The effects of intensive rotational grazing on soil carbon sequestration and greenhouse gas emissions in the northeastern United States

Background/Question/Methods:

The practice of intensive rotational grazing in pasture-based dairy farms is believed to promote soil C sequestration.  An unintended consequence of this increased C storage may be higher soil greenhouse gas emissions, particularly of N₂O, which could offset any gains in climate change mitigation with grazing management.  The goal of this research was to examine the effects of intensive rotational grazing on soil C sequestration and greenhouse gas emissions in small dairy farms of the northeastern US.  Soil C storage was compared between an intensively grazed system and an adjacent farm managed solely for hay production.  The effects of grazing on greenhouse gas emissions was assessed by measuring soil CH₄, CO₂, and N₂O fluxes in the grazed and ungrazed sites.   Differences in forage production and the links among soil physical properties and soil C and N cycling were also assessed. 

Results/Conclusions

There were no differences in soil C storage between the grazed and ungrazed systems, nor did N₂O flux differ between the two sites.    However, forage production was 30% lower and total CO₂ emissions were 25% higher at the ungrazed site over a six month period.   In addition, soil C and N values were positively correlated with the silt and clay soil fractions, suggesting that C sequestration in both grazed and ungrazed systems may be achieved in finer textured soils.  Overall, our findings suggest that site conditions, such as soil properties, and other management activities, such manure applications, may play a stronger role in C sequestration than intensive grazing.