Fertilizers are fundamental agricultural substances that provide essential nutrients to crops and improve soil properties. They are classified into three main categories based on their composition: organic fertilizers, inorganic fertilizers, and bio-fertilizers. Inorganic fertilizers include nitrogen fertilizers, phosphorus fertilizers, potassium fertilizers, and compound fertilizers.
Let’s look at the differences between organic fertilizers and chemical fertilizers:
Compared to chemical fertilizers, organic fertilizers contain a wider variety of nutrients, including nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, and trace elements; while chemical fertilizers are relatively simple, with a limited range of nutrient types. However, although organic fertilizers contain a complete range of nutrients, their concentrations are relatively low. For example, chicken manure contains approximately 1.6% nitrogen, 1.5% phosphorus, and 0.9% potassium, meaning 100 kg of chicken manure contains 1.6 kg of nitrogen (N), 1.5 kg of phosphorus (P₂O₅), and 0.9 kg of potassium (K₂O). Chemical fertilizers contain 46% nitrogen in urea (46 kg of nitrogen per 100 kg of urea) and 60% potassium in potassium (60 kg of potassium chloride per 100 kg of potassium chloride). The nutrient concentration in chemical fertilizers is much higher than that in organic fertilizers.
Organic fertilizers contain a large amount of organic matter, which chemical fertilizers lack. Organic fertilizers, after being applied to the soil, must undergo microbial decomposition and decay before releasing nutrients for crop absorption, while chemical fertilizers can exert their effects immediately upon application.
Therefore, organic fertilizers contain a variety of nutrients, have low concentrations, and release nutrients slowly; chemical fertilizers, on the other hand, contain a single type of nutrient, have high concentrations, and release nutrients quickly. Both have their advantages and disadvantages. Organic fertilizers should be used in combination with chemical fertilizers to maximize their benefits and minimize their drawbacks.
The functions of organic fertilizers:
(1) Improving soil and enhancing soil fertility. The main component of organic fertilizers is organic matter, and applying organic fertilizers increases the organic matter content in the soil. Organic matter can improve the physical, chemical, and biological properties of soil, mature the soil, and enhance soil fertility.
(2) Increase crop yield and improve the quality of agricultural products. Organic fertilizers not only contain nutrients such as nitrogen, phosphorus, and potassium, but also various sugars and amino acids, which not only provide nutrition for crops but also promote the activity of soil microorganisms.
Organic fertilizers also contain various trace elements, such as 2.2–2.4 grams of boron, 2.9–29.0 grams of zinc, 14.3–26.1 grams of manganese, 0.3–0.4 grams of molybdenum, and 2.9–29.0 grams of available iron per 100 kg of livestock and poultry manure. The combined application of organic and chemical fertilizers significantly increases yield and improves product quality, reducing nitrate and nitrite content in vegetables, increasing vitamin C content, and increasing sugar content in fruits and vegetables. Some organic fertilizers, such as straw, peat moss, and compost, are more effective at improving soil fertility and improving soil quality. Others, like human and chicken manure, primarily supply nutrients to crops. This difference mainly depends on the ratio of organic matter to nitrogen content in the different organic fertilizers.
The structural component of organic matter is primarily carbon (C), so this ratio is called carbon-nitrogen ratio (C/N). Organic fertilizers with a C/N ratio greater than 30 primarily improve the soil, while those with a C/N ratio less than 30 primarily supply nutrients. Crop straw has a C/N ratio of around 100. When applied to the soil, it greatly improves the soil. However, because it contains very little nitrogen, it not only fails to release nitrogen during decomposition but also absorbs nitrogen from the soil. In some areas, chemical nitrogen fertilizers are applied when returning straw to the field to accelerate the decomposition process.
