Calcium Sulfate Granular Fertilizer: A High-Quality Nutrient Provider in Agricultural Production

In modern agricultural production, fertilizers, as the "food" for crop growth, directly affect the yield and quality of crops. As an important secondary nutrient fertilizer, calcium sulfate granular fertilizer occupies an indispensable position in the agricultural field due to its unique nutrient composition and excellent application characteristics. This article will comprehensively introduce this high-quality fertilizer from the aspects of its basic properties, production process, agricultural application advantages, usage methods and precautions, as well as market and development prospects, providing practical reference knowledge for agricultural practitioners.​

Basic Properties of Calcium Sulfate Granular Fertilizer​

The main component of calcium sulfate granular fertilizer is calcium sulfate (CaSO₄), which is usually processed from calcium sulfate dihydrate (CaSO₄·2H₂O, commonly known as gypsum) as the raw material. Some products may also contain a small amount of calcium sulfate hemihydrate or anhydrous calcium sulfate. In terms of appearance, high-quality calcium sulfate granular fertilizer is in the form of uniform granules, mostly white, off-white or light gray in color. The particle size is generally between 1 and 4 millimeters, with good fluidity, which is convenient for storage, transportation and mechanized application.​

In terms of nutrient composition, calcium sulfate granular fertilizer can not only provide crops with two important secondary nutrients, calcium and sulfur. The calcium content (calculated as CaO) is usually 20% - 30%, and the sulfur content (calculated as S) is generally 15% - 25%. Moreover, the release rate of these two elements is relatively slow, which can continuously provide nutrients for crop growth. In addition, calcium sulfate itself has stable chemical properties, is not easy to have adverse reactions with other substances in the soil, and will not easily cause soil acidification or salinization like some fertilizers, so it has good friendliness to the soil environment.​

In terms of physical properties, calcium sulfate granular fertilizer has good compressive strength, is not easy to break during storage and transportation, can reduce dust generation and fertilizer loss. At the same time, it has low hygroscopicity and is not easy to agglomerate under general environmental conditions, ensuring the convenience of fertilizer application.​

Production Process of Calcium Sulfate Granular Fertilizer​

Calcium sulfate granular fertilizer is usually produced from natural gypsum (such as gypsum ore mined from gypsum mines) or industrial by-product gypsum (such as desulfurized gypsum from power plants, gypsum waste residue from the chemical industry, etc.) as raw materials, and processed into granular fertilizer through a series of processing techniques. The specific production process mainly includes the following key steps:​

(1) Raw Material Pretreatment​

First, the raw materials are screened and purified to remove impurities in the gypsum (such as sediment, stones, metal particles, etc.) to ensure the purity and quality of the final product. For natural gypsum, it needs to be crushed and ground into fine powder; while industrial by-product gypsum needs to be dried first to remove excess moisture, and may also need to undergo impurity removal and purification processes to ensure that it meets the requirements of fertilizer production.​

(2) Mixing and Conditioning​

According to the nutritional index requirements of the product, the pretreated gypsum powder is mixed with other auxiliary materials (such as a small amount of binders, stabilizers, etc. The binder can improve the granulation rate and strength of the granules, and the stabilizer can ensure the stability of the fertilizer performance) in a certain proportion to form a uniform mixed material. During the mixing process, it is also necessary to adjust the moisture content of the material to make the material reach a suitable molding humidity. Generally, the moisture content is controlled between 10% and 15%, which is conducive to the subsequent granulation process.

(3) Granulation Molding​

Granulation is the core process of processing the mixed and conditioned materials into granules. At present, the commonly used granulation methods mainly include extrusion granulation, disc granulation and drum granulation. Extrusion granulation is to extrude the material into strips through extrusion equipment (such as a twin-screw extrusion granulator), and then cut into uniform granules through a granulating device; disc granulation and drum granulation are to put the material into a rotating disc or drum, and under certain humidity and rotation speed conditions, the granules are gradually formed through the bonding and rolling of the materials. During the granulation process, it is necessary to strictly control the size and uniformity of the granules to ensure that the product meets the relevant standards.​

(4) Drying and Cooling​

The newly made granules have high moisture content and low strength, so they need to be dried. Drying is usually carried out in a dryer (such as a drum dryer, a fluidized bed dryer, etc.). The moisture content of the granules is reduced to 1% - 3% through hot air heating, so as to improve the strength and stability of the granules. The dried granules have a high temperature and need to enter a cooler for cooling to reduce the temperature of the granules to near room temperature, preventing the granules from deteriorating or agglomerating due to high temperature during storage.​

(5) Screening and Packaging​

The cooled granules need to be screened by screening equipment to remove unqualified fine powder and excessively large or small granules, ensuring that the product granules are uniform in size. The qualified granules after screening enter the packaging process, and automatic packaging equipment is used to package them into bagged products of different specifications (such as 25kg/bag, 50kg/bag, etc.), which is convenient for storage, transportation and sales.​

Agricultural Application Advantages of Calcium Sulfate Granular Fertilizer​

As a high-quality secondary nutrient fertilizer, calcium sulfate granular fertilizer has various application advantages in agricultural production, which can effectively improve soil conditions, promote crop growth, and increase crop yield and quality.​

(1) Supplement Secondary Nutrients to Meet Crop Nutrient Requirements​

Calcium and sulfur are essential secondary nutrients for crop growth and development, and play an important role in the physiological functions of crops. Calcium can promote the formation and development of crop cell walls, enhance the lodging resistance and disease resistance of crops, and reduce physiological diseases caused by calcium deficiency in crops (such as tomato blossom-end rot, Chinese cabbage tip burn, apple bitter pit, etc.). At the same time, calcium can also regulate the osmotic pressure of crop cells and improve the stress resistance (such as drought resistance and cold resistance) of crops. Sulfur is a component of many enzymes and vitamins (such as vitamin B1) in crops, and participates in physiological processes such as photosynthesis, protein synthesis and energy metabolism of crops. It can promote the growth of crop leaves and the formation of chlorophyll, improve the photosynthetic efficiency of crops, increase crop yield and improve crop quality (such as increasing the oil content of rapeseeds, improving the taste of vegetables, etc.). Calcium sulfate granular fertilizer can provide both calcium and sulfur elements for crops, and the release of elements is slow, which can continuously meet the nutrient needs of crops at different growth stages.​

(2) Improve Soil Structure and Soil Physical and Chemical Properties​

For saline-alkali soils or soils with severe compaction, the application of calcium sulfate granular fertilizer has a significant soil improvement effect. The calcium ions in calcium sulfate can exchange with the sodium ions on the surface of soil colloids, replacing the sodium ions in the soil and leaching them into the deep soil with rainwater or irrigation water, thereby reducing the salinity and alkalinity of the soil, improving the soil environment of saline-alkali soils, and enhancing the air permeability, water retention and fertilizer retention capacity of the soil. At the same time, calcium sulfate granules can also increase the aggregate structure in the soil, reduce soil compaction, create a loose and fertile soil condition for the growth of crop roots, and promote the extension of roots and the exertion of absorption functions.​

(3) Improve Fertilizer Utilization Rate and Reduce Agricultural Production Costs​

The nutrient release rate of calcium sulfate granular fertilizer is slow and long-lasting, which can avoid nutrient loss (such as volatilization of nitrogen, fixation of phosphorus, etc.) caused by the too fast release of fertilizer nutrients, and improve the fertilizer utilization rate. At the same time, because calcium sulfate granular fertilizer can improve the soil structure and enhance the water retention and fertilizer retention capacity of the soil, it can reduce the application amount of other fertilizers (such as nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer), reduce agricultural production costs, and improve the economic benefits of agricultural production.​

(4) High Safety and Environmental Friendliness​

Calcium sulfate itself has stable chemical properties, is non-toxic and harmless. After application, it will not pollute the soil, water sources and air, nor will it cause phytotoxicity or fertilizer damage to crops. Compared with some chemical fertilizers (such as potassium chloride, ammonium chloride, etc.), calcium sulfate granular fertilizer has less impact on the soil pH value, can maintain the ecological balance of the soil, and is conducive to the sustainable development of agriculture.​

Usage Methods and Precautions of Calcium Sulfate Granular Fertilizer​

(1) Usage Methods​

The usage method of calcium sulfate granular fertilizer is relatively flexible. Suitable application methods can be selected according to different crop types, soil conditions and planting methods. The common usage methods mainly include the following:​

Base Fertilizer Application​

Base fertilizer application is one of the most commonly used methods for calcium sulfate granular fertilizer. It is generally applied to the soil in combination with soil plowing before crop sowing or transplanting. The specific operation method is: evenly spread the calcium sulfate granular fertilizer on the soil surface, and then plow (such as plowing, rotary tillage, etc.) to turn the fertilizer into the deep soil (generally 15 - 25 centimeters deep) to fully mix the fertilizer with the soil. The application amount of base fertilizer is generally determined according to the calcium and sulfur deficiency of the soil and the needs of crops. Usually, the application amount per mu is 50 - 150 kilograms. For plots with severe calcium and sulfur deficiency in the soil or crops that require more calcium and sulfur (such as rapeseed, cotton, tomatoes, potatoes, etc.), the application amount can be appropriately increased; for plots with high soil fertility and low fertilizer demand of crops, the application amount can be appropriately reduced.​

Topdressing Application​

During the growth period of crops, if crops show symptoms of calcium or sulfur deficiency (such as yellowing leaves, slow growth, malformed fruits, etc.), topdressing can be carried out in a timely manner to supplement the nutrients needed by crops. When applying topdressing, methods such as hole application, furrow application or broadcast application can be adopted. Hole application and furrow application are suitable for field crops and fruit trees. The specific method is: dig holes or furrows near the crop roots (generally 10 - 15 centimeters away from the crop roots), apply the calcium sulfate granular fertilizer into the holes or furrows, and then cover with soil; broadcast application is suitable for dense crops such as vegetables. The fertilizer is evenly spread between the crop rows or around the plants, and then watered to make the fertilizer dissolve and be absorbed by the crops. The application amount of topdressing is generally 10 - 30 kilograms per mu, and the specific amount is determined according to the growth status of the crops and the degree of nutrient deficiency.​

(2) Precautions​

When using calcium sulfate granular fertilizer, the following points should be noted to ensure its application effect and safety:​

Reasonably Determine the Application Amount​

Although calcium sulfate granular fertilizer has high safety, it should not be applied excessively. Excessive application will not only increase agricultural production costs, but also may lead to excessive calcium and sulfur content in the soil, affecting the absorption of other trace elements (such as iron, zinc, manganese, etc.) and causing crop nutrient imbalance. Therefore, it is best to conduct soil testing before application, and reasonably determine the application amount of calcium sulfate granular fertilizer according to the nutrient status of the soil and the fertilizer requirement law of crops.​

Pay Attention to the Combined Application with Other Fertilizers​

Calcium sulfate granular fertilizer mainly provides calcium and sulfur elements, and cannot replace macronutrient fertilizers such as nitrogen, phosphorus and potassium and other trace element fertilizers. In agricultural production, calcium sulfate granular fertilizer should be applied in combination with nitrogen, phosphorus, potassium fertilizers and other trace element fertilizers. According to the nutritional needs of crops, a scientific and reasonable fertilization plan should be formulated to ensure that crops obtain comprehensive and balanced nutrients and improve the yield and quality of crops.​

Choose the Appropriate Application Time​

Different crops have different peak absorption periods for calcium and sulfur elements. The appropriate application time should be selected according to the growth cycle and fertilizer requirement characteristics of the crops. Generally speaking, base fertilizer should be applied before crop sowing or transplanting to allow the fertilizer to fully dissolve and transform in the soil, providing nutrients for the seedling growth of crops; topdressing should be applied before the peak fertilizer requirement period of crops, such as the fruiting period of vegetables and the fruit expansion period of fruit trees, to meet the needs of crop growth for calcium and sulfur elements.​

Pay Attention to Soil Conditions​

The application effect of calcium sulfate granular fertilizer varies under different soil conditions. When applied in saline-alkali soil, it can effectively reduce the soil salinity and alkalinity and improve the soil structure; when applied in acidic soil, although it can provide calcium elements, it may increase the soil pH value. Therefore, when applying in acidic soil, the application amount should be reasonably controlled according to the degree of soil acidification and the acid tolerance of crops, and it can be applied in combination with acidic fertilizers (such as superphosphate, ammonium sulfate, etc.) to adjust the soil pH value. In addition, when applying in plots with heavy soil texture and poor air permeability, it should be combined with deep plowing and loosening the soil to improve the air permeability of the soil and promote the absorption and utilization of the fertilizer.​

Precautions for Storage and Transportation​

During the storage and transportation of calcium sulfate granular fertilizer, attention should be paid to moisture prevention, rain prevention and sun protection to avoid the fertilizer from getting damp and agglomerating or affecting the quality due to exposure to the sun. When storing, it should be placed in a dry, ventilated and cool warehouse, and the stacking height should not be too high to prevent the granules from being crushed by pressure; when transporting, a dry means of transportation should be selected to prevent the fertilizer from being wetted by rain. At the same time, it should be handled with care during handling to avoid the granules from being broken by collision and reduce dust generation.