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

Several long-term studies suggest that no-till (NT) practices do not increa se soil organic matter (SOM) sequestration in all situations. We evaluated the interaction of tillage and soil texture effects on SOR I in Illinois Mo llisols and Alfisols by characterizing particulate organic matter (POM), po tentially mineralizable N (PMN), and soil microbial biomass (SMB). Thirty-s ix fields were sampled during spring and summer of 1995 and 1996, Each fiel d had been under either conventional tillage (CT) (disc, moldboard plow, an d/or chisel plow) or NT management for at least 5 gr. No-till fields contai ned 15% (3.0 g C kg(-1) soil) more soil organic C (SOC) than CT fields in t he 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 c m) 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 soi ls. At sand contents below approximate to 50 g kg(-1) soil, NT fields conta ined greater SOC, total N, and POM contents in the 0- to 5-cm depth and low er POM contents in the 5- to 15-cm depth than CT fields. in soils with sand contents higher than approximate to 50 g kg(-1) soil, tillage practices di d not affect the vertical distribution of SOC, total N, or POM.