Boron Deficiency in Florida Citrus Groves

chlorosis, but the addition of urea to the solu tion appeared to enhance the effect of the biuret. Experiment 4. When different amounts of commercial urea and crystalline urea were ap plied to the soil, 10 weeks were necessary for the chlorosis to appear on the trees which had received 60 and 80 grams of the commercial urea. No chlorosis resulted from the crystal line urea. Experiment 5. As a result of the applica tion of different concentrations of biuret, chlor osis began to appear six weeks after the ap plication of the material. Solutions that con tained biuret alone, or a urea combination containing as little as one-half percent biuret, produced chlorosis. A urea-biuret mixture with four percent biuret produced very severe leaf patterns and leaf drop. Fig. 3 shows chlorotic flushes taken from some of the treated trees.