Greater humification of belowground than aboveground biomass carbon into particulate soil organic matter in no-till corn and soybean crops

S. R. Mazzilli, A. R. Kemanian, O. R. Ernst, R. B. Jackson, and G. Piñeiro

Soil Biology and Biochemistry (June 2015)

DOI: 10.1016/j.soilbio.2015.02.014

Abstract Quantifying the amount of carbon (C) incorporated from decomposing residues into soil organic carbon (CS) requires knowing the rate of C stabilization (humification rate) into different soil organic matter pools. However, the differential humification rates of C derived from belowground and aboveground biomass into CS pools has been poorly quantified. We estimated the contribution of aboveground and belowground biomass to the formation of CS in four agricultural treatments by measuring changes in δ13C natural abundance in particulate organic matter (CPOM) associated with manipulations of C3 and C4 biomass. The treatments were (1) continuous corn cropping (C4 plant), (2) continuous soybean cropping (C3), and two stubble exchange treatments (3 and 4) where the aboveground biomass left after the grain harvest was exchanged between corn and soybean plots, allowing the separation of aboveground and belowground C inputs to CS based on the different δ13C signatures. After two growing seasons, CPOM was primarily derived from belowground C inputs, even though they represented only ∼10

keywords: Particulate organic matter; Root carbon inputs; Carbon isotopes; Humification rate; Corn; Soybean

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