Effects of Agricultural Management Systems On Gaseous Carbon Losses From Corn Root Residue.

Globally, mechanized farming contributes 13% of annual greenhouse gas emissions (CO₂, CH₄, and N₂O). Tillage is frequently identified as the primary driver of these high CO₂ emissions as it increases soil carbon (C) losses by altering the soil structure resulting in greater C losses as CO₂. In light of developing C credit markets, which promote management practices based on their soil C storage potential, we must improve our understanding of management system (comprising tillage, fertilization and rotation practices) effects on soil C cycling. Our research addresses the uncertainty surrounding management system effects on soil C storage by measuring gaseous C losses from recent organic matter inputs to the soil across five management systems commonly used in the Upper Midwest. We used ¹³C- and ¹⁵N-labeled corn root residue to track gaseous emissions of corn root C and N from the soil as CO₂, CH₄, and N₂O over two growing seasons. In the early growing season, root residue C accounts for 10-15% of total gaseous C losses, decreasing on average to 5-10% by the end of the growing season. Changes in the contribution of root derived C to total C losses are largely driven by changes in live root respiration, as the seasonal variation in root residue C losses is small (growing season range is 0.1-0.4 g root C/m²/d). We found that management systems (varying in tillage, fertilization and rotation practices) explain only a small proportion of the variability in both the proportion of total soil C losses derived from recent root residue and the cumulative losses of soil C. These results indicate that management systems are not the primary factor controlling the retention of recent soil C inputs and indicate the need for further investigation of controls on C dynamics in managed soils.