505 Sensitivity of Pear and Apple Plants to Urea Fertilizers

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  • 1 Department of Horticulture, Oregon State University, Corvallis, OR 97331

`Gala'/M26 apple and `Bartlett'/OH97 pear trees growing in containers were treated with either 0, 1, 5, 10, 20, or 30g of urea dissolved in 150 mL of distilled water on 7 Sept. 1999. Two weeks after application, a soil sample from each container was analyzed for NH4+ and NO3. One day after treatment, the leaves of the apple trees treated with either 20 or 30 g urea wilted and curled and none of the other apple treatments were affected. However, 20 days later, new lateral and terminal buds broke to grow from these two treatments. In contrast, the pear trees showed signs of wilting and leaf necrosis in the 5, 10, 20, and 30 g urea treatments about 6 days after application. Twenty days after treatment, the leaves from the two highest treatments were completely necrotic and remained attached to the trees, while the leaves of 5- and 10-g treatments were partially necrotic and began defoliating. None of the pear trees produced any new lateral or terminal growth. Soil test showed that NH4+ contents of the soils were 54.9, 104.2, 356.9, 884.28, 1154.9, and 1225.2 mg/kg for `Bartlett'/OH97, and 30.2, 62.9, 359.0, 235.1, 529.9, and 499.0 mg/kg for `Gala'/M26 and NO3 contents of the soils were 40.5, 62.4, 211.0, 129.8, 54.5, and 39.5 mg/kg for `Bartlett'/OH97, and 37.6, 42.0, 178.7, 138.2, 186.2, and 142.1 mg/kg for `Gala'/M26 treated with 0, 1, 5, 10, 20, and 30 g urea, respectively.

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