Abstract
Effects of applying soil amendments and the rate of nitrogen fertilizer application on tree and fine root growth and fruit quality were surveyed in ‘Shiranuhi’ 〔‘Kiyomi’ (Citrus unshiu Marc. × C. sinensis Osb.) × C. reticulata Bla.〕, which shows weak vigor. Soil amendments (bark manure, peat-moss, perlite) were applied to improve the physical condition of the soil and to increase the number of fine roots. Excess supply of nitrogen suppressed fine root development, and enhanced the peel ratio and concentration of soluble solid (Brix) in fruits. The effect of an excess supply of nitrogen was about twice as strong as those obtained from the application of soil amendments. Applications of soil amendments and the conventional amount of fertilizer were necessary to improve tree vigor and the number of fine roots.
