| Abstract: | Forty-one field experiments were carried out on the spring N top-dressing requirements of winter oilseed rape in the years 1973 to 1977. The experiments were in the main rape-growing areas of England and Scotland, and almost all were on rape crops following one or more cereals. Seed and oil yield were increased by N top-dressing in 38 of the 41 experiments, with a mean requirement by satisfactory crops for about 230 kg ha?1 of N. Those experiments with no response to N or no response beyond 90 kg ha?1 of N were mostly low yielding and suffered from lodging, drought or bird damage. N reduced oil content by about 2% on average, but there was a considerably larger depression in 10 experiments, almost always associated with low yield, drought or lodging. N fertiliser increased the N content of the seed by about 0.5%. Timing of N application within the period mid-February to late March had little influence on seed yield or oil content but applying all or half the N in April tended to give a lower yield. There was no advantage from splitting the N application. |
