Interactions of corn stover incorporation and simulated tillage on emission of CO2 : a laboratory study

Annual horticultural systems commonly rely on frequent and intensive tillage to prepare beds and manage weeds and insects. However, tillage increases the loss of soil organic carbon (SOC) through accelerated CO2 emission brought about by improvement in soil aeration and soil and crop residue contact (Angers et al., 1993). In contrast, some vegetable farmers use green manures, organic inputs (e.g. compost, mulch) and crop residues to perform various functions including increasing soil organic matter (SOM). Crop residue management systems that maintain organic materials in situ can benefit SOM (van Groenigen, et al., 2011). The effects of tillage and crop residue management can have opposing influences and may be difficult to isolate (Dalal et al., 2011). The SOC pool in the soil is the balance of C inputs in the form of crop residue and biomass, and C outputs such as CO2 emissions and other losses. The CO2 fixed in plant biomass by photosynthesis is returned to soil that forms SOM, some of which is lost due to tillage (Jarecki and Lal, 2003). Vegetable systems are vulnerable with very little crop residue input and heavy reliance on tillage, reducing SOC. We hypothesised that such systems could be made more resilient by including a high-residue grain crop like sweet corn (Zea mays var. rugosa L.) in the rotation. The subsequent corn stover input in the soil could balance the expected loss of SOC due to tillage. This laboratory study was conducted to separate the effects of residue incorporation and tillage in an associated field trial where sweet corn stover incorporation in a corn-cabbage (Brassica oleracea L.) rotation had a positive effect on SOC, but no differences in SOC for organic and conventional soil management systems. Organic vegetable systems rely on tillage for weed control, whereas conventional systems rely on herbicide. The laboratory study sought to evaluate CO2 emissions in incubated soil after simulated tillage (weed control in organic) with and without the incorporation of ground corn stover.