Nitrogen efficiency of Brussels sprouts under different organic N fertilization rates

The identification of nitrogen efficient varieties is important to improve yielding abilities in organic farming systems which are usually N-limited. This holds true particularly for crops with a long growing period and high nitrogen demand such as Brussels sprouts. Two field experiments with two different fertilizer levels were conducted on a hapludalf soil under the conditions of organic farming. Ten Brussels sprouts varieties with different growing periods were evaluated. For N accumulation efficiency differences between cultivars were not consistent over both experimental years, but similar under different levels of nitrogen supply. An allometric relationship between bud dry matter and total plant nitrogen accumulation comprising all varieties in both years and both fertilizer levels explained 56% of the total variation. Additionally, nitrogen utilization efficiency (NUE) was influenced by bud nitrogen content and harvest index. We found different relationships between bud dry matter and bud nitrogen with contrasting bud nitrogen percentage between years. However, relating bud nitrogen to total aboveground N again gave a linear relationship unifying all factors. Harvest index was linearly related to NUE indicating that dry matter partitioning is a major determinant of NUE. Varietal differences in NUE differed between years. Within years, yields of individual cultivars grown under different nitrogen levels were linearly related. We conclude that nitrogen accumulation in buds is environmentally stable, whereas dry matter partitioning into the same organs is more variable. Apparently, varieties performing well under high nitrogen supply yield also high under limited nitrogen. Further investigations are needed since the large genotypic variation between years is not fully understood. (C) 2011 Elsevier B.V. All rights reserved.