Effects of different leaf-fruit ratios on uptake and partitioning of N and K in 'Uenishiwase' persimmon trees

- Leaf-fruit ratio of persimmon trees was decreased from 20 to 10 by thinning.
- N partitioning to fruits increased from 10% to 17% of the tree total in a year.
- K partitioning to fruits increased from 25% to 44%.
- N and K increases were lower in aerial woods of the trees with low leaf-fruit ratio.
- Total N and K increases per tree were not affected by different leaf-fruit ratios.

To supply appropriate amount of nutrients to persimmon trees with high crop load is critically important for the stable production year after year. This study was conducted to determine absorption and partitioning of nitrogen (N) and potassium (K) in 13-year-old 'Uenishiwase' persimmon trees with different crop loads. The leaf-fruit (L/F) ratio was adjusted to 20 (high) and 10 (low) by fruit thinning on July 2 after the June drop. The trees were harvested in early spring and late autumn, and increases of dry weight (DW) and N and K in different tree parts during the growing season were calculated. As the L/F ratio decreased from 20 to 10, total fruit DW increased from 4.3 to 7.6 kg per tree. Of the total DW increase in a season, fruit accounted for 14% in a high and 24% in a low L/F tree. DW in older than 1-year-old woods accounted for 44% in a high and 41% in a low L/F tree. Different L/F ratios did not significantly affect the increase of tree total DW. Upon decreasing the L/F ratio, the amount of fruit N increased by 1.7-fold where N partitioning to fruit increased from 10% to 17% of the tree total, whereas fruit K increased by 2-fold, increasing its partitioning from 25% to 44%. It was noted that N and K increases were lower in aerial woods of the low L/F trees. Total N per tree increased by about 170 g in both the high and low L/F trees, but the total K increases were 175 g and 202 g in a high and low L/F tree, respectively. The results suggested that a fertilization program for high crop-load trees should take two points into consideration, namely, the magnitude of nutrients removed from the tree by fruit harvest and the reduced nutrients in woody organs essential for tree development the next season.