Climatic impacts of managed landscapes for sustainable biofuel feedstocks production.

Sustainable production of biofuels cannot be achieved without multiple-use landscapes where food, feed, and fuel can be co-produced without environmental harm. Here we use field level measurements in seven biofuel feedstock production systems grown under similar climatic conditions, but on different soils in two Midwestern (USA) states to understand their relative climatic impacts. We studied annual corn stover, and 6 perennial ecosystems including three polycultures: successional vegetation, restored prairie and a 3-species grass mix; and 3 monocultures: poplar, switchgrass, and miscanthus. All studied ecosystems were grown in replicated plots on moderately fertile soils of SW Michigan and highly fertile soils of central Wisconsin. We measured components of greenhouse gas (GHG) balances over 6 years. On the fertile soil perennial monocultures had GHG emission reductions potentials of 53% relative to fossil fuels, while polycultures had 64% reduction; corn stover had an 84% emissions reduction. Net sequestration ranged from 0.6 MgCO2e ha-1yr-1 (successional vegetation) to 3.1 MgCO2e ha-1yr-1, (corn stover). Among feedstocks produced on less fertile soils, perennial monocultures had GHG emissions reduction of 80%, and polycultures had emission reduction of 54%; miscanthus and poplar exhibited the largest sequestration potentials of 5.9 and 3.9 MgCO2e ha-1yr-1 respectively, while polycultures sequestered less then 1.0 MgCO2e ha-1yr-1 on average and corn stover was intermediate with 1.4 MgCO2e ha-1yr-1. All studied systems averaged energy production of 30 GJ ha-1 yr-1, except miscanthus (71 GJ ha-1 yr-1) and successional vegetation (20 GJ ha-1 yr-1). Our results inform the design of multiple-use landscapes: more fertile soils could produce food and feed with residuals collected for bioethanol production and more marginal soils could be used for various poly- or mono-cultures of purpose grown biofuel feedstocks but with differential climate benefits.