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United States Department of Agriculture

Agricultural Research Service

Research Project: GLOBAL CHANGE AND BELOWGROUND PROCESSES IN AGRICULTURAL SYSTEMS
2009 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 ARS-USDA 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 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; a publication on the results is in internal review. 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 with 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. 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 Atmospheric Carbon Dioxide Beneficial to Invasive Weeds. Invasive weeds can impact biodiversity and cost billions of dollars each year in control and lost productivity. Understanding how the rising level of carbon dioxide may alter establishment, spread, and control of invasive weeds will be crucial to future management strategies. Two old, established invasive weeds [sicklepod (Cassia obtusifolia) and Johnsongrass (Sorghum halepense)]as well as one new problem plant [spiderwort (Commelina benghalensis)] had more biomass when grown under elevated carbon dioxide. Data suggests that these invasive weeds will present agricultural producers with even greater problems as atmospheric carbon dioxide continues to rise.

2. Soil Carbon Increased Under Elevated Atmospheric Carbon Dioxide. The global rise in atmospheric carbon dioxide effects plant growth and can increase soil carbon which may enhance soil quality as well as help mitigate the effects of global climate change. A review of the literature shows that southeastern plant systems (crop, pasture and forest) can increase soil carbon storage through enhanced biomass production when exposed to higher levels of atmospheric carbon dioxide. This increased biomass leads to more carbon input to soil which can improve soil quality as well as help mitigate the global rise in atmospheric carbon dioxide.

3. A New, Non-destructive Method for Measuring Carbon in Soil. Interest in carbon as a tradable commodity has landowners managing plant systems to enhance soil carbon storage. This has prompted the need for rapid, non-destructive methods for measuring changes in soil carbon content. We developed a new method for measuring soil carbon using inelastic neutron scattering technology. This nondestructive method can be used in stationary or continuous-scanning modes of operation. Initial findings demonstrated the method was feasible and gave reproducible results with a detection limit between 0.5 and 1% carbon by weight.


6.Technology Transfer

Number of Other Technology Transfer5

Review Publications
Runion, G.B., Torbert III, H.A., Prior, S.A., Rogers Jr, H.H. 2009. Effects of elevated atmospheric carbon dioxide on soil carbon in terrestrial ecosystems of the Southeastern U.S. In: Lal, R. and Follett, R.F. (eds.). Soil Carbon Sequestration and the Greenhouse Effect (2nd Edition). SSSA Special Publication No. 57. Agronomy Society of America-Crop Science Society of America-Soil Science Society of America, Madison, WI. pp. 233-262.

Runion, G.B., Price, A.J., Prior, S.A., Rogers Jr, H.H., Torbert III, H.A., Gjerstad, D.H. Effects of elevated atmospheric CO2 on a C3 and a C4 invasive weed. Botany Research Journal. 1(3):56-62.

Price, A.J., Runion, G.B., Prior, S.A., Rogers Jr, H.H., Torbert III, H.A. 2009. Tropical spiderwort (Commelina benghalensis L.)increases growth under elevated atmospheric carbon dioxide. Journal of Environmental Quality. 38:729-733.

Sage, R.F., Coiner, H.A., Way, D.A., Runion, G.B., Prior, S.A., Torbert III, H.A., Sicher, Jr., R.C., Ziska, L.H. 2009. Kudzu [Pueraria montana (Lour.) Merr. Var lobata]: a new source of carbohydrate for bioethanol production. Biomass and Bioenergy. 33:57-61.

Wielopolski, L., Hendrey, G., Johnsen, K., Mitra, S., Prior, S.A., Rogers Jr, H.H., Torbert III, H.A. 2008. Non-Destructive System for Analyzing Carbon in the Soil. Soil Science Society of America Journal. 72(5):1269-1277.

Last Modified: 12/21/2014
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