Experimental approach to assess fertilizer nitrogen use, distribution, and loss in pear fruit trees

Enhanced use efficiency of fertilizer nitrogen (N) is paramount for sustainable pear fruit production. Sufficient fruit N content is a major factor for pear fruit storage potential, but fertilizer N use efficiency in pear fruit trees is generally low. The objective of this work was to test a methodology to quantify N uptake, partitioning and leaching loss as influenced by different calcium nitrate (Ca(NO₃)₂) fertilizer timings. To this end, 10-year-old 'Conference' pear trees (Pyrus communis L.) were transplanted and grown in soil-filled pallet boxes subjected to different timing of fertilizer addition. A fraction of the calcium nitrate was labelled with ¹⁵N and applied one month before full bloom, during summer and post-harvest. By sampling newly formed biomass (i.e., leaves, fruit and flower buds), temporal dynamics in the N fraction derived from calcium nitrate fertilization were determined. Simultaneously NO₃^- leaching derived from calcium nitrate fertilization was quantified. Our data suggest that spring application of N was most efficiently partitioned to leaves, fruits and buds at the time of harvest with a mean percentage of calcium nitrate derived N (Ndff) of 9.2%, 20.4% and 18.6%, respectively. Summer application of calcium nitrate was far less efficient at the time of harvest with Ndff of 0.56%, 0.89% and 1.4%, respectively, and substantially higher NO₃^- leaching was observed compared to spring fertilization. Post-harvest application showed even higher levels of leaching. Applying a split fertilization scheme with 60 kg N ha^-1 evenly spread over spring, summer, and post-harvest, about 9, 15 and 30%, respectively, of the fertilizer N had leached out as NO₃^- at the end of the growing season. This experimental approach may offer potential for detailed N budget studies for various fruit tree studies.