Test tubes were sealed and incubated in the dark at 40 ± 0.5°C for 2 h and slightly shaken. Developed iodonitrotetrazolium formazan (INTF) was extracted by keeping the test tubes in the dark for 1 h, shaking vigorously every 20 min and finally, filtering the solution. Soil moisture content was maintained at 60% water holding capacity by weighing and correcting for any weight loss, using sterile ultra pure water. The INTF was measured spectrophotometrically at 464 nm, after extraction with 10 ml of N, Ndimethylformamide/ethanol solution. Soil DH-activity and all soil treatments were done in triplicates. Dehydrogenase activity was determined using the following equation: