Study on Cryerts In Song-Nen Plain, NE China.

The paper presents results on the study of the distribution, properties, and identifications of Cryerts in the area at around 47^oN, the county of Beian , in N. Song-nen plain, Heilongjiang province, China. The area belongs to the mid- temperate climate zone with annual temperature about 1.00^oC, and a cryic soil temperature regime. The annual precipitation is 522.6 mm concentrating in summer, so alternatively dry and wet seasons within a year are obvious. Six soil pedons were observed; chemical and physical properties were analyzed, and X-ray diffractions including clay mineral quantification were operated. The dominate soil is Mollisols, also known as Phaeozems. We found the major factors that influence the formation of the Vertisols in the study area, in addition to the climate features, are parent materials, some Mollisols with high content of clay and 2:1 type of expensive clay minerals, and also soil erosions.

Cryerts are formed in places where the top soil turned to be thinner or totally eroded, while the smectite content in subsoil is abundant. Two pedons of Chromic Haplocryerts were identified on the first and second terrace of Wu-Yu-Er River, a major tributary of Song-nen River. The original parent material is a mixture of alluvium-lacustrine deposits (Qp² ) and weathered shale (K). The top of original soils were lost by erosion long time ago. The Cryerts have a series of vertic characteristics, such as cracks, wedge shaped/angular block structures, stress coating with an average COLE_Std value 0.14 cm.cm^-1.and 66.5%-70.2% smectite clay in diagnostic section.

A Typic Haplocryert is found and identified at a first terrace relating to an aged Mollisol derived from alluvial-lake sediment (Qp²) without shale mixtures. In addition to Vertic characteristics, we noticed "gilgai" on the un- cultivated part of the field, and an average 66% smectite clay mineral below the plowing layer with 55-60cm in thickness near the land surface.

Most smectite of the Cryerts in the areas is inherited from the parent material which formed during the mid- and late-Pleistocene when the volcanic ash and weathered products from basalt in the nearby surroundings were transported into lake areas while the paleo-climate was warmer than the present time, and also probably formed in the period of formation of the Mollisols by neogenesis, illuviation, etc. The dominate clay minerals are actively mixed layers of illite and smetitie , and single smectite.

The Vertic subgroups of the Mollisol are extensively distributed, causing soil cracks in dry spring, extra-erosion in raining seasons and in the drawing period of soil frozen. The process of vertisolization indicates the degradation of the Mollisols. Not only impacts the agricultural productivity, but also damages light structures and transportation systems. We recommend controlling soil erosions by any means available and practicable to sustain the soil resources. It is important to recognize that the Cryerts and Vertic subgroups can be formed from certain Mollisols and Qp² sediments mixed with shale in the same high latitude region of Song-Nen Plain as the studied area. Also further investigations for identification and separation of the Vertisols from Mollisols are useful for academic reason. The results might be as a reference for establishing a Cryerts suborder in China’s Soil Taxonomy.(END)