中晩生カンキツ'不知火'の樹体生育と果実品質ならびに細根量に及ぼす土壌改良資材と窒素施肥量の影響(土壌管理・施肥・灌水)  [in Japanese] Effect of Soil Amendments and Nitrogen Fertilizer Application on Tree and Fine Root Growth and Fruit Quality of Medium-late Maturing Cultivar Citrus 'Shiranuhi'(Soil Management, Fertilization & Irrigation)  [in Japanese]

樹勢の弱い中晩生カンキツ'不知火'に対して土壌改良資材の施用と窒素施肥量の違いが樹体生育,土壌物理性,果実品質,細根量に及ぼす影響を調査した.土壌改良資材であるバーク堆肥,ピートモス,パーライトを施用することで,土壌物理性が改善され,細根量が増加した.窒素施肥量を多くすると,細根量は減少し,果皮率と糖度が高くなる傾向であった.土壌改良資材を施用しても,窒素施肥量が多いと,細根量は減少し,その寄与程度は窒素施肥量が土壌改良資材施用の約2倍であった.これらの結果より,'不知火'の細根を増加させ,樹勢を良くするためには,土壌改良資材を施用した上で,過剰な窒素施用は避ける必要があるものと考えられた.

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.