Can Trace Gas Emission Be Modified by Management Scenarios in the Northern Corn Belt

Field plots were established in 2002 in west central Minnesota to compare tillage, rotation and fertilizer treatments and to identify and develop economically-viable and environmentally- sustainable farming systems. Greenhouse gas emission (nitrous oxide, methane and carbon dioxide) was monitored in a subset of treatments. Treatments were selected to represent three different scenarios: "business as usual" (BAU), "maximum C sequestration" (MaxC) and "optimum greenhouse gas benefits" (OGGB). The "business as usual" scenario has chisel or moldboard plow tillage and receives high fertilizer inputs in a corn-soybean rotation. The "maximum C sequestration" scenario is strip tilled with a mole-knife and receives high fertilizer inputs in a corn-soybean-wheat/alfalfa-alfalfa rotation. The "optimum greenhouse gas benefits" scenario differed from "maximum C sequestration" only if those plots did not receive fertilizer inputs. Emissions were monitored with vented static chambers. Two collars per plot were sampled; plants were excluded for row crops but not wheat and alfalfa. The greatest nitrous oxide flux occurred during spring thaw events, especially after corn or alfalfa, which accounted for 33% to 55% of the flux for 2005 and 2006 with minor peaks attributed to N fertilizer events. However, there were no consistent differences among the scenarios despite difference in fertilizer inputs. Season averages ranged from 4.3 to 5.6 kg nitrous oxide-N per ha, which is 2.1 to 3.6% of applied N fertilizer. However, best management practices for nitrogen fertilizer were used to minimize loss. Under these managements, the soil tended to be neutral to slight methane sinks. The apparent additional carbon dioxide emitted from MaxC and OGGB were attributed to the confounding effect of having plants inside the chamber. The largest mass of roots were in the alfalfa plots, but root biomass in the surface 60 cm averaged over three years did not differ among scenarios. [GRACEnet publication]