Effect of a biostimulant on the accumulation of Mg in winter oilseed rape under different mineral fertilization doses

Increased fertilization doses stimulate biomass production and raise plants’ demand for nutrients. Biostimulants may improve absorption of nutrients by plants and prevent nutrient deficiency resulting from their lower concentrations in biomass. The aim of this study was to evaluate Mg accumulation in winter oilseed rape at flowering, fruit development and ripening as affected by the application of a seaweed biostimulant, at different doses of NPK tested in two field experiments, with and without S fertilization. The field experiments were set up in Alfisol, on adjacent plots, in Poland (53°13′N. 17°51′E). In the first experiment, S was used in a dose of 36 kg ha-1; in the second experiment there was no S application. In both experiments, different NPK doses were used: high 180 N, 70 P, 132 K (kg ha-1) or low 144 N, 35 P, 66 K (kg ha-1). In addition, the biostimulant Kelpak SL was applied (in doses 2 dm3 ha-1 in autumn + 2 dm3 ha-1 in spring) or there was no biostimulant application. It was found that the response of oilseed rape to the biostimulant and NPK fertilization level, expressed by the amount of dry matter production and Mg accumulation in whole plants, was more favourable in the experiment with the S application prior to sowing the crop. The biostimulant increased the dry matter production while maintaining a similar Mg concentration in plants as compared with the control. Moreover, in S-fertilized oilseed rape, an increase in the Mg accumulation in response to the biostimulant was the highest (22%) at the ripening stage, whereas in the plants not fertilized with sulphur (the second experiment), this increase was significant only at fruit development. In oilseed rape fertilized with S, higher NPK doses caused an increase in the dry matter production and a decrease in the Mg concentration in the aerial parts at the flowering and fruit development stages. At the ripening stage, with a similar response of dry matter, the Mg concentration in plant remained unchanged, hence the Mg accumulation in biomass was by as much as 26% higher than after the application of lower NPK doses.