As an important resource in agricultural production, the core value of organic fertilizers lies in providing comprehensive and balanced nutrients for crops, while improving soil structure and promoting ecological circulation. Compared with chemical fertilizers, organic fertilizers release nutrients more slowly and last longer, and can significantly improve the soil’s ability to retain water and fertilizer. So, what nutrients do organic fertilizers contain that are essential for crop growth? How do these ingredients act on different growth stages of crops? The following will be analyzed in detail from the source of organic fertilizers, main nutrients and their mechanism of action.
- Main sources and composition of organic fertilizers
Organic fertilizers usually come from animal and plant residues, excrement or fermented organic waste. They are complex and rich in multiple nutrients. According to research data, common organic fertilizers such as livestock and poultry manure, compost, green manure, etc., can be divided into the following categories:
a. Macronutrients: Nitrogen (N), phosphorus (P), and potassium (K) are the three basic elements for crop growth.
Nitrogen: mainly promotes leaf and stem growth, and is key to protein and chlorophyll synthesis. For example, the nitrogen content of decomposed pig manure is about 0.5%~1.5%, while the nitrogen content of leguminous green manure (such as astragalus) can reach 3%~4%.
Phosphorus: participates in energy transfer and root development, and is commonly found in bone meal (containing 11%~15% phosphorus) and poultry manure.
Potassium: enhances crop resistance and regulates water metabolism. The potassium content of wood ash is relatively high, reaching 5%~10%.
b. Medium elements: calcium (Ca), magnesium (Mg), sulfur (S), etc. are essential for crop physiological functions.
Calcium can prevent fruit cracking (such as tomato navel rot), and is commonly found in eggshell powder and lime organic fertilizers;
Magnesium is the core component of chlorophyll, and its content is relatively high in straw fertilizers;
Sulfur participates in amino acid synthesis, and the sulfur content in decomposed cow dung is about 0.1%~0.5%.
c. Trace elements: Although the demand for iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo) and other trace elements is small, they are indispensable.
For example, boron affects pollen development, and boron deficiency will cause rapeseed to “flower but not fruit”; the zinc and iron content in earthworm manure is high, which can effectively prevent crop chlorosis.
d. Organic matter and microorganisms: 30%~60% of organic fertilizers are organic matter, including humic acid, cellulose, etc., which can improve the soil aggregate structure; at the same time, the probiotics it carries (such as nitrogen-fixing bacteria and phosphate-dissolving bacteria) can activate inert nutrients in the soil.
- Nutritional characteristics and applicable scenarios of different organic fertilizers
a. Livestock and poultry manure (such as chicken manure, cow manure):
Chicken manure has high nitrogen and phosphorus content, but it needs to be fully decomposed to avoid root burning, which is suitable for leafy crops;
Cow manure is rich in organic matter but low in nutrients, which is suitable for improving heavy clay soils.
b. Compost and green manure:
Straw compost has a high carbon-nitrogen ratio (C/N) and is suitable for use with high-nitrogen fertilizers;
Green manures such as astragalus can directly supplement soil nitrogen through biological nitrogen fixation, reducing dependence on chemical fertilizers.
c. Industrial by-products (such as sugar residue and mushroom residue):
Sugar residue is rich in potassium and is suitable for fruit trees during the fruit expansion period;
Mushroom residue contains mycelium residues, which can significantly increase the activity of soil microorganisms.
- Mechanism of action and scientific application of organic fertilizers
a. Slow-release effect: The nutrients of organic fertilizers can only be absorbed after being decomposed by microorganisms, so the fertilizer effect can last for 2 to 3 months. For example, applying 2 tons of decomposed pig manure per mu can meet about 60% of the nitrogen demand of a season of rice.
b. Soil improvement: The porosity of soil that uses organic fertilizers for a long time can be increased by 20% to 30%, and the activity of heavy metals can be reduced by more than 50% (quoted from the 2024 Soil Remediation Report of the Ministry of Agriculture and Rural Affairs).
c. Application skills:
Deep application of base fertilizer: bury organic fertilizer 15-20 cm into the soil layer to avoid nutrient loss;
Match with inorganic fertilizer: supplement quick-acting fertilizer during the critical growth period of crops (such as heading period);
Control dosage: The recommended dosage of fruits and vegetables is 3-5 tons per mu, and excessive dosage can easily lead to leggy growth.
- Limitations and development prospects of organic fertilizers
Although organic fertilizers have significant advantages, their unstable nutrient content and high transportation costs are still difficult to promote. At present, “biological organic fertilizers” (such as fertilizers with added phosphate-solubilizing bacteria) produced by microbial fermentation technology are becoming a research hotspot, and their nutrient utilization rate can be increased by more than 30%. In the future, with the popularization of the “combination of planting and breeding” model, organic fertilizers will play a more core role in green agriculture.
Organic fertilizers are the link between natural cycles and modern agriculture, and their comprehensive nutrition far exceeds that of chemical fertilizers. Scientifically understanding its composition and action rules is a key step in achieving the goal of “reducing fertilizers and improving quality”.
