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) cultivars of oilseed rape to spring nitrogen application was examined at Cockle Park, Northumberland in three successive seasons (1987-90). Seed yield and protein content increased in response to increasing nitrogen application. In each season over 85 % of the maximum recorded yield was obtained with an application of 150 kg N/ha. In the absence of spring 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 was significantly increased with nitrogen applications between 0 and 150 kg/ha. Increasing nitrogen beyond 150 kg/ha had little or no effect on seed glucosinolate concentration. The results are examined with reference to the varying effects of increasing nitrogen application rates on seed glucosinolate concentrations reported previously.