|Reeves iii, James|
Submitted to: Brookhaven National Laboratory
Publication Type: Proceedings
Publication Acceptance Date: 7/13/2006
Publication Date: 9/1/2006
Citation: Reeves III, J.B., Mccarty, G.W., Wielopolski, L., Acosta, G., Christy, C., Dahlman, R., Harris, R.D., Martin, M., Ramirez, L.M., Thomson, A.M. 2006. Emerging modalites for soil carbon analysis: sampling statistics and economics workshop. Brookhaven National Laboratory. CD. Interpretive Summary: Carbon (C) is an important part of all living things and soils. However, the release of C in the form of carbon dioxide (CO2) is generally believed to be a major contributor to global warming. While C can be released from soils, it can also be bound into soils (sequestered) for long periods of time and thus soils offer the possibility to store large quantities of C for many years and, in doing so, both help to reduce the rate of increase in global warming and improve soil quality. However, in order to access the ability of different practices, e.g. tillage vs. non-till, cover crops, etc., rapid, accurate and inexpensive methods to determine soil C are needed as present laboratory based methodologies, while often very accurate, are too slow and expensive for the large numbers of samples which will likely need to be analyzed. Also, these methods are nearly impossible to perform on site. A workshop to explore issues important to new measurement methods for soil C analysis was held at Brookhaven National Laboratory on January 19-20, 2006. The goal of this report (BNL Report # 75762-2006) is to provide a summary of the workshop. Several emerging methods were discussed including: Laser Breakdown Spectroscopy (LIBS) in which a high intensity laser is used to vaporize a small sample of soil into a plasma, the composition of which is then determined by the light radiation produced by the individual elements, including C, present in the sample; Near- and mid-infrared spectroscopy (NIRS and mid-IR, respectively) which determine the soil composition based on the absorbance and reflectance of light beyond the human range of sight; pyrolysis-molecular beam mass spectroscopy (PY-MBMS) which determines the soil composition by examining the products produced when soil is decomposed by heating in an inert atmosphere and Inelastic Neutron Scattering (INS) in which a neutron radiation source is used to irradiate the soil. Discussions showed that each method offers advantages and disadvantages and are often complementary rather than competitive depending on the information needed, the speed desired, etc. For example, LIBS and INS determine total C, and not the form of C present, while NIRS, mid-IR and (PY-MBMS) determine the forms of C present. Similarly INS examines samples on the order of a fraction of a cubic meter, while for the others samples are 1000’s to 1,000,000’s of times smaller. Also, work is needed on all the methods to determine the effects of the non-C components (the matrix) of the soil on the measurements, e.g. water, minerals, etc. Other areas discussed were errors in the measurements and how to develop a proper calibration (mathematical relationship between the measurement taken and the actual C value). In summary, newer methods for soil analysis are becoming available and now require joint studies to determine the advantages and disadvantages of each method and to compare results obtained with each method on the same samples.
Technical Abstract: Carbon is an integral part of the global C cycle and plays an important role in soil quality and productivity. In the last 20-30 years detailed knowledge of C balances and transport in the soil, on local, regional, and global scales emerged as being critically important for quantification of soil C stocks needed for assessing sequestration as a mitigating factor for the anthropomorphic emissions of CO2 into the atmosphere. Lack of reliable instrumentation for monitoring belowground C processes and occurring changes exacerbates and hampers implementation of trading policies with C credits. With the ratification of Kyoto Protocol, extensive effort is being devoted to the implementation of strategies reducing the emissions of, and increasing the sequestration of some greenhouse gases, including CO2. The Intergovernmental Panel on Climate Change (IPCC) recognized that agricultural land and forestry offer the potential to sequester from the atmosphere about 80 billion metric tons of CO2 in the next 50 years. It is self-evident that success of these efforts strongly depends on robust instrumentation for measuring, monitoring, and verifying the processes involved. However, belowground processes pose a special challenge. Soil is a dynamic, living system, an intimate mix of living and dead plant matter, fungi, macro- and micro-fauna, plant exudates, and animal waste products, embedded in a matrix of solids, liquids, and gases. When the “black box” of this soil mélange is dissected its function is altered. Current analytical methodologies are not on par with the emerging needs for a fast, reliable, in situ, non-destructive, static/dynamic, and inexpensive instrumentation. A workshop to explore issues cardinal to the emerging analytical technologies, their operations, and the degree to which they satisfy the needs for an in situ, non-destructive soil C analysis was organized by Lucian Wielopolski and held at Brookhaven National Laboratory (BNL) on January 19-20, 2006. The goal of this report is to provide a succinct summary of the various technologies that were brought together and to elaborate on the main points that transpired from the workshop. It was widely recognized that the instrumentation presented is based on different technologies that measure substantially different volumes, ranging from few millimeters cube for LIBS, to a fraction of a cubic meter using INS. In also became apparent that LIBS and INS measure atomic C whereas NIR, MIR, and py-MBMS are sensitive to chemical speciation thus providing different and complimentary information. All the methods indicated existence of some peak interferences and matrix, e.g., soil density and moisture, effects on the measured analyte that require further clarifications and quantification. Error propagation in the measurements was not clarified adequately and it ties in with what constitutes a proper calibration for each instrument. Since there are many ways to calibrate devices, the need became apparent for a standardized procedure or a protocol that would be used at identified sites for independent calibration and double-blind evaluation of the devices. All of the introduced technologies were improving soil analysis by either simplifying it or providing additional information not available with standard soil coring or excavation. The INS method stood apart from the other systems in that it was truly non-destructive, measured large volumes, and it rests upon an analytical response function that enables simulations and synthetic calibrations. However, more detailed information and characterization of all of the systems is required, as discussed in the summary. Nevertheless, it was strongly felt that all methods reached a degree of maturity to warrant joint studies to ascertain the characteristics and performance of each technology, and to cross-correlate the results among themselves,