What are the benefits of applying lime to red soil, and how can you tell in the field whether it is needed?

Red soil is soil developed under tropical and subtropical rainforest, monsoon forest or evergreen broad-leaved forest vegetation. Sowhat are the benefits of applying lime to red soil? How can you tell in the field whether the soil needs lime?

The benefits of applying lime to red soil are:

(1) Lowering soil acidity and raising soil pH;

(2) Reducing the adsorption of phosphorus by red soil, improving the effectiveness of phosphate fertilizer, increasing the availability of elements such as calcium and magnesium in the soil, and reducing aluminum toxicity;

(3) Promoting the reproduction of microorganisms, which both favors the formation of humus and eliminates the harm of organic acids and certain toxic substances produced during the decomposition of organic matter;

(4) Promoting soil aggregation, improving soil physical properties, and favoring the growth of plant roots.

However, when applying lime to acidic soil, by no means apply it excessively or use large amounts year after year, to prevent the deterioration of soil physical and chemical properties and the reduced availability of phosphorus, iron, boron, zinc, manganese and so on.

Appendix: How can you tell in the field whether the soil needs lime?

Lime is an alkaline substance and can improve acidic soil. But too much lime can also bring adverse consequences, such as decreased soil fertility and reduced effectiveness of phosphate fertilizer. Therefore, application should be rational according to the land and the crop.

Look at the land: generally, strongly acidic soil can receive more lime; otherwise, less should be used. Whether the soil is acidic can be judged through “three observations”: first, observe whether there are acid-loving plants among the wild plants; if there are azaleas (ying shan hong), hairy chestnut and so on, it indicates that the soil is acidic; second, observe the soil color; usually acidic soil is red-yellow in color; third, observe the water quality in the field; if the irrigation water is turbid or even shows a rust film, that indicates the soil is fairly strongly acidic. For acidic soil in Zhejiang Province, when growing rice, apply 50-75 kg of lime per 667 sq m; for some cold-waterlogged fields and rust-water fields, the amount can be appropriately increased.

Look at the crop: generally, growing acid-tolerant crops such as tea and potato requires no lime application; while acid-sensitive crops such as barley and sugar beet require more lime.

As for the application method, lime is best applied together with organic fertilizer. For rice, for example, lime is often applied before transplanting when straw is returned to the field, and then plowed into the soil. For dry land, it should be applied when plowing after the previous crop is harvested, or it can be applied in bands at sowing.

In addition, lime should not be applied at the same time as ammonium sulfate or ammonium chloride, nor together with decomposed organic fertilizer, to prevent the volatilization of ammonia gas.