Soil Quality as Affected by Biomass Removal in Tallgrass Prairie

Perennial grasses have been proposed as a source for bioenergy. However, the impact of biomass removal on long-term soil quality needs to be assessed. Soil C and N storage and soil aggregate stability may be used as indicators of soil quality. Long-term experimental tallgrass prairie plots, located at Konza Prairie Biological Station in the flinthills of Eastern Kansas were used to examine soil quality following 16 years of experimental treatments. These plots use burning and mowing for biomass removal, and include nitrogen addition as an additional management practice. These sites are dominated by warm-season C4 grasses (switchgrass, big bluestem, and indian grass). Biomass removal by mowing did not affect aboveground productivity of the dominant grasses. However, annual burning and N addition each increased productivity. In soil collected from 0-5 cm depth, N fertilization increased both soil organic C and N, and increased the proportion of macroaggregates, with a concomitant decrease in microaggregates. Higher organic C and N were observed in both macro- and microaggregate fractions. Burning (annually, early spring) had no effect on soil C in the surface 5 cm, but decreased soil N and increased macroaggregate formation, as compared to corresponding unburned plots. Mowing (in late June), decreased soil C but did not influence soil aggregate formation. Overall, a strong correlation was observed between mycorrhizal hyphal development and aggregate stability, indicating that these fungi may play an important role in soil aggregate formation. Proper management of prairie grasses for bioenergy could sustain soil quality.