Effects of Nitrogen Topdressing Stages on the Starch Granule Size Distribution in Wheat Grains under Different Nitrogen Rates

Purpose The objective of this study was to investigate the effects of nitrogen topdressing on the starch granule size distribution in wheat grains.

Method Two wheat cultivars, Aikang 58 (A58) and Shannong 22 (S22) were used in this study. A fertilizer experiment was designed with different nitrogen topdressing stages under two nitrogen rates of 120 kg/hm² and 240 kg/hm².

Result The starch content in grain of nitrogen topdressing at the jointing stage was significantly lower than that of nitrogen topdressing at the returning green stage (P<0.05), but the starch accumulation in grain of nitrogen topdressing at the jointing stage was significantly higher than that of nitrogen topdressing at the returning green stage under the same nitrogen rate (P<0.05). Compared with the treatment of nitrogen topdressing at the returning green stage, the average particle size of starch granules at jointing stage decreased, meanwhile the volume and surface area percentage of B type starch granules increased observably at the nitrogen rate of 120 kg/hm². The average particle size of starch granules of nitrogen topdressing at jointing stage significantly increased (P<0.05), meanwhile the volume and surface area percentage of A type starch granules increased observably at the nitrogen rate of 240 kg/hm². There was no significant effect of nitrogen rate and nitrogen topdressing stage on the number distribution of starch granules in wheat grains (P>0.05).

Conclusion The delay of nitrogen topdressing increased the volume percentage of B type starch granules under the low nitrogen rate, and hence benefit to the accumulation of starch in grains. The delay of nitrogen topdressing was beneficial to the accumulation of A type starch granules in grains, and hence benefit to the accumulation of starch under the suitable nitrogen rate.