Biomass yield from planted mixtures and monocultures of native prairie vegetation across a heterogeneous farm landscape

Farms in the glaciated tallgrass prairie region of North America are topographically heterogeneous with wide-ranging soil quality. This environmental heterogeneity may affect choice and placement of species planted for biomass production. We designed replicated experiments and monitored farm-scale production to evaluate the effects of landscape position, vegetation type, and year on yields of monocultures and mixtures. Research was conducted on a 262-ha South Dakota working farm where cropland had been replanted with a variety of native grassland types having biofuel feedstock potential. Vegetation type (diverse mixture or switchgrass [Panicum virgatum L.] monoculture) and year interacted to influence yield in replicated experiments (p < 0.10). Mean annual switchgrass yield above a stubble height of 10 cm was 9.3 Mg ha−1 in two replicated experiments, and was greater than yield of mixtures (7.3 Mg ha−1) in 6 of 7 year × vegetation type combinations. Landscape position interacted with year and vegetation type to influence yield (p < 0.10). Variability was generally greatest at the lowest landscape position. On the farm's larger fields (0.4-46 ha), three-year mean yields of switchgrass monocultures cut at ground level (12.7 Mg ha−1) were also greater than yields of mixtures (9.7 Mg ha−1) but both were less than prairie cordgrass (Spartina pectinata Link) monoculture yield (13.2 Mg ha−1) in a restored wetland. A combination of prairie monocultures and mixtures, strategically placed across a farm landscape, could offer a balance of productivity, ecosystem services, and income with potential as biofuel feedstock and other income streams (hay, seed, beef).