Mineral nutrient uptake in the production cycle of knip-type apple trees in the nursery

The nursery production of premium apple trees represents an agricultural sector of growing relevance in Italy. Large amounts of mineral nutrients are often supplied in nurseries to avoid any limitation that may limit tree development and lateral branching. In this study, the nutrient uptake rates during the three-year cycle yielding the final ready-to-be-sold “knip-type” tree have been assessed in a nursery located in the Po Valley (northern Italy). Replicated tree samples have been collected in mid-summer and before complete leaf abscission from (a) a layering field where apple rootstock M9 (T 337 strain) was propagated (~150,000 rooted shoots ha^‑1); from a nursery field where winter grafted trees of the cultivar ‘Fuji’ were grown for a first year (26,000 trees ha^‑1) (b), and for the second and last year, after being cut back in the previous winter at around 70 cm height (c). The main tree organs were analysed for their mineral concentrations. Calculated on ha basis, the rooted rootstocks contained more than 350 kg N and Ca, around 250 kg K, 80 kg Mg and 50 kg P. During their first year after grafting, trees took up around 50 kg N and around 25 kg K. Most nutrient uptake occurred between mid-summer and autumn. In the second and last year in the nursery, nutrient uptake rates were much higher than those absorbed in the first year (120, 16, 81, 112, 23 of N, P, K Ca and Mg, respectively). We estimated that, to produce a 2.3 m tall knip-tree with 17-20 laterals, approximately 9.5 g N, 1.3 g P; 6 g K, 10 g Ca and 1.6 g Mg need to be taken up during its 3-year production cycle. These data could allow fine-tuning of the mineral nutrient supply rates in the nursery to reconcile plant production and environmental concerns.