True value of cover crops to farmers, environment

Planting cover crops in rotation between cash crops — widely agreed to be ecologically beneficial — is even more valuable than previously thought, according to a team of agronomists, entomologists, agroecologists, horticulturists and biogeochemists from Penn State’s College of Agricultural Sciences.”As society places increasing demands on agricultural land beyond food production to include ecosystem services, we needed a new way to evaluate ‘success’ in agriculture,” said Jason Kaye, professor of biogeochemistry. “This research presents a framework for considering a suite of ecosystem services that could be derived from agricultural land, and how cover crops affect that suite of services.”Cover cropping is one of the most rapidly growing soil and water conservation strategies in the Chesapeake Bay region and one we are really counting on for future improvements in water quality in the bay. Our analysis shows how the effort to improve water quality with cover crops will affect other ecosystem services that we expect from agricultural land.”The research, published in the March issue of Agricultural Systems, quantified the benefits offered by cover crops across more than 10 ecosystem services. Benefits included increased carbon and nitrogen in soils, erosion prevention, more mycorrhizal colonization — beneficial soil fungus that helps plants absorb nutrients — and weed suppression.Lead researcher Meagan Schipanski explained that commonly used measurements of ecosystem services can be misleading due to the episodic nature of some services and the time sensitivity of management windows.”For example, nutrient-retention benefits occur primarily during cover crop growth, weed-suppression benefits occur during cash-crop growth through a cover crop legacy effect, and soil-carbon benefits accrue slowly over decades,” she said. “By integrating a suite of ecosystem services into a unified analytical framework, we highlighted the potential for cover crops to influence a wide array of ecosystem services. We estimated that cover crops increased eight of 11 ecosystem services. In addition, we demonstrated the importance of considering temporal dynamics when assessing management system effects on ecosystem services.”Trade-offs occurred between economic metrics and environmental benefits, said Schipanski, who was a postdoctoral scholar at Penn State when she led the cover crop study. Now an assistant professor in the department of soil and crop sciences at Colorado State University, she noted that the planting of cover crops will become more attractive if fertilizer prices rise or if modest cost-sharing programs like the one currently in place in Maryland are developed.Researchers simulated a three-year, soybean-wheat-corn rotation with and without cover crops in central Pennsylvania, which presented agroecological conditions broadly representative of the Northeast and mid-Atlantic regions. The cover crop rotation included red clover, frost-seeded into winter wheat in March, and winter rye, planted after corn was harvested in the fall. The research, funded by the U.S. …

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Wood not so green a biofuel? Logging may have greater impact on carbon emissions than previously thought

June 11, 2013 — Using wood for energy is considered cleaner than fossil fuels, but a Dartmouth College-led study finds that logging may release large amounts of carbon stored in deep forest soils.Global atmospheric studies often don’t consider carbon in deep (or mineral) soil because it is thought to be stable and unaffected by timber harvesting. But the Dartmouth findings show deep soil can play an important role in carbon emissions in clear-cutting and other intensive forest management practices. The findings suggest that calls for an increased reliance on forest biomass be re-evaluated and that forest carbon analyses are incomplete unless they include deep soil, which stores more than 50 percent of the carbon in forest soils.”Our paper suggests the carbon in the mineral soil may change more rapidly, and result in increases in atmospheric carbon dioxide, as a result of disturbances such as logging,” said Dartmouth Professor Andrew Friedland, a co-author. “Our paper suggests that increased reliance on wood may have the unintended effect of increasing the transfer of carbon from the mineral soil to the atmosphere. So the intended goal of reducing carbon in the atmosphere may not be met.”The federal government is looking to wood, wind, solar, hydropower and other renewable energy sources to address concerns about climate change and energy security. Woody biomass, which includes trees grown on plantations, managed natural forests and logging waste, makes up about 75 percent of global biofuel production. Mineral soil carbon responses can vary highly depending on harvesting intensity, surface disturbance and soil type.”Analysis of forest carbon cycles is central to understanding and mitigating climate change, and understanding forest carbon cycles requires an in-depth analysis of the storage in and fluxes among different forest carbon pools, which include aboveground live and dead biomass, as well as the belowground organic soil horizon, mineral soil horizon and roots,” Friedland said.Co-authors included Dartmouth’s Thomas Buchholz, a former post-doctoral student, and Claire Hornig, a recent undergraduate student, and researchers from the University of Vermont, Lund University in Sweden and the Vermont Department of Forest, Parks and Recreation. The research was supported by awards to Friedland from the Northeastern States Research Cooperative and the Porter Fund.Friedland’s research focuses on understanding the effects of atmospheric deposition of pollutants and biomass harvesting on elemental cycling processes in high-elevation forests in the Northeastern United States. He considers many elements including carbon, trace elements such as lead and major elements such as nitrogen and calcium. He also is examining issues related to personal choices, energy use and environmental impact.The results appear in the journal Global Change Biology-Bioenergy.

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