Effects of soil acidity and alkalinity on crop growth

The acidity and alkalinity of the soil depends mainly on the amount of acid and alkali substances in the soil. The acidic substance is derived from the carbonic acid formed by the dissolution of carbon dioxide in water and the organic acid produced by the decomposition of organic matter, and 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 sodium hydrogencarbonate in the soil. Salts such as 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.

High-yield soils suitable for different crops are generally required to be neutral, slightly acidic or slightly alkaline, with pH values ​​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 readily combines with calcium to form poorly soluble phosphorus-calcium salts, which reduce the effectiveness of phosphorus. Also, 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 syndrome in the growing season of micronutrient deficiency, the corresponding organic chelated fertilizer should be used for foliar application in time to reduce the damage degree of physiological diseases.

It is better to apply acidic and physiological acid fertilizers such as superphosphate, ammonium sulfate and ammonium chloride on the calcareous soil, which can reduce and alleviate the hazard of soil alkalinity. It is also possible to appropriately apply gypsum, phosphogypsum, ferrous sulfate, sulfur powder, acid weathered coal, etc., but do not apply alkaline fertilizers such as ammonia water, ammonium hydrogencarbonate, grass ash, etc., and it is particularly contraindicated to apply strong alkaline fertilizer lime. In addition, it is not advisable to apply ammonium chloride fertilizer on saline-alkali soil, and note that ammonium nitrogen fertilizer should be applied to the soil to prevent the loss of ammonia. Phosphate fertilizer can be applied centrally or mixed with manure and compost to reduce phosphorus fixation and improve fertilizer utilization.