New techniques in soil sampling: methods for long-term ecological research

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Carrie Rose Levine
Ruth D. Yanai
Steven P. Hamburg
Tyler K. Refsland

Imprecise, inaccurate, and inconsistent soil sampling techniques are a major source of uncertainty in the calculation of nutrient budgets. Traditional methods of soil sampling include soil coring and excavation of quantitative soil pits. The major problem encountered with soil coring is that rocky soils limit the location and depth of sampling, and therefore the soil volume is not accurately measured. Quantitative soil pits resolve the rock volume bias, but they are notoriously laborious and destructive, making repeated measurements difficult in spatially variable sites. At the Hubbard Brook Experimental Forest and other sites in the in the White Mountain National Forest, New Hampshire, we are testing novel methods of soil collection and analysis. A gas-powered, diamond-bit drill can core through large roots and rocks to a depth of 90 cm or more, thereby eliminating the depth and density biases of manual coring. The samples we collected with this technique will be compared to soils collected from quantitative soil pits to determine if total carbon, nitrogen, and exchangeable cations are consistent between power-cored soils and soils from pits. Analyses of different segments of the cored samples revealed significantly higher concentrations of exchangeable cations at the edge of the core, presumably due to contamination by ground rock. This grinding action may bias exchangeable cation concentrations, but will probably not affect total carbon and nitrogen concentrations. We also tested an inelastic neutron scattering approach, which non-destructively measures belowground carbon and nitrogen concentrations through in-situ spectroscopy of gamma rays. This approach could be highly beneficial to long-term ecological research as it allows for repeated measurements. It does not, however, allow for depth profiling. No method is perfect, but each of these methods offers important improvements in speed and reproducibility over traditional methods of soil sampling. These new methods are applicable to a wide variety of ecosystems, and may improve understanding of carbon and nutrient stocks in soils at other LTER sites.

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