Residue‐ and nitrogen‐induced carbon mineralization varies with soil fertility status

Abstract By increasing the input of corn ( Zea mays L.) residues, synthetic nitrogen (N) fertilization is often assumed to enhance soil storage of organic carbon (C), which could be especially beneficial for improving the fertility of depleted soils. To ascertain whether such a strategy can be effective, C mineralization was compared for two soils with different indigenous N contents by conducting a 60‐day laboratory incubation experiment that involved continuous monitoring of CO 2 emissions with periodic sampling for atmospheric δ 13 C analysis and for determination of soil microbial biomass and cellulolytic enzyme activities. The addition of exogenous N had a stimulatory effect on cumulative CO 2 production that was greater for the low than high N supplying soil and more prominent in the first than in the second month of incubation. During residue decomposition, microbial activities were maximized by incubating the low N soil with exogenous N, whereas cellulolytic enzyme activities were greater for the high N soil. Although intensive N fertilization can substantially increase the productivity of low‐fertility soils, the additional residue inputs thereby generated are more effective for promoting C mineralization than sequestration.