In the conditions of the Right-Bank Forest-Steppe, the cultivation of winter rapeseed crops after winter wheat usually leads to a delay in sowing the latter and deterioration of autumn plant development. Based on data from a field experiment conducted in 2016/2017, 2017/2018 and 2018/2019, the aim of this study was to investigate how sowing delay affects seed yield, nitrogen uptake by seeds and significant efficiency of nitrogen use by winter rape plants; to check the ability of autumn and spring application of nitrogen fertilizers to compensate for the negative impact of delays in sowing crops; and estimate the minimum autumn development for optimal seed yield. To solve the set tasks, a combination of four sowing dates (from the first week of August to the third week of September) and four autumn nitrogen applications (0, 30, 60 and 90 kg / ha per year) was fixed. In each of these 16 variants, nitrogen application was performed 5 times in the spring (0/0, 40/40, 80/80, 120/120, 140/140 kg / ha, etc.) in order to estimate the individual nitrogen reaction curves. Nitrogen accumulation by aboveground mass of plants in autumn, seed yield and nitrogen uptake by seeds were determined. It was found that sowing the crop after mid-September significantly reduced yields. Application of nitrogen fertilizers in autumn in the amount of at least 30 kg / ha per year increased the yield and absorption of nitrogen seeds without any significant interaction with the sowing period and spring application of nitrogen fertilizers. Increasing the dose of spring fertilizer application to 130 kg / ha increased seed yield. Nitrogen utilization efficiency decreased with increasing application rate when winter oilseed rape plants used nitrogen applied in the fall to a lesser extent than in the spring. In order to achieve high yields, it was necessary for the above-ground mass of plants to absorb nitrogen at the level of at least 10-15 kg / ha at the end of the autumn vegetation. From an ecological point of view, the optimal autumn development of plants should be achieved by choosing an adequate sowing date, rather than using additional nitrogen in autumn.
Contribution of Nitrogen Uptake and Retranslocation during Reproductive Growth to the Nitrogen Efficiency of Winter Oilseed-Rape Cultivars (Brassica napus L.) Differing in Leaf Senescence
