Root Inputs Drive C Storage Differences in Corn- and Prairie-Based Cropping Systems.

Placing more C in the soil is desirable because doing so increases soil quality and decreases the amount of C in the atmosphere.  The potential to restore soil C through the reconstruction of prairie systems is unclear because measuring changes in soil C is inherently difficult.  We sought to determine differences in C storage between the predominant corn-based agricultural systems and reconstructed prairie by focusing on changes to the C pool contained in the root mass.  A six-year field study was conducted near Boone, IA in which root mass was measured to a 1 m depth at the end of every growing season and root tissues were analyzed for C and N content.  We found that six years after establishment of the prairie, an unfertilized prairie contained 6.5 times more root C mass (3.8 Mg C ha-1) than corn-based treatments (0.58 Mg C ha-1) and a N-fertilized prairie contained 3.5 times more root C mass (1.5 Mg C ha-1).  Unfertilized prairie root mass in the last year of the study was greater in the lowest depth increment (60-100 cm) than root mass at any depth increment in the corn-based treatments.  Unfertilized prairie root mass C:N ratios averaged across 1 m in the last year of the study were 140.8 for unfertilized prairie, 61.4 for fertilized prairie, and 29.4 for corn-based systems.  After six years of growth, prairies placed more C belowground, in a form that is more difficult to decompose, at depths that are less favorable for decomposition.