Chemical properties of plant-based biochar to be used as soil fertiliser in Galicia (NW Spain)

The excessive use of chemical fertilisers can cause soil acidification, depletion of soil quality, and biodiversity loss. Alternatively, biochar can improve crop productivity due to its ability to bind macronutrients and micronutrients and also adsorb various contaminants. However, the properties of the biochar depend among other factors on the material used to produce the biochar and the pyrolysis process. This study aims to evaluate the total nitrogen concentration of different types of biochar produced from forest plants to be used as fertiliser and amendment in acidic soils of Galicia (NW Spain). In this experiment, the biochar was produced from different tree fractions (branches, dry leaves, green leaves) of six tree species (Pinus radiata D. Don, Pinus sylvestris L., Pinus pinaster Aiton, Betula alba L., Quercus robur L., Castanea sativa Mill.) under different pyrolysis times (30, 60 and 120 minutes) at a temperature of 300°C. The results obtained showed that Betula alba L. and Pinus sylvestris L. increased the total nitrogen concentration in the biochar, independently of the tree faction. The same result was observed for Quercus robur L. when the branches and green leaves were used to produce biochar. Moreover, a pyrolysis time of 60 minutes increased the total nitrogen in the biochar, mainly in the case of Pinus radiata D. Don and Pinus pinaster Aiton. Therefore, the biochar produced from these tree species and fractions with a pyrolysis time of 60 minutes could be used as amendment and fertiliser in the Galician soils.