Nitrous oxide emissions from agricultural soils differ with crop but causes remain elusive even under long-term scrutiny
Hickory Corners, Michigan — For agriculture to help mitigate climate change, understanding emissions of greenhouse gases from farm fields is crucial. For field crops such as corn and soybeans, the potent greenhouse gas nitrous oxide is the main gas of concern. Nitrous oxide is 300 times better than carbon dioxide at absorbing heat in the atmosphere, and mainly comes from cropland soils.
Unfortunately for scientists, emissions of nitrous oxide from soils are hard to evaluate and predict. Greenhouse gas fluxes vary a lot from field to field and through time, but long-term comparisons of fields in the same location can help to reveal subtle management effects. Analysis of 20 years of data from a long-term field experiment at the W.K. Kellogg Biological Station (KBS) in southwest Michigan does just that.
The study, published today in Global Change Biology, is the longest continuous record of nitrous oxide emissions ever published, and compared nitrous oxide emissions from different cropped and natural ecosystems in the KBS Long-term Ecological Research experiment.
Measurement showed big differences between some management practices. Emissions were lowest in the natural systems, as expected, but just as low in perennial bioenergy crops like poplar trees and grasses. Surprisingly, however, overall fluxes between different annual cropping systems did not differ: the organic cropping system emitted just as much nitrous oxide as the conventionally managed system. However this was not the case for specific crops, for which organic management emitted less (wheat) or more (corn and soybean) nitrous oxide.
Lead author Dr. Ilya Gelfand, an MSU researcher, notes the importance of long-term studies for revealing these sorts of patterns, and notes further that “Even with these long-term data, we couldn’t predict daily emissions of nitrous oxide with environmental factors like soil moisture and temperature. This suggests that we still have a very incomplete understanding of the specific factors that control nitrous oxide emissions in agricultural soils.”
The full paper can be accessed at: http://onlinelibrary.wiley.com/doi/10.1111/gcb.13426/full
Michigan State University’s Kellogg Biological Station Long-term Ecological Research (KBS LTER) Program studies the ecology of intensive field crop ecosystems as part of a national network of LTER sites established by the National Science Foundation. More information at http://lter.kbs.msu.edu