Contribution of wheat and maize to soil organic carbon in a wheat-maize cropping system: a field and laboratory study

Retention of crop biomass is widely recommended to improve soil organic
carbon (SOC). However, the magnitude of contribution of aboveground
residues and belowground roots from C3 and C4 crops to SOC is unclear.
Data from a 10-year field experiment and a 60-day laboratory incubation
were synthesized to identify the respective contribution of C3 (e.g.,
wheat) and C4 (e.g., maize) residues and roots to SOC, as well as its
underlying mechanisms under no-till (NT) using 13C labelling trace in
wheat-maize rotations. The field experiment showed that residue retention
significantly increased SOC accumulation, and SOC derived from wheat was
126.0% higher than that from maize. Conversion to NT promoted SOC derived
from wheat and thus accumulated 17.6% higher SOC stock compared with plow
tillage (PT) under residue returning at 0-20 cm soil depth
(P<0.05). The data from laboratory incubation revealed the
mechanisms that lower priming effects at 0-10 cm depth decreased total
mineralization by 91.8% after inputs of wheat residues and roots compared
with that of maize residues and roots, especially under NT compared with
PT. Priming effects were negatively correlated with enzyme activities
associated with the C recycle, SOC, and total nitrogen (TN) contents
(P<0.01). NT increased enzyme activities, SOC, and TN contents and
thus reduced priming effects and improved residual C. Synthesis and
applications. These results suggested that wheat may contribute more to
SOC accumulation than maize, and carbon increment efficiency in farmland
could be enhanced by considering the crucial roles of C3 crops in SOC
accumulation. NT practice sustains the benefits of C3 crops to SOC
sequestration in the upper soil depths.