Assessing the effects of air-drying and rewetting pre-treatment on soil microbial biomass, basal respiration, metabolic quotient and soluble carbon under Mediterranean conditions

Soil biochemical properties are useful indicators of soil quality as they are very sensitive to disturbance. Sample storage or pre-treatments could affect the results in these assays, which are normally determined on fresh samples, kept cold or frozen. The objectives of this study were to (i) evaluate the effect of air-drying or incubation of rewetted air-dried soil samples on microbial biomass carbon (MBC), basal soil respiration (BSR), qCO2 and water soluble carbon (WSC), in soils from different locations, with different degradation status and sampling seasons, and (ii) assess if air-drying or incubation of rewetted air-dried soil samples is an accurate sample storage and pre-treatment procedure for these soil properties in soil quality evaluations under semiarid Mediterranean conditions. Our results showed that air-drying does not have the same effects on MBC, BSR, qCO2 and WSC depending on the geographical situation and sampling date. It seems that the warmest and driest place and season show less variation when using air-dried soil samples, with values representative of those obtained under field-moist conditions. Short incubations (4, 8 and 12 days at 23 °C) provoked a general decrease in all properties, probably due to labile organic compounds depletion. Hence, air-dried soils can be used as part of soil quality analysis to estimate these biochemical properties in summer time in the semiarid region of South-East Spain, because they have not suffered severe affections. Moreover, MBC could also be determined using air-dried soil in the driest zones during all year. In contrast, estimations with incubated soil samples are not, in any case, representative of field-moist soil values.