Structural Changes of Compacted Soil Layers in Northeast China due to Freezing-Thawing Processes

Soil compaction has become a global concern that reduces soil quality and may jeopardize agricultural sustainability. The objective of this study is to evaluate if the freezing-thawing process can alleviate the negative effects of soil compaction during overwinter time in Northeast China. The field experiment was a split plot design including two surface treatments (bare and mulch) and three compaction levels (low, moderate, and high compactions with initial bulk densities of 1.2, 1.4 and 1.6 g cm(-3)). Results showed that compared with initial values in the fall, freezing-thawing events increased soil porosity (by 4.28% to 25.68%) and the ratio of large-size pores (by 44.5% to 387.6%) after thawing in the spring. The greatest changes were observed in the high compaction treatment, and mulch-enhanced soil structural transformation. Additionally, the ratio of large-size aggregates (>1 mm) was increased and the fraction of small-size aggregates (<1 mm) was decreased. These changes in soil structural characteristics were attributed mainly to the modification of ice-filled pores space during the overwinter period. We concluded that the freezing-thawing process was an effective natural force for ameliorating soil compaction in Northeast China.