Productivity and ecosystem services from purpose-grown energy crops
Purpose-grown energy crops are hypothesized to make significant contributions toward achieving the bioenergy and climate goals of the U.S. There is significant uncertainty regarding the biomass yield, environmental and climate outcomes associated with scaling up production of perennial bioenergy crops to meet these targets. This dissertation aims to investigate four key areas: (i) assess the impact of Nitrogen (N) on the long-term productivity of purpose-grown energy crops, (ii) evaluate ground-truth and Vegetation Indices (VIs) from Unmanned Aerial Vehicle (UAV)-based traits for N management of purpose-grown energy crops at field-scale, (iii) establish an economic criterion for identifying marginal land suitable for purpose-grown energy crops, and (iv) evaluate ecosystem services co-benefits associated with field-scale production of purpose-grown energy crops. Results from two aging miscanthus (Miscanthus x giganteus) stands (10-year and 16-year old) highlight the significance of N-fertilization strategy for long-term productivity. Generally, N rates of 112 kg N ha-1, applied annually, is sufficient for sustainable biomass yield. The results suggest that quadrat harvests, when scaled to a per-hectare basis, may overestimate end-of-season miscanthus yields by up to 40%. However, tiller weight estimates from quadrats correlate with biomass yield and can serve as a valuable proxy for monitoring field-scale biomass yields and stand health. Furthermore, quadrat-measured morphological traits can predict end-of-season biomass yield, with August-September canopy height and leaf chlorophyll content as the most effective linear predictors. Normalized difference red edge vegetation index (NDRE) from UAV flights between mid-July and late August reliably predicts end-of-season biomass yield, providing substitute for the ground truth methods. Additionally, the results indicate that NDRE can monitor stand health changes in response to N management, with suboptimal rates resulting in stand health degradation. Finally, economic analysis shows that land can be considered economically marginal – and thus suitable for switchgrass (Panicum virgatum) cultivation – at farmgate prices of $66 Mg-1 when replacing rotations with frequent corn (Zea mays) phases and $88 Mg-1 for rotations with frequent soybean (Glycine max) phases. To promote widespread adoption and potentially increase incomes through monetizing ecosystem services, a three-year study suggests field-scale switchgrass replacing corn cultivation can reduce groundwater nitrate leaching by 25-80% with without increasing water use relative to corn. The study also finds that switchgrass cultivation reduces nitrous oxide (N2O) emissions by half compared with corn cultivation, although this reduction might be offset by a 50% increase in carbon dioxide (CO2) emissions. The elevated CO2 emissions, however, suggests autotrophic respiration from increasing switchgrass root biomass, which implies an increase in below-ground C storage. Overall, these results demonstrate the viability of commercial-scale, purpose-grown energy crops and provide evidence of their ability to generate ecosystem services, supporting a long-term supply of low-carbon intensity sustainable aviation fuel (SAF).
Miscanthus × Giganteus, Switchgrass, Biomass Yield, Ecosystem Services, Greenhouse Gas Emissions, Carbon Dioxide, Nitrous Oxide, Nitrate Leaching, Water Use
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign