Soil organic carbon and microbial biomass carbon under organic and conventional vegetable cropping systems in an Alfisol and a Vertisol

Despite scant crop residue input, tillage to control weeds in vegetable systems reduces soil organic carbon (SOC) levels. We hypothesized that vegetable production systems could be made more resistant to the negative effects of tillage on SOC by including a high-residue crop in rotation. Effect of sweet corn (Zea mays L. var. rugosa) residue incorporation in a corn-cabbage (Brassica oleracea L.) rotation in two soil management systems (SMS) (organic or conventional) in two soil types [a Chromosol (Alfisol) and a Vertosol (Vertisol)] on SOC and microbial biomass C (MBC) levels was tested for 2 years. Confounded factors (weed management and fertilisers) in the field experiment were separated in a multi-factorial laboratory experiment. In the field, total organic C (TOC) concentration was increased by 6.5 % in the 0-0.1 m depth by incorporating residue; however SMS exhibited inconsistent results. Organic fertilisers increased TOC whilst simulated tillage decreased it in laboratory. Soil MBC data showed that the biological fertility of soil can be improved by incorporating residues or by combining residue with organic fertiliser. In field residue incorporation in soil increased TOC, but organic fertilisers behaved inconsistently. However, in a laboratory microcosm, both residue and organic fertilisers individually mitigated tillage-induced loss of TOC.