Abstract: The acidic substance is derived from the carbonic acid dissolved in water and the organic acid produced by the decomposition of organic matter, as well as the inorganic acid produced by oxidation, as well as the acidic substance added by fertilization. The alkaline substance is mainly derived from sodium carbonate and carbonic acid in the soil. Salts such as sodium hydrogen and calcium carbonate.
Due to the difference in climate between the north and the south of China, the south is humid and rainy, the soil is mostly acidic, the north is dry and rainless, and the soil is mostly alkaline. Soil partial (over) acidic or partial (over) alkaline, will reduce the effectiveness of soil nutrients to varying degrees, the specific performance has the following five aspects:
One is to reduce the effectiveness of soil nutrients. The effectiveness of phosphorus in soil is obviously affected by acidity and alkalinity. When the pH exceeds 7.5 or lower, phosphoric acid and calcium or iron and aluminum form a delayed state, which reduces the effectiveness. Calcium, magnesium and potassium are easily replaced in acidic soils and are easily leached. Calcium and magnesium have low solubility and strong effectiveness in strongly alkaline soils. Trace elements such as boron, manganese and copper are greatly less effective in alkaline soils, and the precipitation of molybdenum in strongly acidic soils with free iron and aluminum reduces the effectiveness.
2. It is unfavorable for the benign development of the soil and destroying the soil structure. Strong acid soil and strong alkaline soil have more hydrogen and sodium, but calcium is lacking, it is difficult to form a good soil structure, which is not conducive to crop growth.
3. It is an activity that is unfavorable to soil microorganisms. The most suitable pH for soil microorganisms is a neutral range between 6.5 and 7.5. Both peracids and overbases severely inhibit the activity of soil microbes, thereby affecting the conversion and supply of nitrogen and other nutrients.
4. It is the growth and development of unfavorable crops. General crops are most suitable for growth in neutral or near-neutral soils. Beet, sable, and red clover are not suitable for acid soil; tea requires strong acidity and acid soil, and neutral soil is not suitable for growth.
5. It is easy to produce a variety of toxic substances. Soil peracid is prone to produce free Al3+ and organic acids, which directly harm crops. After a certain amount of soluble salt in alkaline soil, it will directly affect the germination and normal growth of the crop. An alkalized soil containing more sodium carbonate is more toxic to crops.
High-yield soils suitable for the growth of different crops generally require a neutral, slightly acidic or slightly alkaline reaction, and the pH value is between 6 and 8. Because in acidic soils, soluble phosphorus easily combines with iron and aluminum to form iron phosphate and aluminum, which reduces the effectiveness. Exchangeable potassium, calcium, magnesium, etc. in the soil are easily replaced by hydrogen ions, and once they encounter rain, they are lost. Acidic soils are also often deficient in sulfur and molybdenum.
Lime should be added to acidic soil to neutralize soil acidity, eliminate aluminum toxicity and improve nutrient availability. At the same time, attention should be paid to the application of organic fertilizers to reduce the effects of acidity on soil and crops through the buffering effect of organic fertilizers. For chemical fertilizers, alkaline fertilizers such as ammonia water, ammonium bicarbonate, calcium magnesium phosphate fertilizer should be used. In alkaline soils, especially calcareous soils, soluble phosphorus easily combines with calcium to form poorly soluble phosphorus-calcium salts, which reduces the effectiveness of phosphorus.
In calcareous soils, the effectiveness of many trace elements such as boron, manganese, molybdenum, zinc, and iron is greatly reduced, and crops often feel that these nutrients are insufficient and various physiological diseases occur. Therefore, it is necessary to pay attention to and select the above-mentioned micro-fertilizer as the base fertilizer or topdressing.
When the base is applied, the micro-fertilizer can be rotted together with the organic fertilizer for a certain period of time to increase the effectiveness of the micro-fertilizer. In the case of deficiency of micro-fertilizer growth season, the corresponding organic chelated fertilizer should be used for foliar application in time to reduce the damage of physiological diseases. In addition, it is better to apply acidic and physiological acid fertilizers such as superphosphate, ammonium sulfate and ammonium chloride on the calcareous soil to reduce and reduce the alkalinity of the soil. Do not apply alkaline fertilizers such as ammonia or ammonium hydrogencarbonate. , grass ash, etc., especially the application of strong alkaline fertilizer lime.
In addition, it is not appropriate to apply ammonium chloride fertilizer on saline-alkali soil. And pay attention to the ammonium nitrogen fertilizer to apply deep soil to prevent the loss of ammonia volatilization. Phosphate fertilizer can be applied centrally or mixed with manure and compost to reduce phosphorus fixation and improve fertilizer utilization.
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