Abstract
We examined the nitrogen topdressing timing 15N labeled ammonium sulfate for increasing grain protein content above 12% in the wheat cultivar for Chinese noodles ‘ChikushiW2gou’. The topdressing at the full heading and 7 days later stably increased grain protein content above 12% regardless of the year. Also the number of days from full heading to topdressing correlated negatively with the ratio of nitrogen content of ripe grain derived from topdressing to topdressing nitrogen amount (nitrogen availability) and total nitrogen contents in ripe grain (nitrogen contribution ratio). Topdressing at full heading or 7 days later resulted in almost 60% of the nitrogen availability and 30% of nitrogen contribution ratio. The nitrogen availability in topdressing at 14 days after full heading time was affected by the rain after the topdressing. Topdressing at 21 or 28 days after heading hardly contributed to protein accumulation, resulting in a protein content of ripe grain of less than 12%. In this study, we concluded that the appropriate time of nitrogen topdressing for increasing grain protein content above 12% in “ChikushiW2gou” is from full heading to 7 days later, where the availability of topdressed nitrogen is more than 60% and the contribution ratio of topdressed nitrogen to grain protein is above 30%.
