Campus Units

Agronomy, Ecology, Evolution and Organismal Biology

Document Type


Publication Version

Accepted Manuscript

Publication Date


Journal or Book Title

Global Change Biology





First Page


Last Page





Global maize production alters an enormous soil organic C (SOC) stock, ultimately affecting greenhouse gas concentrations and the capacity of agroecosystems to buffer climate variability. Inorganic N fertilizer is perhaps the most important factor affecting SOC within maize-based systems due to its effects on crop residue production and SOC mineralization. Using a continuous maize cropping system with a 13 year N fertilizer gradient (0–269 kg N ha−1 yr−1) that created a large range in crop residue inputs (3.60–9.94 Mg dry matter ha−1 yr−1), we provide the first agronomic assessment of long-term N fertilizer effects on SOC with direct reference to N rates that are empirically determined to be insufficient, optimum, and excessive. Across the N fertilizer gradient, SOC in physico-chemically protected pools was not affected by N fertilizer rate or residue inputs. However, unprotected particulate organic matter (POM) fractions increased with residue inputs. Although N fertilizer was negatively linearly correlated with POM C/N ratios, the slope of this relationship decreased from the least decomposed POM pools (coarse POM) to the most decomposed POM pools (fine intra-aggregate POM). Moreover, C/N ratios of protected pools did not vary across N rates, suggesting little effect of N fertilizer on soil organic matter (SOM) after decomposition of POM. Comparing a N rate within 4% of agronomic optimum (208 kg N ha−1 yr−1) and an excessive N rate (269 kg N ha−1 yr−1), there were no differences between SOC amount, SOM C/N ratios, or microbial biomass and composition. These data suggest that excessive N fertilizer had little effect on SOM and they complement agronomic assessments of environmental N losses, that demonstrate N2O and NO3 emissions exponentially increase when agronomic optimum N is surpassed.


This is an article from Brown KH, Bach EA, Drijber RA, Hofmockel K, Jeske ES, Sawyer JE, Castellano MJ. 2014. A long-term N fertilizer gradient has little effect on soil organic matter in a high-intensity maize production system. Global Change Biology doi: 10.1111/gcb.12519. Posted with permission.

Copyright Owner




File Format


Published Version