Topdressing depends on acidity and basicity.

Soil can be divided into acidity and alkalinity. In fact, there are also chemical fertilizers. However, many farmers only care about the nutrient content and the nutrient distribution ratio of nitrogen, phosphorus and potassium when they buy and apply chemical fertilizer, which leads to poor fertilization effect.

The acidity and alkalinity of chemical fertilizer can be divided into chemical acidity-alkalinity and physiological acidity-basicity. Ammonium sulfate and calcium superphosphate are acidic or weakly acidic in water, ammonia and potassium carbonate are alkaline or weakly alkaline in water, and urea, potassium sulfate and calcium nitrate are neutral in water, so they belong to chemical acid / alkaline / neutral fertilizers respectively. Ammonium bicarbonate, urea and so on, after the soil is absorbed and utilized by plants, the soil is neutral or close to neutral, so it belongs to physiological neutral fertilizer.

Soil acidity and basicity can not only affect the dissolution and precipitation of soil nutrients, but also affect the activities of microorganisms, and indirectly affect the availability of soil nutrients. Alkaline or physiologically alkaline fertilizers must be selected in acidic soils, such as calcium nitrate, ammonia, calcium magnesium phosphate, etc., while in alkaline soils, acidic and physiologically acidic fertilizers such as calcium superphosphate, ammonium sulfate and ammonium chloride should be applied.