Integrating Targeted Sheep Grazing in Organic Systems: Impacts on Weed and Ground Beetle Communities.

Organic production has become a major agricultural, economic, and cultural force.  However, in the face of unprecedented climate change and market demand, organic producers in water-limited environments need to increase the resiliency of their enterprise to secure long-term environmental and economic sustainability.  One approach to achieve this goal is to develop integrated crop-livestock production systems that replace mechanical practices with targeted grazing to terminate cover cops and manage weeds.  While integrated crop-livestock production can benefit producers through low-capital entrepreneurial partnerships and represents an ecologically-based approach to manage crops, its impact on the associated biodiversity is largely unknown.  If grazing shifts biological communities to assemblages of less desired species, producers are unlikely to adopt this practice.  In a series of on-farm and experimental-plot studies conducted in small-grain and horticultural vegetable production organic systems, we compared pathogens, weeds, and carabid beetles (Coleoptera:Carabidae) between cover crops terminated by sheep grazing and those mechanically terminated.  We further assessed legacy impacts of cover crop termination strategies on the associated biodiversity, and subsequent soil health and crop yield.  Our studies indicated that pathogen pressure and weed communities did not differ between grazed- and mechanically-managed plots.  Despite temporal differences in species richness and activity-density, carabid diversity, species richness, and activity-density also did not differ between grazed and mechanically-terminated plots.  We further found no difference in subsequent crop yield, and associated biodiversity between previously grazed and mechanically managed plots.  Overall, our results suggest that grazing and mechanical tactics act as similar ecological filters of pathogen, weed, and carabid beetle communities.  Integrated crop-livestock systems may help organic land managers reduce their reliance on fossil fuels and tillage, thus potentially reducing input costs and enhancing the environmental sustainability of production.