Chiang Mai Journal of Science

 The nutrient cycle and organic matter decomposition are catalyzed by soil enzymes. In this study, enzymatic activities of catalase, dehydrogenase, alkaline phosphatase, and urease are studied in soils amended with compost (C), moss (M), or biochar (B) and irrigated with heavy metal-contaminated wastewater (HM-CW), when Nicotiana alata L. and Petunia hybrida L. was grown in pots. The irrigation of HM-CW reduced the soil enzyme activities. However, combined used of 5% M+C+B, results in the improved soil enzyme activities. In case of N. alata and P. hybrida, catalase activity was 222.03 ± 9.24 and 402.34 ± 10.48 mg KMnO₄ g^-1 soil h^-1, respectively, with M+C+B, which was up to 94% higher than non-amended treatment. Similarly, the M+C+B treatment also showed higher activity for dehydrogenase i.e., 180.24 ± 6.95, and 156.79 ± 8.31 μg TPF g^-1 soil h-1 for N. alata and P. hybrida, respectively, that were 73% and 49% higher than non-amended treatment. Alkaline phosphatase production (μg p-nitrophenol g^-1 soil h^-1) for N. alata with M+C+B was 40.10 ± 1.92 and with C+B was 38.41 ± 2.00, while for P. hybrida with M+C+B was 39.33 ± 2.05, which is significantly higher as compared with the non-amended treatment. Urease activity at M+C+B application in soil with P. hybrida was 83.22 ± 5.54 mg urea g^-1 soil h^-1, which was much higher than that of N. alata. In general enzyme activity enhanced in the soil with N. alata or P. hybrida along with soil amendments. It shows that application of these organic amendments individually or in combination with N. alata or P. hybrida increased enzyme activities possibly through affecting soil nutrient dynamics.