Relationships between nitrogen, dry matter accumulation and glucosinolates in Eruca sativa Mills. The applicability of the critical NO3-N levels approach

Abstract

Rocket salad (Eruca sativa Mills) is one of the major leafy vegetables produced worldwide and has been characterized as a rich source of chemoprotective glucosinolates (GSL). The relationship between N fertilization and the resulting plant biomass and N status with GSL quantity and quality in rocket leaves was examined. A pot experiment was conducted, applying ten different N-rates and destructive sampling was carried out 15, 30 and 45 days after transplanting (DAT). The Mitscherlich equation was used to establish NO3-N critical levels at each growth stage and as an indicator of N demand for relative maximum dry matter accumulation and glucosinolate content and composition was determined. Glucosinolate content was significantly influenced by N rate, growth stage and their interaction. Different GSL types showed dissimilar responses to N fertilization: aliphatic GSLs were significantly reduced under increased N rates whereas indole GSL showed the reverse. Under excess N fertilization (> 1.04 g/plant), dry matter accumulation remained constant, NO3-N was significantly increased and total GSL content was significantly reduced, factors that could lead to an anticipated product quality decline. The application of the critical NO3-N level approach used to identify optimal N fertilization rates for plant growth could serve as means to obtain optimized GSL content in the edible plant parts.