Winter oilseed rape is the key oil crop in temperate climate regions of the world. Yield of seeds depends the most on nitrogen management throughout the season. The evaluation of N status in the oil-seed rape canopy was studied in 2008, 2009, and 2010 seasons. The one factorial experiment to verify the formulated hypothesis, consisting of six treatments, was as follows: absolute control (AC), NP, NPK, NPK + MgS - 1/3 rate of total planned rate applied in Spring (NPKMgS1), NPKMgS - 1.0 rate in Autumn (NPKMgMgS2), NPK+MgS - 2/3 in Autumn + 1/3 in Spring (NPKMgS3). Plant samples were taken at three stages: i) full rosette (BBCH 30), ii) the onset of flowering (BBCH 61), iii) maturity (BBCH 89). The total plant sample was partitioning in accordance with the growth stage among main plant organs such as leaves, stems, straw, and seeds. Yield of biomass, nitrogen concentration and content were determined in each part of the plant. The study showed an existence of two strategies of dry matter and nitrogen accumulation by oil-seed rape throughout the season. In 2008, and partly in 2010 revealed the strategy of yield formation relying on relatively slow, but at the same time a permanent increase in nitrogen and biomass accumulation during the season. This strategy resulted in a high seed density in the main branch. The size of this yield component significantly depended on nitrogen content in leaves at the onset of flowering. In 2009 revealed the second strategy of yield formation by oilseed rape. Its attribute was a very high rate of nitrogen accumulation during the vegetative growth, resulting in a huge biomass of leaves at the onset of flowering. This growth pattern, as corroborated by yield of seeds, was not as effective as the first one. The main reason of its lower productivity was the reduced seed density, especially in pods of the secondary branch, resulting from an excessive nitrogen content in leaves at the onset of flowering. Irrespectively on the strategy of nitrogen management by the oilseed rape canopy, the best predictor of the final yield was nitrogen content in seeds. It can be concluded that any growth factor leading to the nitrogen sink decrease, such as reduced plant density and/or disturbed N management throughout the season, can be considered as a factor negatively impacting yield of seeds.
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