Soil acidity and alkalinity are the basic characteristics of soil and one of the important factors affecting soil fertility and crop growth. Soil acidity and alkalinity mainly depend on the amount of acid and alkali substances in the soil. Acidic substances come from carbonic acid formed by carbon dioxide dissolved in water and organic acids produced by decomposition of organic matter, inorganic acids produced by oxidation, and acidic substances added by fertilization.Alkaline substances mainly come from soil sodium carbonate, sodium bicarbonate, calcium carbonate and other salts.Due to the difference of climate，in wet and rainy area, soil is acidic, while soil is alkaline in dry and rainy.
Soil slightly acidic or alkaline will both reduce the effectiveness of soil nutrients, which is manifested in the following five aspects:
One is to reduce the effectiveness of soil nutrients.The availability of phosphorus in soil is obviously affected by the acidity and alkalinity. When the pH value is more than 7.5 or less than 6, the phosphoric acid and calcium or iron and aluminum form a late acting state, which reduces the availability.Calcium, magnesium and potassium are easily substituted and leached in acidic soils.The solubility of calcium and magnesium in strongly alkaline soil is low and the effectiveness is reduced.Boron, manganese, copper and other trace elements are significantly less effective in alkaline soil, while molybdenum is precipitated with free iron and aluminum in strongly acidic soil, reducing its effectiveness.
Second, it is harmful to the benign development of soil and damages the
soil structure.Strong acid soil and strong alkaline soil have more hydrogen and sodium, but lack of calcium, it is difficult to form a good soil structure, is not conducive to crop growth.
Third, reduce the activity of soil microorganism. Generally, the most suitable pH value for soil microorganisms is the neutral range between 6.5 and 7.5.Excessive acidity or alkalinity severely inhibited the activities of soil microorganisms, thereby affecting the conversion and supply of nitrogen and other nutrients.
Fourth, it is not benefit for crop growth and development.General crops grow bestly in neutral or nearly neutral soil.Beet, alfalfa and red clover are not suitable for acidic soil.Tea requires strong acid and acid soil, neutral soil is not suitable for growth.Calcium superphosphate, ammonium sulfate, ammonium chloride and other acidic and physiological acid fertilizer are better, in order to reduce the harm of soil alkalinity, do not apply alkaline fertilizer.
Fifth, it is easy to produce a variety of toxic substances.
Too acidic soil is prone to produce free Al3+ and organic acids, which directly harm crops.The amount of soluble salt in alkaline soil will directly affect the germination and normal growth of crops.Alkaline soil containing more sodium carbonate is more toxic to crops.
Suitable for the growth of different crops in high-yield soil, generally requires a neutral, slightly acidic or slightly alkaline reaction, the pH value is mostly between 6 and 8.
Lime should be added to acidic soil to neutralize soil acidity, eliminate the toxicity of aluminum and improve the effectiveness of nutrients.At the same time pay attention to add
organic fertilizer, through the buffer effect of organic fertilizer, reduce the impact of acidity on soil and crops.Chemical fertilizer should choose ammonia water, ammonium carbide, calcium magnesium phosphate fertilizer and other alkaline fertilizer.However, in alkaline soil, especially calcareous soil, soluble phosphorus is easy to combine with calcium to form insoluble phosphate and calcium salts, which will reduce the effectiveness of phosphorus.
In addition, ammonium chloride fertilizer should not be applied on saline soil.It was also noted that ammonium nitrogen fertilizer should be covered with soil deeply to prevent the loss of ammonia volatilization. Phosphate fertilizer can be applied centrally or mixed with barnyard
livestock manure organic fertilizer with
compost process to reduce the fixation of phosphorus and improve the utilization rate of fertilizer.
