Mitigation of Whole Farm GHG Emissions.

The main greenhouse gases (GHG) emitted from agricultural practices are methane and nitrous oxide. Most studies have focused in measuring either enteric or manure methane emissions, nitrogen (N) excretion or nitrous oxide emissions separately. Studies investigating the possible synergy or tradeoffs that may exist between methane mitigation and reduction in nitrogenous inputs are largely lacking. The goal of mitigation actions should be on net reduction of emissions from the whole farm.  For a sustainable operation of a farm, mitigation practices that reduce the overall carbon, N and water footprints need to be identified and assessed in a holistic manner. Some of the mitigation practices target reducing enteric methane production through dietary manipulation, methane from manure deposits/lagoons, improving N use efficiency in cattle, reducing herd size through herd management and improved animal health, reducing ammonia and GHG emissions from animal housing and manure storage, and enhancing N utilization, decreasing ammonia and GHG losses from fertilizer and manure applications in feed and forage production. Additionally, food safety considerations, particularly type, amount and survival of pathogens should be assessed when introducing mitigation options in the farm. Mathematical models are suited in integrating crop-livestock-soil systems and analyzing the effect of mitigation options such as dietary manipulation on GHG emissions from the whole farm. Animal models that deal with production, gaseous emissions and nutrient excretion should be integrated with manure storage and soil models to assess environmental sustainability of the whole farm. Additionally, linear (or dynamic) programming models can help identify strategies that optimize production with reduced GHG emission conditions. The advantage of holistic integrated modeling approach is that mitigation options can be assessed on the net reductions of carbon, N and water footprints before field based assessment can be conducted.