Biochar Substrates and their Combination with Fertilization as a Factor Affecting the Changes in pH and Surface Charge of Soil Particles in Soils with Different Texture

In 2017 the field experiments were established at two localities of the South-west Slovakia (1 Dolná Streda: sandy Arenosol and 2 Veľké Úľany: loamy Chernozem). The experiments involved biochar substrates (1 BS1 mix biochar, sheep manure and 2 BS2 mix biochar, sheep manure and digestate) in two application doses (10 and 20 t ha-1), which were applied independently compared with the unfertilized control (Co-NF) and combined with additional fertilization versus the fertilized control (Co-F), in order to verify their impacts on the changes of soil properties. In the spring and autumn of 2018–2020, within these experiments the soil samples were taken to determine the range of effect of the tested biochar substrates (BS) and also their combination with fertilization (F) on the changes of soil pH and surface charge of soil particles in the soils different in texture. The results pointed out the fact that a more significant effect of tested BS on soil pH was detected in sandy soil than loamy soil. In sandy soil, only the application of BS2 in doses 10 and 20 t ha-1 statistically significantly increased the soil pH in H2O in comparison with Co-NF. The application BS1 + F in dose 10 t ha-1 and BS2+F in dose 20 t ha-1 statistically significantly increased pH in KCl compared with Co-F. The fertilization to BS eliminated the considerable decrease of the soil pH in H2O both soils. In sandy soil, pH was substantially regulated by the content of alkali cations themselves in BS; however, in loamy soil, it occurred as a result of the increase of the content of soil organic carbon after the application of BS (R2 = 0.339), but also BS + F (R2 = 0.468). In sandy soil, the application of BS itself, owing to the change of the surface charge, influenced predominantly the sorption of anions. Conversely, the additional fertilization to BS treatments had an impact on the sorption of cations. In loamy soil, the application of BS and BS + F as a result of the change of surface charge did not have any significant effect on the total soil sorption.