Relationship between planting density and growth of 'Starking Delicious' apple trees grafted on dwarfing and semidwarfing rootstocks

In 1975, 'Starking Delicious' apple trees (Malus domestica Borkh.) grafted on dwarfing (M. 9 and M. 26) and semidwarfing (M. 7 and MM. 106) rootstocks were planted radially in a geometric series to examine the relationship between the planting denstiy and tree growth. This system provided seven planting densities ranging from 453 to 3,178 trees per hectare for trees on M. 9 and M. 26, and eight planting densities ranging from 330 to 3,178 trees per hectare for trees on M. 7 and MM. 106. 1. A high correlation coefficient (r=0.994 double dagger double dagger) was obtained between the standing crop (total dry matter yield Y) and the trunk cross-sectional area (TCA; theta) regardless of the differences in rootstock and tree age. The regression equation is: Y=0.726 theta-12.636-(1) 2. In the 3rd leaf of 'Starking Delicious'/M. 26 and on M. 7; the 5th leaf of trees on MM. 106; and the 6th leaf of trees on M. 9, a slight inhibition in the increase of TCA was observed in the higher density plots. As the trees aged, the inhibition shifted to lower density plots. This shifting rate was accelerated in trees on M. 26, M. 7, and MM. 106, compared with trees on M. 9. These results suggest that the effect of the density on tree growth depends on the kinds of rootstocks as well as tree age. On all four rootstocks, the above-mentioned relationship between the planting density (rho) and the TCA (theta) could be represented by the following reciprocal equation, 1/theta=A rho+B-(3) where A and B depend on the tree age and rootstocks. 3. The average net production per hectare calculated by Eqs. (1) and (3) increased with increasing density, reaching a constant level at the density of 3,000 similar to 4,000 trees per hectare. Also, the average net production tended to increase for the trees grafted on semidwarfing rootstocks more so than on dwarfing stocks.