Soil acidity and alkalinity are usually expressed by pH, which refers to the degree of acidity and alkalinity of the soil. Soil acidity and alkali are divided into 7 levels. The grading indicators are as follows: PH reflects the intensity: 4.5 is extremely acidic; 4.5 to 5.5 is strongly acidic; 5.5 to 6.5 is acidic; 6.5 to 7.5 is neutral; 7.5 to 8.5 is alkaline; 8.5 to 9.5 is strongly alkaline;
Generally, the soil in the north is neutral or alkaline, and the pH is between 7.0 and 8.5. The red soil and yellow soil in the south are mostly acidic. The pH is between 5.0 and 6.5, and the individual soil has a pH of 4.
Soil acidity and alkalinity is one of the important factors affecting the soil nutrient availability. Most nutrients are most effective or nearly highest at pH 6.5-7.0. In terms of phosphorus, when the soil pH is 5, the soil has more active iron and aluminum, and often forms iron phosphate and aluminum phosphate with less solubility in the water-soluble phosphate in the phosphate fertilizer, thereby reducing the effectiveness; Water-soluble phosphate easily interacts with free calcium ions in the soil to form calcium phosphate salts, which greatly reduces their effectiveness.
In the case of calcareous soil pH 7:5, iron is precipitated due to iron, which causes iron deficiency in crops due to reduced iron availability. The solubility of the iron salt increases as the acidity increases (pH 5 to 7.5). In strongly acidic (pH 5) soils, crops are often damaged due to the high amount of free iron.
The pH of the soil varies, and the form of certain nutrients in the soil changes, and the effectiveness of nutrients also varies. It will eventually be reflected in the absorption of nutrients by crops. Therefore, understanding the relationship between soil acidity and alkalinity and nutrient availability is beneficial to efficient fertilization.
In addition, we can also control the effectiveness of soil nutrients by regulating soil acidity and alkalinity. When improving strong acid soil; lime is usually applied. The lime requirement is the amount of lime required to be applied per acre based on the amount of potential acid. In general, strong acid soils should be applied with tens of kilograms to hundreds of kilograms of lime per acre, once every few years. When improving the strong alkaline soil, the method of applying gypsum is generally employed.
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