窒素施肥量の違いがカンキツ'不知火'幼木の樹体生育・果実品質および葉中無機成分含有率に及ぼす影響(土壌管理・施肥・灌水)  [in Japanese] Effect of Nitrogen Fertilizer Application Rates on Tree Growth, Fruit Quality and Leaf Mineral Content of Young Citrus 'Shiranuhi' trees(Soli Management, Fertilization & Irrigation)  [in Japanese]

カンキツ'不知火'幼木において,樹体生育に合わせ窒素施肥量を変え,窒素施肥量の違いが樹体生育,果実品質,樹体栄養へ及ぼす影響を4年間調査し,以下のことが明らかになった.収量は2倍量区(7年生で448 kgN・ha^<-1>)で最も多くなった.また,施肥量が多いと,果皮率が高くなり,果実比重が小さくなる傾向であった.糖度は施肥量が多いと高くなる年(2003)と差のない年,クエン酸含量は低くなる年(2002)と差のない年があった.葉中窒素含有率は施肥量が多いと高くなったが,2倍量区と3倍量区で差は認められなかった.半量区では葉中窒素適正値を大幅に下回った.以上の結果,'不知火'幼木の適正な施肥量は基準量から2倍量(7年生で224〜448 kgN・ha^<-1>)の範囲にあることが推定された.

A study was carried out to determine the most effective nitrogen fertilizer application rate for optimal tree growth, fruit quality, and leaf mineral content of the young citrus 'Shiranuhi' ['Kiyomi' (Citrus unshiu Marcow x C. sinensis (L) Osbeck) x C. reticulata Blanco] trees. The study was conducted over a period of four years from April 1999 to March 2003. Fruit yield increased with increasing nitrogen fertilizer application rate up to twice the recommended application rate (448 kgN・ha^<-1> for 7-year-old trees). Fruit quality was also influenced by nitrogen fertilizer application rate. Increasing the nitrogen in application rate increased the proportion of the peel in the fruit in 2001 and decreased the specific gravity in fruit in 2001 and 2003. The concentration of total soluble solids (Brix) increased with increasing nitrogen fertilizer application rate in 2003, whereas the citric acid level in the fruit decreased with increasing nitrogen fertilizer application rate in 2002. Total nitrogen concentration in the leaves increased with increasing nitrogen fertilizer application rate up to twice the standard application rate. However, no further increases in leaf total nitrogen concentration were observed in the N-application rate of three times the recommended rate. Lowering the nitrogen fertilizer application rate to half the recommended rate resulted in leaf total nitrogen concentration that was below the accepted content for optimal plant nutrition. From this study, the optimal annual nitrogen fertilizer application rate for 7-year-old 'Shiranuhi' trees appears to be between 224 kgN・ha^<-1> and 448 kgN・ha^<-1>.