Effect of nitrogen topdressing at jointing stage or anthesis on the kernel weight of Hokkadido-bred wheat cultivar 'Haruyutaka' in warm parts of Western Japan.

摘要

We attempted to increase the kernel weight of Hokkaido-bred wheat cv. Haruyutaka by increasing the net assimilation rate (NAR) without inducing an over-luxuriant canopy during the ripening period. Nitrogen was applied as topdressing during jointing in 1999/2000 and during anthesis in 2000/2001 using the Kyushu-bred rice cv. Daichinominori as a control. However, kernel weight of either cultivar did not increase with topdressing in either season. In addition, topdressing in cv. Haruyutaka increased neither the NAR during the ripening period nor the crop growth rate (CGR). On the other hand, the amount of nitrogen in the whole plant increased from anthesis to maturity only in plants supplied with nitrogen topdressing. The amount of nitrogen in the kernels increased rapidly from the milk ripe stage to maturity in both plots with and without topdressing in both cultivars, and that at maturity accounted for most of the nitrogen in the whole plant. However, the nitrogen topdressing significantly increased the nitrogen content in the leaf blades at the milk ripe stage and that in the kernels at maturity in both cultivars. These results suggested that nitrogen topdressing increased the nitrogen contents in the whole plant, and increased the translocation of nitrogen into the kernel resulting in an increased nitrogen content of kernel. However, kernel weight did not increase with topdressing; neither did NAR nor CGR. We suppose that this is because the respiration rate in leaves increased due to the over-luxuriant canopy caused by the topdressing, especially in cv. Haruyutaka.