Soil enzymatic activity and nitrous oxide emission from light-textured spodosol amended with biochar

Soil amendment with biochar has been proposed as a tool to mitigate soil N2O emissions by altering soil physical, chemical and biological properties. Little work has been focused on the effect of biochar on the soil enzymatic activity as the most sensitive indicator to diagnose the changes in soil quality. The 90-day laboratory experiment to study the effect of biochar on the dynamics of some soil enzymes and cumulative N2O emissions from the loamy sand Spodosol was conducted with the aim to justify the sensitiveness of the enzymes to soil amendments with biochar. The experimental setup was a randomized block design with 9 replicates and included the soil control (K), the soil with biochar (BC), the soil with mineral fertilizer (N16P16K16,N90) and the soil with fertilizer and biochar mixture (N90 + BC). The hydrolases (urease) and oxidoreductases (catalase, peroxidase and polyphenol oxidase) were selected due to their high sensitivity to the changes in the soil quality and the significance in the nitrogen cycle. The results of the experiment have shown that the soil amendment with 10 t/ha of biochar significantly (p < 0.05) reduced (1.4-fold) cumulative N2O emissions from the soil compared to the K and N90 treatments. The presence of biochar in the soil had no significant effect on the urease activity, while activity of the catalase, peroxidase and polyphenol oxidase was significantly (p < 0.05) higher (1.2 times in average) due to the changes in the physical properties of the soil (aeration in particular). There was high positive correlation between N2O flux and catalase activity ( r = 0.85 and 0.87 for BC and N90 + BC, respectively). Based on the calculation of the humification coefficient (polyphenol oxidase activity to peroxidase activity) revealed that soil mineralization increased by 10-13 % after soil amendment with BC, compared to the treatments without BC. The soil amendment with biochar significantly changed the red-ox soil conditions. That was reflected in the changes of enzymatic activity, N2O emission and mineralization of humic substances. All the studied enzymes, except urease, were sensitive bio-indicators of soil conditions and could be used in the environment assessment methodology for land-use systems with biochar amendments.