Biofuel Feedstocks: Implications for Sustainability and Ecosystem Services.

Diverse biofuel plantings such as perennial grasses and annual crops are being considered as potential feedstocks in the USA. As policymakers consider which biofuel crops to support with incentives, we want to make sure they know about all the benefits provided by a range of crops. Therefore the effectiveness of nine bioenergy plant candidates of experimental area established in 2007 at Manhattan, Kansas, USA was tested by a dataset of six sustainability criteria. The objectives of this study were to gather sustainability data that documents soil physical, chemical and biological properties; quantify the total root and shoot biomass for different energy crops; characterize soil microbial diversity and abundance under each bioenergy crop. Soil and root samples were taken to a depth of 120cm; and additional soil quality indicators for soil structural stability, soil microbial abundance and diversity from 0 to 30cm will be evaluated. For each bioenergy crop, root biomass was quantified in increments of 0-5, 5-15, 15-30, 30-45, 45-60, 60-75, 75-90 and 90-120 for inter-rows, between plants and at the center of the plants respectively. For the annual crops, root biomass was concentrated in the surface 15 cm (>90%). Switchgrass (Panicum virgatum) and Miscanthus (Miscanthus giganteus) had significant root biomass to 90 cm with 15 and 30 % root biomass respectively below 30 cm. The greater rooting depth of the perennial crops may result in a much lower carbon turnover rate and thus greater soil organic matter stabilization. Shoot biomass increased from 2007 to 2009 for miscanthus (3.36, 12.76, 15Ton/ha and switchgrass (4.25, 9.18, 11.4Ton/ha). Corn (Zea mays)and sorghum (Sorghum bicolor) provides greater plant biomass per hectare. Despite differences in root biomass production among energy crops and within the soil profile, differences in soil carbon between energy crops were not significant after 3 years and averaged 260 Mg C ha-1 to a depth of 120 cm. Utilizing the bioenergy plants, miscanthus, switchgrass, big blue stem (Andropogon gerardii Vitman), different varieties of sorghum and corn we can examine feedbacks of these systems on soil properties and C and N cycles. Specifically we are addressing changes in soil microbial diversity and soil structural stability between these energy crops. Soil microbial community composition will be characterized using phospholipid fatty acid (PLFA) analysis. We will provide quantitative values to classify the different energy crops based on a soil sustainability index.