The Effects of Flat Covers on Overwintering and Nutritional Value of Leeks

In a field study conducted in 2003-2005 leek cv. Kenton F₁ planted in June was harvested in November or after overwintering in a field conditions. During the winter season plants were covered by perforated clear polyethylene film (PE) with 50 holes per 1 m² or non-woven polypropylene agrotextile (30 g·m^-2), which were removed just before the I^st and II^nd term of harvest conducted at the end of March or April. The application of both tested covers considerably increased the winter hardiness of plants in comparison to non covered control. They provided the similar protection against frost damage in early spring harvest, while for delayed one to the end of April, more beneficial cover was found to be agrotextile material. Plants harvested in spring season contained lower amounts of dry matter, total sugar and vitamin C, and higher level of reducing sugar and nitrates. During the II^nd term of spring harvest there was observed a decrease of dry matter and vitamin C and some increment of nitrates content in leeks in comparison to that conducted at the end of March.