To fresh soil (2.5 g), an appropriate volume of 0.1% (w/v) TTC in 0.5 M Tris buffer (initial pH 7.6) or distilled water was added to achieve 3.25, 6.25 or 12.5 mg TTC g-’ dry soil, and was incubated at 30, 37 or 40°C for ;!4 or 48 h. The total volume of added solution (TTC + distilled water) was 2.5 ml. The TPF was extracted with 25 ml methanol and
measured spectrophotometrically at 485 nm against a control of metha.nol extract of soil without TTC.