Long-Term Trend of Yield, Greenhouse Gas Emissions and Carbon Footprint of Corn Continuous Monoculture or In Rotation with Legume.

Better understanding and management of carbon (C) footprint is an important issue in sustainable food production as it influences climate change. Data from a 19-yr (1992-2010) field experiment were used to determine the effects of N fertilizer rates and crop rotations on i) corn grain yield, ii) total greenhouse gas (GHG) emissions on a per ha basis (kg CO2eq ha-1), and iii) C footprint (kg CO2eq kg-1 grain). On average, continuous corn with well fertilized treatment (200 kg N ha-1) produced 8.1 Mg ha-1 of grain yield, similar to rotational corn with soybean (8.0 Mg ha-1) or lower than corn following alfalfa or red clover (8.9 Mg ha-1), both received 100 kg N ha-1 in the corn year. Continuous corn production had an average of annual total emission of 3440 kg CO2eq ha-1 and C footprints of 0.45 CO2e kg-1 of grain. The annual total emission was 40% less and C footprint 30-44% less for rotational corn than the well fertilized continuous corn. Our results suggest that excessive use of N fertilizer is the main driver of GHG emissions and C footprints and corn-legume crop rotation not only reduces fertilizer consumption, and improves productivity, it also reduces the C footprint.