1a. Objectives (from AD-416):
1.A. Develop tools to facilitate the selection of species mixtures for pastures, the distribution of pasture types across a farm, and the assessment and monitoring of pastures at multiple scales to improve forage/grassland system function and reduce production risks. 1.B. Identify new grazing management and supplementation strategies that complement grazing preferences of dairy cattle to optimize the utilization of mixed-species cool-season pastures of the Northeast U.S. and to reduce inputs costs for pasture-based producers. 2.A. Identify management systems that minimize net greenhouse emissions in forage, grassland, and energy crop systems in humid-temperate climates. 2.B. Determine optimal management and environmental benefits of perennial and annual bioenergy cropping systems in the Northeast U.S. to reduce production costs and increase yields.
1b. Approach (from AD-416):
1.A. A trait-based index will be developed to relate pasture plant community composition (both species presence and abundance) to ecosystem function in grasslands. A multi-site field-plot trial will be conducted to test the hypothesis that mixed plant communities with greater species evenness produce more herbage and are more resistant to weed invasion than mixtures with lower evenness or monocultures. Science-based decision support tools will be developed for forage species selection within pastures and across farms to meet producer goals for ecosystem functions given the climate, landscape and soils. 1.B. Observational research will be conducted on pasture-based dairy farms feeding a range of supplementation strategies with varying pasture composition to characterize the effects of supplementation on grazing behavior and diet selection. Ingestive behavior will be quantified on during spring, summer, and fall grazing. Detailed feeding and milk production information will be collected from farm records and personal interviews. Continuous culture fermenters will be used to identify ruminal fermentation products that influence grazing patterns via post-ingestive feedback mechanisms. Sward-box studies will be used to evaluate cattle grazing behavior responses to monocultures and mixtures of selected grasses and legumes. 2A. Multi-location field plot and farm-scale trials will be conducted to determine the greenhouse gas emissions and economics of perennial and annual crops grown for bioenergy. Differences in C isotope discrimination (d13C) of C3 and C4 species will be exploited to partition respiration between new C respired from C3 plants such as orchardgrass and white clover and old C respired from the active pool of soil organic matter that has formed under the C4 species, big bluestem. 2B. Biomass yield, feedstock quality, and greenhouse gas emissions of current annual and proposed perennial bioenergy crops under the same climate and soil will be measured, and the resulting data will be used to validate the DAYCENT biogeochemical model at a site in the northeastern U.S.
3. Progress Report:
Under objective 1.A.1, trait- and process-based indices have been developed and tested against field data from other pasture studies, but validation of the trait-based index against evenness studies conducted under 1.A.2 has been delayed somewhat by departure of the scientist responsible for this sub-objective. Validation against the data from 1.A.2 will be completed by the end of the fiscal year. Under objective 1.A.2, use of the data collected in 1.A.2 for validating mathematical indices has been delayed somewhat by departure of the scientist responsible for 1.A.2. This validation process will be completed by the end of the fiscal year. Under objective 1.A.3, optimization methods have been used to create preliminary trait- and process-based planting recommendations for pasture mixtures to provide particular ecosystem services. Because these recommendations have not yet been validated against independent data as intended, they cannot be distributed to producer groups. A manuscript on the research component is in progress, and will be completed by the end of the fiscal year. For objective 1.B.1, results were presented to farmers, researchers, and industry personnel at 4 pasture walks/field days, 2 webinar presentations and 1 invited trade journal article. For objective 1.B.2, results were presented to farmers, researchers, and industry personnel at 3 pasture walks/field days, 2 farmer-oriented conferences, and 1 webinar presentation. Under objective 2.A.1 monitoring of crop productivity and soil C continued. We determined that data collection needs to continue for several additional years before cropping system C sequestration potential can be properly assessed. Manuscript preparation will be delayed until additional data are available. Under objective 2.A.2, all soil respiration data have been collected and are being summarized. Under objective 2.B.1, annual and perennial crops were established at the Penn State Hawbecker farm and other management practices were completed as appropriate during growing season including biomass harvest. Under objective 2.B.2, switchgrass yield, feedstock quality, and ancillary data from different seasons and harvest frequency were measured as scheduled.
1. Flaxseed Supplementation. Flaxseed can be fed to dairy cows as an energy supplement to boost milk production and improve beneficial fatty acids (i.e. conjugated linoleic acid- CLA) in milk. Flaxseed has also shown promise in decreasing methane output in dairy cows fed conserved forages such as silage or hay. However, flaxseed has not been evaluated in grazing dairy cows. Flaxseed is available in certified organic form, therefore there is interest in the organic dairy industry in the potential benefits of supplementing grazing dairy cows with flaxseed. ARS researchers at University Park, Pennsylvania evaluated the effects of flaxseed supplementation of a pasture diet on ruminal fermentation and methane output using a continuous culture fermenter system which simulates digestion in the rumen. As flaxseed supplementation increased, methane output decreased which would be a positive environmental impact. However, nutrient digestibility also decreased as flaxseed supplementation increased, making the digestive process less efficient. These tradeoffs must be evaluated at the cow level to include other factors such as milk production and compositions (i.e. CLA) to develop feeding recommendation strategies to reduce the environmental impact of milk production without impairing productivity and profitability.
2. Savings achieved when displacing fuel oil with densified switchgrass. Many studies focus on quantifying the life cycle greenhouse gas (GHG) emissions of biofuel use without considering the economic implications. Given that biomass is a limited resource, ARS researchers at University Park, Pennsylvania considered both in evaluating its displacement of fuel oil, natural gas, and coal. Agricultural Research Service (ARS), Drexel University, and Penn State University scientists found that switchgrass 1) was a cheaper fuel than fuel oil (could save consumers in NE US $2.3 – $3.9 billion annually), 2) displaces more than twice as much petroleum when replacing fuel oil compared with gasoline, and 3) is a cheaper GHG mitigation strategy when it replaces fuel oil rather than electricity in the NE US (reduces GHGs at a cost savings of $10 – 11.6 billion annually). This study highlights the importance of explicitly targeting GHG reductions and petroleum offsets so biomass is not distributed towards more expensive options, such as the electricity sectors as with RPS legislations.
3. Switchgrass establishment date and weed control method affect yield. Controlling weeds is important for accelerating biomass production from switchgrass, however, since it is a new bioenergy crop, few chemical weed management options are available. ARS researchers at University Park, Pennsylvania tested both approved and new chemicals and establishment time as methods to control weeds. Agricultural Research Service (ARS) and Penn State University scientists found that when a combination of new and approved chemicals were used to control weeds, the earlier seeding date yielded more biomass. However, with a later seeding date, when weed pressure was lower, all treatment methods were equally effective. This study highlights the importance of identifying new weed management strategies to maximize the yields of switchgrass.
4. GHG mitigation strategies for bioenergy feedstock production. State and federal regulations reward innovation for improvements in the life cycle greenhouse gas (GHG) emissions of the fuel pathway and the type of feedstock chosen for conversion to biofuel. However, there is not an incentive strategy in place to reward the further reduction of GHG emissions from production of a particular feedstock. Agricultural Research Service (ARS), National Renewable Energy Laboratory, Drexel University, and DuPont scientists reviewed and analyzed data from GHG life cycle assessments, demonstrating that feedstock production can contribute more than 50% of the total GHG emissions. Instead of tracking all the components of life cycle GHG emissions in feedstock production, which would be overwhelming, ARS researchers at University Park, Pennsylvania identified the most important components contributing to GHG emissions which have potential for mitigation, N fertilizer material, N2O emissions, and tillage impact on soil carbon. This study provides a practical path forward to capture further reductions in life cycle GHG emissions by adopting the identified mitigation strategies.
Wilson, T., Mcneal, F.M., Spatari, S., Abler, D.G., Adler, P.R. 2011. Densified biomass can cost-effectively mitigate greenhouse gas emissions and address energy security in thermal applications. Environmental Science and Technology. 46(2):1270-1277.