The effect of various nitrogen fertilization and foliar nutrition regimes on the concentrations of sugars, carotenoids and phenolic compounds in carrot (Daucus carota L.)

The aim of this research was to determine the influence of various forms, diverse doses, and dates of application of nitrogen fertilizers and foliar nutrition on the concentration of sugars, carotenoids and phenolics compound in carrot. Two field experiments (Experiment I in 2003–2005 and Experiment II in 2004–2005) with carrot ‘Kazan F1’ were conducted in Trzciana (50°06′N; 21°85′E) in Poland. Both experiments were arranged in a split-plot design with four replications. Two sub-blocks were identified in both experiments: sub-block (A) without foliar nutrition and sub-block (B) with plant foliar nutrition. In sub-block (B), plants were sprayed three-times with: 2% (w/v) urea, a 1% (v/v) solution of multi-component ‘Supervit R’ fertilizer, and again with 2% (w/v) urea. Combinations with diversified nitrogen fertilization were distinguished within both sub-blocks. The treatments in Experiment I consisted of: (1) Control, (2) 70 kg N ha−1 as Ca(NO3)2, (3) 70 + 70 kg N ha−1 as Ca(NO3)2, (4) 70 kg N ha−1 as (NH4)2SO4 and (5) 70 + 70 kg N ha−1 as (NH4)2SO4, where 70 kg N ha−1 was used preplant and 70 + 70 kg N ha−1 was applied preplant and as a top dressing, respectively. The treatments in Experiment II consisted of: (1) Control, (2) 35 + 35 kg N ha−1 as ENTEC-26, (3) 70 + 70 kg N ha−1 as ENTEC-26, (4) 105 + 105 kg N ha−1 as ENTEC-26, (5) 35 + 35 kg N ha−1 as NH4NO3, (6) 70 + 70 kg N ha−1 as NH4NO3, (7) 105 + 105 kg N ha−1 as NH4NO3, where 35 + 35, 70 + 70, 105 + 105 kg N ha−1 was applied preplant and as top dressing, respectively. Solid nitrogen fertilizer was added to the soil, as produced: Ca(NO3)2—Yara International ASA (Hydro), (NH4)2SO4—Zakłady Azotowe w Tarnowie, Poland, NH4NO3—Zakłady Azotowe w Puławach, Poland and ENTEC-26–COMPO GmbH & Co., KG, Germany. In Experiment I, the highest sugar concentrations were found in carrot fertilized with (NH4)2SO4 70, while in Experiment II in the control and after fertilization with ENTEC-26 35 + 35 kg N ha−1. In both experiments N-fertilization affected an increase in phenolic compound concentrations in comparison with the control. Experiment I revealed no significant effect of N-fertilization on carotenoid concentrations in carrot, however in Experiment II the highest concentration of these compounds was characteristic for the control plants and carrot fertilized with ENTEC-26 35 + 35. The foliar nutrition applied in Experiment I caused a decline in sugar concentration and an elevated carotenoid concentration, however it had no influence on the phenolic compound concentrations in carrot. Yet the foliar nutrition in Experiment II led to a decrease in phenolic and carotenoid compound concentrations, but it did not affect sugar concentration in carrot.