Many farmers buy chemical fertilizers and apply chemical fertilizers. They basically do not consider the acidity and alkalinity of cultivated soil, and do not consider the acidity and alkalinity of chemical fertilizers. They only consider the nutrient content of chemical fertilizers and the ratio of N, P, K, which results in poor fertilization. In fact, mastering the acidity and alkalinity of fertilizers is very helpful for rational fertilization.
Chemical acidity refers to the acidity and alkalinity of the fertilizer dissolved in water. Such as ammonium sulfate, superphosphate and other chemical acidic fertilizers; ammonia, potassium carbonate and other chemical alkaline fertilizers; urea, potassium sulfate and other chemical neutral fertilizer.
Physiological acidity refers to the acidity and alkalinity of the soil after the fertilizer is applied to the soil and absorbed by the crop. According to this, fertilizers can be divided into physiological acidic fertilizers, physiological alkaline fertilizers, and physiologically neutral fertilizers. Ammonium sulfate is a commonly used nitrogen fertilizer that can be decomposed into ammonium and sulfate ions in soil after application. Although both of these ions can be absorbed and utilized by plants, the amount of ammonium ions absorbed by plants is much greater than that of sulfate. Therefore, most of the sulfate is left in the soil. When the plant absorbs ammonium ions, it releases hydrogen ions and makes the soil acidic, so it is called physiological acidic fertilizer. After sodium nitrate, calcium nitrate and other fertilizers are applied to soil, the soil is alkaline, which is called physiological alkaline fertilizer. Ammonium bicarbonate, urea, etc., applied to the soil, the soil appears neutral or close to neutral, called physiological neutral fertilizer.
The pH of the soil can directly affect the dissolution and sedimentation of nutrients in the soil, and can also affect the activities of microorganisms, indirectly affecting the effectiveness of soil nutrients. In acidic soils, soluble phosphorus easily combines with iron and aluminum to form iron phosphate and aluminum phosphate, which reduces effectiveness. Exchangeable potassium, calcium, magnesium, etc. in the soil are easily replaced by hydrogen ions and will be lost as soon as rain is encountered. Acidic soils also often lack sulfur and molybdenum. Therefore, alkaline or physiological alkaline fertilizers such as calcium nitrate, ammonia, ammonium bicarbonate, calcium magnesium phosphate, etc. must be used on acidic soils.
In alkaline soils, especially calcareous soils, soluble phosphorus is easily combined with calcium to form insoluble calcium phosphate salts, which will reduce the availability of phosphorus and the effectiveness of many trace elements such as boron, manganese, molybdenum, zinc, and iron. It will also be greatly reduced, resulting in the crops often feel that these nutrients are insufficient, and various physiological diseases occur. Therefore, acidic and physiological acid fertilizers such as calcium superphosphate, ammonium sulfate, and ammonium chloride should be applied to calcareous or alkaline soils to increase the acidity of the soil, so that phosphorus is not easily combined with calcium to form insoluble calcium phosphate salts, which reduces The availability of phosphorus can also increase the effectiveness of boron, manganese, molybdenum, zinc, iron, and copper. On the contrary, it will cause secondary salinization, structural deterioration and fertility degradation of the soil.
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