Variation in nitrogen response among spring rape ( Brassica napus) cultivars and its relationship to nitrogen uptake and utilization

Abstract

Growth, development and yield of 40 diverse spring rape ( Brassica napus) cultivars were measured at three different levels of applied nitrogen in the field. There were significant cultivar differences in yield under a limiting N supply and in yield response to higher N application rates. Cultivars with the lowest yields at the lowest N level generally responded more markedly to increase in N application rates than cultivars with higher yields in this treatment. A greater yield response was associated with relatively greater rates of growth and development at higher N levels. Measurements of dry weights and N contents of above-ground plant parts over a period between 42 and 66 days after sowing of the field experiment were used to calculate N-uptake rates and N-utilization (change in dry weight/unit change in N content) indices. Significant cultivar differences were observed only at the lowest N level for N-utilization index and only at the intermediate level for N-uptake rate. If cultivars were grouped on the basis of their geographic origin—Japanese, Canadian, European—those of Japanese origin generally had the highest uptake rates and utilization indices in the respective treatments in which significant differences were detected. Two solution-culture experiments were also conducted in a daylight phytotron at 20/15°C with the same cultivars. Significant cultivar differences in N-uptake rate and N-utilization index were detected with an initial concentration of 1m M N, but not with an initial concentration of 8 m M N. Cultivar differences in root growth and N uptake per unit root dry weight were significant at both concentrations. Again, most of the cultivars with the highest uptake rates or utilization indices were of Japanese origin. Uptake rate was correlated with uptake rate per unit dry weight, but not with initial root dry weight or increase in root weight over the course of the experiment. The significance of geographic variation in N-uptake rate in both field and controlled experiments is discussed with particular reference to the use of this character as a selection criterion in breeding programs utilizing recently developed another culture techniques.