Project ID



Much of the available soil organic carbon (SOC) is in subsoil, yet few studies have evaluated how crop rotation affects SOC below the plow layer. This project looks at whether crop rotations with greater belowground C inputs would increase SOC stocks by delivering C to subsoil with relatively low SOC levels.

Key Question

How do differences in above- vs. belowground allocation of plant carbon inputs, mediated by differences in crop rotation, affect the storage of soil organic carbon in surface- and subsoils?


Extended crop rotations had higher soil organic carbon concentrations than the simple rotations down to 1m depth in two of three long-term field experiments. The proportion of organic matter in different physical and chemical fractions was similar for simple and extended rotations. The rate of soil organic carbon storage over the last 12 years was greater at depth than at the surface, but was not affected by crop rotation.

Principal Investigator(s)

Michael Castellano

Principal Investigator(s) Bio

Michael Castellano is an assistant professor in ISU Agronomy. His research focuses on biogeochemical cycling and transport within the soil as it extends to the atmosphere and subsoil. He is a member of the Iowa Nutrient Reduction Taskforce and led development of a USDA-funded Midwest greenhouse gas monitoring network of corn-based cropping systems. He also is a member of an ISU task force that assists Des Moines Water Works in managing its nitrate-removal facility. He has degrees from the University of Rhode Island and Saint Louis University and a Ph.D. in soil science from Pennsylvania State University.


Hanna Poffenbarger, Matthew Liebman

Year of Grant Completion