Response of yield and quality of cauliflower varieties (Brassica oleracea var. botrytis) to nitrogen supply

Summary

The fertilizer nitrogen (N) inputs to some vegetables such as cauliflower (Brassica oleracea var. botrytis) can be large. One approach to decreasing the input of N may be to select for cultivars efficient in the use of nitrogen. The objective of this investigation was to identify a cultivar which was nitrogen efficient in terms of producing a high yield under nitrogen (N) limiting conditions. Field trials were conducted in 1993 and 1994 with the cauliflower F₁-hybrids (B..oleracea var. botrytis) `Marine', `Lindurian' and `Linford' at the Ruthe (Germany) and Schermer (the Netherlands) sites. Optimum N supply was 250 kg ha<sup>21</sup> as the sum of the inorganic N content of the soil (N<sub>min</sub>) at planting and fertilizer N. Limiting N supply consisted of N<sub>min</sub> at planting and mineralization of N during cultivation. The N<sub>min</sub> at planting was 116 and 66 kg ha<sup>21</sup> at Ruthe and 84 and 20 kg ha<sup>21</sup> at Schermer in 1993 and 1994, respectively. The yield in terms of total dry-matter and quality (measured as percentage class 1 curds) was highest with `Marine' both at limiting and optimum N supply. Additionally, in quality `Marine' was the least sensitive variety to N shortage. Thus, `Marine' could be regarded as being nitrogen efficient. `Linford' could be considered as nitrogen inefficient in quality, whereas `Lindurian' generally performed inconsistently. The reduction in quality with N shortage was due to an increase in loose curds, indicating that limiting N supply promoted the process of bolting. Quality defect buttoning increased in part with N shortage. `Marine' produced no buttoned curds. Bracting was not affected by N supply and appeared only in Ruthe 1994 with `Lindurian' and `Linford'. It was concluded that the improved efficiency with `Marine' in terms of total dry matter and quality might have been achieved either through a higher N uptake capacity of the root system (uptake efficiency) and/or through a greater utilization of nitrogen by the plant (N utilization efficiency).     

Rooting pattern and nitrogen uptake of three cauliflower (Brassica oleracea var. botrytis) F1‐hybrids

In a two‐year field trial at the sites Ruthe (Germany, loess soil, Orthic Luvisol) and Schermer (The Netherlands, marine clay soil, Eutric Fluvisol) the cauliflower F₁‐hybrids Marine, Lindurian and Linford were compared in their efficiency of N use from limiting and optimum supplies of N. Limiting N was N_min at planting. Optimum N was 250 kg ha^—1 as the sum of inorganic N content of the soil (N_min) at planting and fertilizer‐N. Marine was the most efficient variety, producing the highest shoot dry‐matter and quality (% class 1 curds) at both limiting and optimum N supplies. The N supply did not affect the horizontal and vertical distribution of root length density per soil volume (RLD, cm cm^—3) irrespective of variety. The RLD decreased exponentially with increasing soil depth. Varietal differences in RLD were not found at Ruthe, whereas at Schermer Marine had the highest RLD in all soil layers investigated (0 to 60 cm). No correlations were found between RLD and residual N_min at harvest, except at limiting N supply in Schermer where a strong negative correlation was found between RLD in the 45 to 60 cm layer and N_min at harvest. Thus, varietal differences in N efficiency are speculated to be rather due to different internal N‐use efficiency than to differences in N‐uptake efficiency.