1. To clarify the effects of fruiting on the manganese content and other mineral compositions of spring cycle leaves, four 67-year-old trees were selected in an orchard. In 1963, two trees (No. 22 and 25) of them were in“off”year in fruiting and the others (No. 1 and 42) were in“on”year as referred to Fig. 1. From each tree, eight 2-year-old fruiting shoots (F) and non-fruiting shoots (V) were taken just before the harvest time in the middle of November. On the 2-year-old fruiting shoot, 7-month-old leaves of spring cycle growth were divided into three types (FFF, VFF and VVF) as referred in Fig. 2. There was only one type of 7-month-old leaves (VVV) on the 2-year-old non-fruiting shoot.
2. Mean dry weight of leaves on new shoot from“off”year trees was considerably higher than that of“on”year trees, while the mean dry weight of leaves was lower on new fruiting shoot (FFF) compared with those of other three types of new non-fruiting shoot (VFF, VVF and VVV).
3. Leaves from“on”year trees had significantly higher contents of N, Ca and Mn, and lower content of K than those from“off”year trees. There was no significant difference in the levels of P and Mg between“on”and“off”year trees.
4. Leaves on new fruiting shoot (FFF) were significantly higher in Mg, and lower in N, P and K than those on new non-fruiting shoot (VFF, VVF and VVV). No significant difference was found in the levels of Ca and Mn between fruiting and non-fruiting shoots.
5. The adjacency of a fruit affected most strongly the concentration of K in the leaf, viz. the lowest K concentration in the leaves behind fruits (FFF) and the highest K concentration in the leaves from“VVV”shoots. There were not clear gradients in the concentrations of another elements between the leaves from four different types of shoot.
6. In the experiment of 1966, highly significant difference was found in the manganese content of leaves on non-fruiting shoots (VVV) between“on” and“off”year trees growing on four different groves which had fairly low available manganese in soils.
7. Results from the present study suggest that differing from potassium, the manganese concentration of Satsuma orange leaves is not affected directly by the fruiting, but, is fluctuated by tree growth habits in the previous season.