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Urea solutions of 0.5 to 3% were applied by the foliar spray of different frequencies in pre- and post-harvest season to the trees under different crop loads of ´Miyagawa wase´ and ´Hayashi unshiu´ Satsuma mandarin (Citrus unshiu Marc.). The effects of urea applications on the leaf composition and cold resistance during winter were examined. The higher concentrations and frequencies of urea spray significantly increased N content in leaf, decreased P content, and tended to increase K content. Leaf chlorophyll and N contents were increased by the earlier harvest, and the lower contents by the later harvest were offset by the foliar spray of urea. Increase in chlorophyll and N by the foliar spray of urea was more conspicuous than that by the soil application. The increase in leaf proline and cold resistance by urea spray was most stimulated by the double sprays, one week before harvest and one week after harvest, and by the post-harvest triple sprays at intervals of one week. The earlier the harvest, the higher the leaf proline and cold resistance, and the lower the defoliation ratio. Soil application of urea also increased the leaf proline and cold resistance, and decreased the defoliation during winter. But the effect of soil application was less noticeable than that of foliar spray of 1 % urea. Content of total sugars in the leaf was not affected by the foliar spray of urea.
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