Effect of biodegradable nonwoven covers on yield and chemical composition of overwintering onion

Floating row covers are important pre-harvest factors for maximizing the yield of vegetable crops grown under open-field conditions. It is necessary to replace oil-based nonwoven covers with biodegradable ones that are environmentally friendly. The aim of this study was to investigate the effects of biodegradable nonwoven covers, made of aliphatic-aromatic copolyesters, with or without fatty acid dimers (SB20/13, SB21/13, and SB28/13), on yield and chemical composition of ‘Glacier’ and ‘Swift’ winter onions. In the first experiment, we observed a higher total marketable yield and higher harvest index for onions covered with SB21/13 (by 24% and 3%, respectively) when compared to the control (polypropylene nonwoven). The SB20/13 cover significantly decreased mean bulb weight by 15.3% than in control. Bulbs harvested from the plots covered with SB21/13 had lower dry weight by 3.2-3.7% and those covered with SB28/13 showed the lowest L-ascorbic acid content when compared to all other treatments (by 6.3-10.3%). The lowest total sugar content was found in control onion bulbs, but it was significantly different only from bulbs covered by SB20/13, which had more sugar by 10.6%. In the second experiment, plants covered with the SB28/13 had a 1 st grade yield of onions higher by 47% than that of the control. The highest mean bulb weight was obtained from plants covered with the SB21/13 nonwoven. Covering with nonwovens caused a decrease in dry weight (SB20/13 and SB21/13, by 1.3-1.7%, respectively) and L-ascorbic acid (all nonwovens, by 15.6% for SB21/13 up to 22% for SB20/13) in onion bulbs in comparison to the control. Since the tested biodegradable nonwovens covers did not cause any decrease in the yield of winter onions compared to polypropylene nonwovens, the former appear to be a suitable environmental-friendly solution for the open-field cultivation of this important vegetable crop.