How is salinization formed in arid areas of China? The worst season of salinization in northwest China?

Soil salinization means that the soil salt content is too high (more than 0.3%), which makes crops low-yield or unable to grow.

There are two conditions for the formation of saline-alkali soil: first, the climate is dry and the groundwater level is high (above the critical water level); The other is low-lying, with no drainage outlet. Groundwater contains a certain amount of salt. For example, its water surface is close to the ground and the area is relatively dry. After the water rising to the surface evaporates due to capillary action, salt is left: over time, the salt content of soil gradually increases, forming saline-alkali soil; If it is a depression and there is no drainage outlet, the water in the depression will evaporate, leaving salt and forming saline-alkali land.

Adverse effects:

1, soil hardening, fertility decline.

2. It is unfavorable for crops to absorb nutrients and hinder crop growth.

Prevention and control:

Measures to control saline-alkali land include water conservancy improvement measures (irrigation, drainage, silting, rice planting, seepage prevention, etc.). ); Agricultural improvement measures (leveling land, improving farming, applying exotic soil, fertilizing, sowing, crop rotation, interplanting, etc.). ); Biological improvement measures (planting salt-tolerant plants and pasture, green manure, afforestation, etc.). ); And chemical improvement measures (using gypsum, phosphogypsum, calcium sulfite and other improving substances. ). Four aspects. Because each measure has a certain scope of application and conditions, it must be treated comprehensively according to local conditions. Supplementary answer: soil salinization

Soil salinization refers to the phenomenon or process of soluble salt accumulation on the soil surface, also known as salinization. Saline soil or saline-alkali soil in China is widely distributed, with a large area and many types, with a total area of about 654.38+0 billion hm2. Mainly occurs in arid, semi-arid and semi-humid areas. Soluble salts in saline-alkali soil mainly include sulfate, chloride, carbonate and bicarbonate of sodium, potassium, calcium and magnesium. Sulfate and chloride are generally neutral salts, and carbonate and bicarbonate are basic salts.

China is also a country where saline soil is widely distributed. When compiling the saline soil map of China, it is roughly calculated that the saline soil area of China is about l.0x 108ha, of which modern saline soil accounts for about 37%, residual saline soil accounts for about 45% and potential saline soil accounts for about 18%. Saline soil in China is distributed in Liaoning, Hebei, Heilongjiang, Hebei, Shandong, Henan, Shanxi, Xinjiang, Shaanxi, Gansu, Ningxia, Qinghai, Jiangsu, Zhejiang, Anhui, Fujian, Guangdong, Inner Mongolia and Tibet. According to the natural geographical conditions and soil formation process, it is divided into eight sub-regions, such as coastal humid-semi-humid seawater immersion saline area, northeast semi-humid-semi-arid grassland-meadow saline area, Huanghuaihai semi-humid-semi-arid meadow saline area, Gan Xin desert saline area, Qinghai extreme desert saline area and Tibet alpine desert saline area, which are used to guide production practice.

Supplementary answer: Rocky desertification, that is, karst rocky desertification or petrochemical, is similar to the present situation of desertification in northwest China and is one of the extreme forms of land degradation and evolution. There used to be a large area of carbonate rocks in Guangxi and Guizhou, but the original vegetation was destroyed due to continuous land reclamation. The barren soil layer formed after thousands of years was quickly eroded by wind and rain, and finally only stones that could not grow any plants were left on the surface. The rate of rocky desertification in western China is quite fast, in which the carbonate rocks in Guangxi account for 37.8% of the total land area, and the rocky desertification is increasing by 3%-6% every year. Rocky mountainous areas not only form a vicious circle of "poor people in poor mountains enter wasteland", but also are the most difficult "hard bones" for afforestation because of thin soil and lack of water and drought. Rocky desertification

Rocky desertification refers to the phenomenon of land degradation in tropical and subtropical humid and semi-humid climate. Karst and its development are disturbed by human activities, which destroys the surface vegetation and causes serious soil loss, and large areas of bare karst or gravel accumulation. This is an extreme form of land degradation in karst areas.

Desertification, including rocky desertification, is one of the most serious environmental and socio-economic problems in the world today. 1At the United Nations Conference on Environment and Development in June, 1992, desertification control has been included in the agenda of 2 1 century as an important part of sustainable development. Rocky desertification, as a new subject, has been included in the national economic and social development plan for the first time. The outline of the Tenth Five-Year Plan reads: "Accelerate the management of small watersheds and reduce soil erosion. Promote the comprehensive management of rocky desertification in karst areas of Guizhou, Guangxi and Yunnan. "

Rocky desertification is the abbreviation of "rocky desertification". Rocky desertification is an evolutionary process in which the contradiction between man and land is prominent, vegetation is destroyed, soil erosion, land productivity is reduced or lost, and rocks with similar desert landscape are gradually exposed under the fragile ecological environment of karst. From the cause of formation, the main factor leading to rocky desertification is human activities. For a long time, natural vegetation has been destroyed continuously, and a large area of steep slope has been reclaimed, resulting in bare surface. In addition, the karst mountain area has thin soil layer, shallow exposed bedrock and strong rainstorm scouring ability. After a lot of soil erosion, rocks gradually emerged, showing the phenomenon of "rocky desertification", and with the passage of time, the degree and area of "rocky desertification" are also deepening and developing. The most direct consequence of rocky desertification development is the loss of land resources. Due to the lack of vegetation and water conservation in rocky desertification areas, it is often accompanied by serious drinking water difficulties for people and animals. The phenomenon of "rocky desertification" after the continuous loss of water and soil resources not only worsens the agricultural production conditions and ecological environment, but also makes people lose their basic living conditions. Many places have to consider "ecological migration", such as Mashan area in Guizhou Province, which is a typical example. According to investigation and statistics, there are about 450,000 people who need to move due to ecological deterioration in karst rocky desertification mountainous areas of Guizhou Province, and measures are being taken to gradually move.

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