Effect of Time and Rate of Nitrogen Application on Root Growth with Special Reference to Chinese F1-hibrid Rice "Shanyou 63".

Abstract

The effect of time and rate of nitrogen application on root growth and their relations with constituents of top per hill were investigated using Chinese F1 hybrid rice (cv. Shanyou 63) under water culture conditions. Treatments of several nitrogen rates were applied in three growth stages : early growth stage (before 14.5 Plant age in leaf number), middle growth stage (13.5 to 17.0 plant age in leaf number), and late growth stage (17.0 plant age in leaf number to maturity). The number of crown root primordia and emerged crown roots, root dry weight, and some constituents of top per hill were investigated. In the early growth stage, root dry weight per hill increased as nitrogen concentration increased, and correlated rather with the root number than with the mean dry weight of root axis. In the middle growth stage, root dry weight per hill decreased with the increment of the nitrogen rate, especially in the roots of the upper three nodes. In the late growth stage, root growth was largely affected by nitrogen application during the middle growth stage, while little effect of the nitrogen rate was observed in root dry weight. The increment of root dry weight per hill in the middle growth stage was the largest followed by that of the early growth stage, and only a slight increment was observed in the late growth stage. High positive correlations were observed between the number of crown root primordia and the concentration of nitrogen of the top per hill at the crown root primordia differentiation time, and between the emergence rate of the crown roots and the concentration of starch at the time of emergence. From these results, it is believed that nitrogen and carbohydrate are the factors that promote the differentiation of crown root primordia and the emergence of crown roots, respectively.