华北平原大气降水对土壤淋洗脱盐的影响

华北平原属季节性干旱半湿润太平洋季风气候区,降水量500-600 mm,年际和年内降水分布不均,旱涝盐碱灾害并存,成为农业生产可持续发展的主要制约因素。降水量74%集中在雨季,对土壤发生淋洗脱盐作用。一般在雨季7-8月份降水量超过300 mm,土体表现为脱盐。次降水量超过25 mm,根层土壤发生淋洗脱盐。海河平原自1964年逐年开挖骨干排水河道,使海河五大河流水系都有了自己的入海尾闾, 在排洪排涝的同时也排走了大量的盐分。20世纪60年代末,开始大规模开发利用地下水,井灌的同时降低了地下水位,起到井排作用,减少了潜水蒸发,增大了降雨入渗,加强了降雨淋洗脱盐作用,并引河水回灌补源,淡化了地下水。华北平原控制了灌区土壤次生盐碱化,而且大面积盐碱地得到改良。

INFLUENCE OF ATMOSPHERIC PRECIPITATION ON SOIL LEACHING AND DESALINIZATION IN THE NORTH CHINA PLAIN

In the North China Plain, the average annual precipitation is 500 - 600 mm,74% of which is concentrated in the rainy season,triggering soil leaching and desalinization. When the precipitation exceeds 300 mm in July and August,soil desalin-ization will be observed, and when a rainfall is over 25 mm, the effect of desalinization in root zone soil will be seen. The key to enhancing the effect of rainfall on salt leaching and desalinization lies in setting up drainage and water management systems. Beginning from 1964, main drainage rivers had been excavated and dredged in the Haihe River Plain year by year, and in 1975 all the five rivers systems of the Haihe River got their own drainage outlets to drain flood, excessive rainwater and saline groundwater. Along with the water drainage a lot of salt is drained into the sea. The end of the 1960s the beginning of large-scale exploitation and utilization of groundwater for irrigation. The practice of well irrigation lowers the groundwater table, thus functioning as drainage, reducing phreatic evaporation, increasing rainfall infiltration and consequently enhancing the effect of rainfall on salt leaching and desalinization. And the practice of replenishing the groundwater with river water freshens the groundwater. As a result, soil secondary salinization has been controlled,and large areas of saline-alkali land ameliorated in the North China Plain.