Can organic fertilizer replace chemical fertilizer?

Organic fertilizers, also known as farmyard manure, include human and animal excrement and urine, green manure, compost and other miscellaneous soil fertilizers. Chemical fertilizers are inorganic fertilizers. Nitrogen fertilizers include ammonium sulfate, ammonium nitrate, urea, ammonium bicarbonate and ammonia water. Phosphorus fertilizers include superphosphate and calcium magnesium phosphate. Potassium fertilizers include potassium sulfate, potassium chloride and potassium nitrate. There are also compound fertilizers and trace element fertilizers. 
Before the advent of chemical fertilizers, all the fertilizers used in rural areas were organic manure. Whether as base fertilizer or top dressing, they were all made from the excrement of domestic animals such as cattle, sheep and pigs, and from the bedding of straw and weeds trampled by domestic animals. At that time, the more large livestock a household raised, the more organic manure it had, and the higher the grain yield was.

Before the 1970s, there were no chemical fertilizers. Oil cakes (rapeseed cake, soybean meal, peanut meal, cottonseed cake, sesame cake, tea seed cake, etc.) were mainly used as top dressing. The oil cake powder was finely ground and mixed with bone meal for thorough fermentation, and then a certain amount of chemical fertilizer was added as top dressing. Due to the different varieties of oil cakes and the different methods of pressing and extracting, the content of various nutrients varies. Generally, oil cakes contain 75-86% organic matter and are organic fertilizers with relatively high nitrogen content, and also contain a considerable amount of phosphorus, potassium and trace elements. For example, tea seed cake contains 80% organic matter, 4.6% nitrogen, 2.5% phosphorus and 1.4% potassium, and is therefore called "fine fertilizer". 
The nitrogen and phosphorus in cake fertilizer are mostly in organic form and must be decomposed by microorganisms before they can be absorbed and utilized by crops. Rapeseed cake decomposes quickly and its fertilizer effect is both fast and long-lasting after a little fermentation. In the past, due to the lack of advanced planting techniques, good seeds and chemical fertilizers, the grain output was low and unstable, only about half of the current output. Organic fertilizer mainly has the disadvantages of low nutrient content, slow fertilizer effect and large application amount, generally more than 2,000 kilograms per mu each time. Chemical fertilizer, on the other hand, has the advantages of high nutrient content, fast fertilizer effect and small application amount.

Since the widespread use of chemical fertilizers in the 1980s, agricultural production has continued to increase year after year. The use of chemical fertilizers has raised agricultural production to a new level, and the effect on increasing crop yields is very significant. However, chemical fertilizers have certain drawbacks. First, chemical fertilizers cannot enrich the soil. Long-term use of chemical fertilizers can cause soil compaction. The current farmland is getting thinner and thinner with lower soil fertility. Second, if the amount of chemical fertilizer applied this year is lower than that of last year, farmers will have difficulty increasing production. Third, agricultural production relies entirely on chemical fertilizers. Due to the general shortage of nitrogen in the soil, the yield of crops increases significantly after applying nitrogen fertilizer, but the consumption of soil organic matter and other nutrients also increases, and phosphorus and potassium fertilizers cannot be replenished. The proportion and dosage are out of balance, and deficiency symptoms and physiological diseases of crops have emerged in some areas one after another. If the amount of chemical fertilizers does not continue to increase, crop yields cannot achieve high yields. Therefore, the application amount of chemical fertilizers has been increasing year by year. Fourth, because the application amount of chemical fertilizers per mu is small, even the base fertilizer now uses chemical fertilizers, the organic matter in the soil is lacking. Fifth, due to the heavy reliance on chemical fertilizers, the demand is increasing year by year, and the prices are increasing year by year, resulting in an increase in the cost of agricultural production and a decrease in profits year by year.

Organic fertilizers cannot completely replace chemical fertilizers. Farmyard manure can only be used as base fertilizer. Topdressing still requires chemical fertilizers. Without chemical fertilizers, it is very difficult to achieve high yields. Organic fertilizers have been used in China for over 4,000 years. The ability to maintain certain agricultural yields and ecological balance is inseparable from the long-term use of organic fertilizers. Organic fertilizers can balance soil nutrients. After the 1970s, the amount of chemical fertilizers used in China increased sharply, accounting for approximately 20% of the world's nitrogen fertilizer usage. Due to the widespread nitrogen deficiency in the soil, the yield of crops increased significantly after applying nitrogen fertilizers. However, this also led to an increase in the consumption of soil organic matter and other nutrients. Phosphorus and potassium fertilizers could not be replenished, and the proportion and dosage were out of balance. Symptoms of nutrient deficiencies and physiological diseases of crops appeared in some areas. If the amount of chemical fertilizers did not continue to increase, crop yields could not achieve high levels. Therefore, the amount of chemical fertilizers used has been increasing year by year. Only by using organic fertilizers and chemical fertilizers in combination can the effect of balanced nutrients be achieved.