Soil organic matter characteristics as affected by tillage management

Soil organic matter (SOM) is of primary importance for maintaining soil productivity, and agricultural management practices may significantly influence SOM chemical properties. I low,ever, how SOM chemical characteristics change with agricultural practices is poorly understood. Therefore, in this study, we evaluated the impacts of tillage (conventional vs. conservation) management on the structural and compositional characteristics of SOM using cross-polarization magic-angle-spinning (CPMAS) and total sideband suppression (TOSS) solid-state C-13 nuclear magnetic resonance (NMR) and diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy. We characterized both physically and chemically isolated SOM fractions from a Norfolk soil (fine-loamy, siliceous, thermic Typic Kandiudults) under long-term tillage management (20 yr). The solid-state C-13 NMR results indicated that humic acid (HA) from conventional tillage (CT, 0-5 cm) was less aliphatic and more aromatic than HA from conservation tillage (CnT). The aliphatic C content decreased with increasing depth (0-15 cm) for both CT and CnT treatments. The reverse trend was true for aromatic C content. Based on reactive/recalcitrant (O/R) peak ratio comparisons, HA was more reactive in the top soil (0-5 cm) under CnT than CT. Both soil organic C (SOC) and light fraction (LF) material were higher in the 0- to 5-cin soil of CnT than CT treatment. Our results show that long-term tillage management can significantly change the characteristics of both physical and chemical fractions of SOM.