Field measurement of CO₂ assimilation rate in plant leaves is done by clumping the leaf with a chamber and waiting a few minutes for each measurement using special carry on equipment. This costly and labor-intensive method has hindered the acquisition of large-scale data on photosynthesis of field grown plants. We created MIC-100, a new closed-type photosynthesis measurement device with a novel infrared gas analyzer cell that enables high-throughput measurement of leaf CO₂ assimilation rate. The measurement time required for a single leaf using MIC-100 was reduced to one-seventh that of conventional open system devices, while similar values were obtained for the same leaf under high-light conditions. We also created two supporting technologies to obtain rapid photosynthesis measurements for field-grown rice: the upper-limb assist suit and the leaf area measurement system with a commercial document scanner. These systems enabled large-scale surveys of the natural genetic variation and ontogenetic changes among diverse sets of rice accessions. MIC-100 and the related systems will be useful for physiological studies with many other plant species and for growth surveys in the agricultural fields.

This study was conducted to elucidate a suitable controlled release fertilizer and to develop a fertilizing style in which topdressing is limited to once for two-rowed barley for food. Two types of ¹⁵N-labeled linear type polymer-coated urea with different nitrogen elution periods (LP20 and LP30) were tested to elucidate the controlled release fertilizer effect suitable for a labor-saving fertilization method. We investigated the grain nitrogen content (GNC) and fertilizer nitrogen utilization rate (FNUR) of LP20 and LP30 at the full heading time and maturity stages in barley plants. At the full heading stage, GNC and FNUR were significantly higher in LP20 than in LP30. However, at the maturity stage, there was no difference between the two fertilizer types. Because the amount of nitrogen content at the full heading time affects the yield, it was judged that LP20 is suitable for the labor-saving fertilization of barley. Furthermore, the growth, yield, and suitability for the milling of barley via one-time topdressing system using LP20 were investigated. As a result, compared with the conventional plot, the maturity stage was one day later, the lodging index was the same, the yield was 5% higher, and the pealing aptitude was the same. Based on these findings, the applying mixed fertilizers composed of LP20 and fast-acting fertilizers at the tillering fertilizer application is a labor-saving fertilization method that can omit topdressing at the panicle formation stage.

In direct seeding of non-coated rice seeds with a puddling seeder, seeds need to be stored to avoid overlapping of the timing of seed pretreatment with that of field preparation work. Assuming that seeds may be stored at room temperature for short-term storage but require lower temperatures for long-term storage, the optimum temperature for low temperature storage was investigated for both pre-germinated and root-elongated seeds. Seeds were incubated at 5°C, 10°C, and 15°C for 0, 5, 10, 14, and 21 days, before seeded in a growth cabinet to assess seedling emergence and growth. Compared to 5°C and 15°C, emergence and growth rates were not lowered in seeds stored at 10°C for more than 14 days. Therefore, 10°C was considered suitable for long-term storage. Then, both pre-germinated and root-elongated seeds were stored at room temperature (15.9°C–22.4°C) for 0 (control), 5, 10, and 15 days, and at 10°C for 20 to 29 days. When compared to the control, no significant differences were found in initial growth, establishment, and heading date of seeds stored at room temperature for 5 to 15 days and seeds stored at 10°C for 20 days. These results suggest that both pre-germinated and root-elongated seeds can be stored for up to 15 days at room temperature and up to 20 days at 10°C.

The occurrence of Phytophthora root and stem rot (PRSR) varies significantly depending on the presence or absence of wounds on the soybean hypocotyl as well as waterlogging and excessive soil moisture. However, the actual situation of wound incidence in the field and factors that cause wounds are not clear. To gain insight into the mechanism of PRSR in the field, we investigated the frequency and depth of naturally occurring wounds on soybean stems, and examined the factors that increase wound development. Wounds were observed in 1.7 to 7.1% of the individuals in the Kyoto University research field (Kizu farm in Kizugawa City, Kyoto farm in Kyoto City). The mean depth of wounds was 224 ± 193 µm (standard deviation), and 62% of the wounds were greater than 145 µm, which could accelerate PRSR occurrence significantly. Wounds were observed more in Kizu farm than in Kyoto farm, and the percentage of wounds in Kizu farm decreased with fine harrowing before sowing. Plants grown from seeds with wrinkle, seedcoat cracking, or seedcoat puffing tended to have more wounds. These results indicate that wounds of a depth that could promote PRSR occur with a considerable frequency under natural conditions, and that seed and sowing conditions are related to wound incidence. Further investigation is needed to determine the extent to which natural wounds contribute to PRSR occurrence.

The phenological development model for transplanting rice as a function of temperature and photoperiod from emergence date (referred to as standard model) could not predict heading date accurately in direct-seeded rice which starts cultivation at sowing. Therefore, we developed a novel phenological development model for dry direct-seeded rice using phenology data of cultivars ‘Fusakogane’, ‘Koshihikari’ and ‘Akidawara’. First, from sowing to emergence, we compared the accuracy of emergence date predicted using six developmental rate (DVR) equations with different structures. A logistic model which showed relatively high DVRs at a low temperature could provide better prediction in all three cultivars. Second, in the prediction of heading date using the training data, the models from the predicted emergence date obtained from the above DVR equations and from the date reached at 100 and 120°C day on cumulative daily mean temperature assuming the water absorption process showed higher accuracy than the standard model calculated from the sowing date. From the prediction of heading date by these developed models and test data, the model divided at the predicted emergence date showed higher accuracy than the standard model calculated from the sowing date in ‘Koshihikari’. In ‘Fusakogane’ and ‘Akidawara’, the model considering the water absorption process showed relatively high accuracy. Since the model using the observed emergence date gave the highest accuracy in all three cultivars, improvement of prediction accuracy of emergence date could improve the accuracy of the prediction of heading date.

We examined the effects of the occurrence of damaged seeds on the number of seeds per pod and seed yield of soybean sown in June (June plot) and July (July plot) in Kanagawa Prefecture, Japan. Field experiments were conducted at the experimental farm of the College of Bioresource Sciences, Nihon University (Fujisawa City, Kanagawa Prefecture) in 2018 and 2021. The cultivars used in this experiment were ‘Satonohohoemi’, ‘Enrei’, and ‘Tachinagaha’ in 2018 and ‘Enrei’ in 2021. The above-ground growth at the beginning of the seed filling stage was more vigorous in June plots than in July plots in both years and all cultivars. However, the percentage of putrefied seeds at the maturity stage was higher in the June plot than in the July plot. The number of seeds per pod and the number of pods per node in the June plot were lower than those in the July plot, and there was no difference in seed yield among the plots. Moreover, the temperature during the seed filling stage in the June plot was higher than that in the July plot, and the field condition in the June plot was more susceptible to pathogen occurrence. From the above results, there was no difference in seed yield between the June and July plots in Kanagawa Prefecture. Moreover, it will be possible to decrease the amount of pesticide applied by delaying the date of sowing to July sowing in Kanagawa Prefecture.