Non-instrumental Real-time Soil Respiration Rate and Soil Microbial Biomass Carbon Determinations

Soil microbial property is one of the fundamental indicators of soil health and quality, yet it has not been routinely examined in most soil testing protocols most likely due to the inconvenience of the current procedures. This study was initiated to validate a microrespirometry (MicroRes) method on real-time soil microbial respiration rate determinations with an infrared gas analyzer (IRGA) respirometer. The results showed that the two were agreeable (slope = 0.971, r(2) = 0.977, n = 24). We then used the MicroRes, in place of an IRGA respirometer, to determine the substrate-induced-maximum-initial-respiration (SIR) microbial biomass carbon (SMBC) on the 63 soil samples collected from 28 states of the US and three provinces of Canada. We also determined the10-day incubation mineralized carbon after rewetting the dried soils on the 63 soil samples. The SIR-SMBC determined correlated well with the 10-day incubation mineralized carbon (slope = 0.688, r(2) = 0.816, n = 63). MicroRes is a much simpler and cost-effective alternative to IRGA respirometers in real-time soil respiration rate and SIR-SMBC determinations. Its application makes routine real-time soil microbial property examinations possible under laboratory or filed conditions.