[Micro-scale soil characteristics in salinization area of Songnen plain]

The study by the methods of in situ observation and laboratory analysis showed that the micro-relief in salinization area of Songnen Plain area was composed of flat land, micro-slope land, depression margin, and depression. Isohumusols distributed in depression, while alkalic halosols distributed in depression margin, micro-slope land, and flat land. The exchangeable sodium percent (ESP) in alkalized layer (15-30 cm) of alkaline soil in flat land was 60%, and the maximal ESP in surface soil layer in micro-slope land could reach to 75%. The alkalized soil layer in depression margin was mainly at the depth of 10-30 cm, where the maximal ESP could reach to 30% -40%. Nearly no alkalized layer was found in the soil profile in depression. The soils developed on the four micro-relief units had obvious differences in their water retention curves. The maximal saturation moisture content in the soils of micro-slope land was only 25%, while that of 0-10 cm soil layer in depression reached to 45%. The freezing-thawing process in different micro-relief units differed markedly, with the maximal frozen depth in micro-slope land and depression being 157 and 136 cm, respectively. The surface soil moisture content in depression increased from 20% before freezing to 50% during freezing period. Among the four micro-relief units, micro-slope land had the most obvious variation of surface soil salt content during freezing-thawing, with the increment after thawing being as high as 80%.