Root‐Derived Contributions to Soil Respiration as Influenced by Agricultural Management Systems

Agricultural management practices have the potential to significantly alter soil C storage through changes in C inputs and losses. Plant roots represent a significant, but poorly understood source of C inputs. Corn ( Zea mays L.) root C was 13 C‐labeled in a field experiment to examine the effects of tillage and fertilization, crop rotation diversity, and fertilizer type on root‐derived C cycling in Mollisols in the Upper Midwest. Daily and cumulative root‐derived C emissions, their contribution to total soil respiration, and the turnover of root‐derived C were quantified during the soybean [ Glycine max (L.) Merr.] phase of crop rotations. Over two growing seasons, the average corn root‐derived contribution to cumulative soil C emissions was 8.5%, and on average 35% of the initial root‐derived C was respired. Environmental conditions were the primary control over daily root‐derived C emissions, but management system effects on cumulative growing season emissions were evident. In both seasons organic fertilization led to lower cumulative root‐derived emissions and root‐derived contributions to cumulative C emissions than synthetic fertilization. In 2005, more intense tillage and synthetic fertilization positively affected cumulative root‐derived C emissions and the root‐derived fraction of cumulative soil C emissions (moldboard > chisel plow). Root‐derived C turnover was negatively affected by rotation diversity in 2006 (2‐yr > 4‐yr rotation). We suggest that rotation diversity has an important influence on soil C storage and root‐derived C turnover through effects on the quantity of root‐derived C inputs.