Many soil labs are adding the Solvita test to their repertoire as a means to reveal soil biological activity and N-mineralization potential. The test was originally designed for soils with medium to low organic matter, as is (unfortunately) now the case with most farmed soils in America. What about soil respiration for high OM soils? Will the range that Solvita is calibrated for work? Collaborative research between Woods End Labs, USDA-ARS (Texas) and University of Maine Soil Lab (Orono, ME) evaluated this. Orono  randomly selected 48 archived soils from gardens, turf and pastures that had over 5% OM – some as high as 19%. Two soil labs split the samples and ran the regular soil Solvita (lo-CO2 detectors) and Solvita high-CO2 probes, the latter normally used for composts since the CO2 rate of compost can be 5-20 times higher than soil.
The results showed that CO2 respiration does not appear to increase proportional to the tested OM level, but tends to level off. This indicates that the lo-CO2 probes normally used for soils are not underestimating respiration for high OM soils. The researchers also correlated the soil tests with the standard 7-day anaerobic N-mineralization test. The ratio of release of N to CO2 respiration of ppm, as measured by Solvita, was only slightly greater than the ratio seen with soils that are less than 5% OM. This suggests that high OM soils are less efficient in supplying organic N from stored OM, than are low OM soils. One explanation is that high OM soils may have accumulated crude or non-microbial organic matter (not humified) and therefore do not contribute to the soil nitrogen cycle.