The influence of potential biofuel cover crops on nitrous oxide (N2O) emissions from Midwest row-crops

Neville Millar, Dean G. Baas, and G. Philip Robertson
W.K. Kellogg Biological Station; Dept. of Plant, Soil and Microbial Science, Michigan State University; Michigan State University Extension, Michigan State University

Presented at the All Scientist Meeting (2015-04-15 to 2015-04-16 )

Nitrous oxide (N2O) is the largest contributor to the greenhouse gas burden of cropping systems in the US, with emissions primarily due to N fertilizer inputs and other soil management activities. The practice of including winter cover crops in corn-based row-crop systems is not widely adopted but is increasing. Perennializing annual crop systems through year-round soil cover can: reduce nutrient run-off and soil erosion; provide a cellulosic biofuel feedstock additional to the primary grain crop; provide climate stabilization through additional soil carbon storage and perhaps N2O mitigation. Potential biofuel cover crops include grasses, legumes and Brassicas. There is little N2O emissions data from cover crop systems. Here, we will present three years of N2O emissions data from a corn-soybean-winter wheat rotation, either with or without cover crops (grass, legume and Brassica), situated at the Kellogg Biological Station in SW Michigan. Results show that: including potential biofuel cover crops in annual crop systems affected total N2O emissions compared to their absence (the red clover, and to a lesser extent annual ryegrass, increased total N2O emissions, whereas the oilseed radish did not); average daily N2O emissions from biofuel cover crop treatments decreased in the order Legume > Grass > Brassica; late cover crop termination time increased N2O emissions in the red clover treatment, but not the annual ryegrass treatment; N2O emissions were highest in corn (vs. wheat and soybean) in all years, irrespective of cover crop presence or absence; highest N2O fluxes occurred following fertilization, soil disturbance (annual crop planting and cover crop termination), and rainfall. Including Grass and Brassica cover crop species into annual crop rotations can provide additional biomass for biofuel conversion without much effect on soil N2O emissions.