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To elucidate a suitable fertilizer application method for early sowing of winter type wheat Iwainodaichi, we investigated the effect of late topdressing on growth and grain yield over a 4 year period. Late top dressing decreased the total dry weight at the fl owering stage, but did not affect the morphological characters of leaf and stem, leaf area index (LAI) at fl owering stage and sink size. The grain yield was increased by late topdressing in 2 of the 4 years as compared with early or standard topdressing. In those 2 years, late topdressing did not affect the number of fl orets per spike but increased the number of grains per spike and SPAD value during ripening. In the plant with late topdressing, sink size and grain yield were larger in Iwainodaichi than in Chikugoizumi in 3 of the 4 years. This seems to be attributed to the larger potential sink size of Iwainodaichi. These results suggest that in order to get a high grain yield of wheat sown early, large sink size and high SPAD value during ripening are required, and in this respect, late topdressing is advantageous for Iwainodaichi.

: To elucidate the suitable seeding rate for early sowing of winter type wheat Iwainodaichi, the effect of sparse sowing on growth and grain yield was investigated for 2 years. Although the number of shoots, leaf area index (LAI) and total dry weight at maximum tiller stage were smaller in sparse sowing than in standard sowing, LAI, total dry weight and sink size at fl owering stage with sparse sowing were not different from those in standard sowing. These results show that sparse sowing did not affect the yield potential at the fl owering stage as compared with the standard sowing. Sparse sowing did not affect culm length, the number of internode and the length of each internode, but increased the number of spikelets and fl orets per spike, leaf length and width, and diameter of internode. During ripening, SPAD value was higher in sparse sowing. The number of spikes per area was smaller in sparse sowing but the number of grains per spike was larger in sparse sowing than those in standard sowing, and thousand grain weight was not different between sparse and standard sowing. As a result, grain yield in sparse sowing was similar to or more than that in standard sowing. Sparse sowing, also, gave high lodging resistance. These results suggest that sparse sowing is superior to standard sowing in early sowing of Iwainodaichi.

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