Sulphur fertilisation affects yield and quality in friarielli (Brassica rapa L. subsp. sylvestris L. Janch. var. esculenta Hort.) grown in a floating system

The influence of nitrogen and sulphur fertilisation on yield and quality was studied in two ecotypes of friarielli (Brassica rapa L. subsp. sylvestris L. Janch. var. esculenta Hort.) grown in a floating system. In the first experiment, we assessed the effects of different levels of N fertilisation on friarielli yield. In a second experiment, we tested three concentrations of S in the nutrient solution [2.6 mM, 4.0 mM, and 8.5 mM; corresponding to N:S concentration ratios of 10:1, 6.5:1, and 3:1, respectively] with the objective of fine-tuning the nutritional requirements for N and S to optimise both friarielli yield and quality. The main findings can be summarised as follows: (i) friarielli can be grown efficiently in a hydroponic system; (ii) both yield and quality in friarielli are strongly dependent on the N:S ratio of the nutrient solution; (iii) S may affect shoot nitrate accumulation in response to N availability; (iv) the response to S fertilisation is genotype-specific; (v) the anti-oxidant capacity of shoots increases with increasing S concentrations in the nutrient solution; and (vi) 26 mM N and an N:S concentration ratio of 10:1 in the nutrient solution are suggested for the best performance of hydroponically-grown friarielli.