Prospects and Limitations of Nitrogen Fertigation and Summer Application in ‘Conference’ Pear Trees

Fruit trees generally exhibit inefficient fertilizer nitrogen (N) uptake. Matching N fertilization to fruit tree requirements is key to sustainable fertilizer use. This requires knowledge of the effect of timing and method of N fertilizer application on N uptake dynamics and allocation. In this study ‘Conference’ pear trees were used. Different calcium nitrate application schemes and methods were set up from 2018 until 2020 in which the summer fractions of 2019 were labelled with 15N. Treatments allowed a comparison between granular application and different fertigation schemes. No significant effects for pear yield nor pear N content were obtained. With fertigation, yield and pear N content can be maintained while reducing (25%) both the amount of fertilizer N application and nitrate leaching risk. The advantage of applying a fraction of the N fertilization during summer was twofold: 1) reduction of nitrate leaching, and 2) enhanced replenishment of tree N reserves. Younger tree structures were preferred as reserve structures. Summer fertilization should, however, not be used to stimulate fruit N content in the prevailing growing season since little fertilizer-derived N was retained in pear fruits