Basic knowledge of soil: Analyzing the aging of dryland soil

Soil is the "foundation" of crop growth, and dryland soil is prone to acidification and aging due to nutrient loss and salt leaching, which in turn hinders crop growth. This article provides a detailed explanation of its acidification mechanism, improvement plan, and precautions, providing practical guidance for safeguarding the vitality of dryland soil.
(1) What is the aging of dryland soil
Compared to paddy soil that is constantly affected by water and in a state of restoration at any time, dry field soil, although not affected by iron and manganese loss, can lose topsoil or nutrients due to rainwater, making the land barren.
In recent years, a large amount of fertilization, combined with rainfall, has led to the loss of calcium, magnesium and other salt bases, resulting in acidic soil and poor crop growth. This is also a phenomenon of soil aging.

Most plants can grow smoothly when the soil is slightly acidic to neutral; But once the soil becomes acidic, the growth of crop roots is hindered.
In addition, acidic soil can make phosphoric acid insoluble, while aluminum, iron, manganese, and other substances become soluble, causing crops to lack or excessively absorb specific substances, resulting in physiological disorders that prevent normal growth.
(2) The mechanism of acidification
The mechanism that promotes soil acidification is as follows.
The fine soil colloids that make up the soil have a negative charge on their surface and can absorb positively charged cations. Soil suitable for crop production, soil colloids will adsorb salt based cations (calcium, magnesium, potassium, ammonium, sodium, etc.), resulting in a balanced potential.
On the other hand, carbon dioxide in the air will dissolve in rainwater, forming a faint carbonated water containing carbonate ions and hydrogen ions. The strength of ions adsorbed by soil is in the order of hydrogen>calcium>magnesium>potassium, ammonia>sodium. Therefore, when rainwater seeps into the soil, hydrogen ions will detach the salt base originally adsorbed on soil colloids and adsorb themselves on soil colloids (ion exchange, displacement), causing the soil to gradually become acidic.
In addition, if a large amount of chemical fertilizers containing acidic ions such as sulfuric acid are applied, or if water containing acidic substances is used for irrigation, it will also cause the salt bases originally adsorbed on soil colloids to replace with hydrogen ions, promoting soil acidification.
(3) Improvement and precautions for acidity
The improvement of soil acidity is relatively easy, as long as salt matrix materials are applied. The commonly used materials are calcareous materials such as calcium carbonate, clay materials such as magnesium sulfate, or clay lime containing both of the above.
Colloids in acidic soil can adsorb hydrogen ions, and once bitter ash is applied, hydrogen ions will replace calcium and magnesium ions to form neutral colloids, keeping the pH value in a normal state.

However, if a large amount of lime material is applied at once, the soil colloids will become excessively saturated, and the free salt radicals will increase, making the soil alkaline. Improving alkaline soil is very troublesome, please be careful not to apply too much. If too much is applied at once, crops may suffer from manganese or iron deficiency problems, and special attention must be paid.