Two-year simultaneous records of N2O and NO fluxes from a farmed cropland in the northern China plain with a reduced nitrogen addition rate by one-third

Abstract

Given the common problem of fertilizer overuse, agronomists are calling for a reduction of the high nitrogen dose by 1/3. We carried out a field experiment over two full winter wheat–summer maize rotations in the North China Plain (NCP) to determine whether this degree of nitrogen reduction will significantly reduce the emissions of nitrous oxide (N2O) and nitric oxide (NO). Three treatments were investigated in the field trial: a control with no nitrogen application, the conventional practice with nitrogen over-application and the optimal practice with a reduced dose of nitrogen by 1/3. Our observations across all treatments over the experimental period reveal significant correlations of the fluxes of either gas with soil temperature and moisture as well as the concentrations of soil ammonium, nitrate and dissolvable organic carbon. There were strong correlations within the functions of the dual Arrhenius and Michaelis–Menten kinetics, giving apparent activation energy values of 40–97 and 59–92kJmol−1 for N2O and NO fluxes, respectively. Our results provide annual direct emission factors of 0.48–0.96% for N2O and 0.15–0.47% for NO and demonstrate a significant correlation between N2O emission induced by fertilization and fertilizer nitrogen use efficiency (NUE). The correlation indicates a significant potential of N2O mitigation via enhancing NUEs. A reduction in the nitrogen dose did not obviously mitigate either the annual NO emission in both rotations or the annual N2O emission in the second one. However, nitrogen reduction significantly decreased the annual total N2O emission by 38% during the first rotation. These inconsistencies in the responses of N2O emission to the reduced nitrogen dose can be attributed to improper fertilization practices, such as broadcasting urea prior to heavy rainfalls or irrigation events during the maize season, which implies a need for further fertilization practice options/techniques in addition to the reduction of nitrogen doses.