Early planting contributed to increased soybean yields in the U.S. Because a double-cropping system dominates in southwestern Japan, early planting is not performed; it is thus unclear how much the yield potential could be increased by early planting. To address this question, we planted seven U.S. and five Japanese cultivars on around 20 May (early planting), measured the agronomic traits, including yield, yield components, and oil and protein contents, and compared these traits with those of the same cultivars planted on around 20 July (normal planting). In the early planting, the yields of the U.S. cultivars were 322-453 g m −2, whereas the highest yield among the Japanese cultivars was only 315 g m , and oil contents, but negatively correlated with the sterile pod rate, 100 seed weight and protein content. In the early planting, the U.S. cultivars had greater pods m −2 , seeds pod −1 and oil content and less sterile pod rate, 100-seed weight, and protein content than the Japanese cultivars. These results suggest that early planting can increase the yield in southwestern Japan, if cultivars with agronomic traits observed in the U.S. cultivars of this study are grown.
Forage rice (Oryza sativa L.) has attracted attention as a potential crop in Japan, but no optimal agricultural product system has been extensively established. The objective of this study was to determine the effects of cultivar (high‐yielding indica cultivar Hokuriku 193, high‐yielding indica‐japonica hybrid cultivar Mizuhochikara, or standard japonica cultivar Akisayaka) and sowing pattern (broadcast or drilling) on grain yield using a new sowing machine for a well‐drained paddy field. Hokuriku 193 had the highest grain yields. Hokuriku 193 and Mizuhochikara had much more spikelets than Akisayaka. Hokuriku 193 and Akisayaka had a higher percentage of filled spikelets than Mizuhochikara. At full heading, Hokuriku 193 had the highest nonstructural carbohydrate (NSC) amount. Thus, the high NSC amount of Hokuriku 193 supported a high grain yield and high percentage of filled spikelets in spite of its very many spikelets. Broadcast gave a higher rough grain yield, grain yield, and number of panicles than that of drilling, but it had no effect on the percentage of filled spikelets or the 1000‐grain weight. At full heading, broadcast gave a higher NSC amount than drilling. Therefore, broadcast of high‐yielding indica or indica‐japonica hybrid cultivars might increase grain yield, in spite of its very high panicle number, without decreasing the percentage of filled spikelets or the 1000‐grain weight by increasing the NSC amount at full heading.
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