Magnesium fertilizer is indispensable for southern red soil

Magnesium, as a necessary medium element for plants, plays an important role in plant metabolism and growth. Due to the high temperature and rain in the red soil region of southern China, the weathering of magnesium minerals in the soil and the leaching of magnesium in the soil are strong, resulting in weak soil magnesium supply, and the symptoms of magnesium deficiency in crops in many areas.
The field results of 236 crops of 22 crops in five major categories: cash crops, oil crops, food crops, vegetable crops and fruits showed that the application of magnesium fertilizer in the soil can improve crop yield and quality. About 25% of dry land (including gardens, woodlands, and available barren hills) in southern red soils is deficient in magnesium, covering an area of ​​300 million mu. Generally, about 4 kg of magnesia is applied per mu, which can greatly improve the utilization efficiency of nitrogen, phosphorus and potassium nutrients, which can increase the yield by about 12% and increase the pure income by 60~125 yuan/mu. Calculated according to the average income of 80 yuan per mu, 300 million mu of magnesium-deficient dry land can create economic benefits of more than 24 billion yuan.
The technical points for effective application of magnesium fertilizer are as follows: 1. Consider the effective magnesium content of the soil. Magnesium fertilizer was negatively correlated with crop availability and soil available magnesium. When the effective magnesium in the soil is less than 25 mg/kg, the yield increase of magnesium on soybeans, peanuts and tea leaves is large, ranging from 9.8% to 40.2%. When the soil available magnesium is less than 50 mg / kg, the application of magnesium fertilizer has different degrees of stimulation, an increase of 2.7% to 11.2%.
2. Consider the interaction between potassium and magnesium. The effect of applying magnesium is limited by the application of potassium in the soil. After a large amount of potassium is applied to the soil, the amount of magnesium in the soil is insufficient. The potassium and magnesium in the soil have a mutual restriction effect. The suitable ratio of potassium to magnesium is the basis for high yield and high efficiency. After repeated field trials, the suitable potassium and magnesium ratio is 3.3, cassava 5.1, peanut, soybean 2.1, jute, sweet potato 2.4, and watermelon 1.7.
3. Consider crop types and magnesium fertilizer requirements. The yield-increasing effect of magnesium fertilizer is related to the magnesium requirement of different crops and the sensitivity to magnesium levels. Flue-cured tobacco is sensitive by magnesium application, followed by rapeseed and soybean, and the sensitivity of wheat is low.
4. To choose the appropriate magnesium fertilizer variety. Different magnesium fertilizer varieties have different properties and different application effects. Magnesium carbonate (magnesia powder) and magnesium oxide were best applied on red soil, and the dry matter yield of crops increased by 76.1% and 87.3%. Secondly, magnesium sulfate and sepiolite powder (magnesium-rich fibrous silicate) increased respectively. 31.0% and 22.5%; magnesium chloride is the worst.



Author: Soil and Fertilizer Institute of Chinese Academy of Agricultural Sciences researcher Xu Gang
Source: Farmers Daily
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