Maximum soil organic carbon storage in Midwest U.S. cropping systems when crops are optimally nitrogen-fertilizedReport as inadecuate




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Nitrogen fertilization is critical to optimize short-term crop yield, but its long-term effect on soil organic C SOC is uncertain. Here, we clarify the impact of N fertilization on SOC in typical maize-based Zea mays L. Midwest U.S. cropping systems by accounting for site-to-site variability in maize yield response to N fertilization. Within continuous maize and maize-soybean Glycine max L. Merr. systems at four Iowa locations, we evaluated changes in surface SOC over 14 to 16 years across a range of N fertilizer rates empirically determined to be insufficient, optimum, or excessive for maximum maize yield. Soil organic C balances were negative where no N was applied but neutral maize-soybean or positive continuous maize at the agronomic optimum N rate AONR. For continuous maize, the rate of SOC storage increased with increasing N rate, reaching a maximum at the AONR and decreasing above the AONR. Greater SOC storage in the optimally fertilized continuous maize system than in the optimally fertilized maize-soybean system was attributed to greater crop residue production and greater SOC storage efficiency in the continuous maize system. Mean annual crop residue production at the AONR was 22% greater in the continuous maize system than in the maize-soybean system and the rate of SOC storage per unit residue C input was 58% greater in the monocrop system. Our results demonstrate that agronomic optimum N fertilization is critical to maintain or increase SOC of Midwest U.S. cropland.



Author: Hanna J. Poffenbarger , Daniel W. Barker, Matthew J. Helmers, Fernando E. Miguez, Daniel C. Olk, John E. Sawyer, Johan Six, Micha

Source: http://plos.srce.hr/



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