1. Due to the lack of organic matter in cultivated soil, unreasonable cultivation and irrigation, massive application of chemical fertilizer, soil acidification and soil secondary salinization, soil agglomeration was destroyed and soil compaction was caused. Soil compaction directly leads to the lack of oxygen, water and fertilizer in the soil-plant system, which affects the material conversion and energy exchange in the soil-plant system, and even some physiological activities and life metabolism can not proceed normally, or stop, or transform to harmful directions.
2. Due to long-term excessive use of physiological acid fertilizer and chemical nitrogen fertilizer, acid substances in the soil are increasing and accumulating, and alkaline substances such as calcium and magnesium in the soil are absorbed and utilized by crops or reduced by leaching. The lack of necessary supplementary regulation leads to soil acidification. Soil acidification will accelerate soil degradation, activate harmful heavy metals, increase harmful microorganisms, especially parasitic fungi, and seriously cause soil-borne diseases.
3. Due to the long-term excessive use of chemical fertilizers, the soil salt accumulation, especially nitrate accumulation. These salts accumulate upward along with soil moisture to the surface, resulting in secondary salinization of soil surface, destruction of soil structure, deterioration of physical, chemical and biological properties. In light cases, they can affect germination of seeds, hinder nutrient absorption and crop growth, and in severe cases, they can cause physiological drought, nutritional disorders, salt damage and death of plants. Even lost agricultural use value.
4. In production, it does not apply fertilizer in proportion to nutrient elements required by crops, does not test soil formula fertilization, blindly overapplication of nitrogen, phosphorus and potassium, and does not apply organic fertilizer or little application of medium and trace element fertilizer, resulting in enrichment of nitrogen and phosphorus in soil, depletion of potassium, silicon, calcium, magnesium, boron, zinc, iron, molybdenum and other medium and trace elements in soil, leading to imbalance of nitrogen, phosphorus and potassium ratio. The nutrient ratio between a large number of elements and medium and trace elements is unbalanced, and the beneficial elements such as silicon are missing, which leads to the antagonism of soil nutrient elements.
5. Due to the "three wastes" pollution outside the agricultural system, excessive fertilizer, pesticide, agricultural film residue pollution, untreated organic fertilizer pollution, and harmful pathogen pollution in the agricultural system, often enter the cultivated soil. When the accumulation of these pollutants exceeds the soil self-purification capacity, it will "overflow", directly causing heavy metals, organic compounds and disease-causing organisms pollution in cultivated soil. Cultivated land soil is polluted, it will destroy the soil ecological balance, make soil beneficial organisms die, soil biological population decrease, soil physical and chemical biological properties deteriorate, soil activity decline, soil function deteriorates, serious polluters will make soil lose production capacity, lose agricultural use value.
6. The main manifestations of soil erosion in cultivated land are water erosion, wind erosion and tillage erosion. Mainly due to excessive reclamation of slope soil, especially the slope with slope greater than 15 degrees, frequent surface soil cultivation disturbance, resulting in soil and water loss. Secondly, there is a lack of conservation tillage measures such as slope conversion ladder, horizontal ditch tillage and hedgerow after reclamation. Instead, the land is dug and ploughed at will, which not only causes tillage erosion, but also aggravates wind erosion and water erosion. Long-term soil and water loss, resulting in soil desertification, thinning soil layer, nutrient loss, water and fertilizer retention capacity reduced, soil barren, reduced arable land area.