| Chloroform fumigation extraction method (FE) has been widely used since itwas first advanced, and it was regarded as one of the standard methods for measuringsoil microbial biomass carbon (SMBC) in aerobic soils, however, FE method is notsuitable for measurement of SMBC in water-saturated or waterlogged soils attributingto the decline of fumigation efficiency. To overcome this limitation, Inubushi et al.proposed the directly addition of chloroform into waterlogged soil, however, someproblems caused by chloroform addition. We carried out series of experiments uponthe ecologic characteristics of waterlogged paddy soils in order to understand andsolve these problems, and finally we developed a method for measurement of SMBCin waterlogged paddy soils. Main original conclusions are shown as follows.1,The effect of soil water contents on the measurement of the FE method wasstudied. The SMBC decreased rapidly with the soil water content increasing in arange of 60-100％of water holding capacity. The values of SMBC in thewaterlogged soils were obviously lower than which in the corresponding aerobic soils.The results indicated that the FE method for measuring SMBC was influenced by soilwater contents.2,The effect of the dehydration methods on the determination of SMBC wasstudied and discussed. For the centrifugation treatments, the water contents ofwaterlogged soils were not declined to the level of aerobic soils after 10 mincentrifugation at 500r min-1, 1500r min-1 and 2500r min-1, respectively. The valuesof SMBC measured after 10min centrifugation at 500 r min-1 and 2500 r min-1,respectively, were significantly lower than the control. The values measured after10min centrifugation at 1500 r min-1 was closed to the control, however, bothfumigation extractable C and unfumigation extractable C were obviously decreased.For both treatments of cold-wind and nature-dried, the water contents of thewaterlogged soils declined to the lever of aerobic soils, however, the values ofFumigation extractable C and SMBC were obviously higher than the control. Theresults indicated that the methods which measured SMBC in waterlogged soil after these dehydration treatments, were invalid.3,The effect of directly addition of chloroform into waterlogged soils onmeasurement with TOC analyzer. The results showed that the measurement with TOCanalyzer was interfered with chloroform addition, however, the interference could beremoved with 100℃bath treatment, and the SMBC and non-biotic extractable Cwere not affected by this bath treatment.4,The required amounts of chloroform addition were determined. The amountsof fumnigation extractable C raised with increasing of the amounts of CHCl3, thenretained relatively consistent. The amounts of CHCl3 ranged from 20 to 40μl g-1 drysoil when the maximums of fumigation extractable C were obtained. For the all testedsoils, the maximums of fumigation extractable C could be obtained by using 10g soil(oven-dry basis) and 40-60μl CHCl3 g-1 dry soil, and retain consistent with increasingof the amounts of CHCl3, furthermore, considering the contents of clay and organicmatter among the test soils varied widely, we therefore concluded that the proportionof 10g soil (oven-dry basis) and 40-60μl CHCl3 g-1 dry soil should be appropriate formost of waterlogged paddy soils.5,Based on the studies above, we presented a new method: Chloroformfumigation extraction—bath method (CFEB), for measurement of SMBC inwaterlogged soils. It overcome the limitation in fumigation efficiency when FEmethod apply to waterlogged soils and avoid the interference with directly addition ofchloroform into waterlogged soils. The results showed that the fumigation efficiencyof CFEB method in waterlogged soils was similar to FE method in aerobic soils.When the CFEB method applied to the long-term waterlogged paddy soils, Theresults showed reliable and reproducible estimates of SMBC, suggesting that theCFEB is a rapid and effective method for measuring SMBC in waterlogged soil.
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