Environmental implications of feedstock production practices for bioenergy
Abstract
A grand challenge to US ethanol production involves the determination of suitable, stable and efficient feedstocks for the production of ethanol in the United States. The overall goal of this project was to quantify the long-term water quality impacts associated with bioenergy feedstock production scenarios on intensively-managed landscapes in the United States. The GLEAMS-NAPRA model was used to quantify long-term runoff, percolation estimates and annual losses in erosion, total phosphorus, nitrate-nitrogen, herbicide and foliar fungicide attributed to biofeedstock production. The bioenergy production systems evaluated covered first- and second-generation biofeedstocks and involve cropping system shifts (corn-soybean rotations to continuous corn), corn ( Zea mays) grain plus multiple stover harvest options, and whole-plant corn silage. In addition, fertilized switchgrass (Panicum virgatum ) and Miscanthus x giganteus production on agronomically marginal land were evaluated and compared with corn-based production systems. Winter cereal rye (Secale cereal) cover crop was evaluated as a best management option to mitigate potential risks in soil erosion. A ratio of ethanol yields (per thousand liters) to erosion impacts was proposed and evaluated as an environmental indicator to better interpret risks involved in second-generation production practices. The results show that shifts to a continuous corn cropping system would significantly impact (p<0.05) percolation, erosion, nutrients and pesticides losses from agricultural fields and could potentially have greater impacts on runoff losses of those pollutants compared to losses in corn-soybean rotations. Corn stover removal at the rates 38% (2.40–3.19 t/ha), 52.5% (3.32–4.41 t/ha) and 70% (4.42–5.88 t/ha), with no-till practices, would result in statistically significant higher annual erosion losses (p<0.05) when compared with no residue removal. Winter cover crop reduced soil erosion associated with corn silage production but not to levels at, or below, traditionally grown corn grain production. Corn produced under no-till practices produced higher total phosphorus losses when commercial fertilizer was surface applied as opposed to the incorporation method practiced with conventional tillage. Miscanthus and switchgrass production on marginal soils reduced annual surface runoff by an insignificant amount (p>0.05) of 1 to 4 mm and percolation by 11 to 40 mm when compared with corn-based bioenergy production systems. However, erosion losses associated with perennial grasses were significantly lower (p<0.05) than tilled corn and no-till corn with high levels (70%) of stover removal. However, establishment-year tillage operations and switchgrass failure scenarios would produce erosion higher than the soil loss tolerance value (4.48 to 6.72 t/ha) on agronomically marginal land, suggesting that conservation measures would be required when establishing dedicated perennial grasses on highly erodible soils. Nitrates leached from fertilized Miscanthus production on marginal soils were low (0.2 to 1.2 kg/ha) when compared with fertilized switchgrass and corn production systems. The results point to necessities in establishing new sets of regional specific soil and water conservation criteria to address erosion and water quality concerns associated with bioenergy feedstock production practices.
Degree
Ph.D.
Advisors
Chaubey, Purdue University.
Subject Area
Alternative Energy|Natural Resource Management|Agricultural engineering|Environmental engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.