Tillage impacts on depth distribution of total and particulate organic matter in three Illinois soils

The benefits of no-tillage (NT) practices to soil organic matter (SOM) are inconsistent in fine-textured, poorly drained soils. Tillage imparts on SOM were investigated in central Illinois, assuming particulate organic matter (POM) would accumulate where SOM aggraded. Soils were collected in 1994 and 1995 from a trial established in 1985 at Ferry and Monmouth (somewhat poorly drained Aquic Argiudoll silt loams), and DeKalb (a poorly drained Typic Haplaquoll silty clay loam). In general, NT practices increased SOM-C and POM-C ;contents 25 and 70% compared with conventional till (CT) at the soil surface (0-5 cm). This was at the expense of C at depth (5-17.5 cm), which decreased by 4 and 18%, respectively. Tillage effects varied among sites. No-till increased SOM C and POM C more than 30 and 100%, respectively, in the top 5 cm of the two silt loams. In the silty clay loam, NT reduced SOM C 14% in the 5- to 17.5-cm depth and POM C more than 20% in the 5- to 30-cm depth. Bulk density was greater under NT than CT at the DeKalb (0-17.5 cm) and Monmouth sites (0-5 cm). No-till only increased C and N sequestration, assessed on an equivalent mass basis, at Monmouth. Accumulation of POM in the surface depth of the NT silt loams may have improved soil quality in those erosion-prone soils. Reduced POM contents in the NT silty clay loam may reflect SORI degradation. The high clay and organic matter content and low bulk density of the DeKalb soil may have contributed to the atypical effect of NT practices on SOM at that site.