Deal, M. 2011. Net primary production in three bioenergy crop systems following land conversion. M.S. Thesis, University of Toledo, Toledo, Ohio, USA.
Many factors influence net primary production (NPP) and the distribution of fixed carbon © within an agro-ecosystem which includes, but is not limited to, management activities, microclimate variables, the amount of carbon available from photsynthate, soil structure, soil texture, nutrient availability, plant phenology and crop species. The objectives of this study were to: (1) determine the differences in aboveground net primary production (ANPP), belowground net primary production (BNPP), shoot to root ratio (S:R), and leaf area index (LAI) in three bioenergy crop systems, (2) evaluate the production of these three systems in two different land-use conversions, and (3) identify the key biophysical drivers of NPP in the first year after conversion. This investigation included three agriculture sites converted from conservation reserve program (CRP) management to bioenergy crop production (corn, switchgrass with oat cover crop, and prairie-mix with oat cover crop), three sites converted from traditional agriculture production to bioenergy crop production, and one site left as a reference grassland. The site converted from conventional agriculture produced smaller ANPP in corn (19.03 ± 1.90 Mg ha-1 yr-1) than the site converted from the CRP to corn (24.54 ± 1.43 Mg ha-1 yr-1). The two land conversions were similar in terms of ANPP for switchgrass (4.88 ± 0.43 for CRP and 2.04 ± 0.23 Mg ha-1 yr-1 for agriculture) and ANPP for prairie-mix (4.70 ± 0.50 for CRP and 3.38 ± 0.33 Mg ha-1 yr-1 for agriculture). The BNPP at the end of the growing season in all the bioenergy crop systems was not significantly different (p = 0.75, N = 8). SWC played the most important role in limiting ANPP, while S:R and SOC present before land conversion, had the strongest influence on BNPP. SWC represents an important regulation of photosynthesis in plants and therefore regulates aboveground production in the first year of planting. Belowground production was more closely linked to SOC present at the inception of the study. Understanding the variation in NPP within different scenarios of land-use change will improve the ability to predict the sustainability of bioenergy crop cultivation across the United States.
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