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United States Department of Agriculture

Agricultural Research Service

Research Project: GLOBAL CHANGE AND BELOWGROUND PROCESSES IN AGRICULTURAL SYSTEMS

Location: National Soil Dynamics Laboratory

2010 Annual Report


1a.Objectives (from AD-416)
Reduce uncertainty regarding: (1) the effects of rising atmospheric carbon dioxide concentration on crop and pasture production; and (2) the role of agronomic ecosystems in the sequestration of atmospheric carbon dioxide as organic carbon in soils, as well as the release of carbon dioxide and other greenhouse gases from soil, as affected by agricultural management practices. Specifically, determine effects of carbon dioxide on belowground processes which affect crop productivity, soil physicochemical/biological properties, carbon/nutrient cycling, and trace gas efflux from soil.


1b.Approach (from AD-416)
Two-year rotational cycles of sorghum and soybean will be maintained under two cropping systems: conventional, using tillage without cover crops; and conservation, using no-till with winter cover crops in rotation (wheat, crimson clover, and sunn hemp). Each cropping system will be grown under current and projected levels of atmospheric carbon dioxide. In addition, a Southeastern pasture system study, using bahiagrass exposed to these carbon dioxide levels, has been initiated. Carbon flux to plants (growth, physiology, and yield) and soil will be determined with supporting data on soil physicochemical properties. Emphasis will be given to measuring soil carbon storage, root development patterns, characterizing the rhizosphere, and trace gas efflux from soil. The relationships of nitrogen to carbon dynamics and to water quality will be examined. Root growth, decomposition, and microbial community structure will be quantified in respect to carbon flow. The effects of carbon dioxide on agronomic systems is a critical, yet neglected, area of research. Integrating data from these studies will help provide a mechanistic understanding of the potential of agronomic systems to mitigated global change via sequestration of atmospheric carbon dioxide in soil.


3.Progress Report
Cropping Systems and Tillage; Grazinglands, Conservation Reserve Program (CRP) and Buffers. Global change research at the USDA-ARS National Soil Dynamics Laboratory (NSDL) addresses the impacts of elevated carbon dioxide within differing cropping systems (e.g., conservation vs. conventional) as well as under differing pasture management practices (nitrogen) on soil carbon storage. The final (tenth) year of the cropping systems study was completed. Aboveground biomass data have been collected and analyzed; root data are being processed; soil physicochemical properties, including soil carbon are being assessed. Pasture aboveground biomass data have been collected and analyzed; soil cores for root and soil carbon have been collected and are being processed.

Organic Carbon Transformations. Our research is seeking to understand factors controlling rate, mass, and timing of carbon dioxide sequestered, fate of carbon within the soil, rate of production and turnover of soil carbon pools, and processes and mechanisms of soil carbon loss. We are also investigating the effects of carbon dioxide on changes in plant structure and subsequent impacts on decomposition (e.g., microbial processes), and soil carbon storage. Soil carbon data from the first four years of the cropping systems study have been published; the remaining six years of data have been collected and are being processed. Soil carbon data have also been collected from the pasture study. Carbon dioxide efflux from both systems continues to be monitored as does carbon flow through soil water.

Cropping Systems; Rangelands, Pastures and Wetlands. Our research addresses the impacts of elevated carbon dioxide within conservation vs. conventional cropping systems as well as under differing pasture management practices (nitrogen) on trace gas (carbon dioxide, nitrous oxide, and methane) efflux from soil. Trace gases were monitored throughout the final year of the cropping systems study. Trace gases have also been monitored throughout the pasture study; samples are being analyzed and data summarized.

Cropping Systems; Grazinglands (Range and Pastures). Our research involves measurement of plant responses (above and below the ground) in conventional vs. conservation cropping systems and within improved vs. unimproved pastures to increasing atmospheric carbon dioxide and the ability of these systems to assist in mitigation of this rise via soil carbon sequestration. The final year of the cropping systems study was completed. Aboveground biomass data have been collected and analyzed; root data are being processed; soil physicochemical properties, including soil carbon are being assessed. In addition, a rainfall simulation study on sediment loss and water infiltration following the 10-year cropping system study has recently been completed. Aboveground pasture biomass data have been collected and analyzed; soil cores for root and soil carbon have been collected and are being processed. Minirhizotron and soil nutrient data continue to be collected and processed.


4.Accomplishments
1. Elevated Carbon Dioxide Increased Photosynthesis and Water Use Efficiency in Soybean and Sorghum. The long-term impact of elevated carbon dioxide in different tillage systems remains unknown. Over six years, photosynthesis increased while transpiration decreased, resulting in greatly enhanced water use efficiency in both sorghum and soybean (more so in soybean); residue management had little impact on these gas exchange variables. Results suggest that better soil moisture conservation and high rates of photosynthesis can occur in both tillage systems in Carbon dioxide–enriched environments during reproductive growth.

2. Incidence of Forest Diseases Decreased on Plants Exposed to Elevated Atmospheric Carbon Dioxide. Plant diseases cost growers billions of dollars each year in control and lost productivity. Understanding how the rising level of carbon dioxide may alter incidence and severity of important plant diseases will be crucial to future management strategies. Incidence of both pitch canker and fusiform rust were lower on loblolly pines grown under elevated carbon dioxide; fusiform rust took longer to develop on red oak seedlings exposed to elevated carbon dioxide; and carbon dioxide did not affect disease severity. Data suggests that some plants may benefit from the rising level of carbon dioxide through decreased fungal disease incidence.

3. Cassava and Sweet Potato as Viable Alternative to Corn as Potential Sources for Future Bioethanol Production. Biofuel alternatives to fossil fuel are being investigated as ways to help mitigate the rising atmospheric carbon dioxide concentration while maintaining the sustainability of the global food supply. Both cassava (Alabama) and sweet potato (Alabama and Maryland) yielded higher levels of carbohydrates per unit land area than did corn. Adoption of alternative biofuel sources (other than corn) may alleviate the demand on corn for feed and food while also reducing dependency on fossil fuels and helping to mitigate the rise in atmospheric carbon dioxide.


5.Significant Activities that Support Special Target Populations
We have continued our research efforts into alternative crops (sweet potato, cassava, and kudzu) which small farmers might grow, with little input, for ethanol production.


Review Publications
Runion, G.B., Prior, S.A., Rogers Jr, H.H., Mitchell, R. 2010. Effects of elevated atmospheric CO2 on two Southern forest diseases. New Forests. 39:275-285.

Prior, S.A., Runion, G.B., Rogers Jr, H.H., Arriaga, F.J. 2010. Elevated Elevated atmospheric carbon dioxide effects on soybean and sorghum gas exchange in conventional and no-tillage systems. Journal of Environmental Quality. 39:596-608.

Ziska, L.H., Runion, G.B., Tomecek, M.B., Prior, S.A., Torbert III, H.A., Sicher Jr., R.C. 2009. An evaluation of cassava, sweet potato and field corn as potential carbohydrate sources for bioethanol production in Alabama and Maryland. Biomass and Bioenergy. 33:1503-1508.

Last Modified: 7/24/2014
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