Effects of supplemental fertigation levels on the growth and nutrient composition of pot-grown persimmon (Diospyros kaki) trees with a high crop load

摘要

Supplemental nitrogen (N) and potassium (K) fertilization is of critical importance for maintaining tree vigor and producing high-quality fruits in persimmon [Diospyros kaki), especially under high fruit-load conditions. This study was conducted to determine the effects of four different fertigation levels on pot-grown trees with two different leaf:fruit (L:F) ratios. On July 1, the L:F ratios of 3-year-old 'Fuyu' persimmon trees were adjusted to 20 and 10 through fruit thinning. From early July to early September, the trees in each pot were fertigated with a solution containing no (0 N and 0 K), low (10 N and 7.5 K), medium (20 N and 15 KJ, or high (30 N and 22.5 K) levels of supplemental N and K. The trees with an L:F ratio of 10 had higher yieldsbut smaller fruits with lower soluble solids than fruits from trees with an L:F ratio of 20. Increasing the fertigation level did not significantly affect fruit size in trees with an L:F ratio of 10, but fruits had lower skin color values and soluble solids. A low L:F ratio led to lower amounts of soluble sugars in dormant shoots, which was true even under higher fertigation levels. N concentrations in the shoots of the low L:F trees were significantly greater under higher levels of fertigation. However, increasing the fertigation level resulted in severe cold injury to dormant shoots in trees with both L:F ratios, although it also increased the number of flower buds produced the following year. It was concluded that an excessive supply of supplemental N and K to trees with a high crop load should be avoided because of the unfavorable results.