Influence of Daily Temperature Range on Seedling Emergence and Establishment and Estimation of Early Sowing Limits in Directly Seeded Rice under Submerged Conditions in a Cold-climate Area (Hokuriku Region, Japan)

Although direct seeding in rice cultivation has potential for labor- and cost-saving benefits in comparison with transplanting, the latter remains the predominant method in Japan because the former shows some weaknesses in seedling emergence and establishment, and in lodging resistance. We therefore set out to compare seedling emergence and establishment in direct seeding culture under different daily temperature ranges. We compared a windbreak-shielded and control plot using pot-grown plants under outdoor conditions. In the windbreak plot, which was subject to a high maximum temperature and wide daily temperature range, seedling emergence and establishment rates were higher than in the control plot. Additionally, detailed laboratory tests revealed that the influence of post-seeding daily temperature ranges on seedling emergence was greater under low-temperature than high-temperature conditions. Moreover, changes with time in the measured values for seedling emergence rates and those estimated using the Arrhenius equation were approximately the same. We also used maximum and minimum temperatures to calculate early sowing limits for direct seeding of paddy rice at different locations in the Hokuriku region; previously, daily mean temperature has been used as the basis of early sowing limit calculations. The two calculation methods showed different early sowing limits. Moreover, early sowing limits based on daily temperature ranges were observed to occur earlier in the inland and later in the coastal area when compared with early sowing limits based on daily mean temperature.