A bioszén felhasználásának lehetőségei a talaj tápanyag-utánpótlásában – Szemle | Biochar application in soil nutrient supply – A review

The nutrients in the biochar may be present in three particular form, that determine their availability. The elements in the ash fraction are readily available, while those in the labile fraction (mostly cellulose and hemicellulose) may become available within a few weeks or months after mineralisation. Those in the persistent biochar fraction may not be released for several centuries. The ratio of the three fractions depends on the pyrolysis setup, which thus has a major effect on the nutrient-supplying ability of the end-product. Phophorus and potassium are present in all three fractions, so biochar can act as a direct source of these elements in soil. Nitrogen, however, is only present in the labile and persistent fraction, which is why only the nitrogen content of the labile fraction can be taken into account as a nitrogen source in the short term. Nitrogen should thus be supplied in other forms when biochar is used. Biochar, however, influences the nutrient-supplying capacity of the soil not only through its own nutrient content, but also indirectly by modifying the chemical, physical (e.g. pH, CEC, water management) and microbiological properties of the soil. The di-rect and indirect effects often have an opposite influence on nutrient availability. After biochar application the total nutrient content of the soil may increase, but because of the adsorption capacity of biochar the water-soluble and readily available content may be reduced. The resultant of the two effects determines whether the availability of a given element will improve. In the long term, on the other hand, only the indirect effects are manifested, so it is these that should be considered when making decisions on the application of biochar. At present it seems most unlikely that biochar can be applied in quantities capable of influencing the global climate. However, biochar has a potential to be used as a soil ameliorant and to improve the nutrient availability in the soil. In intensive crop production systems the nutrient supply cannot be ensured using biochar alone, but if utilised in combination with conventional fertilisers it could be a useful additive, since biochar not only improves their performance, but also acts as a soil ameliorant. It may thus have long-term benefits in agricultural production.