EFFECT OF NITROGEN RATE ON NITROGEN USE EFFICIENCY IN WINTER OILSEED RAPE (BRASSICA NAPUS)

Winter oilseed rape is the main oilseed crop in Latvia. High yield production depends on applied plant nutrients, especially nitrogen. Nitrogen is one of the most mobile plant nutrients in the soil and, therefore, nitrogen fertilizer management is an important part of agriculture. The objective of this paper is to evaluate the effect of nitrogen fertilizer rate on nitrogen use efficiency (NUE) in winter oilseed rape. The field experiment was conducted during four growing seasons (2014/2015, 2015/2016, 2016/2017 and 2017/2018) at the Research and Study fann 'Paerlauki' of Latvia TJniversity of Life Sciences and Technologies (56 degrees 30.658' N and 23 degrees 41.580' E). In total, eight nitrogen rates were used in this experiment (kg ha(-1) of N pure matter): NO or control, N60, N90, N120 (80+40), N150 (100+50), N180 (120+60), N210 (120+60+30) and N240 (140+60+40). All NUE parameters were calculated only for five nitrogen rates (NO; N60, N120, N180 and N 240). Results indicated that the nitrogen fertilizer rate had a significant (p<0.001) effect on winter oilseed rape seed yield. The yield increased until the rate N 120-N180. Nitrogen fertilizer rate also significantly (p<0.001) affected N, P20, and K2O removal with oilseed rape biomass. N and K2O removal with seed yield significantly increased until the nitrogen rate N 120 N180, but P2O5 until N60-N180. Results showed that the nitrogen fertilizer significantly (p<0.001) affected NUE, nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE), but it did not have a significant (p=0.840) effect on nitrogen harvesting index (NT II). By increasing the nitrogen fertilizer rate, NTJE, NUpE and NUtE decreased.