Evaluation of Nitrogen Fertilization Systems Based on the in-Season Variability in the Nitrogenous Growth Factor and Soil Fertility Factors—A Case of Winter Oilseed Rape (Brassica napus L.)

Application of nitrogen (N) in contrastive chemical form changes availability of soil nutrients, affecting crop response. This hypothesis was evaluated based on field experiments conducted in 2015/16 and 2016/2017. The experiment consisted of three nitrogen fertilization systems: mineral-ammonium nitrate (AN) (M-NFS), organic-digestate (O-NFS), 2/3 digestate + 1/3 AN (OM-NFS), and N rates: 0, 80, 120, 160; 240 kg ha−1. The content of nitrogen nitrate (N-NO3) and available phosphorus (P), potassium (K), magnesium (Mg) and calcium (Ca) were determined at rosette, onset of flowering, and maturity of winter oilseed rape (WOSR) growth from three soil layers: 0.0–0.3, 0.3–0.6, 0.6–0.9 m. The optimum N rates were: 139, 171 and 210 kg ha−1 for the maximum yield of 3.616, 3.887, 4.195 t ha−1, for M-NFS, O-NFS, OM-NFS. The N-NO3 content at rosette of 150 kg ha−1 and its decrease to 48 kg ha−1 at the onset of flowering was the prerequisite of high yield. The key factor limiting yield in the M-NFS was the shortage of Ca, Mg, O-NFS—shortage of N-NO3. Plants in the OM-NFS were well-balanced due to a positive impact of the subsoil Mg and Ca on the N-NO3 content and productivity. The rosette stage was revealed as the cardinal for the correction of WOSR N nutritional status.