Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 10/21/1998
Publication Date: N/A
Technical Abstract: Determination of soil microbial biomass C (SMBC) by chloroform fumigation-incubation normally involves subtraction of an unfumigated control. Subtraction, however, may create spurious results. We compared cumulative CO2 evolution from fumigated and unfumigated soils for 40 d. Evolution of CO2 was measured daily for the first 10 d and then periodically to 40 d. Four Texas soils ranging in total organic C from 7 to 14 g/kg and clay contents from 24 to 36% were used. Fumigated soils from near Lubbock and Amarillo exhibited lower CO2 evolution from 4 to 40 d compared to unfumigated controls, while this result did not occur for soils from near Corpus Christi and College Station until 30 d. SMBC with subtraction of controls was negatively correlated with 40-d C mineralization (r2=0.18), while SMBC without subtraction was positively related (r2=0.83). Carbon mineralization from dried and rewetted soils was intermediate to that from field moist-fumigated and field moist-unfumigated samples. The CO2 flush in the first day after rewetting dried soil was highly correlated to 40-d C mineralization (r2=0.999).