# Agricultural Waste-Based Biochar for Agronomic Applications
## 3 Biochar as a Soil Amendment
### Impacts on Soil Microbiology and Enzymes  
Soil microbial populations play a primordial role in the decomposition of organic substances, in nitrogen fixation and in nutrient cycling. In many investigations, biochar application to soil has been proven to increase microbial biomass and to affect nutrient cycling, enzyme activities and crops health ([PERSON] et al., 2018). Soil microbial populations are affected, as biochar has an influence on soil chemical and physical properties including pH, nutrient availability, and water retention capacity ([PERSON] et al., 2018). Biochar provides space for colonization, forms habitats for different microorganisms ([PERSON] et al., 2018), and potentially protects them from desiccation and predation. Biochar amendment is accompanied by a general change in the use of carbon sources and can therefore lead to substantial changes in the microbial functional diversity and activity and in the taxonomical composition of the microbial community ([PERSON] et al., 2018). [PERSON] et al. (2018) recorded in a -maize/legume intercropping system that biochar addition not only affectedthe bacterial community structure and the diversity of the rhizosphere, but also made plant-derived C assimilable to more microbial species following biochar addition. [PERSON] et al. [129] reported an increase in the bacterial abundance by about 161% when straw- and wood-derived biochars were applied to soil; this increase was especially remarkable for Gram-positive bacteria. In a study performed by [PERSON] et al. [130], among 45 bacterial genera, 21 genera were affected by biochar in cotton soils. The results show an increase in the abundance of Sphingomonas and Pseudomonas genera, while the abundance of nitrite-oxidizing bacteria was reduced [130]. Nitrospira is one of the nitrite-oxidizing bacteria, which is, in addition to other contributors in the N cycle, reported to be influenced by biochar application [131]. [PERSON] et al. [132] observed at a rate of 4% biochar addition an increase in the diversity of genes (nirK and nirS) related to denitrifying bacteria. [PERSON] et al. [133] observed that biochar in the presence of phosphate-solubilizing bacterium Lysinobacillusfusiformis can also improve the retention of phosphorous and nitrogen by maize plants by about 61.5% and 23.1%, respectively. Biochar was also proved for its ability to suppress soil pathogens and diseases. [PERSON] et al. [134] observed a significant decrease in the intensity of the disease caused by foliar fungal pathogens in pepper and tomato upon biochar application. Similarly, [PERSON] et al. [135] obtained results for strawberries. [PERSON] et al. [127] reported that biochar allowed the suppression of Fusarium crown and tomato root-rot, which leads simultaneously to an improvement in tomato plant growth. In another study, [PERSON] et al. [136] showed that biochar decreases the sensitivity of rice plants to root knot nematode infections. Biochar has been also reported to enhance plant defense systems against fungi and to significantly reduce the colonization of roots by arbuscular mycorrhiza fungus [137] and to suppress the infection of tomato plants by Fusarium oxysporum.sp. lycopeneski [138]. Although a high number of studies have examined the impact of biochar on the microbial population in the soil, some points nevertheless need to be investigated. The interrelation of soil microorganisms with biochar and the special scale of this interaction have to be studied. The long-term impact of biochar and biochar ageing on soil microorganisms should be further clarified to prevent any possible negative impact. The large-scale study of the biochar impact on the microbial population of the soil under field conditions is still missing [139].Enzymes in the soil play a crucial role in decomposing organic substances and make both energy and NH\({}_{4}\) available to plants.