A Summary of the Day
The PRSSS 2011 workshop began with keynote speaker Bill McGill from UNBC presenting on the release of greenhouse gases from soils and the biochemical reactions driving these emissions. The nitrogen cycle is often simplified, whereas in actuality nitrification and denitrification involve multiple pathways. McGill argues that chemical energy is what limits and drives microbial activity. The oxidation of soil organic matter by microbes generates electrons and in aerobic conditions oxygen is the acceptor. If soil oxygen is depleted, microbes can use soil nitrogen as an electron acceptor. The consequences of microbes using nitrogen instead of oxygen as an electron acceptor is the release of nitrogen oxides instead of CO2 into the atmosphere and loss of plant available nitrogen from the soil. N2O is the GHG with the longest residence time and hence has a larger impact on climate change than CO2. It is important to properly understand biogeochemical cycling in soils to understand the role of soils in releasing GHGs into the atmosphere.
Dr. Shabtai Bittman presented his research on using of whole farm nitrogen budgets to minimize fertilizer use and GHG emissions on dairy farms. N budgets aim to minimize N losses from the system in the form of gaseous emissions, leaching or run-off, while maximizing uptake by crops. The talk focused on the challenges faced in using cow manure applications instead of chemical fertilizers. One problem is the ineffectiveness of broadcasting manure and in response machinery has been developed that buries the manure in strips along the ground as it is being applied to reduce volatization losses. A second major problem is the imbalanced P:N ratio in the manure which results in phosphorus overloading to apply enough N. The separation of manure solids and liquids through settling, followed by the application of the solids only, has shown to result in more readily available N and reduced P loading.
Dr. Susan Ames works for a land rehabilitation company called Rescan Environmental Services. Ames presented the work she is currently undertaking to measure carbon stocks in soils in four different regions. Her presentation raised some complications faced when measuring soil C as well complications faced in analyzing the data when you only have a single measurement. Ames’s discussed financial barriers faced when carrying out research in conjunction with industry.
Lastly Dr. Andy Black spoke on the research his team at UBC is carrying out on carbon fluxes in 3 differently aged Douglas fir stands in order to assess ecosystem carbon sequestration. Black accentuated the role of soils in the presentation stating that soil respiration is an important source of CO2 in the forest ecosystems. Black’s research involves many aspects and this presentation focused on the results of fertilizer application. Black found that, taking into account the production and application of urea, the increased growth that results form forest fertilization has a positive effect on CO2 sequestration. Another important finding that was presented is that following a clearcut and replanting it takes 17 years before the ecosystem is C neutral and another 20 years to compensate for the initial CO2 release from the system.