Potential nitrogen fixation changes under different land uses as influenced by seasons and biochar amendments

Soil nutrient dynamics, potential biological nitrogen fixation (BNF) changes, and their relations were studied using four land use types. Further, we investigated BNF changes in the presence of biochar in soils. Soil samples were collected from arable, vineyard, grassland, and forest soils during four seasons, and analyzed for abiotic contents of total nitrogen, NH4+-N, NO3--N, ammonium lactate (AL)-soluble K2O, P2O5, and soil organic carbon (SOC) concentrations. Potential N-2 fixation was measured as ethylene (C2H4) production from acetylene (C2H2) reduction (ARA). The study focused on the changes in ARA when different types of biochars (T600, T650, and T700) were applied to soil samples in different amounts (0, 0.5, 2.5, and 5.0% wtwt(-1)) under laboratory conditions. We found strong correlations between soil chemical parameters and ARA values, especially in the case of soil pH, total N, SOC, and P2O5 contents. In the case of arable soil, the ARA measurements were up to 227 times higher compared to grassland and forest samples. Biochar application affected N-2-fixing microbial responses among land use types, most notably decreases in arable lands and forest soils. We found that a high amount of biochar added to the soils can greatly suppress N-2-fixing activities. Our results highlight the strong relationship between soil nutrient changes and the intensity of anthropogenic influence.