Secondary salinization _ shenhuwan

Secondary salinization overview secondary salinization, also known as "secondary salinization." Means as unreasonable farming irrigation and soil salinization process. Mainly occurs in arid or semi-arid areas with high groundwater, groundwater runoff impeded, groundwater contains more soluble salts of alluvial plain, as China North China plain, a parcel of land in songliao plain and Plains, the Weihe River plain. Due to the impact of the measures is not reasonable to groundwater uplift, evaporation than precipitation conditions, the soil surface salinity increase, causing soil salinization. Prevention is the key to control the water level, so irrigation and drainage system should be sound, take reasonable measures for agricultural irrigation and other technology to prevent groundwater elevation and soil to salt. After the founding of the secondary salinization in case our founding on saline soil water-salt of lack of awareness, in the development of large-scale irrigation, irrigation development, expanding irrigation area, also make extensive soil appeared serious secondary qualitative, causing adverse effects. For example, a 1956 1961, in North China plain yellow irrigation in a big way. Hebei, Shandong, Henan province plain old saline 3200 million mu, the total cultivated area l0% (except for the coastal zone). After liberation, many old saline after drainage flushing, dig trenches rice, cited hung warping, combined with appropriate agricultural practices, improvement and utilization. But since 1950 in the extensive cited the North China plain water irrigation and plain water, ignored the drainage, causing large Northern Plains soil salinization, saline soil 2800 Mu area increased to 48 million acres, after l0 years of governance was restored. The North China plain area 35 000 km2, is cultivated 2.7 million acres, is the country's most important agricultural area. At that time, the yellow irrigated area once reached 2.3 million acres, resulting in the rapid rise in groundwater, groundwater from the original 2 ~ 4m reduced to 1 ~ 2m, secondary salt strengthen rapidly expanded. According to the investigation at that time, several large irrigated, secondary salinization area jingda actual irrigated area of 1/3. Some areas in the open irrigation after one or two years, salinization is outcrops, or in part regional development. Three, four years after that there are many secondary saline appears, causing secondary direct Harada is the evolution of the yellow irrigation upset and truncated drainage system, and overflowing, irrigation works not matching, etc. A large number of irrigation water leakage, caused a rise in groundwater. A spring and early autumn the North China plain water, moisture and early, early flood characteristics, nature of the terrain and level, but also many river ask closed depression, high ground water level (General buried 2 — 3m), salinity, and large (a Syria-2 ~ 10g/l), the soil is loamy soil or sand loam viscous, with easy saline conditions. Massive secondary salinization of indirect because at that time, regardless of the condition and biased "to the policy of" putting energy storage, River on the dam or built plain reservoir, the so-called "one acre of land on — MU days" and "baby", "grape bunches" abound. Therefore the irrigation area is not on the water, irrigation, no row or for irrigation waste discharge. The more water, the water level higher, the larger the scope of influence, soil salinization, marshes of the more serious. This results in a man-made disaster, many low-lying plain areas become swamps. For example, Zi Yang County, Henan province for the development of irrigation water storage and shipping, river cascade on the dam that river water levels are obstructing high elevation within the groundwater, the town was once also require boat, water-base damage along the coast, the housing down drowning, many fertile land drastically or even into a barren land. At the time of Yucheng, Shandong liaocheng-tuhai collapse between five road dam, Hebei province East of small river irrigation dam collapse of seven road, collapse of dam heilonggang 29 road. In the absence of drainage conditions, overflowing, promote soil salinization. Gaotang County, Shandong province in the affluent district xiajin, known as the Golden gaotang, silver summer law, but at that time because of the harm, Yancheng, into a piece of grey wilderness, productivity road damage, people giving to earn a living along the way, shocking. Because secondary salinization of ordinary occurrence and rapid development of the masses on irrigation produced concerns, many people have called "Ning, dry dead death does not call the base" idea. CPC Central Committee in 1962, ordered the yellow stop irrigation, after lessons, take dredging discharge, irrigation equipment, only make the situation gradually improves. In the late 1960 's and 70 's gradually restore irrigation. For example, Northwest of plain 1956 yellow irrigation, 1962, 1967 — stop irrigation 1979 complex irrigation. At present each year a Yellow River 50 60 billion m3, drought and irrigation 1000-1700 million acres, of which irrigated 800 a 900 million mu, but little scope of secondary salinization continue to occur, not like years ago so serious, but it is also noteworthy. Secondary salinization formation largely to bring many of groundwater. As groundwater makes the water level continues to drop, along the sandy yellow sea and Bohai Sea and the coastal zone of the bedrock fracture occurred in a seawater intrusion of salt water distribution region of salt water boundaries move to fresh water area. For example, Shandong coastal areas due to the significant drop in groundwater, Lai, Bay forming area 11th, the underground water level decline 400km2 funnel, where groundwater in the area of the sea to 2400 km2, 1988 funnel Center of groundwater in the sea 20 m, Lai, Bay seawater intrusion groundwater aquifers, sea water intrusion in the area of 730.7km2. Shandong Yantai, Weihai, and has also occurred in Qingdao seawater intrusion. Groundwater decline resulting in Dalian City, Liaoning province, Jinzhou, jinxi, Yingkou, Qinhuangdao city, Hebei province, and seawater intrusion and water quality deterioration. 1992 sea water intrusion in Liaoning province area of 434 km2, Qinhuangdao 55.4 km2. In Guangxi Province, Beihai city waterfront city and wei State island have long caused by overexploitation of groundwater, water quality of seawater intrusion. Comprehensive management of salinization method proved that the improvement of saline soils is a complex, difficult, requiring a long time, should be considered throughout the country, depending on the development of measures. (1) establish perfect irrigation system, the ground water depth at the critical depth below. The Soviet Academy of Sciences v.AKovda, experts believe that may be caused by soil salinization of mineralized groundwater depth average 2.5 ~ 3m. (2) the establishment of modern drainageSystem: ① horizontal drainage, mainly in the pools where, in the form of underground pipes, both to reduce groundwater level, and can emit salt in the soil; ② vertically (vertical) drainage, vertical drainage price low, not covers, water, water quality, groundwater control and regulatory flexibility, less maintenance work, while the combination of irrigation and vertical set well to coupling with effect as well. (3) chemical improvement. Some developed countries such as the United States and Australia in saline soils, especially in the chemical fertilizer on alkali soil improver, such as: gypsum, sulfuric acid, slag (phosphogypsum), because land types, applying a different amount, timing depends on local experiences and financial conditions. Use conditioner after you wash with plenty of water, in the absence of water resources applications is difficult, and costly. However, in this way makes the soil water from 379 days down to 145 days, water seepage from 292mm rose to 605mm. Chemical improvement although costly, but from the economic perspective is useful. (4) growing rice on improvement of alkali soil more effective. Hungary, Romania, Thailand, the former Soviet Union, China has a large salt soil on rice, making good soil yield. Hungary experts through Central and Eastern Europe region basin study suggested leaving soil irrigation washing, applying chemical conditioner and rice improvement in combination of improvement measures, such measures as the current improvement salinization of key measures. But this measure requires smooth horizontal pai water. (5) the University of Tokyo research to soil inject polyacrylate solution, and soil formation 0.5cm of impermeable, reducing soil moisture evaporation, reduce salt with capillary water evaporation from the surface soil accumulation, so that the marked increase in crop yield. Iraq pedologist study will pitch mixing with the soil surface 5cm, then rinse, increases soil temperature 1.3 — 2.3 ℃, which increases the solubility of the salts, increase the elution effect. (6) the use of salt water irrigation. Salt water irrigation although can increase soil in salt, but also can increase soil moisture, and reduce the concentration of soil solution. United States, Tunisia, Italy, Central Asia, the Arab and North Africa are less than 1 or 3 1g/— 8g/1 of salt water irrigation, India also use dilute got water irrigation. United States and the former Soviet Union for use of salt water irrigation offers a wide range of theoretical and practical Foundation. (7) the planting of trees and alkali resistance, particularly to nitrogen-fixing species of salt-tolerant plants (green manure) and plants that can reduce evaporation of surface water, prevention of soil surface area of salt, can lower the water table and salt, soil physical traits, increase organic matter and soil microorganisms, reducing soil pH value, thereby radically improve the surrounding environment.