Long-Term Effects of Drainage and Compaction on Microbial Biomass, Total and Active Carbon Content of Soil.

Information on long-term effects of drainage and compaction on soil organic matter (SOM) is limited. A randomized complete block experiment was conducted to evaluate the impact of drainage and compaction (1983-2007) on SOM, especially total (TC), active (AC), and microbial biomass (SMB) C content in drained and undrained Hoytville clay loam with corn-soybean rotation with trafficked and untrafficked lanes. The heaviest axle load was approximately 4 Tons. The experimental plots used were established in 1982 with drain lines installed at 80 cm below the surface and spaced 6 m apart. In 2007, composite soil samples at 0-15 and 15-30 cm depth were randomly collected, 2-mm sieved, and analyzed for bulk density (rb), TC, AC, and SMB content. Averaged across compaction and depth, undrained soil had significantly higher rb (4%), AC (85), and AC:TC but lower PC:AC than drained soil. However, the SMB did not vary significantly in response to drainage impacts. In contrast, SMB (22%), SMB:TC and AC (13%) except rb (6%) were significantly higher in untrafficked lanes compared to trafficked lanes. Except rb, higher values were found near the surface than at deeper depths. Both drainage x depth and compaction x depth had significant interaction on rb, TC, AC, PC, SMB, and SMB:TC. However, drainage x tillage x depth had significant interaction only on SMB and SMB:TC.