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The influence of calcium (Ca++) nutrition on the growth and root tissue electrolyte leakage (EL) of carrot (Daucus carota) was investigated using a hydroponic culture system. Seedlings of `Navajo' carrot were grown for 10 weeks with roots submersed in hydroponic nutrient solutions containing 0, 0.1, 1, 2, 4, or 8 meq/L Ca++. The nutrient solution was replenished weekly with its pH maintained at 5.8 for the entire experimental period. The tap root lengths increased as solution Ca++ concentration increased. The diameter and fresh and dry weights of the tap roots increased as Ca++ concentration increased up to 4 meq/L, and then decreased at 8 meq/L Ca++. The root and petiole concentrations of sugar, potassium, and nitrate were unaffected by changes in nutrient solution Ca++ levels. The tissue EL, when tested for the stored roots, decreased as solution Ca++ concentration increased (r = 0.602). Results of this experiment suggest that calcium nutrition is essential for maintaining cell wall integrity in hydroponically grown carrot roots.
The influence of calcium nitrate fertilization on the storage characteristics of carrot (Daucus carota) roots was investigated. Plants of `Navajo' carrots grown under irrigation were sprayed with a 2% solution of Ca(NO3)2 4H2O at a rate of 50 kg/ha Ca 10 days before harvest. Quality of carrot roots stored at 5 °C was evaluated monthly for sweetness, tissue electrolyte leakage, disease development and visual characteristics. For disease development, the crown portion of the carrot roots was inoculated with an ascospore solution (2 × 109 spores/mL) of white mold (Sclerotinia sclerotiorum) before storage. When determined after 1 month of storage, percent tissue electrolyte leakage in the Ca-treated carrots decreased 52% as compared to that obtained from the control. Sugar contents of the cortex and xylem tissues were not affected by calcium nitrate fertilization. Changes in other quality parameters of carrot roots for an extended storage period, including white mold development, will be presented. Initial findings of this research suggest that foliar calcium feeding at the final stage of plant growth may enhance the quality of carrot roots during storage.