Vanishing Process of 15-year fertilization on the Paddy Field

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Rice cv. Mineasashi was cultivated with no pesticides in the following nine different fertilization regimes as no fertilizer in two plots and in 7 plots fertilized by chemical fertilizers, and organic fertilizer during 15 years from 1993 to 2008 in the paddy field converted from volcanic ash soil upland field. In 2009, fertilization regimes in these nine plots changed under no fertilizer up to 2013.The effects of applying fertilizers on rice growth, rice yield, and protein content of brown rice were observed and analyzed. Plots with fertilizers had so more tiller emergence that more rice yield and more protein content than plots with no fertilizer. However, mean rice yield with no fertilizer from 2009 to2013 in 9 plot was almost the same. Judging from these results, the effect of continuous application of fertilizers during 15 years, regardless of chemical or organic, completely vanished in the first year when no application of fertilizer was started.