Abstract
A differential nitrogen (N) fertilization trial for a high density planting of satsuma mandarin was conducted for 11 years starting in 1982 on 13-year-old trees. Satsuma mandarin (Citrus unshiu Marc. cv. Sugiyama) trees, which had been grown in a 0.4 ha field with little or no fertilizer, were administered a combination of 2 levels of organic matter application and 3 levels of N triplicated in a factorial arrangement. Levels of organic matter were +OM (rice straw application of 20 t·ha-1·year-1) and -OM (sod culture system). Levels of N fertilizers were N-1 : 100, N-2 : 200, and N-3 : 300 kg·ha-1·year-1. The total soluble solids-titratable acidity (TSS-TA) ratio of the juice, the 'a' index of peel color, percentage of mesocarp, and specific gravity of fruit in the -OM treatment were slightly higher than those in the +OM treatment. In contrast, TA content in the juice and mean fruit weight were slightly increased by organic matter application. TSS-TA ratio, the color indices of 'L', 'a' and 'b', % of mesocarp, and specific gravity of fruit decreased with increased N application, whereas TA content in the juice increased. The N and K contents in the leaves and leaf color index in the +OM treatment were slightly higher than those in the -OM treatment. Leaf N content and the leaf color index increased, but leaf P and K contents decreased with increased N application. TSS, TSS-TA ratio, the 'L', 'a' and 'b' color indices, % of mesocarp, and specific gravity of fruit were negatively correlated to leaf N content, wherease TA content correlated positively with leaf N.
