Tillage and Crop Rotation Impact on Soil Organic Matter Quality.

Management practices influencing soil organic matter quality responsible for carbon sequestration are still not very clear. A randomized block experiment in 2 (tillage) x 3 (crop rotation) factorial arrangement was laid-out to evaluate tillage and crop rotation impact (1990 to 2007) on organic matter quality at different soil depths. An untilled grassy was used as control. Tillage treatments (conventional tillage, CT and no-till, NT) were factored into continuous corn (CC), corn-soybean (CS), and corn–soybean-wheat-cowpeas (CSW) rotation. Soil cores were randomly collected at 0-7.5, 7.5-15, 15-22.5 and 22.5-30 cm depths, 2-mm sieved, air-dried, extracted humic substances with 0.5M NaOH (pH 13.4). The extracts were filtered, air-dried, and analyzed for functional group components by using Fourier Transformation Infrared (FTIR) Spectroscopy. Results showed that extracted humic substances were dominated by OH, C=C and C-C groups. In both NT and CT, the functional groups were dominated by OH and C=C for corn and corn-soybean rotation. Including wheat in the rotation under both NT and CT showed C-C peak. Likewise, humic substances extracted from grass land showed peaks of OH, C=C and C-C groups. However, continuous corn under NT showed only OH peak.