Greenhouse Gas Emissions in a Terraced Field and along Concentrated Water Flow Paths.

As modern agricultural practices have spread globally with increased use of nitrogen fertilizers, the potential for N₂O release into the atmosphere and contribution to the greenhouse effect have also increased. Net emissions of GHGs (CO₂, N₂O, and CH₄)_, from agroecosystems account for about 20-25% of the annual increase in radiative forcing of climate change (IPCC, 2007). Specifically, hydrological influence or water flow at the field and watershed scale levels may be large factors influencing the hot spots (where) and hot moments (when) of GHGs emission. As such, conservation structures such as terraces that reduce surface runoff may also regulate GHG production and emission.  The hypothesis is that conservation structures (i.e, terraces) alter water flows (soil moisture variability) and nitrate paths and thereby alter the magnitudes of GHGs emissions. The objective is to quantify soil GHG emissions including hot spots and hot moments along the water (and nutrient) flow paths to include an upland hill of terraced and non-terraced fields, concentrated flow channel, and near riparian zones. Series of gas chambers were installed along toposequences in a 6-ha terraced field and a 4-ha non-terraced field along concentrated water flow paths in June 2009. Gas measurements were made weekly and/or after rainfall during spring, summer, and fall. Results of GHG flux and ancillary data will be presented.