Thursday, November 16, 2006 - 8:55 AM

Residue Aggregation Effects Nitrous Oxide Emissions.

Terry Loecke and G. Philip Robertson. Michigan State University, 10255 40th St., 10255 40th St., Hickory Corners, MI 49060, United States of America

Nitrous oxide emission from soils is primarily controlled by the bio-availability of soluble C, nitrate, and oxygen.  In most soils these driving factors are heterogeneously distributed in soil at scales important to microbial activity.  We tested the hypothesis that the aggregation of plant residue affects N2O emissions by manipulating the spatial distribution of plant residue in soil into an aggregation gradient.  Corn was planted into a homogenized 1:1 mixture of sand and loam soil in 50L containers and placed in the field.  We created a residue aggregation gradient by dividing 38g of finely ground Trifolium pretense shoots into 8, 24, or 72 randomly distributed patches or uniformly into soil.    Aggregated residue increased N2O flux substantially for the first few weeks of measurement, after which fluxes were similar to soils in which residue was uniformly distributed.  Moderately aggregated residue had the highest but short-term rates of N2O flux. Nitrous oxide fluxes in response to highly aggregated residue were intermediate but persisted longer than where residue was moderately aggregated.  Fluxes from the uniform distribution were similar to no-residue control at all dates except one.  Our data suggest that soil heterogeneity in the form of residue aggregation has a significant impact on N2O emissions.  Soil heterogeneity is influenced by many soil management practices, thus managing heterogeneity may be a tool for reducing agricultural N2O emissions.