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United States Department of Agriculture

Agricultural Research Service


Location: Soil Dynamics Research

2012 Annual Report

1a. Objectives (from AD-416):
Objectives include: (1) determine what carbon sequestration potentials exist within nursery systems; (2) develop strategies for increasing carbon (C) sequestration above current levels; 3) measure greenhouse gas emissions from nursery production systems; and (4) develop practices to reduce greenhouse gas emissions from nursery production systems.

1b. Approach (from AD-416):
Measurement of potential carbon (C) sequestration will be accomplished by making soil and gas sampling measurements in an existing alternative substrate study. Auburn University Horticulture Department has an ongoing effort to develop alternative substrates for horticultural production. Within this study, C sequestration levels will be monitored and compared to soil conditions which have not been disturbed by planting. In a second study, three pot sizes commonly used in the nursery industry (trade gallon, gallon, and 3 gallon) will be examined. Greenhouse gas emissions will be measured weekly from these pots over the course of the growing season.

3. Progress Report:
Auburn University, in cooperation with USDA-ARS, is conducting work to develop strategies for increasing carbon sequestration and to decrease green house gases (GHG) emissions within nursery systems. The contribution of the horticultural industry to the rising level of carbon dioxide (CO2) (and other trace gases) in the atmosphere is unknown. The trace gas study using dwarf yaupon holly grown in four commonly used container sizes (trade gallon, gallon; two gallon, three gallon) using standard production potting media and growing practices has been completed. Trace gas emissions were assessed weekly using the static closed chamber method according to USDA’s Greenhouse Gas Reduction Through Agricultural Carbon Enhancement network (GRACEnet) protocols. Gas samples were taken at 0, 15, 30, and 45 min intervals following chamber closure to calculate gas flux rates and analyzed using gas chromatography. There was a significant positive relationship of container size with both CO2 and nitrous oxide (N2O) efflux, with the highest fluxes occurring in the largest containers (3 gallon). Methane flux was consistently low and had no significant effect on total GHG emissions. This study begins to address uncertainties regarding the environmental impact of the horticulture industry on climate change while providing baseline data of GHG emissions from container production systems needed to develop future mitigation strategies. A new GHG study, using the same protocols as the container size study, with azaleas grown using three different fertilizer application methods (broadcast, incorporated, dibble) to identify which will minimize GHG loss has recently been completed. CO2 fluxes were lower when fertilizer was dibbled compared to the other two methods. Nitrous Oxide (N2O) fluxes were consistently highest when fertilizer was incorporated. Methane flux was generally low with few differences among treatments. This study begins to provide data which can be used to implement mitigation strategies in container plant production which will help growers adapt to possible emission regulations and benefit from future GHG mitigation or offset programs. In the carbon sequestration study, plants were grown in containers using three differing substrates (pine bark, clean chip residual, and whole tree) for one season prior to field outplanting. Soil samples were collected in the summer of 2009, 2010, and 2011 for soil carbon (C) and nitrogen (N). Automated Carbon Efflux Systems (ACES) were installed adjacent to three plant species (crape myrtle, magnolia, and Shumard oak) to monitor (24 hr d-1) C lost through soil respiration. Biomass has been assessed to determine the amount of C in plant material. Information on both inputs (biomass) and outputs (respiration) will allow for determination of C sequestration potential. In this study, crape myrtle had higher soil carbon dioxide efflux than magnolia, possibly due to a larger root system or faster growth rate. Pine bark had lower soil efflux than clean chip residual in crape myrtle, while in magnolia this relationship was reversed. However, whole tree had significantly lower soil flux than either pine bark or clean chip residual. Whole tree has a higher percentage of wood than either pine bark or clean chip residual which may cause it to break down slower, resulting in lower soil flux. With crape myrtle, all three media had significantly different soil flux values; there was no effect of media for magnolia. Soil flux data for Shumard oak are currently being analyzed. Currently, three shrub species (Indian hawthorn, loropetalum, cleyera) are being assessed using the above methodologies. Our results indicate that C storage potential may increase with utilization of whole tree as a growing media for container crops. Additional data such as plant biomass increase and changes in soil C levels over time will also be needed to fully understand the impact of these growing media on soil carbon dioxide emission.

4. Accomplishments

Last Modified: 10/18/2017
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