Effect of nitrogen fertilizer application rates on tree growth, fruit quality and leaf mineral content of young citrus 'Shiranuhi' trees
2008
Sugiyama, Y.(Shizuoka-ken. Research Inst. of Agriculture and Forestry (Japan) . Fruit Tree Research Center) | Emoto, Y. | Hamasaki, S. | Suzuki, H. | Ooshiro, A.
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 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 and 448 kgN/ha.
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