*3.3.3 Soil biological sproperties*

Biochar as a soil amendment is confronted with the challenge that it must benefit soil health as it can by no means be separated from soils once it is added. Soils can be viewed as complex communities of organisms that are continually changing in response to soil characteristics, climatic and management factors and especially in response to the addition of organic matter. However, compared to the addition of fresh organic matter, the addition of biochar to soils is likely to affect the diversity, abundance and activity of soil biotic communities [46]. Owing to its highly porous nature, biochar helps to provide habitat for microorganisms and also modify the biological functionality by altering the availability of substrate and activity of enzyme on, or around, biochar particles [47]. Biochar has the potential to affect microbial biomass and composition and the microbes are also able to change the properties of biochar [46]. Abujabhah et al. [48] reported that microbial abundance was improved after the addition of biochar. Biochar pores may provide physical protection for soil microorganisms. Soil reaction greatly influence microbial activity, diversity and abundance. The buffering capacity of the soil solution imparted by biochar CEC may also help to minimize pH fluctuations and maintain appropriate pH conditions in the microhabitats within biochar particles [49]. Studies have shown that biochar and fertilizer application increased microbial Biomass compared to mineral fertilizer. Microbial immobilization is an important mechanism to retain N in soils affected by leaching. Increased C availability stimulates microbial activity resulting in greater N demand, promoting immobilization and recycling of NO3 − Biochar enhanced the PSM activity for P mobilization in phosphate rich soils and significantlyimproved the crop yield in P deficient soils [50]. The effect of biochar application on soil health under different soil types are summarized in **Table 4**.

