Ex-situ soil respiration assessment using minimally disturbed microcosms and dried-sieved soils; comparison of methods to assess soil health.

Soil respiration measurements are commonly used as soil health indicators. Several ex-situ soil respiration methods exist, but comparative performances between them have rarely been analyzed. Specifically, there is a lack of comparisons between intact microcosms and destructive methods. The objective of this study was to analyze and compare three different ex-situ soil respiration methodologies: minimally disturbed microcosms using fresh soil, dried-sieved 24h_burst_test, and dried-sieved 10_days incubation. We hypothesized that (1)_the respiration rates for the three methods are correlated to each other; (2)_the respiration rates are strongly correlated with soil physico-chemical parameters; (3)_disturbance caused by drying and sieving reduces regression coefficients compared with microcosms; (4)_drying and sieving soil produces larger respiration rates. Soil was collected in the Province of New Brunswick, Canada. Total carbon and nitrogen, pH, aggregate stability, dissolved C and N, NO3 and NH4, texture, and labile C were determined prior to incubations. Our results showed that the three methods had CO2 efflux in similar ranges. However, the methods had low to no significant correlations between soil physico-chemical parameters and respiration. Total dissolved N had the strongest correlation with CO2 efflux. The results of the microcosm method significantly correlated with the results for 24h burst test but not with the 10 days incubation method. We conclude that drying and sieving soil prior to performing ex-situ soil heterotrophic respiration measurements using the 24 hour burst tests can produce ‘cautiously reliable’ results. Despite the disturbance, results from the 24 hour burst tests are comparable with the results of the microcosm method.