Responses of Seed Yield and Quality to Nitrogen Application Levels in Two Oilseed Rape (Brassica napusL.) Varieties Differing in Nitrogen Efficiency

The relationship between nitrogen efficiency (NE), defined as seed yield per unit nitrogen (N) application, and seed quality was examined in two oilseed rape (Brassica napus L.) varieties at 5 N application levels, 0.6, 3, 6, 12, 15 mmol L−1, N1, N2, N3, N4 and N5, respectively. Seed yield, oil yield and protein content were increased with the increase in N application level, but NE and oil content were decreased, and the fatty acid composition in seed was hardly changed. Analysis of seven fatty acids revealed aslight decrease in the contents of erucic acid and arachidonic acid with the increase in N application level, but no obvious change in the contents of palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid. Compared with the low NE variety H29, the seed yield and contents of erucic acid and arachidonic acid in the high NE variety bin270 were more markedly increased with the increase in N application level, and the oil content was hardly changed. The seed yield, oilcontent and oil yield were higher in the high NE variety than in the low NE variety at all 5 N application levels. There were no significant differences in protein, palmitic acid, stearic acid and oleic acid contents between the varieties at any of the 5 N application levels, but there were slight differences in the linoleic acid and linolenic acid contents between the two varieties. In brief, N application improved oil yield more greatly in the high NE variety than in the low NE variety, but hardly affected the fatty acid composition. Therefore, the seed quality and oil content of oilseed rape may not be decreased by breeding of a high NE variety with a high N absorption efficiency and high N use efficiency.