THE INFLUENCE OF SPRING NITROGEN ON YIELD, YIELD COMPONENTS AND GLUCOSINOLATE CONTENT OF AUTUMN-SOWN OILSEED RAPE (BRASSICA-NAPUS)

The response of low glucosinolate, low erucic acid (double low) cultiv ars of oilseed rape to spring nitrogen application was examined at Coc kle Park, Northumberland in three successive seasons (1987-90). Seed y ield and protein content increased in response to increasing nitrogen application. In each season over 85 % of the maximum recorded yield wa s obtained with an application of 150 kg N/ha. In the absence of sprin g nitrogen, seed yield varied considerably over the three seasons. The variation in seed yield and protein content between 1987/88 and 1988/ 89 can partly be explained by differences in the availability of soil nitrogen in the different seasons. Seed glucosinolate concentration wa s significantly increased with nitrogen applications between 0 and 150 kg/ha. Increasing nitrogen beyond 150 kg/ha had little or no effect o n seed glucosinolate concentration. The results are examined with refe rence to the varying effects of increasing nitrogen application rates on seed glucosinolate concentrations reported previously.