Genotypic differences in nitrogen efficiency of white cabbage (Brassica oleracea L.)

In vegetable production, N balance surpluses are especially high which increases the risk of environmental pollution. The cultivation of N-efficient cultivars may contribute to alleviate the problem. A 2-year field experiment was conducted with eight white cabbage cultivars of three different maturity groups at two N fertilization levels. Genotypes differed both in N efficiency (head fresh weight at low N supply) and in yield at high N supply. These differences were not related to N uptake but to N utilization efficiency. At low N supply, harvest index was the main determining factor for genotypic yield differences. For earlier maturing cultivars a slower leaf emergence was responsible for the low harvest index. The response of the cultivars to low N supply was dependent on the weather conditions, particularly temperature, (highly significant year × cultivar × N supply interaction) at early growing stages. This suggests that breeding of cultivars with generally low-temperature tolerance could contribute to enhancing N utilization. Especially at high N supply, a high N harvest index was important for yield formation due to its effect on head water accumulation. For late cultivars, a high N retranslocation from leaves to the heads was related to yield both at low and high N supply. The study suggests that breeding of N-efficient cultivars may reduce N release to the environment by reducing the necessary N input and reducing the N content remaining in the crop residues.