What happens to in situ net soil nitrogen mineralization when nitrogen fertility changes?

Does net soil nitrogen (N) mineralization change if N-fertility management is suddenly altered? This study, conducted in a long-term no-tillage maize (Zea mays L.) fertility experiment (established 1970), evaluated how changing previous fertilizer N (PN) management influenced in situ net soil N mineralization (NSNM). Net soil N mineralization was measured by incubating undisturbed soil cores with anion and cation exchange resins. In each of three PN fertilizer application plots (0, 84, and 336 kg N ha⁻¹), another three fertilizer application rates (0, 84, and 336 kg N ha⁻¹) were imposed and considered the current fertilizer N (CN) management. Generally, PN-336 (336 kg N ha⁻¹) had significantly greater NSNM than PN-0 (0 kg N ha⁻¹) or PN-84 (84 kg N ha⁻¹), which reflected differences in soil organic-C (SOC) and soil total-N (STN). The three CN rates had no significant effect on NSNM when they were applied to PN-0 or PN-84, but CN-336 (336 kg N ha⁻¹) had significantly higher NSNM than CN-0 (0 kg N ha⁻¹) or CN-84 (84 kg N ha⁻¹) in the PN-336 plots. The CN or “added N interaction” used the indigenous soil organic matter (SOM) pool and the added sufficient fertilizer N. Environmental factors, including precipitation and mean air temperature, explained the most variability in average daily soil N mineralization rate during each incubation period. Soil water content at each sampling day could also explain NSNM loss via potential denitrification. We conclude that “added N interaction” in the field condition was the combined effect of SOM and sufficient fertilizer N input.