Effect of crop load on mineral uptake and partitioning in D'Anjou pears

Graduation date: 1987Three thinning levels were applied to\ud twenty-five-year-old D'Anjou pear trees in a completely\ud randomized design with five single-tree replicates on June 2,\ud 1985. Samples of wood, shoot leaves, shoot twigs, spur\ud leaves, spur twigs and fruits were taken every month during\ud the season of growth for mineral analysis. Sampling an entire\ud tree was not logistically possible, so biomass estimates were\ud made on a branch basis using two branches from each tree.\ud Leaf shoots and spurs were counted for each branch at every\ud sampling time, and representative spurs and leaf shoots were\ud collected from the entire tree. By determining average shoot\ud dry weights, leaf dry weights, fruit dry weights and spur leaf\ud dry weights for the entire tree, it was possible to estimate\ud biomass and mineral partitioning for each branch. Thinning\ud did not increase shoot growth, and both total dry matter\ud production and minerals uptake were higher in the unthinned\ud trees. Fruit removal altered spur and shoot leaf mineral\ud concentrations of H, P, Ca, and Mg but most other tissues were\ud unaffected and most other elements did not show treatment\ud effects. Thinning reduced total demand for nutrients. In the\ud case of N and P, the input into the branches was not reduced\ud by thinning as much as dry matter, thus concentration\ud increases were apparent in the leaves. Although more\ud magnesium and calcium was required for the larger biomass in\ud unthinned branches, the additional fruit appeared to enhance\ud uptake and translocation, and Mg and Ca leaf concentrations\ud also increased. Shifts in leaf mineral content would only\ud severely alter diagnostic interpretation for N. Vigor and\ud crop load must be evaluated in interpreting N concentrations.\ud Unless partitioning between leaf and fruit biomass is known,\ud nitrogen concentrations are difficult to interpret