Variable impacts of reduced and zero tillage on soil carbon storage across 4–10 years of UK field experiments

Aims: Reduced tillage has been advocated as a practical measure to increase soil carbon in long-term cropping soils. We examine three medium-term experiments in sites with contrasting soil and climatic characteristics in the UK. The objectives were to determine the effects of different reduced and zero tillage practices on bulk density and soil carbon storage and depth distribution and to quantify the effect of stones in their calculation. Methods: The treatments were zero tillage, minimum tillage, conventional plough, deep non-inversion tillage and plough compaction. Soil samples were collected from three sites at five depth intervals to approximately 60 cm. Results: Deep non-inversion and minimum tillage led to 6.5 and 1.6 Mg ha−1 greater SOC than conventional plough in sites under rotation systems. In a monoculture system in Scotland, conventional plough had 25.3, 21.6 and 17.7 Mg ha−1 greater SOC than plough compaction, minimum tillage and zero tillage, respectively. After harvest, bulk density was greater in the soil surface of conventional plough compared with minimum tillage. Conclusions: Our results suggest variable impacts of reduced tillage on SOC storage. Overall there is limited benefit in using shallow minimum tillage and zero tillage practices in the UK to increase soil carbon storage when a soil profile of 60 cm is considered but other benefits associated to these systems, such as speed of working and timeliness of operations, should be considered.