Abstract:Bulk density is the basic physical property of soil. The variation of soil bulk density is affected by soil moisture under agricultural machinery or rammed pressure. In this study, compaction experiment was conducted to evaluate the characteristics of bulk density for brown soil and cinnamon soil under different moistures. The results showed that bulk density of brown soil increased rapidly first and then tended to be stable with the increase of compaction energy, but cinnamon soil reached the stable state slowly. The change of soil bulk density with moisture was different under different compaction times, for brown soil, bulk density increased firstly and then decreased slightly, but when the moisture was 88.3 g/kg bulk density was slightly decreased under less compaction times, while bulk density of cinnamon soil decreased first and then increased with the increase of soil moisture when the compaction times was relatively low. However, when the compaction times was more, bulk density decreased firstly and then increased and finally decreased again with the maximum value appeared at moisture of 136.5 g/kg. The effects of moisture and compaction energy on soil bulk density were different under tillage condition (≤1.6 g/cm3) and engineering condition (>1.6 g/cm3). The main factors influencing the compaction density of brown soil were moisture and compaction times, respectively, but for cinnamon soil only was compaction time. Under tillage condition, the compaction density of brown soil was lowest at low moisture (<50 g/kg), and changed little with the increase of compaction times. While the lowest bulk density of cinnamon soil appeared at the lower compaction energy (<90 kJ/m3), and was less affected by moisture. Under engineering condition, when the moisture was about 150 g/kg the compaction energy required to obtain larger bulk density was the lowest.