1, fertilizers and pesticides unreasonable use
According to statistics, China's annual use of fertilizers has exceeded 41 million tons, becoming the world's first major consumer of fertilizers [2]. In order to increase the amount of agricultural products to increase the amount of chemical fertilizers containing phosphorus, nitrogen and other chemical fertilizers are used in large quantities, the long-term use of these chemical fertilizers, will destroy the soil structure, disturb the balance of nutrients within the soil, resulting in soil clumping, deterioration of the soil quality, water storage function is reduced, and so on a series of problems. The quantity of agricultural products is greatly improved, but their quality is worrying. Because excessive use of fertilizers will make some crops in the growth process to absorb too much nitrate, animals or human beings eat these crops containing nitrates, will affect the body of oxygen transport, so that the disease, and in serious cases, or even death.
Similarly, the use of large quantities of pesticides on the soil has also caused great harm. Most of the pesticides are organic pesticides, which contain many harmful chemicals, such as phenoxystreptanate pesticides, polycyclic aromatic hydrocarbons, dioxins, phthalates and so on. These harmful chemicals nearly 1/2 will remain in the soil, over time, in biological, abiotic, and sunlight and other *** with the role of harmful chemicals into the soil components, planted on the soil crops and from the soil to absorb harmful substances in plant roots, stems, leaves, fruits and seeds in the accumulation of food through the human body and animals will cause a variety of diseases after consumption.
2, heavy metal elements caused by soil pollution
The excessive use of agricultural chemicals, industrial pollution intensified, making heavy metal pollution increasingly serious. Heavy metal elements in the soil are mainly from three sources: with solid waste into the soil of heavy metals, with sewage irrigation into the soil of heavy metals and heavy metals with atmospheric deposition into the soil. Solid wastes are of various types and complex structures, among which the solid wastes generated by industry and mining are the most seriously polluted. And solid waste contains a large number of heavy metals, through the sun and rain and other effects, heavy metals will be absorbed by the soil and spread. Domestic sewage, petrochemical sewage, industrial and mining enterprises sewage and urban mixed sewage are the four major sources of sewage, sewage contains a large number of lead, chromium, mercury, copper and other heavy metals, sewage discharge arbitrarily or unreasonable treatment will lead to sewage in the transfer of heavy metal elements to the soil, thus affecting the deterioration of soil quality. All of these heavy metal pollutants into the soil, because of its poor mobility, long stagnation time, most of the microorganisms are difficult to decompose it, and it can pass through the water, plants and other media ultimately jeopardize human beings.
3, livestock excreta and biological residues on the soil pollution
Livestock and human feces, as well as slaughtering waste is often not effectively dealt with directly discharged into the soil, where the parasites and viruses will cause soil and water pollution, and sometimes make the soil poisoned, changes in the soil's original state of normality, the harmful soil through the water and crops and ultimately endangered to human beings.
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4, sewage irrigation pollution of the soil
China is a large agricultural country, need a lot of water to irrigate crops. However, the water veins are connected, domestic sewage and industrial wastewater once discharged without scientific treatment, making a large amount of sewage flow to the farmland, the crops irrigated by sewage will be with a variety of harmful substances, resulting in the consumption of human beings and animals sick.
5, atmospheric pollution on the soil
Sulfur oxides in the atmosphere, nitrogen oxides and particulate matter and other harmful substances, after a variety of chemical and physical reactions, the formation of acid rain, acid rain into the soil, so that the soil acidification. The metal oxide dust emitted by metallurgical industry, on the other hand, enters into the soil in the form of precipitation under the effect of gravity, forming a point pollution centered on the discharging factory with a radius of 2-3km [3]. This will change the soil composition and affect the nature of the soil, which is not favorable to the growth of plants.
6, soil erosion
Soil erosion mainly includes desertification, dust storms and desertification. Earth's ulcer disease is the image of land desertification description, the natural environment of water erosion, salinization, rocky desertification, etc., making the earth's ulcer disease more and more serious. For example, China's loess slopes, the soil composition is mainly powdered sand, powdered sand adhesion is poor, but also easy to be dissolved by water, once encountered in bad rainstorms, will be washed away by the water, not only is not suitable for the growth of vegetation, biological survival, but also cause siltation of the riverbed, reducing the capacity of the rivers and lakes of the flood storage and drainage. In recent years, China's dust storms in many cities has increased, which is closely related to the indiscriminate reclamation of grasslands, excessive felling of trees and soil erosion caused by wind. Soil erosion caused by wind erosion is serious, vegetation growth difficulties, so that most of the land can not be utilized.