EFFECT OF SOIL TYPE AND HYDROLOGY ON THE COMPOSITION OF NITROGEN GASES EMITTED FROM RIPARIAN BUFFERS

Abstract

The US Corn Belt States are the leading contributors to nitrate (NO3-) enrichment and the so-called dead-zone in the Gulf of Mexico. Located at the interface between agricultural fields and surface water bodies, riparian buffers have shown great capacity to remove NO3- from agricultural runoff, and thus reduce fertilizer N export to streams. Under the right conditions (organic carbon, moist to wet soils), riparian soil microbes can convert NO3- into nitrous oxide (N2O) and dinitrogen (N2).However, from an air quality standpoint, a low N2O production relative to N2 (mole fraction of N2O) would be preferred because N2O contributes to the greenhouse effect and depletion of the ozone layer, With the hypothesis that frequent water saturation is favorable to the reduction of N2O into N2 (thus a low N2O mole fraction), a study was conducted to identify controlling factors of N2O mole fraction across various riparian buffers, including well-drained (WR), artificially-drained (LWD), and poorly-drained (SF) sites. The relative production of N2O and N2 was measured in the laboratory using the acetylene (C2H2) block technique. In the absence of C2H2, there was no difference in N2O production rate among the sites. However, in the presence of C2H2, N2O production at SF (30 μg N2O kg-1 soil h-1) was much higher than at the other sites (3.31 at LWD and 8.42 at WR). Conversely, the N2O mole fraction at SF (0.11) was lower than at WR (0.28). These results are consistent with the greater soil moisture, and higher total soil organic C at SF compared to the other sites. The low N2O production at LWD is probably due to the presence of tile drains and infrequent soil saturation. Future studies will examine the impact of tile-drain on the composition of N gases from these types of buffers.