Integrated crop-livestock effects on soil carbon and nitrogen in a semiarid region

Integrated crop-livestock (ICL) system effects on soil organic carbon (SOC) and total nitrogen (TN) are highly variable due to differences in ecoregion-specific management practices, historical land use, and inherent climatic/edaphic attributes. Few studies have evaluated ICL system effects on SOC and TN in semiarid regions, where soil attributes change slowly. This study quantified ICL system effects on SOC and TN in a long-term experiment near Mandan, ND. Effects of three residue management treatments (Grazed, Removed, Control) on SOC and TN were determined at five depths (0-0.08, 0.08-0.15, 0.15-0.31, 0.31-0.61, and 0.61-0.91 m) in 1999 and 2014. No-till practices were employed throughout the study following conversion of perennial grass pastures. A significance criterion of P <= .10 was used to assess treatment effects as the experimental design was constrained to two replications. Residue management affected SOC and TN in near-surface depths only, with greater concentration of SOC and TN at 0-0.08 m under Grazed compared to Removed in 2014 (P = .0844 and .0576). When expressed on an equivalent mass basis, SOC stocks were greater under Grazed and Control compared to Removed. Soil organic C and TN stocks increased over time in the Control by 11.2 Mg C ha(-1) and 1.2 Mg N ha(-1), respectively (P = .0728 and .0868). Soil organic C stocks also increased over time under the Grazed treatment by 10 Mg C ha(-1) (P = .0630). Study results highlighted the importance of residue retention and livestock grazing for increasing SOC and TN in ICL systems under semiarid conditions.