Seasonal differences, soil texture and uptake of newly absorbed nitrogen in field-grown pear trees

Abstract

The early-season availability of newly applied nitrogen was evaluated in ‘Comice’ pear trees grown in sandy loam and clay soils in Medford, Oregon. In 1988, labelled N applied to the sandy soil four weeks before full bloom (FB) appeared considerably in developing tissues two weeks after FB. However, during 1989, labelled N from pre-bloom fertilizer was apparent in the flower clusters and early growth. Temperatures during the weeks before and after bloom were higher in 1989 than either 1988 or the corresponding longterm average. In 1989, labelled N was also applied before bloom to the clay soil. At FB, 20% of the N in the flower clusters had come from the labelled fertilizer in the sandy soil, but only a tiny amount was present in the clay soil until four weeks after FB. During the first weeks after FB, newly absorbed N was preferentially partitioned to spur leaves regardless of soil type or seasons, while shoot leaves were more dependent on stored N.