Nitrite (NO2 −) accumulation and associated production of nitric oxide (NO) and nitrous oxide (N2O) gases in soils amended with nitrogen (N) fertilizers are well documented, but there remains a poor understanding of their regulation and variation among soil types. We examined responses to urea inputs in two soils at five temperatures from 5 to 30 °C and developed a process-driven model to describe the dynamics. A microcosm system was used to measure ammonia gas (NH3), ammonium (NH4 +), NO2 −, nitrate (NO3 −), NO, N2O and pH over 12 weeks. Unexpectedly, NO2 −, NO and N2O production tended to increase as soil temperature declined in both soils. The maximum NO2 − concentration, or compensation point (CP), differed by soil type but the time required to reach CP decreased exponentially with increasing temperature in both soils. A two-step nitrification model (’2SN’) accounted for interactions of ammonia-oxidation (AmO), nitrite oxidation (NiO), urea hydrolysis, NH4 + sorption, N gas production and pH dynamics. Both steps of nitrification (AmO and NiO) were modeled using NH3 inhibition kinetics. The model adequately simulated the observed dynamics and temperature responses and showed that increased uncoupling of AmO and NiO at colder temperatures resulted from their differential temperature responses. The dynamics observed here may be important following high-rate and banded N fertilizer applications and in ruminant urine patches. The results may help explain elevated N2O emissions observed under cold temperatures. The 2SN model can account for interactions among multiple processes and may be useful for studying the effects of management practices and climate factors, including climate change scenarios, on soil N cycling.
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The authors acknowledge and thank Dr. Emerson F.C. Souza, Michael Dolan, Xinci Tan and Carrie O'Connor-Walker for their assistance with the experiments, Scott Mitchell for logistical help and Dr. Larry Hendrickson and two anonymous reviewers for their review of an earlier draft of the manuscript. This work was supported in part by a grant from the Minnesota Corn Growers/Minnesota Corn Research and Promotion Council , and by the Agricultural Research Service under the Soil and Air National Program no. 212.
- Nitric oxide
- Nitrous oxide