Nitrogen Dynamics and Greenhouse Gas Emissions In a No-till Chronosequence.

No-till (NT) farming has gained wider acceptance in the US and world agriculture, and has yielded various environmental quality benefits including topsoil retention and carbon sequestration.  However, long-term effects of NT on nitrogen dynamics and greenhouse gas emissions (GHG; CO₂, CH₄, and N₂O) are not well documented.  This study conducted in a NT chronosequence (ranging from 9 to 48 years) under corn-soybean rotation across Ohio examined the effects of NT on GHG emissions and nitrogen dynamics in comparison to conventional tillage (CT) and forest soils.  Preliminary data (September 2009 to May 2010) indicated an increase in CO₂ and N₂O emissions and CH₄ consumption with an increase in NT duration.  Greater CO₂ emissions were recorded at the forest than at the cropland sites with minor differences between tillage treatments.  While CH₄ consumption was observed at almost all the study sites, uptake rate was higher under NT than at the sites under CT.  The difference between tillage practices was even clearer when soil drainage class was considered.  For example, at sites under NT for 48 y, uptake rate at a well-drained site was 10-12 times than that at a poorly-drained site.  At the younger NT sites, N₂O emissions did not differ with CT sites. Soil ammonium-N increased with NT duration, especially at the surface (0-10 cm) soil layer.  In the 0-5 cm layer, nitrate-N was higher under NT than CT in most sites of the chronosequence.  These results will be discussed in relation to the evolution of various soil physical and biological properties under NT farming.