Crop season effects on yield and quality of hydroponically grown Brassica rapa var. Sylvestris

A Brassica rapa var. Sylvestris native of Southern Italy, and locally known as ‘Friarielli’, was studied to assess quality changes associated to a delayed cropping throughout the year. Plants were cultivated on a floating system in an unheated greenhouse in Naples (Italy), in two growing cycles: spring growing cycle, SGC (March 2005 - May 2005) and winter growing cycle, WGC (December 2005 – March 2006). The days from sowing to harvest were 41 (SGC) and 85 (WGC). At harvest, yield and quality were evaluated and related to the environmental conditions occurred during the different crop cycles. Higher daily temperature and solar radiation during the SGC enhanced both leaf area and plant growth rate. Lower total yield was obtained in the WGC compared to the SGC (9.5 vs. 11.2 kg m-2). The leaf nitrate content was reduced in the SGC compared to the winter cycle (1800 vs. 2400 mg kg FW-1) possibly as a consequence of higher nitrate reductase activity associated to higher light intensity. Nevertheless, the nitrate content was generally lower than the threshold values established by EU regulation for other leafy vegetables. Both lipophilic and hydrophilic antioxidant activities were higher in the SGC compared to the WGC. Although in the winter cycle the yield was similar to that obtained during the spring cycle, the latter ensured a shorter seed-to-harvest time and an improved quality of the fresh produce.