Impact of Freezing and Thawing on Bulk Density of Black Soil

In order to make sure whether freezing and thawing could help to solve the bulk density increased problem due to no tillage or reduced tillage, a freezing and thawing experiment was done in Heshan farm of Heilongjiang Province. The water content treatments were 10%, 25.93%, 30.86%,and 37.84% respectively, and soil bulk density treatments were 1.01, 1.17 and 1.32g cm-3 respectively. The soil studied was silty loam and sieved by 2 mm in advance, then put into a barrel after harvesting and before the winter. Depth of the soil was 25cm. Before planting, soil bulk density was measured at the internal of 5cm in 20cm depth. The results showed that bulk density in 20cm depth was less after freezing and thawing of the soil with different water contents and with the same soil bulk density of 1.30g cm-3. But decreasing range was not absolutely direct proportion with water content. Variation of soil bulk density with the depth was: when soil water content was high, decreasing range of soil bulk density on the surface was more than the lower; when it was low, the variation was reverse. Freezing and thawing inflected much soil bulk density on the surface of the soil with different bulk density and with the same water content of 30%. It made soil with low bulk density compacted and high loosened. Generally, it was freezing and thawing that could overcome the disadvantage of soil bulk density increased by no tillage or reduced tillage in the black soil in a certain extent.