Soil carbon and nitrogen fractions after 19 years of farming systems research in the Coastal Plain of North Carolina

Abstract

AbstractLong‐term agricultural experiments in the Coastal Plain of the southeastern United States are needed to understand biogeochemical processes and design better systems to overcome a changing climate and other perturbations. We determined a suite of soil organic C and N fractions after 19 yr of management from a diverse farming system project in Goldsboro, NC. Soil was collected at 0‐ to 6‐, 6‐ to 12‐, and 12‐ to 20‐cm depth increments from 14 treatments that were subsets of five overarching treatments of conventional cropping, integrated crop–livestock systems, organic cropping, plantation forestry, and old‐field successional land use. Surface residue C and N were greater with woody (i.e. plantation forestry and successional) than with cropping systems (7,491 and 2,896 kg C ha−1, respectively; 138 and 60 kg N ha−1, respectively). Soil‐test biological activity was greater with alternative cropping (i.e. integrated crop–livestock and organic systems) than conventional cropping (314 vs. 220 kg CO2–C ha−1 3 d−1, respectively). An integrated crop–livestock system with grazed pasture in long rotations with crops had greater net N mineralization than hayed forage in shorter rotations (111 vs. 92 kg N ha−1 24 d−1, respectively). Total organic C and particulate organic N concentrations were highly stratified with depth, but stocks were not different between conventional and no‐till cropping when summed to 20 cm. We conclude that alternative cropping systems with forage‐based rotations, limited tillage, and organic inputs can create long‐lasting improvements in soil organic C and N fractions than conventional agricultural and more naturalized systems.