FATES OF SOIL CARBON AND NITROGEN IN AGRICULTURAL AND BIOENERGY CROP SYSTEMS

Achieving a balance between sustainable, economically viable, agriculture and the preservation of clean air, clean water, and healthy ecosystems is a grand environmental challenge for the 21st century. This balance is especially difficult to achieve with the nitrogen (N) and carbon (C) cycles. Agriculture is an important driver of changes in regional nitrogen cycles because inorganic nitrogen fertilizers and legume cultivation are integral high yielding crop production. Society is increasingly looking to agricultural ecosystems to mitigate changes in the global C cycle by storing more carbon in soils and expanding production of bioenergy crops with low global warming potential. The overall goal of this project is to increase our understanding of the fates of C and N in agricultural and bioenergy cropping systems of Pennsylvania and surrounding states. Our specific goals are to: 1) evaluate the potential to replace synthetic N fertilizer with biological N fixation by soil microorganisms and cover crops, 2) improve computer simulation models to provide new tools for soil fertility testing and N fertilizer recommendations, and 3) evaluate whether expansion of bioenergy crops in the region could provide a fuel with low global warming potential.To meet these goals we will monitor existing and establish new field experiments at the Penn State research station and on private farms. We are comparing nitrogen losses from corn-soybean-wheat rotations with no cover crop, with monoculture cover crops, and with polyculture cover crop mixtures. Our hypothesis is that the high diversity cover crop mixtures provide more ecosystem services than monocultures. We are monitoring C and N cycles in willow, switchgrass, miscanthus, and biodiverse conservation grasslands to determine which bioenergy cropping systems may have low global warming potential. In some of these experiments we assess greenhouse gas emissions from different portions of the landscape (e.g. well drained slopes vs excessively wet valley bottom positions) to determine how the placement of bioenergy crops on marginal land may affect emissions. We are coupling a new type of soil fertility testing (the CO2 burst method) with a computer simulation model to develop a new tool for farmers seeking N fertilizer recommendations on lands with high cover crop N inputs. Finally, we are quantifying how microorganisms (cyanobacteria) growing on the surface of the soil affect soil quality and N inputs to the ecosystem.