|BARON, VERN - Agriculture And Agri-Food Canada|
|BELANGER, GILLES - Agriculture And Agri-Food Canada|
Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 3/3/2015
Publication Date: 7/12/2015
Citation: Baron, V., Skinner, R.H., Belanger, G. 2015. Carbon sequestration potential for forage and pasture systems. Journal of Animal Science Supplement. S3: 530.
Interpretive Summary: An interpretive summary is not required.
Technical Abstract: Grassland soils represent a large reservoir of organic and inorganic carbon. Regionally, grasslands are annual CO2 sources or sinks depending on crop and soil management, current soil organic carbon (SOC) concentration and climate. Land management changes (LMC) impact SOC sequestration rate, the duration and C-store at steady state. A common hypothesis is that increasing grassland productivity will increase SOC sequestration to a higher steady-state level. High SOC-sequestration rates occur for the first 5 to 10 yr. after LMC, but continue slowly up to 50 yrs. Permanent grasslands are usually at steady state for CO2 exchange. The most significant LMC for SOC accumulation is conversion from cropland to grassland where soil disturbance is minimized and C-inputs from perennial roots and residues are higher than annual crops. Residue- and root-C inputs for Alberta perennial hay and pasture systems were 2.3 to 3 times greater, than barley silage. SOC sequestration rates for improved pastures on degraded croplands in South-Eastern US were up to 1.4 Mg SOC ha-1 yr-1. Increasing soil nitrogen via fertilizer, manure and legumes increased SOC through higher root-C inputs, but not always permanently, as the inputs increase the degradable-C fraction. Manure-C application is effective in replacing surface soil-C on Quebec dairy farms and elsewhere. However, micro-meteorological studies on net ecosystem exchange (NEE) on old pastures in Pennsylvania, and in Alberta on high organic matter soils (> 6%), indicated that when harvested forage-C was subtracted from NEE, net Biome-C loss occurred in 90% of the study-years. Also, increasing productivity through N-application in Pennsylvania resulted in lost SOC, but a five-species forage mixture had higher productivity and sequestered significantly more SOC than a two-species mixture. Specific LMC per se within this grassland was not as important to sequestration rate as initial SOC content. Studies in Quebec show that grass and legume species respond differently to increased atmospheric temperature and CO2 concentration. The Quebec research also showed that elevated temperature and CO2 caused a higher root C: N ratio, resulting in a lower in vitro degradation rate, indicating that reduced SOC-degradation rates under future climates might be possible. How a concomitant change in species mixture affects SOC and what impacts of changing moisture and temperature regimes have on potential SOC-sequestration at a regional level can only be speculated.