Landscape design and biogeochemical cycling are conditioned by nutrient amendment source in agroecosystems

Rachel Rozum, Yuning Shi and Armen Kemanian, Plant Science, The Pennsylvania State University, State College, PA, Lorne Leonard, Institutes of Energy and Environment, The Pennsylvania State University, State College, PA

Background/Question/Methods
Innovations associated with landscape design are conditioned by estimates of animal manure. We estimated field-by-field carbon and nitrogen inputs from manure in agroecosystems across Iowa based on publicly available information about location of confined animal feeding operations and livestock inventories. We simulated 50 management scenarios with the agroecosystem model Cycles, focusing this work on scenarios resulting in the greatest effects on nutrient cycling and landuse change. We simulated 871,595 agricultural fields, accounting for approximately 29M acres, 5M of which received manure. The dominant landuse is a maize-soybean rotation.
Results/Conclusions
No-till, a practice considered environmentally friendly, caused carbon losses in the soil profiles and increased leaching, mostly where manure needs to be disposed, due to lack of incorporation and carbon saturation of the topsoil. Maize stover removal for bioenergy may decrease nitrate leaching, but the results can vary substantially with location. Within the South Fork Bend and North Raccoon River headwaters, a 30% simulated stover removal resulted in roughly 50% decrease in nitrate leaching. Evaporation and its impact on soil drying and percolation are important drivers. Overall, wetter areas showed lesser effects of removing stover on nitrogen leaching. On average, leaching increased in some no-till scenarios (roughly an additional 2 kg/ha/yr of N was lost in no-till compared to tilled scenarios) because higher soil moisture creates more soil hydrological continuity.
In manured landscapes, maize is not only a commodity but a sink needed for manure disposal. Perennializing the landscape with switchgrass is therefore better suited for areas with lesser manure disposal. Yet, manure deposition in the landscape is a major source of nitrogen pollution. Relaxing landscapes to increase biodiversity and reduce pollution can be restricted by constraints imposed by manure management plans. It may also lead to the displacement and concentration of manure within the landscape, increasing the potential for nitrogen pollution.