Why should chemical fertilizers and organic fertilizers be applied in combination?
Uncomposted organic fertilizer carries a large number of pathogenic microorganisms and parasitic roundworm eggs. After being applied to farmland, some of them attach to crops and cause direct contamination, while some enter the soil and cause indirect contamination. In addition, after uncomposted organic fertilizer is applied to the soil, it must undergo fermentation before it can be absorbed and used by crops,...
Applying chemical fertilizers in combination with organic fertilizers is a science-based fertilization decision. This is determined by the properties and characteristics of organic fertilizers and chemical fertilizers. The characteristics of organic fertilizers and chemical fertilizers are compared and analyzed as follows: (1) High-quality organic fertilizers mostly contain large amounts of organic matter. Applying high-quality organic fertilizers year after year can not only increase the organic matter content of the soil, but also enable soil organic matter to be continuously renewed, thereby improving the physical and chemical properties of the soil, and thus having a clear soil-improving effect. Chemical fertilizers, by contrast, do not contain organic matter and generally have no direct soil-improving effect. This shows that organic fertilizers are the basic material for building high-yield and stable-yield farmland.
(2) There are many kinds of organic fertilizers, and the nutrients they contain are comprehensive, so people often call them complete fertilizers. However, the nutrient content of organic fertilizers is very low. About 1000 kg of high-quality barnyard manure contains only 5 kg of nitrogen (N). Chemical fertilizers, by contrast, have a high nutrient content. For example, 100 kg of urea contains 46 kg of nitrogen. Calculated on a 1000 kg basis, it contains 460 kg of nitrogen, which is 92 times that of barnyard manure. However, the shortcoming of chemical fertilizers is that the types of nutrients they contain are relatively limited. Take urea for example: it contains only nitrogen among the three major elements nitrogen, phosphorus, and potassium, and does not contain phosphorus or potassium, while calcium superphosphate contains only phosphorus and does not contain nitrogen or potassium. Applied alone, they cannot meet the needs of crops.
(3) Most of the nutrients in organic fertilizers are in organic form and must be continuously decomposed by soil microorganisms before they can be transformed into nutrients that crops can absorb and use. Therefore, organic fertilizers have a slow fertilizer effect, but it lasts a long time and has residual effects. In contrast, most of the nutrients contained in chemical fertilizers are water-soluble and can be directly absorbed and used by crops. Therefore, chemical fertilizers have a rapid fertilizer effect and take effect quickly, and can provide more nutrients when crops most need them, but their fertilizer effect is short and cannot last. It can thus be seen that rational application of chemical fertilizers is the material guarantee for increasing crop yield per unit area.
(4) Organic fertilizers must undergo decomposition and transformation before they can release nutrients for crops to absorb. Therefore, the utilization rate of organic fertilizers in the current season is not high. For example, the nitrogen utilization rate of decomposed organic fertilizer is only 20%-30%, but when it decomposes, nutrient loss is small and the nutrient supply period is long. In contrast, the nutrient content of chemical fertilizers is high, and most of it is readily available nutrients, which are easily lost through volatilization, leaching (especially nitrogen fertilizer), and other pathways, resulting in a low fertilizer utilization rate in the current season. For example, the nitrogen fertilizer utilization rate is generally about 35%, phosphate fertilizer about 10%-25%, and potassium fertilizer above 40%.
From the comparison between the two, it is not difficult to see that organic fertilizers and chemical fertilizers each have advantages and disadvantages, and some advantages of organic fertilizers are precisely the disadvantages of chemical fertilizers, while some advantages of chemical fertilizers are precisely the disadvantages of organic fertilizers. Therefore, applying the two in combination can draw on each other's strengths to offset their weaknesses and give full play to their respective characteristics. This is the necessity and scientific rationale for applying the two in combination.