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白土是北亚热带主要的水稻土类型之一,在我国淮河以南与长江中下游一带以及日本的九州、四国与本州南部均有广泛的分布,这一地带是主要的稻麦两熟地区。白土之所以分布在这一地带是农业生物特点所决定的。大凡在这一地区的地带性土壤与其下的紅棕色风化壳及其再沉积物上改种水稻后,普遍出現白土化过程。紅棕色风化壳在这一地区有极广泛的分布,其特点是活性铁錳量低,而易于还原淋洗,质地为重壤-轻粘土,其中粉砂量高,这便为白土的形成提供了客观基础,因之白土多分布在丘陵谷址、河流阶地及古老平原上,而在現任河流与湖泊沉积地区白土并不多见。白土形成过程是在氧化还原交替情况下进行的,包括二个主要方面,即化学淋洗与机械淋洗,在这二个过程作用下,使出现了白土的典型特征——剖面上部养分与活性鉄锰贫乏,粘粒含量降低,而粉沙含量增加,从而出現明显的淀浆板結現象。
Clay is one of the main types of paddy soil in the northern subtropics. It is widely distributed in the areas south of the Huaihe River and the middle and lower reaches of the Yangtze River in Japan, as well as in Kyushu, Shikoku and southern Honshu of Japan. This area is the major rice-wheat double cropping area. The reason why the clay is distributed in this area is determined by the characteristics of agriculture. Alleviating the rice generally occurs in the zonal soils of the area and the reddish brown weathered crusts and their re-sediments, the process of albinism is widespread. Reddish weathering crusts are extremely widespread in this area and are characterized by low levels of active iron and manganese and easy reduction and rinsing, with heavy soil-light clay, of which the amount of silt is high, which provides for the formation of clay The objective foundation, because of the distribution of white clay in the valley sites, river terraces and ancient plains, and in the current sediments of rivers and lakes are rare. The process of clay formation is carried out under the redox alternation, which includes two main aspects: chemical leaching and mechanical leaching. Under the action of these two processes, the typical characteristics of clay are presented - the nutrients and activity in the upper part of the profile Manganese poor, clay content decreased, while the content of silt increased, resulting in obvious phenomenon of the formation of slurry.