西喜马拉雅北麓山间谷地农区灌淤土的形成特点

CHARACTERISTICS OF WARPED IRRIGATED SOIL FORMATION IN AGRICULTURAL AREAS OF SOME VALLEYS AT THE NORTHERN FOOT OF THE WESTERN HIMALAYAS

笔者在西喜马拉雅北麓朗钦藏布和马甲藏布河谷农区发现灌淤土是主要的人为土壤类型。和其他省区的灌淤土一样,具有三个典型的基本发生层:1.耕作层:厚17cm左右,有机质平均含量32.4g/kg,是原土壤的2—10倍,肥力较高,普遍呈氮高、磷丰、钾有余的特征;2.老灌淤熟化层:厚度大多在50—80cm以上,有大量的炭渣及少量陶、铁之类文化遗存物,有机质8g/kg—10g/kg。该层是区别于其他耕种土壤的重要发生层;3.原来土壤埋藏层:朗钦藏布河谷灌淤土之原来土壤为雏漠土,马甲藏布河谷则为寒钙土,大多埋藏在1m以下,全剖面设有原来土壤的碳酸钙淀积或表聚特征,也不出现双重熟化层段。

In the agricultural areas of Langqin Zhangbu and Maji Zhangbu valleys in northern foot of the western Himalayas, warped irrigated soils are a primary type of cultivated soils. Warped irrigated soils in Tibet generally have three typical genetic horizons: 1) plough horizon with a thickness of 17 cm or so, an average organic matter content, of 3.24%, which is 2—10 time as much as that of original soil, higher fertility and higher contents of N, P and K; 2) old urigated and cultivated horizon with a thickness of 50—80 cm, more carbon residues, few pieces of pottery and sheets of iron and an organic matter content of 0.8%—1.0%, being an important genetic horizon distinguished from other cultivated soils; and 3) original soil horizon with a burial depth of more than 1 m, being haplo-desert soil in ,Langqing Zhangbu Valley and being cryocalic scil in Majia Zhangbu Valley. In these proffiles of warped irrigated soils, there are neither deposition or surface accumulation CaCO_3 occurring in the original soils nor double mellow horizon.