2.1. Organic amendments
Organic amendments were added to the soil in 2014. The biochar was produced from the biomass of the following two species: miscanthus (Miscanthus × giganteus ) and winter wheat (Triticumaestivum L.). The miscanthus and winter wheat straw were air dried at 70 °C, ground into fine particles (<4 mm), and mixed to ensure homogeneity. The plant material was pyrolysed in an electrical laboratory furnace equipped with a temperature controller at a temperature of 300 °C for 15 min; with limited air access to reduce C losses (International Biochar Initiative 2014; Gondek and Mierzwa-Hersztek 2016). The furnace heating occurred at a rate of 10 °C min−1. The time and temperature were set according to the research of Lu et al. (2013), Mendez et al. (2013), Gondek et al. (2014) and Domene et al. (2015). The basic chemical characteristics of the feedstocks are presented in Table 1.