Cold tolerance, yield, and fruit quality of 'd'Anjou' pears influenced by nitrogen fertilizer rates and time of application

Low and moderate rates of ammonium nitrate (NH,NO,) fertilizer were applied in late winter or late summer to mature 'd' Anjou' pear (Pyrus communis, L.) trees (planted 1963, 1965) from 1976 to 1994. Data on cold tolerance, nutrition, yield and fruit quality in relation to nitrogen (N) fertilization were collected between 1980 and 1988. Early autumn cold tolerance was higher for trees receiving low N rates versus moderate N rates in either late winter or late summer. In late autumn and early winter, cold tolerance increased for all trees, and little difference in winter hardiness existed for any N treatment. By mid-winter, cold tolerance was higher for trees receiving the moderate rate of N in late winter versus low N in late summer. Cold tolerance was relatively high throughout autumn and winter freeze-test periods for trees fertilized with low N in late winter. Tree vigor, fruit size, leafN, and fruit N were highest for trees receiving the late winter, moderate rate of N. Yield was lowest, but fruit firmness, fruit quality and fruit calcium (Ca) concentrations were highest for trees treated with the late winter, low rate of N. The incidence of cork spot was lower from trees with the late winter, low N treatment than for the late summer, moderate N-treated trees.