Changes in biological and physical parameters of soils with different texture after biochar application

Maintaining a favorable microbial and physical state of soils using new management practices is one of the key directions of sustainable land-use. Application of biochar (BC) is one of the new ways to improve soil quality and sustainability by increasing carbon sequestration and making significant changes in soil properties. Slow and fast pyrolysis is used to produce BC from different feedstock. Technological conditions of pyrolysis and feedstock type have key impacts on BC properties and its interaction with soils. Many previous studies have revealed a positive effect of BC on soil properties and crop yields. Nevertheless, there are uncertainties in the understanding of BC effects on microbial processes of nitrogen and carbon transformation in soils. In the present study, two types of BC were used: BC1 and BC2 were produced by fast and slow pyrolysis of wooden feedstock, respectively. The aims of the study were, firstly, to assess differences in the effects of BC1 and BC2 on hydrophysical properties of sandy and clayey loam soils, and, secondly, to assess the effects of differences in soil texture on the degree of impacts of BCs on soil nitrification and denitrification. Samples of sandy and clayey loam gleyic Fluvisols (Slovakia) were used in the experiment. An amount of the applied BC on a hectare-scale was equal to 15 and 30 tones. Water retention of the soil samples was measured using a pressure-plate apparatus at water potentials from -0.1 to -300 kPa. Nitrification and denitrification rates were determined in laboratory conditions by measuring nitrous oxide accumulation in flasks in which the soils were incubated for 48 hours at 25 °С. Soil moisture content for nitrification and denitrification was equal to 48-55 % of the full saturation and 100 % saturation, respectively. The results indicate that BC1 and BC2 application increased water retention more for the sandy soil than for the clayey loam soil in the whole range of water potentials. Of the two biochars, BC2 had a greater influence on the water retention of both soils. Application of BC1 resulted in a significant decrease (p < 0.01) while application of BC2 produced only an insignificant decrease in nitrification rates in the clayey loam soil. BC1 and BC2 had no effect on nitrification rates in the sandy soil. Moreover, the application of the BCs at both rates contributed to a greater decrease in nitrification rates in the clayey loam soil than in the sandy soil.