Interaction of tillage and soil texture: Biological active soil organic matter in Illinois

Several long-term studies suggest that no-till (NT) practices do not increase soil organic matter (SOM) sequestration in all situations. We evaluated the interaction of tillage and soil texture effects on SOM in Illinois Mollisols and Alfisols by characterizing particulate organic matter (POM), potentially mineralizable N (PMN), and soil microbial biomass (SMB). Thirty-six fields were sampled during spring and summer of 1995 and 1996. Each field had been under either conventional tillage (CT) (disc, moldboard plow, and/or chisel plow) or NT management for at least 5 yr. No-till fields contained 15% (3.0 g C kg^-1 soil) more soil organic C (SOC) than CT fields in the 0- to 5-cm depth; however, tillage did not affect SOC contents in the 5- to 15- or 15- to 30-cm depths, or in the overall sampling depth (0-30 cm), Fields under NT contained 33% more POM (1.4 g C kg^-1 soil) and 54% more PMN in the 0- to 5-cm depth, but there was no tillage effect on POM (0-15 cm) or PMN (0-30 cm) contents overall. Average POM contents were 29% lower (0.73 g C kg^-1 soil) in the 5- to 15-cm depth of the NT than of the CT soils. At sand contents below ≈50 g kg^-1 soil. NT fields contained greater SOC, total N, and POM contents in the 0- to 5-cm depth and lower POM contents in the 5- to 15-cm depth than CT fields. In soils with sand contents higher than ≈50 g kg^-1 soil, tillage practices did not affect the vertical distribution of SOC, total N, or POM.