# Duality of Biochar and Organic Manure Co-Compositing on Soil Heavy Metals and Enzymes Activity
## 4 Conclusions  
Soil microbial activity, impacted by soil nutrient recycling, is controlled by N, C and P cycles, and their impacts on the activities of urease, invertase, acid and alkaline phosphatase, respectively, along with other soil-hydrolyzing enzymes. Animal manure is a source of nutrients required for growing vegetables and fruits, and has the potential to replace the expensive inorganic mineral fertilizers. However, animal manure, such as sewage sludge, horse manure, chicken manure, and vermicompost, can contain various heavy metals that may affect soil enzyme activity. Additionally, the application of biochar, produced through the incination of biomass, as a soil amendment is suggested to enhance plant nutrient availability, increase soil electrical conductivity, and improve soil organic  
Figure 8: Impacts of soil treatments on the activity of acid phosphatase (**A**) and alkaline phosphatase (**B**). Each bar is an average of three replicates \(\pm\) standard error. Statistical comparisons were made between soil treatments amended with biochar and soil treatments not amended with biochar using the ANOVA procedure (SAS Institute 2016). Values accompanied by different letter(s) are significantly different (\(p\leq 0.05\)) using [PERSON]’s multiple test for mean comparisons.  
matter. Biochar is also considered a potential solution for mitigating climate change and retaining soil water content. Nonetheless, the heavy metals present in both biochar and animal manures can act as enzyme inhibitors. Using enzyme activity as a bioindicator to assess soil health is an effective method for monitoring the impacts of heavy metals and animal manures on soil-hydrolyzing enzymes' activities when evaluating the effectiveness of soil remediation techniques.  
The results of this investigation reveal that biochar added to vermicompost, or horse manure treatments did not influence soil urease activity, whereas biochar added to inorganic fertilizer, sewage sludge or chicken manure reduced the activity of urease. Adding biochar to organic mineral fertilizer significantly increased urease activity. In addition, the results also reveal that adding biochar to horse manure, municipal sewage sludge or chicken manure treatments did not affect invertase activity, whereas the biochar added to inorganic mineral fertilizer and organic elemental fertilizer reduced invertase activity, and this might be because of the effects of the heavy metals in biochar on the soil microbial activity. On the contrary, vermicompost amended with biochar showed significantly increased invertase activity, indicating that the biochar and vermicompost formulations significantly increased the diversity of bacterial and fungal communities in soil. Accordingly, this chapter highlights the importance of combining biochar and vermicompost as organic amendments for promoting the physicochemical properties of soil. However, some analytes in biochar and animal manure, such as heavy metals, may act as enzyme inhibitors. The use of enzyme activity as a bioindicator for testing soil health and the potential impacts of heavy metals and animal manure on soil enzymes is a simple and safe way to monitor soil health and the efficiency of remediation techniques.  
This project is funded by a grant from the United States Department of Agriculture, National Institute of Food and Agriculture (USDA/NIFA), given to the Kentucky State University under the agreement # KYX-10-23-80P Accession 7005611 to Kentucky State University.  
Not applicable.  
The original contributions presented in the study are included in the article, and further inquiries can be directed to the corresponding author ([EMAIL_ADDRESS]).  
I thank [PERSON], [PERSON], [PERSON], and the farm crew at Kentucky State University Research Farm for their support in undertaking farm work.  
The author declares no conflicts of interest.