Effects of Organic Amendments on Phenol Oxidase, Peroxidase, Urease, and Nitrogen Mineralization: A Laboratory Incubation Study

Mitigating climate change and enhancing fertility in agricultural systems require the adoption of more sustainable fertilizer management practices. Applications of recycled organic materials, such as animal and green wastes, can promote soil carbon stabilization via changing extracellular enzyme activities while providing the necessary nitrogen (N) for plant growth. The goals of this study were to quantify the effects of compost type (cow manure, green manures, mixtures of green and cow manure at various proportions, and inorganic fertilizers) on (1) enzyme activity (phenol oxidase, peroxidase, and urease), and (2) mineralized N under laboratory incubation at 30 °C over an eight-week period. The lowest oxidative enzyme activities (phenol oxidase and peroxidase) were found in the soil treated with a mixture of 50% cow manure and 50% green manure (2.45 μmol h−1 g−1) and a mixture of 30% cow manure and 70% green manure (3.21 μmol h−1 g−1) compared to all other fertilizer treatments. The highest phenol oxidase activity was found in soils amended with green manures (3.52 μmol h−1 g−1), while the highest peroxidase activity was found in soils amended with a mixture of 70% cow manure and 30% green manure (5.68 μmol h−1 g−1). No significant differences were found in total net mineralized N content among all organic fertilizer treatments, but these were significantly lower than total net mineralized N in soil treated with inorganic fertilizers. These results indicate similar effects of organic amendments and mixtures in providing plant-available N, but different effects on lignin-degrading enzyme activities, which may lead to differences in soil organic carbon cycling and long-term C storage depending on which organic amendment is utilized.