Nutrient Management Research Database

The relationship between nitrous oxide (N₂O) flux and N availability in agricultural ecosystems is usually assumed to be linear, with the same proportion of nitrogen lost as N₂O regardless of input level. We conducted a 3-year, high-resolution N fertilizer response study in southwest Michigan USA to test the hypothesis that N₂O fluxes increase mainly in response to N additions that exceed crop N needs. We added urea ammonium nitrate or granular urea at nine levels (0–292 kg N ha⁻¹) to four replicate plots of continuous maize. We measured N₂O fluxes and available soil N biweekly following fertilization and grain yields at the end of the growing season. From 2001 to 2003 N₂O fluxes were moderately low (ca. 20 g N₂O-N ha⁻¹ day⁻¹) at levels of N addition to 101 kg N ha⁻¹, where grain yields were maximized, after which fluxes more than doubled (to >50 g N₂O-N ha⁻¹ day⁻¹). This threshold N₂O response to N fertilization suggests that agricultural N₂O fluxes could be reduced with no or little yield penalty by reducing N fertilizer inputs to levels that just satisfy crop needs.

This study investigated how N fertilization influences nitrous oxide emissions.

Urea ammonium nitrate and granular urea were applied at 9 different rates (ranging from 0-260 lbs N/acre).

Nitrous oxide emissions and soil N levels were measured every other week following fertilization.

Grain yield was also measured.

Nitrous oxide emissions differed among different fertilization rates. Emissions remained low from 0 to 90 lbs N/ac and then showed a sharp increase at 120 lbs N/ac. Emissions dropped back down when fertilizer was applied at the 150 and 180 lbs N/ac levels before increasing again for the 220 and 260 lbs N/ac levels.

Grain yield increased up to 90 lbs N/ac before leveling off for higher application rates.

These results show that with proper fertilization rates yield can be maintained while decreasing nitrous oxide emissions.