2011 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.
One field site in our long-term carbon balance research had to be relocated, due to loss of land at the University of Minnesota Rosemount Research Center. A new site was established in a nearby field, which necessitated installation of a new instrument mast for gas exchange measurements and extensive soil sampling. A field experiment was conducted to compare the efficacy of helicopter seeding of winter rye into soybeans versus broadcast seeding with a high-clearance tractor. A full year of automated measurements of soil respiration and N2O production was obtained with chambers installed in a corn field under 3 different levels of residue removal. A review was conducted on the existing research in determining the stability of biochar after adding to soil. The potential of converting biomass into biochar (charcoal) represents one potential mechanism to reduce atmospheric CO2 levels by returning this charcoal back to the soil. Biochar has also been observed to increase soil fertility. However, the mechanisms behind these increases in soil fertility and plant growth are not fully understood. We examined historical studies of charcoal and its use in improving crop yields, which provides additional insight and direction in future research related to potential beneficial uses of biochar in agriculture. These uses may benefit from other potentially higher value end markets for biochar that will aid in establishing an improved market which could drive the economics of biochar production. A new field study was initiated in a tile-drained soil in Lamberton, MN examining fertilizer source and drainage management effects on N2O emissions and nitrate leaching. One field study was continued for the second year examining the effects of alternative versus conventional fertilizer management on both N2O emissions and nitrate leaching in a moderately-textured soil 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 different N fertilizer sources and using different application techniques (i.e., banded versus uniformly broadcast).
Separating the sources of CO2 between plant and soil microbial respiration. In carbon cycle research, it is often difficult or impossible to determine if CO2 emitted from an ecosystem was produced from autotrophic plant activity (e.g., root respiration) or heterotrophic respiration of soil microorganisms. ARS scientists in St. Paul, MN recently developed tunable diode laser spectroscopy systems (TDLAS) that can help to do this by separately measuring the release of the two stable isotopes of CO2, 12- and 13-CO2. We measured the exchange of both forms of CO2 in such a system using a TDLAS. We found that the contribution of root (autotrophic) respiration to total soil respiration increased linearly during the early growing season, reaching a peak of 55%. We also found diurnal variability in the total isotope composition of respiration, suggesting either different temperature sensitivities for autotrophic and heterotrophic respiration, or different source depths. This method should prove useful in further carbon balance studies, particularly in developing management strategies to minimize heterotrophic respiration. Thus, this technique is expected to provide insights to help farmers select management systems that can maximize the amount of carbon that is retained in the soil as opposed to being emitted to the atmosphere as CO2.
Nitrogen fertilizer sources effects on N2O and NO emissions. Adding fertilizer to soil can produce nitrous oxide (N2O), which is an important greenhouse gas, and nitric oxide (NO) which is a gas that can affect local air quality. Anhydrous ammonia (AA) and urea are important nitrogen (N) fertilizer sources in the U.S. However, there is little information regarding how AA and urea may differ in their effects on N2O and NO gas emissions. Also, few studies examining N2O and NO emissions have also evaluated crop performance together with atmospheric impacts. ARS scientists in St. Paul, MN compared N2O and NO emissions, crop yields, and N fertilizer recovery efficiency (NFRE) in a corn production system that used three different fertilizer practices: urea that was broadcast and incorporated (BU), and AA that was injected at a conventional depth (0.20 m) (AAc) and at a shallower depth (0.10 m)(AAs). Averaged over two growing seasons in an irrigated loamy sand in central Minnesota, N2O emissions increased in the order BU < AAc < AAs. Emissions of N2O were 40% greater with AAc than with BU and were more than 100% greater with AAs than AAc. In contrast, NO emissions were more than 100% greater with BU than either AAc or AAs. Expressed as total N loss (NO + N2O), emissions increased in the order AAc < BU < AAs. Despite having the greatest emissions of N2O and total N oxides, the AAs treatment did not have reduced NFRE compared with the BU treatment, and had greater NFRE compared with the AAc treatment. These results provide evidence that AA emits more N2O, but less NO, compared with broadcast urea. Also, these results show that specific practices to reduce N2O emissions may not always noticeably improve N use efficiency. These results provide specific information that farmers can use to help reduce emissions of N2O from corn production systems.
Sorbed organics on biochar. Biochar is produced when organic materials such as plant residues are combusted in the presence of low amounts of oxygen, in a process referred to as pyrolysis. The incorporation of biochar into soil is being considered as a potential means of stabilizing carbon that might otherwise be emitted to the atmosphere as carbon dioxide (CO2). However, the full impacts of biochar on the soil and plant communities are not known. ARS scientists in St. Paul, MN observed high variability of sorbed organic compounds on biochar. These sorbed compounds when released in soil can trigger both plant and microbial reactions due to their role as plant and/or microbe signaling compounds. There was high variability in the type and concentrations of these sorbed organic compounds that appeared to be more related to the manner in which the biochar was produced and processed than the composition of the material used to produce the biochar. These observations could lead to insights into explaining how biochar may stimulate seed germination, seedling growth, root development, and soil greenhouse gas production. Farmers and regulators interested in utilizing biochar as a soil amendment will find this information useful.
Spokas, K.A., Bogner, J. 2011. Limits and dynamics of methane oxidation in landfill cover soils. Waste Management. 31(5):823-832.
Baker, J.M., Griffis, T.J. 2010. A simple, accurate, field-portable mixing ratio generator and Rayleigh distillation device. Agricultural and Forest Meteorology. 150(12):1607-1611.
Chanton, J., Abichou, T., Langford, C., Spokas, K.A., Hater, G., Goldsmith, D., Barlaz, M. 2011. Observations on the methane oxidation capacity of landfill soils. Waste Management. 31(5):914-925.
Spokas, K.A. 2010. Review of the stability of biochar in soils: predictability of O:C molar ratios. Carbon Management. 1(2):289-303.
Bogner, Spokas, K.A., Chanton, J. 2011. Seasonal greenhouse gas emissions (methane, carbon dioxide, nitrous oxide) from engineered landfills: Daily, intermediate, and final California cover soils. Journal of Environmental Quality. 40(3):1010-1020.
Venterea, R.T., Hyatt, C., Rosen, C. 2011. Fertilizer management effects on nitrate leaching and indirect nitrous oxide emissions in irrigated potato production. Journal of Environmental Quality. 40(4):1103-1112.
Wilhelm, W.W., Johnson, J.M., Lightle, D., Karlen, D.L., Novak, J.M., Barbour, N.W., Laird, D.A., Baker, J.M., Ochsner, T.E., Halvorson, A.D., Archer, D.W., Arriaga, F.J. 2011. Vertical distribution of corn stover dry mass grown at several U.S. locations. BioEnergy Research. 4(1):11-21.
Wilhelm, W.W., Hess, J.R., Karlen, D.L., Johnson, J.M., Muth, D.J., Baker, J.M., Gollany, H.T., Novak, J.M., Stott, D.E., Varvel, G.E. 2010. Balancing limiting factors and economic drivers for sustainable midwestern U.S. agricultural residue feedstock supplies. Industrial Biotechnology. 6(5):271-287.
Karlen, D.L., Varvel, G.E., Johnson, J.M., Baker, J.M., Osborne, S.L., Novak, J.M., Adler, P.R., Roth, G., Birrell, S. 2010. Monitoring soil quality to assess the sustainability of harvesting corn stover. Agronomy Journal. 103:288–295.
Johnson, J.M., Wilhelm, W.W., Karlen, D.L., Archer, D.W., Wienhold, B.J., Lightle, D.T., Laird, D.A., Baker, J.M., Ochsner, T.E., Novak, J.M., Halvorson, A.D., Arriaga, F.J., Barbour, N.W. 2010. Nutrient removal as a function of corn stover cutting height and cob harvest. BioEnergy Research. 3:342-352.
Griffis, T.J., Baker, J.M., Sargent, S.D., Erickson, M., Corcoran, J., Chen, M., Billmark, K. 2010. Influence of C4 vegetation on 13CO2 discrimination and isoforcing in the Upper Midwest, United States. American Geophysical Union. 24(1):1-16.