Quality of Carrots Grown for Processing as Affected by Nitrogen Fertilization and Harvest Term

In 2007-2008 the effect of nitrogen fertilization and harvest term on quality of two carrot cultivars was investigated. The field experiment was carried out in Żelazna Experimental Station of Warsaw University of Life Sciences. Karotan F₁ and Trafford F₁ cultivars, commonly grown for juice industry, were the objects of the experiment. Carrot seeds were sown at the beginning of May. Nitrogen fertilization was applied in five rates, ranged from 0 to 120 kg·ha^-1 and in two terms — before sowing and in the middle of growing season. Roots were harvested in three terms: mid-September, mid-October and the first decade of November. After harvest there were determined: nitrates (NO₃) content in carrot roots and juice, soluble solids, colour parameters of juice in CIE L^*a^*b^* system. The dose and the term of nitrogen fertilization influenced nitrates content in carrots, and the highest NO₃ concentration was found in carrots fertilized with 120 kg·ha^-1 of N before sowing. Karotan showed higher nitrates accumulation than Trafford. The content of nitrates in the roots was markedly higher than in carrot juice. Nitrates content in carrots decreased with delaying of harvest time, in opposite to soluble solids content. Soluble solids content and colour parameters of carrot juice were not affected by nitrogen fertilization, but the lowest L^*, a^* and b^* values were observed at the last term of harvest.