2008 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.
We developed a new sensor for measuring transmission of both direct and diffuse photosynthetically active radiation through plant canopies that can be constructed in any shop with commonly available parts, and provides accurate data that will be useful in predicting growth and development of underseeded winter cover crops.
We developed a model to compare ET of winter cover crops to that of bare fields exposed to the same atmospheric forcing. Model performance was evaluated against eddy covariance measurements of latent heat flux in two adjacent fields, one bare and one planted with winter rye, over two growing seasons. Both model and measurements show that frequency of precipitation, timing of cover crop removal, and soil albedo are key determinants of relative water use of cover-cropped versus bare fields.
We developed a model that predicts accumulation of trace gases inside of gas flux chambers as a function of soil physical properties, chamber dimensions and other factors. The model allows for evaluation of error in chamber-based gas flux estimates and therefore provides a basis for improving accuracy of soil gas flux estimates. Further work is being conducted to determine the influence of soil consumption process on biologically active greenhouse gases including nitrous oxide and methane and the effect of analytical measurement error on gas flux estimate error.
We are measuring the effects of controlled-release nitrogen fertilizers compared to conventional urea on soil nitrous oxide fluxes in three different cropping systems: corn (irrigated and non-irrigated) and potato (irrigated) each planted in a loamy sand and corn (non-irrigated) planted in a silt loam.
Subsurface CO2 concentrations were observed in phase with barometric pressure, temperature and/or wind speed changes while the soil was frozen. Rapid increases in subsurface CO2 concentrations were observed upon thawing. These results provide insight into the seasonal dynamics of trace gas emissions.
Increased CO2 and N2O production (lab) along with increased strawberry yields (field) have been observed following pyraclostrabin use. In the field, pyraclostrabin was only detected in the surface residue (straw mulch covering) and has not been detected in the soil following application.
Manuscript was published on development of an improved thermo-TDR sensor for non-destructive bulk density measurement. Improvements were made in procedures for collecting heat pulse ratio data that can be used to estimate near surface soil water fluxes, e.g. infiltration. Second year of data on heat flow in frozen soil were collected.
Completed first year of study evaluating effectiveness of strip-tillage in a corn/kura clover companion cropping system. Completed first year of study of effects of corn/kura clover companion cropping on partitioning of gaseous/leaching N losses and N use efficiency.
These activities contribute to National Program 202, Problem Area 5 "Adoption and implementation of soil and water conservation practices and systems" and to the Carbon Cycle and Carbon Storage and Trace Gases Problem Areas in the Global Change Program National Program (NP-204).
Development of improved method for analysis of errors in estimating chamber-based greenhouse gas flux estimates from agricultural soils
While chamber methods for measuring greenhouse gas fluxes from agricultural soils are widely used, it is well known that these methods are prone to potentially large errors resulting from the alteration of near-surface concentration gradients. In general, these errors result in an underestimation of the actual rate of gas transfer from soil to atmosphere. However, there is little information available for quantifying these errors. A numerical model was developed and theoretical analysis was performed which can be used together with soil physical property data to quantify method-specific chamber-based measurement errors. Application of these error analysis tools will result in more accurate estimates of emissions of greenhouse gases including carbon dioxide and nitrous oxide from agricultural soils. In turn, this will result in improved national- and global-scale estimates of agricultural contributions to greenhouse gas emissions.
This accomplishment contributes to to the Carbon Cycle and Carbon Storage and Trace Gases Problem Areas in the Global Change Program National Program (NP-204) under the GRACEnet multi-location project, and in particular to achievement of product (iv) improved national inventories of trace gases.
Development of improved method for measuring heat flow in frozen soil
Scientists are currently unable to fully measure the exchanges of energy at the soil surface during freezing and thawing events. In particular, there is no existing method to measure the amount of energy flowing into or out of the soil as it freezes and thaws. The difficulty lies in the fact that the thermal properties of soil change dramatically over very small temperature ranges near the freezing point. We have developed a method that will permit soil thermal properties and energy flow to be accurately monitored during freezing and thawing events. This will benefit scientists who will apply the method to gain greater understanding of how Earth's weather and climate are influenced by freezing and thawing of the land surface. The design of improved reduced tillage, cover crop, and companion crop systems may also be facilitated by more accurate measurements of heat flow near the soil surface.
This accomplishment contributes to National Program 202, Problem Area 5 "Adoption and implementation of soil and water conservation practices and systems."
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Olmanson, O.K., Ochsner, T.E. 2008. A partial cylindrical thermo-time domain reflectometry sensor. Soil Science Society of America Journal. 72:571-577.
Maggi, F., Gu, C., Riley, W.J., Hornberger, G.M., Venterea, R.T., Xu, T., Spycher, N., Steefel, C., Miller, N.L., Oldenburg, C.M. 2008. A mechanistic treatment of the dominant soil nitrogen cycling processes: Model development, testing, and application. Journal of Geophysical Research-Biogeosciences. Available at: http://www.agu.org/journals/jg/jg0802/2007JG000578/2007JG000578.pdf.
Spokas, K.A., King, J., Wang, D., Papiernik, S.K. 2007. Effects of soil fumigants on methanotrophic activity. Atmospheric Environment. 41:8150-8162.
Lachnicht Weyers, S.L., Schomberg, H.H., Hendrix, P.F., Spokas, K.A., Endale, D.M. 2008. Construction of an electrical device for sampling earthworm populations in the field. Applied Engineering in Agriculture. 24(3):391-397.
Venterea, R.T., Stanenas, A.J. 2008. Profile analysis and modeling of reduced tillage effects on soil nitrous oxide flux. Journal of Environmental Quality. 37:1360-1367.
La Scala, Jr., N., Lopes, A., Spokas, K.A., Bolonhezi, D., Archer, D.W., Reicosky, D.C. 2008. Short-term temporal changes of soil carbon losses after tillage described by a first-order decay model. Soil & Tillage Research. 99:108-118.
Griffis, T.J., Sargent, S.D., Baker, J.M., Lee, X., Tanner, B.D., Greene, J., Swaitek, E., Billmark, K. 2008. Direct Measurement of Biosphere-Atmosphere Isotopic Exchange Using the Eddy Covariance Technique. Journal of Geophysical Research. Available: http://www.agu.org/pubs/crossref/2008/2007JD009297.shtml.
Ochsner, T.E., Baker, J.M. 2008. In Situ Monitoring of Soil Thermal Properties and Heat Flux during Freezing and Thawing. Soil Science Society of America Journal. 72(4):1025-1032.