Wielopolski, Lucian (Brookhaven National Laboratory, Environmental Sciences Department, Bldg. 490D, Upton, NY, 11973; Phone: 631-344-3656; Fax: 631- 344- 7244l; Email: wielo@bnl.gov)

Long Term Non-destructive Soil Carbon Monitoring in Tillage and No-tillage Systems

L. Wielopolski *, S. Mitra, D. Tyler, P. Denton, N. Eash, M. Essington

Increasing soil carbon content serves as a balancing act attempting to mitigate anthropogenic CO₂ emissions into the atmosphere in order to slow down gradual global warming. In addition, it is well recognized that an increase in carbon soil content improves the soil quality and productivity. However, lack of non-invasive tools for soil analysis and our limited understanding of the belowground processes hinders our ability to evaluate carbon sequestration efficacy and assess soil carbon stores. One of the methods, looked upon here, of increasing soil carbon sequestration is switching from till to no-till soil management practices. Carbon has been shown to increase in many continuous no-tillage systems compared to tilled systems. Less is known about the fate of carbon when systems are changed relative to tillage. Carbon will be measured on long-term research plots (established in 1981) comparing three no-tillage soybean-cropping systems to three tilled systems. In the spring of 2002 all plots were randomly split and sampled for soil carbon and nitrogen on each side. After sampling, one side of each of the no-till and tilled plots was converted to the other tillage system. Converted plots were then sampled after the tillage conversion and all plots have been sampled each year since conversion. These data will allow the opportunity to monitor carbon changes in long-term and short- term no-tilled and tilled systems in a controlled randomized replicated experiment. We also will be sampling landscape transects across soil types and positions to evaluate terrestrial carbon spatial variation and storage. This data set, obtained by conventional destructive sampling and wet chemistry, will be compared to results obtained with a novel Soil Carbon ANalysis (SCAN) instrument that measures non-destructively soil carbon content in a continuous scan over large area. The instrument probes the soil to an approximate depth of 20 to 30 cm, depending on the soil conditions, with a footprint of about 150 cm. Such a measurement, besides being non-destructive, provides a mean carbon value for a large volume thus smoothing any possible normal lateral variability in the soil carbon content. The instrument can be used in a stationary mode, or in a mobile mode for an integrated estimate over a large area. This is in contrast to core samples that represent point measurements and for larger field sizes require a large number of cores to reduce the error to an acceptable level. The results will be rank correlated and using in-field calibration will be compared in carbon-estimated values. The predictions of the carbon content for the entire field based on stationary and scanning results will be also evaluated. Discussion of the planned experiments and the analysis will be presented