Nitrogen fertilization to maximize carrot yield and quality on a sandy soil

Nitrogen is required for successful carrot production on sandy soils of the southeastern United States, yet carrot growers often apply N in amounts exceeding university recommendations. Excessive fertilization is practiced to compensate for losses of N from leaching and because some growers believe that high rates of fertilization improve vegetable quality. Carrots (Daucus carota L.) were grown in three plantings during Winter 1994-95 in Gainesville, Fla., to test the effects of N fertilization on yield and quality. Yield increased with N fertilization but the effect of N rate depended on planting date; 150 kg ha(-1) N maximized yield for November and December plantings but 180 kg.ha(-1) N was sufficient for the January planting. Concentration of total alcohol-soluble sugar was maximized at 45 mg.g(-1) fresh root with 140 kg.ha(-1) N for 'Choctaw' carrots, whereas sugar concentration of 'Scarlet Nantes' roots was not affected by N fertilization. Carrot root carotenoid concentration was maximized at 55 mg.kg(-1) fresh root tissue with 160 kg.ha(-1) N. Generally, those N fertilization rates that maximized carrot root yield also maximized carrot quality as determined by sugar and carotenoid concentrations.