Topdressing requires checking acidity and alkalinity; clarifying this point before fertilizing is crucial

Soil can be acidic or alkaline, and in fact, chemical fertilizers can be too. However, many farmers buy and apply chemical fertilizers caring only about nutrient content and the nitrogen-phosphorus-potassium nutrient ratio, which leads to poor fertilization results.

The acidity and alkalinity of chemical fertilizers can be divided into two types: chemical acidity/alkalinity and physiological acidity/alkalinity. Ammonium sulfate, superphosphate and others dissolve in water to become acidic or weakly acidic; ammonia water, potassium carbonate and others dissolve in water to become alkaline or weakly alkaline; urea, potassium sulfate, calcium nitrate and others dissolve in water to become neutral, so they respectively belong to chemically acidic/alkaline/neutral fertilizers. Ammonium bicarbonate, urea and others, after being applied to soil and absorbed and used by plants, leave the soil neutral or nearly neutral, so they are classified as physiologically neutral fertilizers.

The acidity and alkalinity of soil can affect both the dissolution and precipitation of nutrients in the soil and the activity of microorganisms, indirectly affecting the availability of soil nutrients. On acidic soil, alkaline or physiologically alkaline fertilizers must be chosen, such as calcium nitrate, ammonia water, calcium magnesium phosphate and others; while in alkaline soil, acidic and physiologically acidic fertilizers such as superphosphate, ammonium sulfate, ammonium chloride and others should be applied.