Nitrogen application method for improving yield and protein content of "Kitanokaori", a new variety of winter wheat [Triticum aestivum] for bread use in Hokkaido [Japan]

"Kitanokaori" is a new variety of winter wheat (Triticum aestivum L.) for bread use bred at the National Agricultural Research Center for Hokkaido Region. The grain protein content of wheat for bread use should be higher than 120 g kg-1. Much nitrogen application is necessary to obtain high grain protein content. Therefore, it is necessary to determine the optimum amount of nitrogen to obtain the required protein content and to prevent nitrogen from remaining in the soil. Field experiments were conducted for four years from sowing in 2000 to study the effect of the amount of nitrogen and the time of top-dressing. In the experiment in which sowing was carried out in 2003, nitrogen treatments were 40, 40-60, 40-60-0-60, 40-60-0-60-30, 40-60-0-60-60, 40-60-60-60, 40-60-60-60-30, 40-60-60-60-60, 40-60-30-30, 40-60-30-30-30 and 40-60-30-30-60 (each value showing the amount of applied nitrogen at sowing-re-growing stage-panicle formation stage-flag leaf stage-full heading stage, kg ha-1). The experiments were conducted in Andosol, which has moderate nitrogen fertility, and in Histosol, which is fertile soil. Kitanokaori did not lodge with high-applied nitrogen, and both yield and protein content increased with an increase in applied nitrogen. In a moderate climate, Kitanokaori reached a protein content of 120 g kg-l when the amount of absorbed nitrogen was about 190 kg ha-1, and the yield was about 7.8 Mg ha-1 at that time. The top-dressing at the panicle formation stage was effective to raise the yield and the top-dressing at the full heading stage was effective to raise the grain protein content. It is recommended that the amount of applied nitrogen should be 160 kg ha-1 until the flag leaf stage, and additional nitrogen should be applied at the full heading stage to obtain a grain protein content of more than 120 g k-1. Nutritional diagnosis at the full heading stage will be necessary to determine whether more nitrogen is needed to achieve the required protein content. When the amount of total applied nitrogen did not exceed 220 kg ha-1, the amount of absorbed nitrogen was over 90% of applied nitrogen, and there was little inorganic nitrogen in the soil after harvest. Therefore, it was considered that the residue of nitrogen in the soil was small within 220 kg ha-1 of nitrogen application, while favorable growth and high yield were obtained.