Effect of Tillage and Fertilization on Soil Carbon Dynamics, Greenhouse Gas Emissions, and Nutrient Export in Saskatchewan Forage Systems.

The forage sector has a high potential for human-induced climate change mitigation as conversion of marginal cropland to forage results in significant soil organic carbon content increases in prairie soils.

An important part of this mitigation measure is retention of the stored carbon in the face of demands to bring the forage land back into annual crop production.  Stand termination through tillage versus herbicide is likely to affect decomposition of organic carbon over the following year.  A common practice in the forage seed industry is to broadcast urea fertilizer in the fall.  Nitrogen fertilization and stand termination method are postulated to affect the production of nitrous oxide and carbon dioxide from the soil when the forage stand is terminated.  

Research sites to examine the influence of stand termination method and nitrogen fertilization on soil carbon content and greenhouse gas fluxes were established in the fall of 2013 in northeastern Saskatchewan (53.21 N, 103.51 W; 53.13 N, 103.47 W). To assess termination effects on carbon dynamics, four carbon pools were quantified and compared: total organic carbon, light fraction organic carbon, microbial biomass carbon, and dissolved organic carbon; as these pools are likely to show a response to short-term management changes. Greenhouse gas emissions were assessed using intact soil core incubations.

Results from the first incubation experiment showed no significant effect of N fertilization of the forage stand on nitrous oxide production. This may be a consequence of large losses of N from the broadcast method of application and the short history (2 yrs) of N fertilizer application. The CO₂ emissions were significantly higher in fertilized versus unfertilized plots, with the largest difference observed  between no-till fertilized plots and tilled unfertilized plots.