Ecosystem response of cool-season grass pasture to management for livestock in southern Wisconsin

Livestock production for meat and dairy represent major agroecosystems in Wisconsin and comprise much of the State's landscape. Farmers' desire to remain profitable while at the same time practicing environmentally sound management techniques has led to a growing phenomenon in the upper Midwest, management-intensive rotational grazing. I employed a randomized complete block field experiment to test specific ecological and agronomic research questions under four pasture management practices typical of the upper Midwest -- management-intensive rotational grazing, continuous grazing, haymaking, and land that has been set aside with no agronomic management. First, I compared forage production, forage quality, and belowground net primary production finding forage production was significantly greater under management-intensive rotational grazing when compared to continuous grazing, mechanical harvest for hay, and no agronomic management. Forage quality was also significantly higher under management-intensive rotational grazing, while belowground net primary production was significantly lower under grazed treatments compared to non-grazed treatments. Second, I used an ecosystem carbon balance approach to quantify the net ecosystem C accumulation or loss of pastures under the treatments described above. Management-intensive rotational grazing lost significantly less C in 2006 than all other treatments, while in 2007 MIRG was the only treatment that was a sink for C. The potential for sequestering C in perennial pastures exists, but if considered at scales broader than the pasture boundary, import and export of C need to be taken into account. And lastly, I used a hybrid phospholipid fatty acid and fatty acid methyl ester analysis to assess microbial biomass, fungal-to-bacterial ratios, and guild composition in the surface 15-cm of soils under the four pasture treatments. Microbial community structure was assessed with principal components analysis, and regression trees and linear mixed-effects models were used to explore factors related to microbial community response to management. There was a general effect of grazing on microbial communities, but different grazing management (i.e., management-intensive rotational grazing vs. continuous grazing) did not affect microbial community composition or biomass. Production increases with management-intensive rotational grazing likely stem from the direct effect of defoliation on plant developmental stage and community composition rather than indirectly via microbial mediated feedbacks.