# Biochar as a Multifunctional Component of the Environment--A Review
## 6 Biochar as Soil Conditioner  
Interest in biochar as a potential soil enhancer began with the discovery of preta de Indio--Indian black earth (in Amazonia), notable for its high content of carbon and nutrients [127]. As shown in previous research, the soils were created a few thousand years ago as a result of the burning of forests and natural fires, as well as soil improvement with the use of charcoal applied by pre-Columbian natives [128]. From the agricultural point of view, the application of carbonization products for soil amelioration seems to be beneficial because the treatment improves the conditions for plant growth, leading to a better yield (Figure 4, Table 7) [129]. Furthermore, due to the rapid effects and relatively low costs of such treatment, biochars are more and more frequently used in processes of soil remediation and conservation [130]. Figure 4: Influence of biochar on soil properties [131]. Figure 3: Types (mechanisms) of metal ion adsorption on the surface of carbonization products [124]. The activity of biochar, after it is introduced into the soil environment, depends predominantly on the feedstocks used in its production and the parameters of the pyrolysis process. These determine the contents of macro- and micro-elements as well as harmful substances, such as e.g., heavy metals. The heterogeneous chemical composition of biochars enables their interactions with a large variety of organic and inorganic compounds present in the soil [138]. The diverse properties of biochar materials enable reactions with mineral and organic fractions of soil and the accumulation of combined mineral and organic complexes [139]. Biochars introduced to the soil are characterized by a high stability and resistance to biological decomposition, therefore they are recognized as a highly effective medium for the sequestration of carbon dioxide in soil [33]. Moreover, the application of biochars to soil leads to increased contents not only of carbon but also of other biogenic compounds, such as phosphorus, potassium, magnesium and nitrogen [39; 140]. Owing to their large ion-exchange capacities and specific surface, biochars also produce such effects as the reduced leaching of biogenic elements from soils and a decreased emission of nitrous oxide [141]. Recent study has highlighted that crop biochar also contains biogenic silica (phytoliths) and can quickly release bioavailable silicon to enhance plant biomass and promote the biological silicon cycle in soil [142]. One of the functions of the biochar addition is to modify the nitrogen and phosphorus cycle. Biochar as an additive to soils has the ability to store nitrogen by increasing NH\({}_{3}\) and NH\({}_{4}\)\({}^{+}\) retention, reducing N\({}_{2}\)O emissions and eluting NO\({}_{3}\) ions, as well as inducing the development of nitrogen bacteria which directly affects the increase in soil productivity. Biochar is characterized by very different potassium contents, depending on the type of batch material used in production. Of all macronutrients present in carbonates, potassium is the best available element for plants, and the proportion of biosorptive forms is up to 95% of the total content [33]. Biochar fertilizers also lead to increased soil pH [143]. The related research has shown that carbonization products contain numerous alkaline substances, e.g., calcium carbonate, which may affect soil reaction, and the best effects, i.e., the highest pH increase, may be achieved in strongly acidified soils. Increased pH which is beneficial in acid tropical soils like terra preta but reduces yield in soils of high pH as in many temperate regions [41; 144]. Biochar also impacts the physical properties of soil by improving its water retention, capacity to form aggregates, and resistance to erosion [145]. The improvement of the physical characteristics of soils resulting from the use of biochar as a soil ameliorant mainly depends on the properties of the biochar, and these are predominantly determined by the technology applied in its production [146; 147].