Characteristics and Scientific Application Methods of Calcium-Magnesium-Phosphorus-Potassium Fertilizer

Calcium-magnesium-phosphorus-potassium fertilizer is a multi-element fertilizer based mainly on phosphorus and potassium nutrients while also containing calcium, magnesium, silicon and various other medium and trace elements. It is usually made from phosphate rock combined with potassium-bearing and magnesium-bearing minerals, processed through high-temperature melting, water quenching for rapid cooling, and fine grinding. It generally appears as a grayish-white, grayish-green or dark gray powder, with stable physical properties; it does not readily absorb moisture or cake, making it easy to store and transport.

In terms of its nature, it is a weakly alkaline citrate-soluble slow-release fertilizer. The nutrients it contains are insoluble in water but soluble in weak acids. After application to the soil, they are gradually released by relying on the acidic substances secreted by crop roots and on soil acidity, so the fertilizer effect is steady and long-lasting, and the nutrients are not easily lost with water. Its application effect is especially pronounced on acidic and slightly acidic soils, as it can both supplement phosphorus and potassium and neutralize soil acidity and improve the soil.

When used, it is mostly applied as a base fertilizer and seed fertilizer, and it is best applied early and deep, generally plowed into the plow layer together with tillage so that the roots come into full contact with the fertilizer. Crops such as rice, beans, rapeseed and fruit trees in the red soil and yellow soil regions of southern China have relatively high demands for calcium, magnesium and silicon, and the application effect is comparatively better. When applied together with decomposed farmyard manure, the organic acids can also promote the decomposition of nutrients and increase the fertilizer use efficiency.

It should be noted that calcium-magnesium-phosphorus-potassium fertilizer takes effect relatively slowly and is not suitable as an emergency means of quickly supplementing phosphorus and potassium. When a topdressing is urgently needed, water-soluble fertilizers can be used together with it, or foliar spraying can be adopted as a supplement. In addition, because it is alkaline, it should be avoided from being stored or applied directly mixed with fertilizers that decompose easily, such as ammonium nitrogen fertilizers, so as to prevent nutrient loss. For daily storage, keeping it dry and ventilated is sufficient; long storage generally does not affect the fertilizer effect.