长江流域的主要地区皆属于湿润的亚热带地区,因而决定了该区土壤的性质和特征。众所周知,亚热带土壤形成的一个极主要特性是:整个生物和化学分解作用十分强烈;它是在热、光和水分充足的条件下,以及在较长时间内较深的土层都是湿润和温暖的,并且在生物无休眠期的情况下进行的。这种对有机体生命活动有利的条件加速了上述的分解过程,一般比我们所处的温暖亚热带快二至三倍。无论是在天然生长的木本和草本植物群落地区,或者是在几乎全年种植作物的田地上,有机物和土壤中有机残余物的积累都有相应的增加。有机物的分解和矿物质化在微生物活动十分强烈的情况下进行得这样快,一方面,不能促成土壤中腐殖质的大量积累;另一方面,加速了生物循 The main areas of the Yangtze River basin belong to humid subtropical areas, thus determining the nature and characteristics of the soil in the area. It is well-known that one of the most important characteristics of subtropical soils is that the entire biological and chemical decomposition is very strong, that it is moist and warm under the condition of sufficient heat, light and moisture, and deeper soil layers for a longer period of time , And in the absence of biological dormant period. This favorable condition for the life of the organism accelerates the above decomposition process, generally three to three times faster than the warm subtropical zone in which we live. There is a corresponding increase in the accumulation of organic residues in both organic matter and soil, both in areas of native woody and herbaceous communities, or in almost all year-old fields. Decomposition and mineralization of organic matter take place so rapidly that microbial activities are very strong, on the one hand, they do not contribute to a large accumulation of humus in the soil; on the other hand,