SOIL MINERAL NITROGEN DYNAMICS IN RELATION TO TILLAGE METHODS AND CROP ROTATION
The aim of the present study was to clarify the effect of conventional and reduced tillage and crop sequences on mineral nitrogen (Nmin.) turnover in soil, including its seasonal and temporal variations, and distribution in soil profile. The experiment was carried out in 2012–2016 in Cambic Calcisol (Aric, Endohypocalcic, Ochric, Endoruptic, Episiltic, Protostagnic, Bathyluvic); texture – silty clay loam. Crop rotations included wheat monocrop, and winter wheat–winter oilseed rape and cereal–winter oilseed rape–faba bean sequences. Every month during the growing season, soil samples at three different depths (0–20, 20–40, and 40–60 cm) were taken and the N–NO3- and N–NH4+ content was analyzed. The content of Nmin. in soil varied significantly among years, and about half of it was found in the upper 0–20 cm soil layer. The tillage method had little effect on Nmin. in soil; however, a trend of its higher concentrations was observed in conventional tillage compared to the reduced one. The average Nmin. content in the 0–60 cm and 0–20 cm soil layer during growing seasons was year-dependent. The least 5-year averaged amount of Nmin. in soil at the depth of 0–60 cm (54.8 kg ha-1 N) was determined under wheat monocrop, whereas the highest Nmin. amount (66.3 kg ha-1 N) was found under cereal–winter oilseed rape–faba bean rotation.