Nitrogen distribution, remobilization and re-cycling in young orchard of non-bearing ‘Rocha’ pear trees

In newly planted orchards, special attention must be paid to fertilization to build up the permanent structure of the trees so that high yield and fruit quality can be reached later on. Nitrogen (N) plays a major role in the fertilization plan, although few studies have assessed its use efficiency in young non-bearing trees, especially in field conditions. In this work, 1–3 years old ‘Rocha’ pear trees, grafted on quince BA29, were planted in a Mediterranean region, and fertigated with 6 g N tree−1 year−1 as ammonium nitrate with 5 at.% 15N enrichment to study the fertilizer N uptake during the vegetative cycle, the overall fertilizer N use efficiency at the end of each year, and the plant–soil N balance for this period. Nitrogen remobilization and the re-cycling of N from senescent leaves were also studied by fertilizing some pear trees with 10 at.% 15N enrichment.Nitrogen uptake was minimum at bud break and peaked in June/July remaining more or less constant until leaf fall. About 25% of the fertilizer N taken up by 3 years old trees in the previous year was found in the new tissues formed (flowers, leaves and 1-year-old shoots), reaching 27% when fine roots were also included. In those trees, 32% and 54% of the 15N stored in the previous year in the trunk and older shoots, respectively, were mobilized to the new growth in the following year.Fertilizer N use efficiency by trees increased from the first to the third year but was generally small (6%, 14% and 33%), and estimated N losses were large (89%, 46% and 53%, respectively in the first, second and third years). Irrigation water and soil provided more N to the trees than fertilizer N.