Microwave assisted biocidal extraction is an alternative method to measure microbial biomass of carbon from cultivated and non-cultivated soils.

Developing simple and cost-effective methods for soil microbial biomass carbon (MBC) measurement eases routine laboratory analysis and enables large numbers of soil samples to be measured in a relatively short period of time. Thus, the objective of this study was to develop a microwave-assisted biocidal-extraction (MWE) method which does not employ CHCl3 as biocide and K2SO4 as C-extractor, to estimate MBC. First, the microorganisms of soil samples are killed using microwave (MW) irradiation at energy level of 800 J g-1 soil as biocide followed by microwave irradiation extraction (MWE) at 562 W (120 J g-1 soil for 1 min), using deionized water as solvent. Microbial biomass of carbon from two contrasting soils microwaved with 80, 100, and 140 J g-1 soil did not differ from those obtained by using the chloroform fumigation-extraction (CFE) method with 0.5 mol L-1 K2SO4 as extractant. To evaluate the robustness of the MWE method, twenty-six soil samples, from cultivated and non-cultivated areas, with clay contents from 70-690 g kg-1, organic carbon from 5.52 to 50.82 g C kg-1 and pH values from 3.9 to 6.8 were analyzed for MBC using MWE and CFE methods. There was a linear regression (MW = - 17.87 + 0.92*K2SO4; R2 = 0.705; p < 0.001) between MWE and CFE. The biocidal microwave-assisted extraction method using 120 J g-1 soil for 1 min is a cleaner method for evaluating MBC, because it does not require chloroform, potassium sulfate salt and takes a shorter time to extract a set of soil samples.