Effects of conservation tillage drills on soil quality indicators in a wheat‐oilseed rape rotation: organic carbon, earthworms and water stable aggregates

The effects of five conservation tillage drills with crop residue levels covering between 17% and 79% of the soil, and tillage depths ranging from 25 mm to 200 mm, were examined over three years. The tillage systems ranged from a relatively disruptive Farm System to a Low Disruption system, with three intermediate treatments labelled Sumo DTS, Claydon, and Mzuri. The study involved field sites on a clay or clay loam soil, where winter wheat and oilseed rape were grown in rotation. In the clay field, the Mzuri and Low Disruption treatments, which produced the highest residue coverage, showed the greatest increase in surface total soil organic carbon (1.1 and 0.48 Mg C ha−1 respectively) between year 1 and 3. The least disruptive tillage system also resulted in the highest density of earthworms (181‐228 m−2), and the most disruptive system produced the lowest densities (75‐98 m−2). In the third year, the least disruptive system also showed a higher proportion of water stable aggregates (29.8%) than the other treatments (22.7‐25.3%). Linear regressions showed positive relationships of both soil organic carbon and earthworm density with surface residue cover, and of the proportion of water stable aggregates with soil organic carbon.