2003 Volume 6 Issue 4 Pages 302-308
To estimate the site-specific optimal amount of nitrogen (N) to be applied as top-dressing (N top-dressing) at panicle initiation, we examined the effects of the amount of N accumulated in the aboveground biomass at the panicle initiation stage (N1), the total N content of soil and the amount of mineralizable soil N (Nm) on the amount of soil N taken up by the plants during the period from panicle initiation to heading (Ns) and the recovery ratio of applied chemical N during this period (J). We analyzed the data obtained in paddy fields with a similar soil type and weather condition in the growth period from 1999 to 2001. The growth of rice plants was regulated by the amounts of N applied before transplanting and at panicle initiation. The relative N uptake rate during the period from panicle initiation to heading (RNR) in the plots without N top-dressing was explained about 89% by multiple regression of N1, the total N of soil and Nm. Ns in the plots with N top-dressing that was estimated using RNR showed a significantly negative partial correlation with N1, the total N of soil and Nm. J in the plots with N top-dressing showed a significantly negative partial correlation with N1, but a significantly positive partial correlation with Nm. These results suggest that the fertilizer N should be applied considering the contribution of N1, the total N content of soil and Nm to Ns and J to fit the site-specific N demand of rice.
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