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United States Department of Agriculture

Agricultural Research Service

2010 Annual Report

1a.Objectives (from AD-416)
Quantify the impact of agricultural practices and environmental changes on surface/atmosphere exchange of greenhouse gases (GHG) in order to develop farming systems that reduce global warming potential (GWP) and promote soil C sequestration; Develop farming systems that permit the removal of biomass for energy production while protecting soil resources; Identify and overcome agronomic impediments to the adoption of farming practices, such as reduced tillage, cover crops, and companion crops, that are developed to reduce GWP and permit stover harvest.

1b.Approach (from AD-416)
We will participate in a multi-location effort to identify farming practices that will help slow the increase in atmospheric concentrations of the greenhouse gases CO2, N2O, and CCH4. Our approach will include continuous, field-scale measurement of the surface/atmosphere exchange of all three gases in three adjacent fields under different management. Parallel plot-scale studies will be conducted with chamber-based gas exchange measurements to permit testing of a broader variety of tillage, nitrogen (N) fertility, and rotation strategies. In the second principal area of inquiry, we, again in cooperation with other ARS locations, will examine the soil sustainability of harvesting corn stover for ethanol production. Our goal is to test the hypothesis that cover or companion crops can fill the role of the removed stover in supplying carbon (C) compounds to maintain soil organic matter. We will explore the use of forage digestibility analyses to characterize the quality and quantity of C compounds contained in corn stover and in cereal rye, kura clover, and selected other cover crops. The third component of this project will focus on identifying and correcting practical, agronomic impediments to adoption of the practices mentioned above. In the upper Midwest, the major hindrance to wider use of cover crops, companion crops, and reduced tillage has been the perception that they will reduce the yield of the subsequent crop, due to such factors as cold, compacted spring seed bed conditions and adverse effects on N availability. We will test and refine theories describing near-surface heat and water flow and develop sensors to more easily measure soil bulk density. We will also conduct plot-scale studies of the effects of reduced tillage and cover crops on N losses by leaching and gaseous emissions. The results of this research will facilitate the development of better reduced tillage and cover crop systems for northern soils.

3.Progress Report
Winter cover crops, planted after a summer season corn or soybean crop and harvested prior to the planting of the next season’s summer crop, offer the potential to produce cellulosic biofuel without interfering with food production. Using a computer simulation modeling approach, we are estimating the potential biomass production of a winter rye cover crop across the U.S. on acreage identified as being cultivated in a corn-soybean crop rotation. We ran the field scale plant-soil-atmosphere model RyeGro to predict harvestable spring aboveground biomass for a winter rye cover crop planted in the fall just after harvest of the previous corn or soybean crop. Thirty locations around the eastern half of the U.S. were selected for the runs; weather inputs were obtained for the years 1980 – 2003. The average biomass values for the 30 locations were used to develop a regression equation that was used to predict the biomass potential in every county with corn-soybean acreage. Laboratory incubations were performed to quantify the impacts of 29 different biochars on soil production of CO2, N2O and CH4 across soils from 3 different ecosystems (agricultural, forest nursery and landfill). The biochars comprise a wide selection of different feedstocks and production conditions. These incubations indicated that there are significant differences in the responses of the soil system as a function of the soil microbial consortia present, since the responses from three different ecosystems were different. In general, the addition of biochar suppressed microbial production of CO2 and N2O and also suppressed the oxidation of CH4. These suppressions were not universal across all biochars. Recent observations have suggested that the sorbed volatiles that are on biochar coupled with the stimulation of ethylene production could contribute to the mechanisms of these suppressions in the rate of GHG production. These results are important due to the growing interest in using soil applied biochar as a means of carbon sequestration. Furthermore, a collaborative project with the USDA-ARS lab in Florence, SC has been initiated examining the GHG production potential of 8 different biochars produced at the Florence lab. Field data was also collected for the second consecutive year from the biochar field plots where there are 5 different biochars being evaluated under continuous no-till corn production in Rosemount, MN. Two field studies were continued that are examining the effects of alternative versus conventional fertilizer management on both N2O emissions and nitrate leaching in a coarse- and moderate-textured soil under dryland and irrigation management, and under conventional and reduced tillage management, for corn production. A mobile, on-site trace gas analysis laboratory and automated gas flux sampling system utilizing six robotically controlled gas-flux chambers was deployed at a third field site for semi-continuous measurement of N2O, CO2, and CH4 fluxes from soils fertilized with anhydrous ammonia for corn production.

1. Observed stimulation of ethylene production resulting from biochar amendments. This observation could provide insight into an additional mechanism for the stimulation effect of biochar on seed germination, seedling growth, root development, and soil greenhouse gas production. This ethylene production also could be related to the observed decrease in soil nitrification rates following biochar additions, since ethylene is a known inhibitor of nitrification. The exact cause of this production is uncertain, but we hypothesize that it is due to the presence of volatile organic compounds sorbed to the biochar as a consequence of the pyrolysis process.

2. Large amounts of nitrogen fertilizer is required for high-value crops such as potatoes. These fertilizer inputs can result in large emissions of nitrous oxide (N2O), which is a potent greenhouse gas. Specialized, coated urea fertilizer products are designed to release nitrogen slowly over the growing season, and thereby better match N supply to plant uptake. This slower release may result in lower N2O emissions. The objective of this study was to compare N2O emissions in a coarse-textured soil fertilized with 270 kg N per ha using sulfur-coated urea (KS), two different polymer-coated urea (PCU) products (ESN and KP), and conventional urea (CU). Crop yields following single, pre-plant applications of KS, ESN, and KP were no different than following multiple split CU applications. N2O emissions with CU tended to be higher than with the coated fertilizers. Of the two PCUs, the product with the greater mass of polymer coating (KP) released N more slowly and also emitted less N2O. Over both seasons, N2O emissions from KP and ESN were approximately 15% and 44% lower than CU, respectively. The amount of N2O emitted was equivalent to 0.10, 0.39, and 0.48% of the amount of fertilizer added for KP, ESN, and CU, respectively. These results show that coated urea can maintain yields while reducing N2O emissions and also reducing costs associated with split applications of conventional fertilizer. The N2O emissions results obtained in this study will assist both scientists and policy makers in improving their estimates of greenhouse gas emissions from agriculture, and in developing improved management practices for mitigating these emissions.

3. Simplified Method for Quantifying Theoretical Underestimation of Chamber-Based Trace Gas Fluxes. Closed chambers used to measure soil-atmosphere exchange of trace gases including nitrous oxide (N2O) and carbon dioxide (CO2) generate errors due to suppression of the gas concentration gradient at the soil-atmosphere interface. A method is described here for estimating the magnitude of flux underestimation arising from chamber deployment. The technique is based on previously established gas transport theory and has been simplified to facilitate application while preserving the fundamental physical relationships. The method avoids the use of nonlinear regression but requires knowledge of soil properties including texture, bulk density, water content, temperature, and pH. Two options are presented: a numerical technique which is easily adapted to spreadsheet application, and a graphical method requiring minimal calculation. In both cases, the magnitude of theoretical flux underestimation (TFU) is determined, taking into account effects of chamber geometry and deployment time, the flux-calculation scheme, and properties of the soil and gas under consideration. Application to actual data and recent studies confirmed that TFU can vary widely within and across sites. The analysis also revealed a highly linear correlation between soil water content and TFU, suggesting that previously observed relationships between water content and trace gas flux may in part reflect artifacts of chamber methodology. The method described here provides a practical means of improving the absolute accuracy of flux estimates and normalizing data obtained using different chamber designs in different soils.

Review Publications
Spokas, K.A., Reicosky, D.C. 2009. Impacts of Sixteen Different Biochars on Soil Greenhouse Gas Production. Annals of Environmental Science. 3:179-193.

Baker, J.M., Griffis, T.J. 2009. Evaluating the Potential Use of Winter Cover Crops in Corn-soybean Systems for Sustainable Co-production of Food and Fuel. Agricultural and Forest Meteorology. 149(12):2120-2132.

Bavin, T., Griffis, T.J., Baker, J.M., Venterea, R.T. 2009. Impact of Reduced Tillage and Cover Cropping on the Greenhouse Gas Budget of a Maize/Soybean Rotation Ecosystem. Agriculture, Ecosystems and Environment. 134(3):234-242.

Spokas, K.A., Koskinen, W.C., Baker, J.M., Reicosky, D.C. 2009. Impacts of Woodchip Biochar Additions on Soil Carbon Net, CH4 Oxidation and Sorption/Degradation of Two Herbicides in a Minnesota Soil. Chemosphere. 77(4):571-581.

Scheutz, C., Kjeldsen, P., Bogner, J.E., De Visscher, A., Gebert, J., Hilger, H.A., Huber-Humer, M., Spokas, K.A. 2009. Microbial Methane Oxidation Processes and Technologies for Mitigation of Landfill Gas Emissions. Waste Management and Research. 27(5):409-455.

Heller, H., Bar-Tal, A., Tamir, G., Venterea, R.T., Chen, D., Zhang, Y., Clapp, E.C., Bloom, P., Fine, P. 2010. Effects of Manure and Cultivation on Carbon Dioxide and Nitrous Oxide Emissions from a Corn Field under Mediterranean Conditions. Journal of Environmental Quality. 39(2):437-448.

Hyatt, C.R., Venterea, R.T., Rosen, C.J., Mcnearney, M., Wilson, M.L., Dolan, M.S. 2010. Polymer-Coated Urea Maintains Potato Yields and Reduces Nitrous Oxide Emissions in a Minnesota Loamy Sand. Soil Science Society of America Journal. 74(2):419-428.

Venterea, R.T. 2010. Simplified Method for Quantifying Theoretical Underestimation of Chamber-Based Trace Gas Fluxes. Journal of Environmental Quality. 39(1):126-135.

Venterea, R.T., Dolan, M.S., Ochsner, T.E. 2010. Urea Decreases Nitrous Oxide Emissions Compared with Anhydrous Ammonia in a Minnesota Corn Cropping System. Soil Science Society of America Journal. 74(2):407-418.

Spokas, K.A., Baker, J.M., Reicosky, D. 2010. Ethylene: Potential Key for Biochar Amendment Impacts. Plant and Soil Journal. 333:443-452.

Last Modified: 8/4/2015
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