reactor in a certain proportion, and appropriate amounts of water and steam are added. The reaction is carried out at a certain temperature and pressure to generate slurry containing nutrients such as nitrogen, phosphorus, and potassium. The concentration of the slurry is generally controlled at about 60%-70%, and the temperature is between 100-120℃.
• Granulation: The prepared slurry is pumped into the drum granulator, and a certain amount of return material (unqualified particles screened out in the previous production cycle) or other solid materials are added to the granulator. The slurry contacts the return material or solid material in the granulator, the water evaporates quickly, and the material sticks into particles. The speed and inclination of the granulator are adjusted according to the actual production situation. The general speed is 8-12 rpm and the inclination is 30°-40°.
• Drying: After the wet particles come out of the granulator, they enter the dryer for drying. The dryer uses high-temperature hot air drying. The hot air temperature is between 200-350℃. The material stays in the dryer for 20-40 minutes, so that the moisture content of the particles is reduced to below 2%-3%.
• Screening: The dried particles are screened by screening equipment to divide the particles into different particle size grades. Large particles larger than the specified particle size enter the crusher for crushing, and small particles smaller than the specified particle size return to the granulator for re-granulation.
• Cooling: The qualified particles after screening enter the cooler for cooling. The cooling method is similar to the granulation method, so that the particle temperature is reduced to below 40℃.
• Coating: The cooled particles are coated to prevent agglomeration. The coating materials and methods are the same as the granulation method.

High tower prilling granulation method

• Raw material pretreatment: Various raw materials are pretreated by impurity removal and crushing to make their particle size uniform and the impurity content meet the requirements. For some raw materials that require special treatment, such as urea, pretreatment such as heating and melting may be required.
• Melt preparation: The pretreated raw materials are put into a high-temperature reactor and reacted at a certain temperature and pressure to generate a melt of nutrients such as nitrogen, phosphorus, and potassium. The reaction temperature is usually between 130-150℃ and the pressure is 0.3-0.5MPa. The composition and properties of the melt are precisely controlled according to the requirements of the product.
• Granulation: The prepared melt is sprayed into the granulation tower through a special nozzle. The granulation tower is usually between 30-50 meters in height. During the falling process, the melt is fully in contact with the cold air entering from the bottom of the tower and quickly cooled and solidified into particles. The size and shape of the particles can be controlled by adjusting the parameters such as the nozzle aperture, injection pressure and the flow rate of cold air.
• Screening: The particles collected from the bottom of the granulation tower are screened by screening equipment to remove unqualified particles that are too large or too small. Unqualified particles can be returned to the melt preparation link for reprocessing.
• Packaging: The qualified particles after screening are directly packaged. Since the compound fertilizer particles produced by the melt granulation method have good physical properties and low moisture content, they generally do not require post-processing processes such as cooling and coating.

BB fertilizer blending method

• Raw material preparation: Select nitrogen, phosphorus, and potassium single fertilizers or compound fertilizer particles with uniform particle size and stable nutrient content as raw materials. For example, commonly used nitrogen fertilizers include urea particles and ammonium chloride particles, phosphate fertilizers include diammonium phosphate particles, and potassium fertilizers include potassium chloride particles and potassium sulfate particles. These raw materials are screened to remove impurities and particles that do not meet the particle size requirements to ensure the quality of the raw materials.
• Ingredient metering: Accurately weigh various raw material particles according to the nutrient formula requirements of the product. Use high-precision metering equipment, such as electronic scales, to ensure the accuracy of ingredients. During the batching process, the ingredients must be weighed strictly according to the formula ratio to ensure that the nutrient content of the product meets the standard.
• Blending: Put the weighed raw material particles into the blending equipment, such as a horizontal mixer, a vertical mixer or a drum mixer. Mix the raw material particles thoroughly and evenly by stirring, tumbling, etc. The blending time is generally 10-20 minutes, and the specific time is adjusted according to the equipment performance and raw material characteristics to ensure the uniformity of the product.
• Packaging: The blended compound fertilizer directly enters the packaging process and is packaged by an automatic packaging machine. During the packaging process, attention should be paid to controlling the accuracy of the packaging weight and the packaging quality to ensure that the product is not damp or leaking during storage and transportation.
• The above four processes have their own characteristics. In actual production, enterprises will choose the appropriate production process based on their own raw material supply, product requirements, equipment conditions and market demand.

Technological Advancements 2025

1. High tower granulation technology

• Product differentiation improvement: Enterprises pay more attention to the development of differentiated products, and increase product functions by adding synergists to compound fertilizers. For example, adding urease or nitrification inhibitors can prolong the release time of nitrogen fertilizers, and adding polyglutamic acid, alginic acid, amino acids, potassium dihydrogen phosphate and other substances can promote crop absorption and improve the absorption and utilization rate of nitrogen, phosphorus and potassium. Produce nitrosulfur-based or pure sulfur-based fertilizers to adapt to the use of cash crops, and develop products combining pesticides and fertilizers to meet the needs of popular products in the current market.
• Capacity optimization and layout adjustment: It is estimated that the capacity of high-tower granulation compound fertilizers has reached 70 million tons. If calculated at 300,000 tons per set, there are about 230 sets of high towers. However, the current capacity utilization rate is low, only about half, and the market competition is fierce. Enterprises have begun to optimize capacity layout according to market demand and their own advantages, no longer blindly pursuing scale expansion, but paying more attention to product quality and market segmentation.

2. Extrusion granulation technology

• The advantages of energy saving and environmental protection are prominent: the extrusion granulation process uses external force to extrude materials into granules. The entire production process does not require water addition and drying. Compared with the traditional slurry method or humidification agglomerate method, it can save a lot of energy used to dry water, and also avoid the generation of a large amount of waste gas, wastewater and waste residue, reducing environmental pollution. At the same time, this process does not require steam, saving boiler construction investment and coal-fired production costs, which meets the energy-saving needs of today's society.
• Enhanced production flexibility: Fertilizers are less affected by the external environment (such as temperature and humidity) during the production process, and have greater operational flexibility and flexible process formulas. It can quickly adjust production parameters according to different raw material characteristics and product requirements to produce NPK compound fertilizers of different specifications and performances to meet diverse market needs.

3. Drum granulation technology

• Improvement of raw material pretreatment technology: Before drum granulation, the pretreatment of raw materials is more refined, and advanced crushing, screening and mixing equipment are used to make the raw material particle size distribution more uniform, which improves the efficiency and quality of granulation. For example, by optimizing the parameters of the crusher and adopting a multi-stage screening process, the coefficient of variation of the particle size of the raw materials can be controlled within a smaller range, providing a good foundation for subsequent granulation.
• Improved automation control level: The drum granulation line is equipped with a more advanced automation control system, which realizes real-time monitoring and precise control of key parameters in the granulation process. For example, by installing intelligent sensors, real-time monitoring of parameters such as the rotation speed of the drum, the humidity and temperature of the material, and feeding back the data to the control system, the system automatically adjusts the operating status of the equipment according to the preset parameters to ensure the stability and consistency of the granulation process and improve the qualified rate of the product.

4. Comprehensive technical aspects

• Precision batching technology: The use of high-precision electronic scales and intelligent batching systems can accurately control the addition of various raw materials to ensure that the proportions of nitrogen, phosphorus, potassium and other trace elements in NPK fertilizers are accurate. For example, the accuracy of the batching system can reach within ±0.1%, which effectively ensures the stability and consistency of product nutrients and meets the precise requirements of fertilizer nutrients for different crops and soil conditions.
• Coating technology innovation: New coating materials and coating processes continue to emerge, which can not only improve the appearance quality of fertilizer particles, but also improve their physical properties and nutrient release characteristics. For example, the use of coating materials with slow-release function can slowly release nutrients in fertilizers, extend the fertilizer effect period, and reduce the number of fertilization times. At the same time, the coated fertilizer particles have better anti-caking and wear resistance, which is convenient for storage and transportation.

Application Techniques for NPK Compound Fertilizers

Soil Application Methods

1. Broadcasting:

• Operation method: Spread NPK compound fertilizer evenly on the soil surface. This method is simple and easy to operate and is suitable for large areas of farmland. For example, in the planting of field crops such as wheat and rice, broadcasting is often used. Generally, before ploughing or sowing, the fertilizer is spread on the field according to a certain amount, and then the fertilizer is mixed into the soil by plowing.
• Dosage: The amount of fertilizer to be spread depends on factors such as crop type, soil fertility and target yield. Taking wheat as an example, generally 30-50 kg of NPK compound fertilizer (15-15-15) is spread per mu of land. If the soil fertility is low and the target yield is high, the amount of fertilizer needs to be appropriately increased.
• Advantages and disadvantages: The advantages are simple operation, high efficiency, and the fertilizer can be quickly applied to the soil. The disadvantage is that the fertilizer utilization rate is relatively low, because the fertilizer is spread on the soil surface and is easily washed away or volatilized by rainwater, resulting in nutrient loss. Moreover, uneven spreading may lead to excessive local fertilizer concentration and burn the crop roots.

2. Strip application:

• Operation method: Dig a furrow between crop rows or in the sowing furrow, apply NPK compound fertilizer into the furrow, and then cover with soil. This method can concentrate fertilizer near the crop root system, which is conducive to the crop nutrient absorption. For example, in corn planting, strip application is often used. Generally, when sowing corn, dig a furrow on one side of the sowing furrow and apply fertilizer, and keep a certain distance between the fertilizer and the seeds to avoid burning the seeds.
• Dosage: The amount of fertilizer used in strip application is generally less than that in broadcast application, because the fertilizer is concentrated near the crop root system and the utilization rate is higher. Taking corn as an example, 20-30 kg of NPK compound fertilizer (15-15-15) is applied per mu of land. The specific amount also needs to be adjusted according to soil fertility and crop variety.
• Advantages and disadvantages: The advantage is that the fertilizer utilization rate is high, and the fertilizer can be accurately applied around the crop root system to meet the nutrient needs of crop growth. At the same time, it reduces the contact area between fertilizer and soil, and reduces the fixation and loss of nutrients. The disadvantage is that the operation is relatively complicated, and it requires trenching and fertilization, which consumes a certain amount of manpower and time.

3. Hole application:

• Operation method: Apply NPK compound fertilizer in the crop planting hole. This method is suitable for crops with large row spacing such as fruit trees and vegetables. For example, in apple tree planting, apply an appropriate amount of compound fertilizer at the bottom of the tree pit, and then fill the soil for planting. Or when transplanting vegetables, apply a small amount of fertilizer in the transplanting hole to provide nutrients for the seedlings.
• Dosage: The amount of fertilizer for hole application depends on factors such as crop type, tree age, and plant spacing. For adult apple trees, apply 0.5-1 kg of NPK compound fertilizer (15-15-15) per hole. When transplanting vegetables, apply 5-10 grams of compound fertilizer to each transplanting hole.
• Advantages and disadvantages: The advantage is that it can accurately apply fertilizer according to the individual needs of crops, with high fertilizer utilization rate, which can effectively meet the nutrient needs of crops in the early stage of growth and promote the growth of seedlings. The disadvantage is that the fertilization efficiency is low, the labor intensity is high, and if the fertilization position is not appropriate, it may damage the root system of crops.

Foliar Fertilization

1. Operation method:

Dissolve NPK compound fertilizer in water to prepare a solution of a certain concentration, and then use a sprayer to evenly spray the solution on the leaves of crops. Foliar fertilization can be carried out at different stages of crop growth, but it is generally more effective when the crop is in a period of vigorous growth or when symptoms of nutrient deficiency appear. For example, in the late stage of cotton growth, foliar fertilization is often used to supplement nutrients due to the decline in the root system's ability to absorb nutrients.

2. Concentration:

The concentration of foliar fertilization is very critical. Too high a concentration can easily burn the leaves, and too low a concentration can not achieve the fertilization effect. Generally, the concentration of NPK compound fertilizer foliar spraying is 0.5% - 2%. For example, for urea (nitrogen content 46%), the spraying concentration is generally 1% - 2%; the spraying concentration of potassium dihydrogen phosphate (phosphorus 52%, potassium 34%) is generally 0.2% - 0.5%. The specific concentration should be adjusted according to the type of crop, growth stage and fertilizer type.

3. Dosage:

The dosage of foliar fertilization is relatively small, and generally 30-50 kg of solution is sprayed per mu of land each time. The specific dosage should be determined according to factors such as the planting density, leaf area and growth status of the crop. For example, in vegetable planting, due to the relatively small leaf area, about 30 kg of solution can be sprayed per mu of land each time; while in fruit tree planting, due to the large crown and large leaf area, the amount of solution sprayed per mu of land can reach about 50 kg each time.

4. Advantages and disadvantages:

The advantage is that the fertilizer is absorbed quickly and can quickly meet the nutrient needs of crops, especially when the root absorption capacity weakens in the late growth period of crops, the effect of foliar fertilization is more obvious. Moreover, foliar fertilization can directly act on the leaves, avoiding the fixation and loss of nutrients by the soil and improving the utilization rate of fertilizers. In addition, foliar fertilization can also be mixed with pesticides for spraying, saving labor. The disadvantage is that the spraying effect is greatly affected by environmental factors, such as temperature, humidity, light, etc. If high temperature, strong light or rain are encountered after spraying, the absorption effect of fertilizer will be affected. Moreover, foliar fertilization can only be used as an auxiliary fertilization method and cannot completely replace soil fertilization, because most of the nutrients needed for crop growth still need to be absorbed from the soil through the root system.

Fertigation Practices

1. Fertilization timing

• Crop growth stage: Different crops have different nutrient requirements at different growth stages. Take corn as an example. In the seedling stage, the demand for nitrogen is relatively small, but phosphorus and potassium are essential for root development. Generally, the first drip irrigation fertilization begins 2-3 weeks after corn sowing. At this time, phosphorus and potassium are the main nutrients, and nitrogen is supplied in moderation. For example, compound fertilizer containing N-P-K ratio of 10-20-20 can be applied to promote root growth. As corn enters the jointing stage, the demand for nitrogen, phosphorus and potassium increases rapidly, and the amount and frequency of fertilization need to be increased. Usually, fertilization is applied once every 7-10 days, and the N-P-K ratio can be adjusted to 20-10-10. In the tasseling and filling stages of corn, the demand for nitrogen and potassium reaches a peak. The ratio of nitrogen and potassium in the compound fertilizer can be appropriately increased, such as applying compound fertilizer with N-P-K ratio of 25-5-20, to meet the needs of corn growth and grain development.

2. Soil moisture and temperature:

• Soil moisture and temperature affect the effectiveness of nutrients and the absorption of nutrients by crop roots. In arid areas, when soil moisture is lower than 60% of field water holding capacity, drip irrigation and fertilization should be carried out in time to ensure that nutrients can reach the crop roots along with the water. For example, in the summer when it is hot and dry, drip irrigation and fertilization may be required every day. The amount of fertilizer applied each time should not be too much. The principle is to apply small amounts and multiple times to avoid nutrient accumulation in the soil, causing waste or burning the roots. In the low temperature season, the vitality of crop roots decreases, and the ability to absorb nutrients weakens. The time for fertilization should be around noon when the temperature is higher, and the amount of fertilizer should be appropriately reduced. For example, for greenhouse vegetables in winter, when the temperature is below 15℃, the fertilization interval can be extended to 10-15 days, and the amount of fertilizer can be reduced by 20%-30%.

Timing and Dosage

1. Crop types and yield targets:

• Different crops have very different requirements for NPK. Taking tomatoes as an example, if the target yield is 5,000 kg per mu, according to the nutrient absorption law of tomatoes and soil fertility, 15-20 kg of pure nitrogen (N), 8-10 kg of phosphorus pentoxide (P₂O₅), and 15-20 kg of potassium oxide (K₂O) are required per mu during the entire growth period. Converted into a compound fertilizer with an N-P-K ratio of 15-10-20, about 100-130 kg is required. For leafy vegetables, such as cabbage, the demand for nitrogen is relatively high. If the target yield is 3,000 kg per mu, 10-12 kg of pure nitrogen, 5-6 kg of phosphorus pentoxide, and 8-10 kg of potassium oxide are required per mu. A compound fertilizer with a N-P-K ratio of 20-10-15 can be used, and the application amount per mu is about 60-80 kg.

2. Soil fertility status:

• The fertility level of the soil itself is an important basis for determining the dosage of fertilizer. Through soil testing, we can understand the content of nutrients such as nitrogen, phosphorus, and potassium in the soil. For example, if the soil is rich in alkaline nitrogen, reaching more than 100mg/kg, when planting wheat, the application of nitrogen fertilizer can be appropriately reduced; if the content of available phosphorus in the soil is low, less than 10mg/kg, the application of phosphorus fertilizer needs to be increased. Generally speaking, for medium-fertility soil, 30-40 kg of compound fertilizer with a N-P-K ratio of 16-16-16 can be applied per mu when planting wheat; for poor-fertility soil, the amount of fertilizer can be increased to 40-50 kg.

3. Irrigation water quality and fertilization method:

• If the irrigation water contains a certain amount of nutrients, such as high potassium ions in groundwater, the amount of potassium fertilizer should be reduced accordingly when fertilizing. In addition, different fertilization methods will also affect the fertilizer dosage. When drip irrigation is used for fertilization, since nutrients can be accurately delivered to the root system of crops, the fertilizer utilization rate is high, and the fertilizer dosage can be reduced by 20%-30% compared with traditional ground fertilization. For example, in cotton cultivation, when drip irrigation is used for fertigation, 30-40 kg of compound fertilizer with N-P-K ratio of 12-8-20 per mu is sufficient to meet the growth needs of cotton, while 40-50 kg is required for ground fertilization.

Benefits and Challenges of Using NPK Compound Fertilizers

Advantages

• Provide comprehensive nutrition: Nitrogen, phosphorus and potassium are essential macronutrients for plant growth and development, and play a key role in plant growth, development and yield formation. Nitrogen can promote the luxuriant branches and leaves of plants and improve the efficiency of photosynthesis; phosphorus helps the development of plant roots, promotes flowering and fruiting, and improves crop resistance; potassium can enhance the plant's resistance to lodging, improve crop quality and resistance to diseases and pests. NPK compound fertilizer rationally combines these three elements to meet the needs of crops for multiple nutrients at different growth stages, and helps to improve crop yield and quality. For example, in rice production, the rational application of NPK compound fertilizer can increase rice yield by 20% - 30%.
• Improve fertilizer utilization: Compared with single fertilizers, the various nutrients in NPK compound fertilizers work together to play a synergistic role, reduce nutrient fixation and loss, and improve fertilizer utilization. For example, the use of phosphate fertilizers in combination with nitrogen fertilizers can promote the absorption and utilization of nitrogen by crops, while reducing the fixation of phosphate fertilizers in the soil, thereby improving the effectiveness of phosphate fertilizers. In general, the fertilizer utilization rate of NPK compound fertilizer is 10% - 20% higher than that of single fertilizer.
• Save fertilization cost: The use of NPK compound fertilizer can reduce the number and amount of fertilization, thereby saving labor and fertilizer costs. Applying NPK compound fertilizer once can provide multiple nutrients required by crops at the same time, without the need to apply single fertilizers such as nitrogen, phosphorus, and potassium separately, simplifying fertilization operations and improving fertilization efficiency. According to statistics, in vegetable planting, the use of NPK compound fertilizer can save 15% - 25% of fertilization costs compared with the application of single fertilizers alone.
• Improve soil structure: The nutrients in NPK compound fertilizer will have a certain impact on soil structure during the process of transformation in the soil and absorption by crops. Appropriate application of NPK compound fertilizer can promote the activity of soil microorganisms, increase the content of soil organic matter, improve the physical properties of the soil, make the soil loose and breathable, and enhance water and fertilizer retention. For example, the bulk density of soil that has been applied with NPK compound fertilizer for a long time will decrease and the porosity will increase, which is conducive to the growth and development of crop roots.

Potential Challenges

• Fixed nutrient ratio: Different crops have different requirements for nitrogen, phosphorus and potassium at different growth stages, while the nutrient ratio of NPK compound fertilizer is usually fixed. This may make it difficult to fully meet the specific needs of crops during the actual fertilization process. If you blindly apply fertilizer according to the nutrient ratio of compound fertilizer, some nutrients may be oversupplied while others may be undersupplied, affecting crop growth and fertilizer utilization. For example, leafy vegetables have a high demand for nitrogen and relatively low demand for phosphorus and potassium. If conventional NPK compound fertilizer is applied, it may cause a waste of phosphorus and potassium nutrients.
• Easy to cause soil compaction: Long-term excessive application of NPK compound fertilizer, especially on some heavy soils, may cause soil compaction. This is because some salt ions in compound fertilizers, such as chloride ions and sulfate ions, accumulate in the soil, which will destroy the soil aggregate structure and make the soil air permeability and water permeability worse. According to research, soils that have been over-applied with NPK compound fertilizers for many consecutive years can have their soil bulk density increased by 10% - 20% and soil porosity reduced by 15% - 25%, seriously affecting the growth and development of crop roots.
• Environmental pollution risk: If NPK compound fertilizers are applied improperly, such as excessive application or application in areas with heavy rainfall, the nutrients in the fertilizers may be lost with rainwater and enter the water body, causing environmental pollution problems such as eutrophication of the water body. According to surveys, in some areas with intensive agricultural production, due to the unreasonable application of chemical fertilizers, the nitrogen and phosphorus content in surface water exceeds the standard, resulting in algae proliferation and water quality deterioration in lakes, rivers and other water bodies. In addition, some components in NPK compound fertilizers, such as nitrogen oxides in nitrogen fertilizers, may also be released into the atmosphere during the decomposition process in the soil, causing certain pollution to the atmospheric environment.
• High cost: The production process of NPK compound fertilizers is relatively complex and requires a large amount of energy and raw materials, so its price is relatively high. For some farmers with poor economic conditions, the use of NPK compound fertilizers may increase agricultural production costs and reduce the economic benefits of agricultural production. Especially in some low-income areas, farmers may reduce the amount of fertilizer or choose poor quality fertilizers due to the high cost of fertilizers, which will affect crop yields and quality.

Environmental Impact and Sustainability Practices

Environmental Concerns

1. Resource consumption

• Raw material mining: The production of NPK compound fertilizer requires a large amount of mineral raw materials such as nitrogen, phosphorus, and potassium. For example, the mining of phosphate ore will lead to a gradual reduction in mineral resources. Although the global phosphate reserves are abundant, the high-quality phosphate resources are limited and unevenly distributed. According to statistics, at the current mining rate, some high-quality phosphate resources may face the risk of depletion in the next few decades.
• Energy consumption: Whether it is the granulation method, slurry method, melt granulation method or blending method, a large amount of energy is consumed. For example, in the drying and reaction links, fossil energy such as coal and natural gas need to be burned to provide heat. Taking an NPK compound fertilizer plant with an annual output of 500,000 tons as an example, the annual coal consumption for the drying process alone may reach tens of thousands of tons, which will increase dependence on non-renewable energy and bring about the emission of greenhouse gases such as carbon dioxide.

2. Pollutant emissions

• Waste gas emissions: During the production process, a variety of waste gas pollutants will be generated. For example, dust will be generated during the raw material processing and drying process. If it is not effectively treated, it will pollute the atmospheric environment and affect the health and ecological environment of surrounding residents. In addition, in some chemical reactions, harmful gases such as nitrogen oxides and sulfur dioxide may also be produced. It is estimated that a medium-sized compound fertilizer plant may emit hundreds of tons of nitrogen oxides each year, which can cause environmental problems such as acid rain and photochemical smog.
• Wastewater discharge: Some links in the production process, such as wet phosphoric acid production and equipment cleaning, will produce wastewater. These wastewaters usually contain a large amount of pollutants such as phosphorus, fluorine, and heavy metals. If they are discharged directly without treatment, they will cause eutrophication of water bodies, cause the death of aquatic organisms, and destroy the water ecological balance. For example, excessive discharge of phosphorus elements will cause algae in the water body to multiply in large numbers, consume dissolved oxygen in the water, and form a "water bloom" phenomenon.
• Waste residue generation: A certain amount of waste residue, such as phosphogypsum, will be produced in the production of NPK compound fertilizers. Phosphogypsum is a by-product in the production of wet phosphoric acid, and about 4-5 tons of phosphogypsum will be produced for every ton of phosphoric acid produced. Large amounts of phosphogypsum accumulation not only occupy land resources, but may also cause soil and groundwater pollution because phosphogypsum may contain harmful substances such as heavy metals and fluorides.

Sustainable Practices

1. Sustainable use of raw materials

• Waste gas treatment: Install efficient waste gas treatment equipment, such as bag dust collectors, cyclone dust collectors, desulfurization and denitrification equipment, etc., to treat waste gases such as dust, nitrogen oxides, and sulfur dioxide generated during the production process so that they meet emission standards. Some enterprises have also adopted advanced technologies such as activated carbon adsorption and catalytic oxidation to further reduce the concentration of pollutants in the exhaust gas. After treatment, the dust concentration in the exhaust gas can be reduced to less than tens of milligrams per cubic meter, and the emission of nitrogen oxides and sulfur dioxide can also meet the national environmental protection standards.

2. Energy conservation and emission reduction measures

• Wastewater treatment: Build a complete wastewater treatment facility and use a variety of treatment methods such as physical, chemical and biological methods to deeply treat the wastewater. For example, first remove suspended matter and large particle impurities in the wastewater through physical methods such as precipitation and filtration, then remove pollutants such as phosphorus and fluorine through chemical precipitation and ion exchange, and finally degrade organic matter in the wastewater through biological treatment methods. The treated wastewater can meet the discharge standards, and some enterprises have even achieved zero discharge of wastewater, using the treated water for cooling, flushing and other links in the production process.

3. Environmental protection and treatment

• Waste residue treatment and disposal: For waste residues such as phosphogypsum, in addition to recycling, scientific treatment and disposal methods are also adopted. For example, phosphogypsum is safely landfilled, and anti-seepage and rain prevention measures are taken during the landfill process to prevent harmful substances in the waste residue from leaking into the soil and groundwater. At the same time, the monitoring and management of waste slag landfills should be strengthened to ensure environmental safety. Some enterprises are also researching and developing new waste slag treatment technologies, such as high-temperature calcination modification of phosphogypsum, to further improve the comprehensive utilization rate of waste slag and environmental safety.

Future Trends and Innovations in NPK Fertilizers

Technological Developments

1. Drum granulation technology Low-temperature eutectic spray granulation technology:

Technical principle:

Urea and ammonium phosphate generate tetraurea phosphate, which has low-temperature eutectic characteristics, lower melting point, higher solubility and high viscosity. Adding tetraurea phosphate low-temperature eutectic liquid during the granulation process can produce a liquid phase that meets the requirements of granulation under low moisture conditions.

Process characteristics:

High-temperature and low-humidity slurry agglomeration granulation, steam-assisted, no need for synthetic ammonia to provide chemical reaction heat and liquid phase, the moisture content of the granulator discharge material is about 2.5%, and energy consumption can be reduced by more than 20%. The product strength can reach more than 25N, the anti-caking and anti-powdering capabilities are significantly enhanced, the dependence on high-quality ammonium phosphate and clay is reduced, the granulation balling rate is high, the system return material is low, it can effectively increase the production load of the device, the operation is stable, and the dependence on the operator's experience is reduced.

2. High tower granulation technology

• Double tower modeling technology: Design double tower modeling, save civil engineering investment, and make the process more connected. The product has a smooth appearance and pinhole shape, which has its own anti-counterfeiting function. Its nitrogen content is the highest in the world's compound fertilizer manufacturing field.
• Adding biological enzyme preparations: Adding biological enzyme preparations during the production process can effectively inhibit the decomposition and loss of various nutrients in the fertilizer in the soil, and improve the fertilizer efficiency.
• Raw material pretreatment, chelation and addition of various preparations: Pretreatment of raw materials before preparing mixed slurry can improve the viscosity, fluidity and crystallization performance of the slurry, better granulation production and improve product quality. Chelation can avoid the loss of certain nutrients and adverse side reactions during the production process, protect important nutrients, improve fertilizer efficiency and reduce costs.

3. General development

• Research and development of new fertilizers: Slow-release fertilizer technology is constantly improving. By adding special coatings to the surface of fertilizer particles or using special production processes, the nutrients in the fertilizer can be slowly released according to the needs of crop growth, extending the fertilizer effect period and improving fertilizer utilization. For example, some polymer-coated NPK slow-release fertilizers can increase nitrogen utilization by about 30%. At the same time, progress has also been made in the research and development of water-soluble fertilizers, which can be quickly dissolved in water, making it easier to carry out precise fertilization through drip irrigation, sprinkler irrigation and other facilities, meeting the efficient demand for nutrients in facility agriculture and cash crops.
• Production process optimization: Green and intelligent technologies have become the development direction. In terms of greening, more environmentally friendly production processes are adopted to reduce the discharge of wastewater, waste gas and waste residue, and reduce pollution to the environment. For example, some companies use new reaction equipment and separation technologies to improve resource utilization and reduce energy consumption. In terms of intelligence, sensors, automatic control systems, etc. are used to monitor and accurately control the production process in real time, improve production efficiency and product quality stability, and reduce manual operation errors.
• Application of precision fertilization technology: With the development of precision agriculture, the application of NPK compound fertilizer is more precise. With the help of global positioning system (GPS), geographic information system (GIS) and remote sensing technology (RS), soil nutrient detection and crop growth monitoring are carried out on farmland. According to the soil fertility and crop needs of different regions, personalized fertilization plans are formulated to achieve precision fertilization and improve the fertilizer input-output ratio.
• Product structure upgrade: The growth of fertilizer demand for traditional bulk crops has slowed down, and the demand for new fertilizers such as cash crops and facility agriculture has grown rapidly. The demand for efficient, environmentally friendly and functional fertilizer products has increased, and the market share of new fertilizer products such as slow-release fertilizers, water-soluble fertilizers, and biological organic fertilizers has continued to increase. For example, in the planting of cash crops such as flowers and vegetables, water-soluble fertilizers are used more and more widely, and its market share is expected to grow at an annual rate of 10%-15% in the next few years. At the same time, the demand for customized and formulated fertilizer products is increasing to meet the specific nutrient needs of different crops and different regions.

Market Trends

• Intensified market competition: The industry has overcapacity and severe homogeneous competition. According to statistics, the utilization rate of compound fertilizer capacity in my country China has been below 70% for a long time. Leading enterprises with technological and scale advantages will gain greater development space and increase market concentration through mergers and acquisitions, technological innovations, etc. At the same time, specialized division of labor will become more obvious, and some enterprises will focus on specific market segments, such as the production of special fertilizers for specific crops or specific regions.
• Increased demand for sustainable development: With the improvement of environmental awareness and the strengthening of relevant policies, sustainable development has become an important trend in the NPK compound fertilizer market. On the one hand, the increasing demand of consumers for organic food and green agricultural products has promoted the development of organic NPK compound fertilizers, and its market size is expected to grow at an annual rate of 10% - 12%. On the other hand, the government encourages enterprises to develop and produce environmentally friendly fertilizers, reduce fertilizer pollution to the environment, and improve nutrient utilization efficiency to meet the requirements of sustainable agricultural development.

Conclusion

In conclusion, NPK compound fertilizers stand at the crossroads of agricultural productivity and environmental stewardship. Their well - balanced composition of nitrogen, phosphorus, and potassium is the lifeblood for plants, fueling growth, enhancing yields, and ensuring the quality of our food and fiber sources. The diverse production techniques, from the time - tested to the cutting - edge, continuously evolve to meet the demands of an expanding global population.

Frequently Asked Question