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Making carbon crediting really work for farmers, Part 2
Mobile field lab to measure soil carbonBy Elaine ViglioneA few months ago, we introduced the measurement challenge associated with the idea of implementing carbon credits for farmers. (See: Part 1: "The search for fast, cost-effective ways to measure soil C in the field.") Regardless of whether one believes that the carbon offset process is a force for good in mitigating atmospheric carbon, or that it will only lead to opportunistic exploitation of the system, no soil carbon enhancement claim is credible without effective methods to assess soil carbon (C) levels and the effect of farming practices on these levels. Specifically, this means developing consistent and effective ways to measure how much carbon is in the soil, determine if it is possible to accurately characterize changes in soil C, and determine whether an adopted farming practice is resulting in additional carbon sequestration. Rodale researchers, funded with grant money from the Pennsylvania Department of Environmental Protection’s Pennsylvania Energy Development Authority (DEP-PEDA), are conducting ongoing tests of different soil carbon measurement methods. Our goal is to advance technologies and procedures that will allow farmers, researchers, extension agents, and carbon-crediting entities to effectively measure soil carbon more quickly and inexpensively than is possible with existing technologies. In the earlier piece, we highlighted findings from the first phase of our work, which studied the relationship between nitrogen mineralization potential (N-min) and soil carbon content. Based on the results, we believe that N-mineralization potential will not prove to be a reliable or cost-effective means to predict changes in soil C. However, we found very strong correlations between farming practices and N-min potential, showing that N-min potential was highest in the organic systems, and low in the conventional systems. Testing a mobile lab In the current phase of the project, we are partnering with researchers at The Pennsylvania State University Department of Crop and Soil Sciences to continue testing methods of soil carbon measurement. We’re working together to develop a mobile lab that will take direct measurements of soil C in the field, right at the sampling point in the field (in situ). The cornerstone of the in situ measurement approach is portable field sensor technology (handheld instruments) that can scan/read the soil sample with little or no physical processing of the specimen. (By comparison, regular carbon measurement technologies require samples to be air-dried and sieved to 2mm for analysis, a process that takes several days at minimum.) These field C measurements are merged with location coordinates, temporal information, and other relevant attributes through a configuration of integrated portable technologies. This data collection system will readily generate soil C distribution maps and other data-derived outputs. In addition to creating a flexible mobile data collection system that can be adapted and generalized for different users and situations, the development of the mobile field lab will also expand the body of knowledge about the sensors’ capabilities to measure soil C in real-world conditions, and provide performance results on the speed of these field measurements. In addition, we will calculate the economic viability of deploying this technology and share other lessons learned about its practical implementation. Sensor Overview Traditionally, soil carbon measurement has been performed in the lab, away from the collection point. Lab analytical techniques to determine the carbon content of soil include several kinds of wet chemical digestion methods and analysis of gases produced by dry combustion. The current gold standard is automated dry combustion, a technology that entails significant costs both up-front and during use. For this high standard of accuracy, we trade off both time and money, and this adds up fast for large sample sets, such as those needed in surveys to monitor many fields or to characterize soil carbon distribution with a single field. In contrast to the dry combustion technique, our approach uses either optical or infrared devices designed to take a reading of the soil at the sampling point. These instruments allow us to eliminate both the time involved in transporting samples to a laboratory and the costs associated with traditional lab testing. These sensors also provide means for nondestructive sampling; that is, measurements can be taken without the need to alter, or in some cases, even remove the sample from the field. Sensors rely on the fact that the waves of energy emitted by a given material, carbon in organic matter for example, vary across the electromagnetic spectrum. Sampling with sensors in targeted parts of the spectrum allow us to read these signatures and estimate soil carbon measurements at the same sampling point in more than one way. We will be sampling in three spectral regions. In the visible and near-infrared regions, we are using hand-held sensors, which collect and analyze spectral measurements of the intact soil core. In the mid-infrared region, we will use portable infrared spectroscopy, after minimal field-processing of the soil specimens.
As the handheld and portable technology becomes increasingly more accessible and versatile, practical implementation of these technologies will depend on our ability to characterize their strengths and limitations for soil C measurement. Integrating the data Other equipment in the mobile field lab is incorporated to rapidly integrate the results of the sensor-scanned soil C values with other data that are essential for their analysis. The unifying database is a universal template that assigns a unique identifier to each sample site that is linked to its sensor readings. Also linked to this identifier is the location of each sample point gathered via global positioning system (GPS) units or a predetermined spatial grid. Sampling forms, displayed on either a personal digital assistant (PDA) or mobile laptop, are customized to allow the investigator to link other attributes immediately at the sampling location. This amount of information alone makes the data immediately viewable in a Geographic Information Systems (GIS) format, allowing for direct feedback on sampling progress and even visualization of some overall trends. On top of direct visualization of the sample points, however, the calibration step and additional analysis capability will allow us to rapidly refine and improve our assessment of carbon present in the soil. Once initial sensor and lab results are compiled and analyzed, a calibration model can be built into the mobile field lab to generate corrected GIS maps of soil C estimates from all inputs. GIS and statistics software allow additional support for modeling and incorporating spatial trends if necessary. The integration and analysis steps can readily accommodate adding sampling points, making it possible to scale the system up or down to any size sampling endeavor. Testing the mobile field lab
 A central advantage to way these mobile technologies are assembled is that the approach is flexible enough to adapt to a variety of choices of sensor technology, hardware, software, and positioning systems. An enterprise may already have a strong GPS/GIS system and soil sampling capability, for example, and need only acquire sensors and a PDA, to populate a template and generate a soil carbon analysis. We are currently in the process of acquiring all equipment needed to complete and test two versions of the mobile field lab system, one at Rodale and one at Penn State. Our next report will include updates on our experiences using the lab and sampling under field conditions, and what we have learned about the system model. Lessons learned on the validation step, as well as our experiences relating to the speed, cost, and efficiency of the system, will all help to advance our knowledge about technologies and procedures that can effectively measure soil carbon more quickly and inexpensively than is possible with existing means. This research was supported with funding by the Pennsylvania Department of Environmental Protection’s Pennsylvania Energy Development Authority (DEP-PEDA), grant number 41000455440, “Rapid, Cost-effective Soil Measurements for Accurate Agricultural Carbon Crediting.” Elaine Viglione is Analysis and Mapping Coordinator for Rodale Institute Part I, Part III, Part IVEnabling research: You can show your support for Rodale Institute's innovative research in carbon sequestration and carbon crediting through organic farming by becoming a member today.
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Mobile field lab to measure soil carbon
This article is very well-written and informative.
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