Climate warming may reduce soybean yield due to the increase in temperature during the reproductive growth period. The temperature during the reproductive growth period of the late-maturing cultivars is seasonally lower. However, there may be inter-varietal differences among these cultivars in the yield response to the increase in temperature. The major late-maturing cultivars, 'Fukuyutaka' and 'Tanbaguro', were grown in a temperature-gradient chamber, and subjected to the ambient temperature in the early growth period. Then temperature-gradient treatment was given from shortly before flowering to the beginning of seed filling. Average temperatures during the treatment period ranged from 25.1–27.1°C in 2014 and 25.6–29.1°C in 2015 The difference between the high-temperature and control plots was 2.0C° in 2014 and 3.3C° in 2015. High-temperature treatment decreased the seed per pod and hundred-seed weight in both varieties, but decreased the harvest index (HI) to a greater extent in 'Tanbaguro' than in 'Fukuyutaka'. Only in 'Tanbaguro', did the high-temperature treatment reduce the percentage of fertilized embryo sacs and seed growth rate which may have contributed to the greater reduction in HI,. The photosynthetic rate decreased after the high-temperature treatment. These results suggest that in late-maturing soybean cultivars HI and photosynthetic activity decrease with a 2 to 3.3 degree increase in temperature, and that there is a cultivar difference in the extent of HI decrease.

Imbibition damage leads to poor early growth in soybean seeds exposed to excessive soil moisture. Rapid water imbibition hampers germination and emergence, even before cotyledons are not sufficiently swollen. Therefore, interindividual variations in amount of water absorption, localization of absorbed water, and morphology of seeds were examined to clarify the mechanism underlying imbibition damage. Furthermore, the relationship between water absorption and plant emergence was examined. Seeds of cultivar “Satonohohoemi” were soaked in water for 10–90 minutes. During soaking, the seed morphology was examined, water intake was quantified, and magnetic resonance images were captured. After seeds were soaked, seed germination and plant emergence rates were assessed. The soaked seeds were classified as normal and over-absorbed seeds. The over-absorbed seeds were further classified into those without a gap between the cotyledons (CL seeds) and those with a gap (OP seeds). The unimpaired seed rates of normal, CL, and OP seeds were 98.3%, 66.7%, and 20.0% after 10 minutes of soaking treatment, the difference being significant. Plant emergence rates of normal, CL, and OP seeds were 93.3%, 53.3%, and 23.3%. Wide interindividual variations in amount of water absorption and morphological change were observed in the same lot of seeds. In addition, water intrusion between the cotyledons was suggested to affect the germination and emergence.

Since 2000, wheat yield per 10 a in Northern Kyushu was about 500 kg in 2007–2008, less than 300 kg in 2010–2011, and about 500 kg again in 2021–2022. Therefore, the effect of climatic conditions on wheat yield in Northern Kyushu was analyzed in detail on a daily basis for 23 years from 2000 to 2022. Three significant weather conditions, namely precipitation from December 10 to 21 and April 12 to 23, and sunshine duration from February 17 to March 1, were adopted as explanatory variables at the 5% level. The standard partial regression coefficients were –0.357 for precipitation from December 10 to 21, –0.433 for precipitation from April 12 to 23, and 0.407 for sunshine hours from February 17 to March 1, with a degree of freedom adjusted multiple correlation coefficient of 0.826 and coefficient of determination of 0.682. Precipitation from December 10–21 decreased the number of ears and grains per square meter, and precipitation from April 12–23 decreased the thousand-grain weight and limited sink size, respectively. Sunshine hours from February 17 to March 1 appeared to be related to sink and source size determination because this is the jointing stage when internode elongation is most active. Avoiding sink size limitation due to precipitation at two specific times of the year, December and April, is important to achieve stable and high yields in wheat in northern Kyushu.

The nutrient index value conventionally used for estimating nitrogen uptake of crop, requires much effort for measurements in the field and calculation. To develop a labor-saving crop growth diagnosis method, we compared the estimation accuracy of dry matter weight and nitrogen uptake of the above-ground part in the paddy rice ‘Niji-no-Kirameki’ using six vegetation indices, calculated from the measurement values obtained with portable spectrometer. Normalized difference vegetation index (NDVI) and simple ratio (SR) tended to saturate with rice growth. Above-ground dry matter weight was estimated with the highest accuracy by green NDVI (GNDVI) at the panicle formation stage, and by normalized difference red-edge index (NDRE) during the heading stage. Chlorophyll index (CI)_green had the highest accuracy in estimating nitrogen uptake at the panicle formation stage. At the heading stage, nitrogen uptake was estimated with the highest accuracy using CI_red-edge. Indices using the ratio of two wavebands were more suitable for estimating nitrogen uptake than the normalized difference indices. Nitrogen uptake could be estimated using CI_green with high accuracy during the panicle formation stage. Since a high correlation was observed between CI_green and spikelet number per square meter within each nitrogen topdressing treatment, these vegetation indices measured at the panicle formation stage with the portable spectrometer, could be used to determine the amount of topdressing nitrogen to achieve the target spikelet number per square meter.

To improve the mechanical harvestability of black soybean 'Tambaguro' edamame (green soybean) cultivars bred in Kyoto Prefecture, we investigated the effects of different cell plug trays for seeding and seedling raising duration on the lower internode length, which affects the height of lower epiphytic pods, during the two-year period from 2021 to 2022. In 2021, we analyzed the effect of three factors in a total of 16 experimental areas. We used the four varieties: 'Natsudoritambaguro 2', 'Murasakizukin 2', 'Murasakizukin 3' and 'Shintambaguro', 128-cell and 200-cell plug trays, seedlings raising duration of 10 and 14 days and the analysis of variance (ANOVA). At the time of transplanting, the effects of all factors and interactions were significant for seedling main stem length, whereas only the effect of varieties was significant for hypocotyl length. At harvest, the effects of variety and seedling raising duration and the interaction between variety and seedling raising duration were significant for both first and second internode lengths. In 2022, two varieties: 'Natsudoritambaguro 2' and 'Murasakizukin 2', four growth methods for raising seedlings using different combinations of cell plug trays and seedling raising durations were investigated. The two factors and eight experimental areas analyzed by the ANOVA. As in 2021, the first and second internode lengths increased significantly at harvest with the increase in seedling raising duration. On the other hand, the effects of cell plug tray difference on the main stem were limited to the seedling growth.