Coring lubricants can increase soil microbial activity in Vertisols

It is essential that sampling procedures for biological measurements are done in a way that reflects the soil processes, whilst limiting sampling artefacts. In heavy clay Vertisol soils, coring lubricants are often considered necessary in order to extract and recover soil for quality and health assessments. Previous reports into the use of coring lubricants have found soil carbon measurements to be inflated but to date, a study to evaluate the effects of these lubricants on soil microbial activity, has not been forthcoming. We measured soil carbon dioxide (CO₂) evolution in response to the addition of common coring lubricants, to determine the effects upon soil microbial activity to the depth of 100 cm. Application of coring lubricants to the surface soil layers of field collected cores did not significantly influence CO₂ evolution however, microbial activity increased in deeper soil layers (30-100 cm) with the use of WD-40, mould stripper and silicone oil. When the ratio of coring lubricant to soil was increased to ~5 g coring lubricant to 100 g^-1 soil, there was a significant (P = .001) effect on microbial activity, with silicone oil and mould stripper inflating measurements by at least 5%, whilst olive oil and WD-40 were similar to the control. The results imply that when using coring rigs to recover soil for microbial functional analysis in Vertisols, the use of coring lubricants is best avoided, with further research recommended.