Glucosinolate content and amino acid composition of rapeseed (Brassica napus) meal as affected by sulphur and nitrogen nutrition

Abstract

AbstractRapeseed plants have been grown in soil‐free culture with varying amounts of nitrogen fertiliser applied as nitrate, and with 50% of the nitrate‐N exchanged for ammonium. The experiment was performed at two levels of sulphate fertiliser. Yield, protein content, glucosinolate content and amino acid composition were studied. The glucosinolate content was lower and the protein content was higher at a high level of nitrogen fertiliser. Exchange of 50% of the nitrate‐N for ammonium caused no significant change in glucosinolate or protein content. The amount of glucosinolate was higher at the high sulphate level. There were no sulphur‐nitrogen interactions. Content of total aspartic acid increased with nitrogen fertilisation, while total content of other amino acids did not change significantly with fertilisation.The effect of a wide variety of applications of sulphate fertiliser on glucosinolate and total amino acid content have been studied in a separate experiment. Although both protein content and methionine content were reduced at a low sulphate level, glucosinolate content was reduced considerably more.Experiments in the field revealed that although a reduction in glucosinolate content of rapeseed may be obtained from using fertilisers low in sulphur on sandy soils this does not seem possible on heavy soils.