Extending the applicability of laser-induced breakdown spectroscopy for total soil carbon measurement

Soils are the major pool of terrestrial C globally. Estimating inventories and detecting changes in the soil C pool have remained elusive, largely because the spatial distribution of soil C varies considerably. New approaches are needed that enable more rapid, cost-effective, and sensitive measurements of soil C and that reduce uncertainty in estimates of C pools and changes in those pools. In this note we extend the application of a new method of total soil C measurement: laser-induced breakdown spectroscopy (LIBS). Carbon analysis using LIBS provides data in seconds from soils with little preparation, whereas conventional methods such as dry combustion require lengthy sample preparation and longer analysis times. Laser-induced breakdown spectroscopy instruments, unlike conventional instruments, can be used while in the field. This promising new method, however, has potential drawbacks, namely interference with Fe at approximately 248 nm. Here we report results of using a different C line at 193 nm to solve the interference problem. We also use a two-element standardization factor to demonstrate that the 193-mn line is nearly as sensitive to C concentration as the C line at 247.8 nm, and that calibration curves can be readily replicated. Overall these results indicate that LIBS is a very promising method to estimate soil C pools and dynamics.