Innovative approaches to agricultural land management are needed to address the future challenges of climate change; meet the nutritional, energy, and other basic needs of future populations; and improve agricultural sustainability and resiliency. The use of second-generation biofuels and other low-carbon energy sources is one solution to reducing greenhouse gas (GHG) emissions, thereby mitigating the impacts of climate change. Their use is also proving to have a beneficial impact on environmental problems related to excess nutrients from agricultural production.
The productive capacity of agricultural lands is highly variable. Even at the field level, some areas are highly productive, while others are low-yielding. Coincidentally, these less productive or marginal areas usually exhibit water stress (too wet or dry for commodity crops) and susceptibility to environmental degradation, such as high nitrate leaching, soil erosion, etc. Perennial bioenergy grasses and short rotation woody crops, such as shrub willow (Salix spp.), are better suited to these marginal areas because of their perennial growth habit and distinct physiological features (e.g., massive and deeper rooting system, dense aboveground biomass growth, and higher nutrient and water efficiencies).
As part of the U.S. DOE-funded project entitled “Biomass Production and Nutrient Recovery,” an on-going field study is being conducted in east-central Illinois. In this study, shrub willow is planted within marginal areas and buffer zones of a 6.5-ha continuous corn field. Under this cropping system, corn is managed under business-as-usual practices. The shrub willows do not receive fertilization, but instead are expected to use leached nutrients from the adjacent corn fields. Producing biomass while intercepting excess nutrients maximizes the use of and economic return for an expensive production input. This approach maximizes biomass production while minimizing off-site nutrient leaching losses, having the added benefit of protecting nearby surface water and groundwater resources. We are currently evaluating the environmental, economic, and ecosystem services (ES) benefits of implementing this and other bioenergy buffer systems through modeling analyses and scaling up to the agricultural Midwest.
Results of the Illinois study have shown that careful placement of a bioenergy crop like shrub willow can reduce off-site nutrient loss from corn fields through passive reuse of excess nutrients (fugitive nitrogen). Emissions of nitrous oxide (a GHG) from soils under shrub willow plots were also significantly reduced compared to areas under corn. Soil water nitrate concentration in willow areas was reduced by up to 87% relative to the adjacent corn. This significant reduction in nitrate could be a critical and cost-effective way to address the problem of excess nutrients from agricultural production in the U.S. Midwest. This in turn could have a beneficial impact on large-scale environmental problems like hypoxia in the Gulf of Mexico (that results from the discharge of excess nitrate via the Mississippi River).
Additionally, we found that the combination of crop type and landscape position influenced the species composition of the soil microbial community, resulting in unique and identifiable communities.
The field research has also spanned multiple collaborations through which this concept and/or our methodologies have been expanded regionally in Midwestern Corn Belt States to test novel switchgrass cultivars Next-Generation Feedstocks for the Emerging Bioeconomy, in Florida (EC-BIOSALTS) to grow energy cane and mitigate red tides and green blue algae, and in the Northern Great Plains (EXCHANGE) to reduce water withdrawals from the Ogallala aquifer. We have also been implementing advanced methods for bird surveys to understand biodiversity benefits of these cropping systems. We are currently developing a geospatial tool intended for public use to help facilitate planning for the sustainable adoption of an integrated bioenergy landscape at a wide range of spatial scales (farm, watershed, county, state, and region), the assessment of the associated ES, and the valuation of ES. Additionally, we are developing a machine learning (ML)-based model with predictive capabilities of the agronomic attributes of advanced switchgrass cultivars grown under marginally productive croplands across geographic locations in the U.S. Midwest utilizing data from our field study sites, generated by remote sensing techniques, and from publicly available databases. Eventually, the ML-based model will be integrated into the geospatial tool to enhance its capabilities to inform relevant analyses for the realization of a thriving U.S. bioeconomy including technoeconomic analysis and life cycle analysis associated with terrestrial bioenergy feedstock production.
Growing Shrub Willow as Bioenergy Buffer on Corn Production System | Conservation Matters from SWCS Events.
Jules Cacho provides a two-minute summary of his work on bioenergy crops for the SWCS "Conservation Matters" video series. Recorded at the 2017 72nd SWCS International Annual Conference in Madison, Wisconsin. Presentation: The viability of growing shrub willow as bioenergy buffer on intensively managed agricultural fields of U.S. Midwest.
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