A. Definition and Classification of Organic Fertilizers
Organic fertilizers, broadly speaking, commonly known as farmyard manure, include materials made from various animal and plant residues or metabolites, such as human and animal feces, straw, animal remains, and slaughterhouse waste. Other categories include cake fertilizer, compost, composted manure, stable manure, biogas manure, and green manure. They primarily supply organic matter to improve soil physical and chemical properties, promote plant growth, and enhance the circulation of soil ecosystems. In a narrower sense, organic fertilizers refer specifically to fertilizers made from various animal and plant wastes, processed to eliminate harmful substances and reach harmless standards, and comply with relevant national standards and regulations.
Compost, made from crop straw, weeds, and other materials, is rich in nutrients, offers long-lasting and stable fertilizer effects, promotes the formation of soil aggregates, enhances soil water and heat retention, and compensates for the drawbacks of chemical fertilizers, such as the limited nutrient content and soil compaction. River and pond mud is an excellent fertilizer resource, providing nutrients to crops, thickening the tillage layer, improving soil physical properties, and enhancing nutrient retention. However, it is a slow-acting fertilizer and is generally applied as a base fertilizer in combination with a faster-acting fertilizer. Cake fertilizer, the residue left after oilseed oil extraction, is rich in nutrients, high in content, and long-lasting, making it suitable for all types of soil and a wide range of crops. When used as a base fertilizer or topdressing, it must be finely ground and thoroughly decomposed to avoid burning crop roots. Green manure is an organic fertilizer applied directly to the green parts of plants. It is rich in organic matter and contains nutrients such as nitrogen, phosphorus, potassium, and various trace elements. It decomposes quickly, has a rapid effect, and can improve soil structure, enhance the field microclimate, and purify the environment.
B. Differences between Organic and Chemical Fertilizers
a. Sources
Chemical fertilizers are primarily produced through chemical processing and have a relatively limited source. Organic fertilizers, on the other hand, come from a wider range of sources, commonly found in crop straw, livestock and poultry manure, green manure, and animal and plant residues. For example, in the northwestern Guizhou region, sources of organic fertilizer include manure, stable manure (cow, horse, pig, sheep, and poultry manure), fermented manure, compost, and soil-based manure.
b. Different Nutrient Composition
Chemical fertilizers contain only nitrogen, phosphate fertilizers contain phosphorus, and potash fertilizers contain potassium. Organic fertilizers contain a variety of nutrients, offering a comprehensive balance of nutrients. They contain not only organic matter, nitrogen, phosphorus, and potassium, but also a variety of trace elements. For example, cake fertilizer, the residue left after oilseed oil extraction, boasts a comprehensive nutrient profile, high content, and long-lasting effectiveness.
c. Different Impacts on Soil
Long-term application of chemical fertilizers can negatively impact soil, causing it to become “weaker with each application,” leading to compaction, decreased fertility, and an imbalance in soil nutrients. Organic fertilizers, on the other hand, contain large amounts of organic matter and have significant soil-enhancing and fertilizing effects. They improve soil aeration, promote the formation of a healthy soil structure, and help regulate and stabilize soil heat, water, air, and fertilizer factors. For example, if you apply large amounts of well-composted organic fertilizer for more than three consecutive years, the soil will become increasingly fertile.
d. Different Fertilizer Efficiency
Chemical fertilizers are characterized by high nutrient content, rapid effects, and short-term effects. Therefore, they should not be applied in excessive amounts at a time, nor should they be applied in large quantities over a long period of time. Organic fertilizers have a slower onset but a longer-lasting effect. They can be applied in large quantities and continuously for long periods of time. The more organic fertilizer you use, the more beneficial it is for improving soil fertility.
e. Different Application Methods
Organic fertilizers are primarily used as base fertilizers and must be fermented before use. Most of the nutrients they contain are organic nitrogen, primarily in the form of protein, and phosphorus, primarily in the form of phospholipids. These nutrients are not easily absorbed and utilized by crops. Therefore, they must be fermented and composted before application to convert the nutrients into inorganic, soluble nutrients before they can be absorbed and utilized by crops. Chemical fertilizers are primarily used as topdressing, and inorganic fertilizers can be applied directly as topdressing.
f. Different Environmental Impacts
Organic fertilizers use the excrement or remains of organisms as fertilizers. They are highly compatible with the environment and do not pollute it. Chemical fertilizers are high-purity inorganic salts buried in the soil. Due to their high concentration, they can easily disrupt the soil’s acid-base balance, causing environmental damage.
g. Different Impacts on Agricultural Product Quality
Organic fertilizers are derived from nature and contain no synthetic chemicals. Long-term application can improve agricultural product quality. Chemical fertilizers are purely synthetic chemicals, and improper application can reduce agricultural product quality.
In summary, organic fertilizers and chemical fertilizers differ significantly in many aspects. In agricultural production, they should be used in appropriate combinations based on specific circumstances to achieve optimal planting results.
C. The Role of Organic Fertilizers
a. Increasing Soil Organic Matter
Organic fertilizers play a crucial role in increasing soil organic matter. Increasing the application of organic fertilizers can gradually increase soil organic matter content, as soil organic matter is the driving force behind almost all nutrient cycling reactions. In addition to providing carbon, energy, fluorine, and phosphorus sources necessary for plant growth, some organic matter components in organic fertilizers also have the ability to neutralize toxicity. Crops grown in soils rich in organic matter and with normal mineralization, as well as soils fertilized with organic fertilizers, are generally less likely to suffer from trace element deficiencies. The products of soil organic matter decomposed by microorganisms and secretions from plant roots can act on soil minerals and promote their dissolution. Organic matter also significantly affects the soil’s cation exchange capacity, increasing its ability to absorb and retain nutrients and significantly buffering and stabilizing soil pH.
b. Increasing Soil Nutrients
Organic fertilizers contain essential nutrients for crop growth, and each nutrient has its own unique characteristics. For example, manure is rich in nitrogen and phosphorus, as well as various trace nutrients such as boron, manganese, copper, molybdenum, and zinc. Organic fertilizers offer a comprehensive range of nutrients and are easily decomposed. The content and ratio of their nutrients are ideal for crop absorption and utilization. Applying organic fertilizers not only replenishes soil nutrients but also, through the perspective of nutrient recycling, regenerates nutrients absorbed by crops from the soil, reducing soil nutrient deficits and improving soil fertility. Research has shown that applying organic fertilizers can increase the availability of soil trace elements such as zinc, manganese, and iron, compensating for nutrient deficiencies in the crop rhizosphere and helping to improve the micronutrient status of crops. Organic fertilizers contain a variety of organic nutrients, including amino acids, proteins, sugars, fats, and humic acid. Some of these nutrients can be directly absorbed and utilized by plants, while others can be absorbed and utilized after decomposition. They are important sources of nutrients for crops and are crucial for improving crop quality. Applying organic fertilizers introduces a large number of microorganisms and enzymes into the soil, promoting the growth and reproduction of soil microorganisms, increasing enzyme activity, accelerating the decomposition and transformation of organic matter, and activating soil nutrients, releasing some fixed elements for crop absorption and utilization. This improves soil nutrient availability and enhances its fertility capacity.
c. Promotes Soil Metabolism
Organic fertilizers promote soil metabolism. The CO₂ produced by the decomposition of organic fertilizers is a significant source of CO₂ in the soil. Applying organic fertilizers increases the soil’s CO₂ release capacity, providing abundant CO₂ nutrients that can be directly absorbed and utilized by plants, thereby improving crop photosynthetic efficiency and increasing yield. The decomposition of organic matter produces CO₂, which green plants use through photosynthesis to synthesize organic matter. This process is of great significance in material circulation and bioenergy conversion. Furthermore, increased soil CO₂ content promotes gas exchange between the soil and the environment, improving soil absorption and enhancing the balance between the soil’s solid, gas, and liquid phases, thus providing favorable conditions for plant growth. Organic fertilizers introduce a large number of enzymes and microorganisms into the soil, adding new life to the soil. This promotes the continuous decomposition and conversion of organic matter into nutrients for plant absorption and utilization, while also continuously producing new compounds, contributing to the continuous accumulation of nutrients in the soil. Microorganisms also release nutrients fixed in the soil and absorb nutrients that are easily leached, thereby improving the soil’s ability to provide and retain nutrients.
d. Enhances crop resistance to stress
Organic fertilizers contain biological substances and antibiotics, which can enhance crop resistance to stress and its ability to adapt to adverse environments. Regarding drought resistance, organic fertilizers can improve soil structure and enhance its water retention capacity. Organic fertilizers also increase soil humus. The lipids, resins, and waxes contained in nonspecific humus, when absorbed by soil aggregates, enhance water flow, reduce soil infiltration, capillary movement, and evaporation, effectively improving crop drought resistance. Organic fertilizers can also play a role in cold tolerance, helping crops better adapt to low-temperature environments.
Organic fertilizers are expected to play a greater role in agricultural production. With the combined effects of continued market demand, technological innovation, and policy support, organic fertilizers will gradually replace other fertilizers and become essential, making a greater contribution to achieving sustainable agricultural development.
