Solvita Soil CO2-Burst: A New Test for Microbial Biomass and Potential N-Mineralization.

Measuring soil carbon dioxide (CO₂) is a direct means to gauge turnover of soil organic matter (SOM). Accumulation of SOM reflects the interaction of crop and manure additions, soil tillage and climate. Flush of carbon dioxide following rewetting dried soil relates to active organic pools and correlates to soil microbial biomass.  Soil microbial biomass plays a critical role in controlling the supply of N to crops.  Even where crops are dependent for N on inorganic fertilizers, turnover and activity of soil biomass often accounts for more than 50% of total crop N uptake. The new SolvitaŽ test enables rapid detection of soil CO₂ evolution correlated with traditional base-trap, infrared IRGA and GC methods.  The use of a standardized 24h rehydration technique enables CO₂-burst to be accurately measured in a short time frame, yet the quantity of the burst closely matched longer term  (up to 28d) respiration. Development of a simple, rapid, and reliable method for quantifying soil biological activity has proven elusive.  To date, measuring potential N-mineralization includes cumbersome methods that have not been cost-effective for routine adoption in commercial labs.  Broader adoption of a test for active soil carbon that is economical for routine laboratory use is likely to help address multiple concerns, including the need to limit nutrient additions based on local soil indications,  the need to monitor soil carbon, and the potential of  soil biology in bioremediation.   We report the CO₂-burst test in 1) measuring of soil biological response following staggered applications of aged manure, and 2) in monitoring background soil N-mineralization as indicated by control plot yield studies.   Additions of manure had consistent biological responses suggesting longer term N-mineralization contributions.    Widespread adoption of the new test may be cost-effective for soil labs, potentially saving farmers money on fertilization, and reducing nutrient pressure on surface and groundwater.