Sustainable management of nitrogen in the oilseed rape canopy depends, in the first place, on the supply of potassium during critical yield formation stages. The K status assessment in plants was made in the 2008, 2009, and 2010 seasons. The one-factorial experiment to verify the formulated hypothesis, consisting of six treatments, was as follows: control (C), NP, NPK, NPK+MgS - 1/3 rate of the total planned dose applied in spring (NPKMgS1), NPK+1.0 MgS rate in autumn (NPKMgMgS2), NPK+MgS -  2/3 in autumn + 1/3 in spring) (NPKMgS3). Plant samples were taken at three stages:  full rosette (BBCH 30), the onset of flowering (BBCH 61), maturity (BBCH 89). At each measurement, the harvested sample was partitioned, in accordance with the stage of development, into subsamples of leaves (BBCH 30), stems and leaves (BBCH 61), stems + pericarp (trashed silique) and seeds (BBCH 89). The biomass yield as well as the potassium concentration and content were determined in each part of the plant. The yield forming effect of potassium absorbed by plants during the critical growth stages was decisive for the yield of seeds, as resulted from path and stepwise analyses. The study showed that the N management in oilseed rape canopy was significantly governed by the K management just before and after flowering. An elevated K supply in the first period, leading to the N saturated status of plant parts, resulted in seed density reduction, in turn decreasing the size of the K seed-sink. The seed yield of oilseed rape significantly depended on the net K content increase in vegetative parts of the crop during the seed-filling period. It can be therefore concluded that an adequate supply of K up to the physiological maturity of oilseed rape is a prerequisite of  high yield.

20.1.2015