Effects of Soil Type and Nitrogen Fertilization Rate on the Nutritional Value of Organically and Conventionally Grown Endive

The aim of this work was to investigate the influence of soil type and fertilization management on crop yield and antioxidant activity of organically and conventionally grown endive. Two different soil types (sandy and clay) and three levels of total nitrogen fertilization (0, 100, 200 kg N ha(-1)) were compared under conventional and organic farming systems. Quantitative (total yield, bunch mean weight, leaf area, dry matter) and qualitative parameters (total soluble solid (degrees Brix), titratable acidity, reducing sugars, colorimetric parameters, nitrates and nitrites content and antioxidant activity (DMPD method for the hydrophilic phase and the ABTS method for the lipophilic phase)) were determined. The yield was 24% lower in organic farming compared to conventional farming whereas higher bunch mean fresh weight and larger leaf area were generally found. Organically grown endive had a higher dry matter content. Increasing nitrogen application from 0 to 200 kg N ha(-1) resulted in increased yield in both organic and conventional farming. The bunch mean weight and leaf area were higher in clay soils vs. sandy soils. The leaf nitrate content was not affected by the farming system (conventional or organic farming), yet it increased in the clay soil and at increasing nitrogen fertilization. Differences in antioxidant activity were associated to a general stress response of organically grown plants rather than to the cultivation regime itself.