## 1 Introduction  
The nearly one meter deep black soil of the Amazon River in South America is rich in carbon, calcium, magnesium, phosphorus, and trace elements. It is estimated that 10% of this area is covered by the so-called \"black soil\" or \"Terra Preta\" soil [1]. The main reason for its productivity is the dead biomass that has undergone thermal decomposition in an oxygen-free condition. The tropical climate can positively influence soil properties, transforming them in a favorable direction over time, without deleterious structural changes. Columbian soils with variable contents of biochar and different layers of carbon content are compared to control soils in Table 1. The fertile layers in those soils are much deeper (between 43 and 210 cm) than the 20 cm fertile layer in control soils nearby. The pH values in general are neutral or less acidic in comparison with the more acidic control soils without biochar amendment. Clay contents in these soils also tend to be greater, which could be related to the enhanced biological activity. The main reasons for the detected positive effects are the better aeration and improved water content of soils, as well as the indirect effects of greater microbiological abundance and activity, which might improve plant nutrition [2, 3]. According to literary data, the Terra Preta soil is suitable for extracting carbon from the carbon cycle over a long period (centuries) and, in this way, the carbon-sequestration potential of soil can mitigate global warming [4]. The same effect was also realized in soilsin which studied ancient biochar production. The carbon in these soils was sequestered and nutrients were absorbed for more than 30 years [5]. Terra Preta has served as a model for soil amendment and biochar industrial products are now used worldwide. During the preparation of biochar, the carbon content of mainly biomass-based feedstock materials is converted to aromatic carbon compounds and amorphous and graphitic-type structures during the process of so-called pyrolysis. By the end of the process, about 50% of the carbon content of the original biomass remains in the end-product. Still, this ratio is highly dependent on the conditions of the pyrolysis process [6]. The product created during such a carbonization process is referred to in the literature as \"biochar,\" referring to its biological, natural bio-origin [7]. Varying the temperature and duration of pyrolysis can create significant differences in the properties of the biochar, even when starting from the same ingredient materials [8]. Three different fractions can be formed during the process. One is the _persistent_ fraction, which remains largely resistant to further biological or chemical degradation for quite a long period [5; 9]. This fraction typically has an amorphous structure that can contain graphite-like crystalline structures [10] consisting of conjugated aromatic structures to which many different functional groups are attached [11]. Toxic molecules (PAHs) also arise in this group of compounds, which must be considered at the point of application [12]. The _labile_ fraction is the second characteristic group of substances. In the case of plant-derived biochar, it consists mainly of cellulose and hemicellulose which have not been converted during pyrolysis. When the pyrolysis process is fast, the carbonization is imperfect, which might result in an increase in the proportion of this group of substances. Once biochar is applied to the soil, this fraction is mineralized relatively quickly, in as little as a few weeks, and its nutrients are made available for crops [13; 14; 15]. The third fraction of biochar is the _ash_ fraction, which is the oxidized residue of the mineral element in biomass. Its ratio increases with the pyrolysis temperature and the amount of oxygen involved in the process. A higher ash content increases the pH of the biochar and the concentrations of readily soluble elements present in a mineralized form [16].