Effect of Green Manure Termination Method on Soil Abiotic Properties and Earthworm Numbers in an Organic Grain Rotation.

Agriculture is a major source of soil degradation worldwide. While no-till crop management is commonplace in conventional agriculture due to the known benefits to soil, organic agriculture still relies heavily on tillage for weed control and incorporation of green manures. This research examines the use of hairy vetch (Vicia villosa Roth) as a green manure (GMr) in Atlantic Canada to improve soil health under various levels of tillage intensity. At both sites an organic grain crop rotation (including full-season hairy vetch followed by wheat) was established in 2013. Three levels of GMr termination are being employed; fall tillage (tilled in the fall and spring), spring tillage (rolled in fall and tilled in spring), and no-till using a crop-roller to terminate the hairy vetch. In the no-till treatment wheat is no-till planted into the surface mulch derived from GMr aboveground biomass. In June 2014 earthworms were sampled in the wheat rotation phase and again in the wheat stubble in 2015 as an indicator of soil ecosystem health. In 2014, earthworm numbers were significantly higher for the no-till plots (91 earthworms/m² –compared to fall tilled (15 earthworms/m²) and spring tilled (7 earthworms/m²). The soil in no-till plots was also cooler and had more moisture in the spring compared to tilled plots. Favourable environmental conditions created by the no-till mulch combined with the lack of physical soil disturbance caused by tillage may both be contributing to the increased earthworm numbers in no-till plots. Decreased earthworm numbers in fall tillage and spring tillage treatments persisted into 2015, the second year after tillage was implemented (30 and 38 earthworms/m² respectively compared to 90/m2 in no-till). Longer periods of time between tillage by implementing no-till techniques in in organic agriculture could allow the earthworm population to recover.