Growth and Yield of Rice in Andosol by Dry Direct Seeding Cultivation using Plowing and Compaction in a Cold Climate Region of Japan

In a cold climate region of Japan, we investigated the growth and yield of rice in Andosol by dry direct seeding cultivation using plowing and compaction (DS) compared with transplanting rice (TR). Leaf number and plant length were lower in DS than in TR at the early growth stage. SPAD value (leaf color) was lower in DS than in TR after the tillering stage. However, the aboveground dry weight in DS was not significantly different from that in TR. Although there was no significant difference in the number of panicles, the percentage of ripened grain was lower in DS than in TR and the number of spikelets per panicle was reduced in DS. The grain yield was lower in DS than in TR, and the grain yield per unit area was significantly correlated with the total number of spikelets. Moreover, the total number of spikelets was significantly correlated with the number of panicles. There were positive correlations between the number of spikelets per panicle and the SPAD value of the panicle formation and meiosis stages. These results suggest that to obtain a yield in DS similar to that in TR it is important to maintain SPAD values at the panicle formation and meiosis stages, as well as to maintain the number of panicles. Moreover, it is necessary to employ cultivation methods that increase the number of spikelets per panicle and the percentage of ripened grain.