Effects of nitrogen application time in spring on absorption by Satsuma mandarin [Citrus unshiu] trees
2009
Ishikawa, K.(Ehime-ken. Research Inst. of Agriculture, Forestry and Fisheries, Matsuyama (Japan). Fruit Tree Research Center)
Effects of application time in spring on nitrogen absorption by satsuma mandarin (Citrus unshiu Marc. cv. 'Nankan No.20') were investigated. Field and pot tests were performed using an sup(15)N-tracer method in which the nitrogen was applied on March 1, April 1, and May 1. In field experiments, the absorption rate by trees was greater in April- and May-plots than in March-plots. The sup(15)N content of one-year-old leaves showed similar changes in the March- and April-plots, which was consistently higher than that in May-plots. The sup(15)N content in newly developed organs, such as new leaves, flowers and young fruit, was apparently greater in March- and April-plots than in May-plots between early May and early June. After late June, however, the sup(15)N content was consistently greatest in May-plots. In pot experiments, the utilization rate of trees receiving nitrogen application in the spring was 31.5%, 34.6% and 37.1% in March-, April-, and May-plots, respectively. Thus, the efficient application timing of nitrogen for spring fertilizing seems to be immediately before the bud burst in early April.
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