Flush of carbon dioxide following rewetting of dried soil relates to active organic pools

Soil quality assessment could become more standardized with the development of a simple, rapid, and reliable method for quantifying potential soil bio logical activity. We evaluated the flush of CO2 following rewetting of drie d soil under standard laboratory conditions as a method to estimate an acti ve organic matter fraction. The bush of CO2 following rewetting of dried so il (3 d incubation at approximate to 50% water-filled pore space and 25 deg rees C) was assessed for 20 soil series containing a wide range of organic C (20 +/- 13 g kg(-1)) from Alberta-British Columbia, Maine, Texas, and Geo rgia. This flush of CO2 explained 97% of the variability in cumulative C mi neralization during 24 d [gamma = 12 + 3.3(x); n = 471], 86% of the variabi lity in soil microbial biomass C [gamma = 337 + 2.4(x); n = 399], and 67% o f the variability in net N mineralization during 24 d [gamma = 18 + 0.10(x) - 0.00002(x)(2); n = 327], Accounting for geographical differences in mean annual temperature and precipitation, which could affect soil organic matt er quality, further Improved relationships between the flush of CO2 and act ive, passive, and total C and N pools. Measuring the flush of CO2 following rewetting of dried soil may have value for routine soil testing of biologi cal soil quality because it (i) is an incubation procedure patterned after natural occurrences in most soils, (ii) exhibits strong overall relationshi ps with active organic pools, (iii) shows relatively minor changes in relat ionships with active organic pools that may be due to climatic variables, ( iv) has a simple setup with minimal equipment requirements, and (v) has rap id analysis time.