Conservation Tillage Effects On Stabilization of Crop Residue-C.

Crop residues in agricultural soils are the primary means of sustaining soil organic matter levels. A field study was set out in 1990 on a loamy sand soil to quantify conservation tillage effects on crop residue-C decay and on its subsequent stabilization. At crop harvest, ¹⁴C-labeled, above-ground residues representative of common agricultural crops grown in southern Ontario, corn (Zea mays L.), soybeans (Glycine max L.), winter wheat (Triticum aestivum L.), winter rye (Secale cereale L.) and tobacco (Nicotiana tobaccum L.), were added to soils managed under conventional (CT) mouldboard plough-disc and conservation tillage (RT). Recovery of crop residue derived-C was measured as ¹⁴C remaining in the upper 40 cm soil and expressed on an equivalent mass basis.  Crop residues exhibited different decomposition patterns as did incorporated residues (CT) vs surface-applied residues (RT). Kinetic analysis of the pattern of crop residue decay showed that under CT the labile component was larger and decayed faster compared with RT. This suggests that incorporated residues were exposed to a more favourable environment for microbial activity compared with residues left on the soil surface. Averaged over all crops, the resistant component was 50.3% larger under RT, though it decayed at a slightly faster rate, t_1/2 = 7.3 y, vs t_1/2 = 8.6 y under CT. These results confirm long-term benefits of adoption of conservation tillage practices on crop residue-derived C sequestration in soil.