Scaling-up: cover crops differentially influence soil carbon in agricultural fields with diverse topography

• Cover crop effects on soil particulate organic C (POC) and short-term C (SMC), were assessed at topographically diverse agricultural fields.
• Despite higher cover crop biomass in topo depressions, cover crop’s effect on soil C was not greater, and even lower, than that on slopes and summits.
• Our results point to the substantially greater importance of the cover crop roots, as opposed to the aboveground biomass, for soil C processes.
• A better detection of the management effects and temporal dynamics was possible with SMC than POC, due to its rapid response and lower variability.

The use of cover crops is a management technique that can potentially increase the amount of carbon (C) sequestered in soil. However, information on cover crop’s role in increasing soil C comes mostly from small experimental plots, while the magnitude of C gains in large agricultural fields may vary spatially in response to topographic and soil variability. Here we assess cover crop effects on soil organic C in 20 large agricultural fields across a topographically diverse landscape under conventional, low-input, and organic managements in corn-soybean-wheat rotation. The low-input and organic managements included rye and red clover cover crops in their rotations. Micro-plots with and without cover crops were laid out within each studied field at three contrasting topographical positions of depression, slope and summit. Soil samples were collected and analyzed for total organic carbon (TOC), particulate organic carbon (POC) and short-term mineralizable carbon (SMC). The magnitude of cover crop effects on SMC and POC varied across topography. The contributions of cover crop’s presence to soil C variables tended to be the highest on topographical slopes and summits. Positive correlations between effects of cover crop presence on SMC with cover crop biomass also were primarily observed on slopes and summits. The results indicate that in the studied agricultural environments preferential placement of cover crops on eroded low fertility elements of the relief can be a particularly effective strategy from both environmental and management standpoints.