TILLAGE AND CROP-ROTATION EFFECTS ON SOIL ORGANIC-MATTER IN A TYPIC HAPLUDULT OF NORTHERN ALABAMA

A study was conducted to determine the impact of long-term (1980-1990) tillage and crop rotation treatments on soil organic C and N concentrations in a Typic Hapludult at Crossville, Alabama. Tillage treatments included conventional tillage (CT) and no-till (NT), and crop rotation treatments were continuous soybean (Glycine max L.)-wheat (Triticum aestivum L.) cover (SW), continuous corn (Zea mays L.)-wheat cover (CW) and corn-wheat cover-soybean-wheat cover (CWSW). Surface soils (0 to 5, 5 to 10, and 10-20 cm depth increments) were sampled on 31 October 1990 and analyzed for organic C and N. After 10 years, soil organic C and N concentrations and degree of stratification were greater under NT than CT due to differential placement of crop residues in relation to the soil surface. Highest levels of soil organic C and N were found under CW and CWSW rotations in combination with NT due to greater amounts of crop residues added over the 10 year cropping period.