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Fig. 1. Carbon fluxes through the crop–soil system. 1 = net crop production, generating organic matter from atmospheric CO2. 2 = aboveground crop residues returned to the soil surface. 3 = belowground C allocation, that is, fluxes of C from shoots to root systems. 4 = root mortality and other inputs of organic matter from root systems to the soil. 5 = root, mycorrhizal, and rhizosphere respiration. 6 = CO2 produced by the heterotrophic oxidation of detritus in the soil. 7 = surface soil CO2 efflux, or soil respiration.
