Multifunctional agriculture: Root and nitrogen dynamics in two alternative systems

The Corn Belt of the Midwestern United States is among the most productive grainproducing regions of the world. Yet the development of the Corn Belt has been accompanied by a suite of environmental concerns. Alternative systems have been proposed that remediate environmental quality while relying on fewer external inputs (e.g., synthetic nitrogen fertilizer) than dominate cropping systems of corn and soybean. Two examples of such alternative systems are diversified crop rotations and perennial bioenergy systems. In diverse and less diverse crop rotations, the supply of nitrogen (N) to crops is mediated by the N flux from external inputs as well as internal soil cycling, although evidence suggests that in diverse rotations internal soil N cycling plays a more prominent role. Chapter 2 explores belowground N cycling and provides evidence that diversifying crop rotations increases organic soil N pools and rates of N release from soil organic matter into labile organic forms. Chapter 3 contrasts perennial and annual bioenergy systems by their standing root biomasses and rates of root decomposition as they vary across landscape positions. Results suggest that root biomass is best predicted by choice of annual or perennial crop, but that within cropping systems root biomass is sensitive to landscape position. In contrast to root biomass, rates of root decay for each crop were constant across landscape positions.