Laboratory Soil Handling Affects CO2 Respiration, Amino-N and Water Stable Aggregate Results

Laboratory analysis of soil traits associated with soil quality or soil health has gained popularity very recently reflecting a trend begun over a half-century ago scrutinizing farming systems for potentially deleterious soil effects. This renewed focus has brought into the forefront concerns about how laboratory soil handling may influence the observed traits. We find evidence in the literature that many but not all these concerns were addressed decades ago before the topic became of widespread interest but also before the soil testing industry modernized to high-throughput methods of soil homogenization not designed for soil quality investigations. Consequently, we find it necessary to retrace some steps in order to better characterize artifacts that may hamper objective evaluation of soil responses associated with soil health before conclusions of management effects of farming systems are drawn. Our study examined soils processed by a soil proficiency program by creating two size groups representing intensive and light soil disturbance and discerned differential effects of sieve sizes and moistening properties depending on which soil quality tests were used. The largest effects were due to wetting and not to sieving when comparing CO2 respiration, whereas sieving significantly influenced extractable amino-N and water stable aggregates. We found no evidence that a colorimetric thin-layer gel method (Solvita) for CO2 capture would lead to different conclusions when compared to an IRGA-infrared respirometer. It is recommended that future work continue to examine soil handling factors commonly employed for nutrient analyses which may be inconsistent with the goals of soil quality evaluation.