Carbon and Nitrogen Dynamics in an Eastern Corn Belt Soil: Nitrogen Source and Rotation

Soil C sequestration may mitigate increasing atmospheric carbon dioxide concentrations. This study was conducted to assess chemical and physical fractions of total organic C (TOC) and total N (TN) as affected by land use, N fertilizer source, and rotation. Particulate organic matter (POM) and non-hydrolyzable C (NHC) fractions were measured in Drummer (fine-silty, mixed, superactive, mesic Typic Endoaquoll) silty clay loam and Raub (fine-silty, mixed, superactive, mesic Aquic Argiudoll) silt loam soil series during two growing seasons. Agroecosystems evaluated were continuous corn (Zea mays L.) (CC) and corn grown in rotation with soybean [Glycine max. (L.) Merr.] (CS) both with urea-ammonium nitrate (UAN), CC with either spring or fall liquid swine manure (CCSM and CCFM, respectively), soybean in rotation with CSUAN (SC), and restored prairie grass (PG). In general, CCFM exhibited the largest soil C and N pools. In corn-soybean rotations, the TOC declined roughly 10% following SC but increased a comparable amount following CSUAN. The 2-yr corn-soybean rotation (SC and CSUAN) had a similar overall effect as CCUAN on TOC (ranging from 22 to 24 g C kg(-1) soil). When compared with CCUAN, PG soils were enriched in TOC, fine POM-C and NHC but not in N pools, reflecting soil C and N dynamics dominated by fine root turnover without fertilization and tillage. Comparison of soil C pools between treatments that differed in TOC revealed that newly sequestered C was preferentially allocated into POM supporting this fraction as an indicator of management effect on C sequestration.