Effects of fertilizer levels on tree growth and fruit quality of 'Hakuho' peaches (Prunus persica)

Effects of fertilizer levels on tree growth and fruit quality of 'Hakuho' peaches (Prunus persica) were evaluated. Three levels, High (H), Medium (M), and Low (L) of complete liquid fertilizers were applied twice a week from bud break. H, M, and L levels of fertilizers contained 160, 80, and 40 ppm of nitrogen (N), respectively. The application rates were reduced to half at the end of the pit hardening stage. Shoot growth proceeded quickly in trees of the H treatment before the pit hardening stage, but it became more vigorous in the M treatment thereafter. Leaf chlorophyll and leaf N contents were higher in trees treated with higher levels of fertilizer, but the photosynthetic rate was low in the H treatment. Total soluble solids (TSS) and sucrose contents of the fruit were highest in the M treatment and lowest in the H treatment at harvest, whereas the titratable acidity, citric acid and malic acid were highest in the H treatment. Skin coloration was poorest in the H treatment fruit. γ-decalactone, a major constituent of peach aroma; was most abundant in fruit of the M treatment and lowest in the H treatment. Sensory evaluation of the M treatment fruit was rated the highest, whereas that of the H treatment was poorest. These results suggest that excessive fertilizer application for peach trees significantly diminishes fruit flavor by reducing sweetness as well as aroma.