Sunflower has been cultivated as a decorative plant in subtropical Okinawa; however, the optimal sowing time and suitable cultivar for oil production have not yet been determined. In this study, six cultivars were grown in four seasons and the growth and yield characteristics were examined to determine the optimal sowing time and suitable cultivar in the region. The effective accumulated temperature from emergence to flowering was 1000–1100°C, and some cultivars showed lower values under short day conditions in autumn and winter sowings. Sunflower can be grown year round in Okinawa because the temperature in winter is above 10°C. However, it is important to consider lodging due to typhoons during the seed harvesting season in sunflower sown in spring or summer (July–October). The results revealed that high growth rates before and after flowering were important for obtaining high yields in sunflower sown in autumn and winter; however, the yield was lowered by decreased biomass at flowering and reduced number of seeds caused by high temperatures in spring and summer. Therefore, the optimum sowing time to harvest sunflower seed for oil production was considered to be from the beginning of October to the beginning of February. By using cultivars that are photosensitive and have a high growth rate after flowering, a high seed yield of 300 kg 10 a⁻¹ and high oil yield of 110 kg 10 a⁻¹ could be obtained.

Although soybean production in the Tohoku region of Japan may be negatively affected by drought due to climate change, it is not clear how the production is affected by drought. In this study, the FAO56 evapotranspiration model was applied to an experimental field at the Kariwano campus of Tohoku Agricultural Research Center by using agrometeorological grid square data, and correlations of soybean yield and 100-seeds weight in a long-term continuous performance test over 33 years at the site with meteorological factors and soil volumetric water content (SWC) were analyzed. By using soil physic parameters such as field capacity, permanent wilting point and effective root layer, the time-course change of SWC during the growing season in the soybean field was well predicted by the FAO56 model. The seed yield and 100-seeds weight over 33 years showed significant negative correlations with air temperature and SWC averaged during August. Furthermore, the partial correlation between seed yield and average temperature of August was insignificant when SWC was used as a control variable, indicating that the yearly variations of seed yield and 100-seeds weight are mainly explained by the variation of SWC averaged during August. This means that drought caused the reduction of seed yield and 100-seeds weight. Thus, it was suggested that the FAO56 model combined with agrometeorological grid square data was effective for assessing accurately the effect of drought on soybean production in Japan.

Target growth of organically grown rice was to produce yields of 550–600 g m^–2. After clarifying the nitrogen uptake rate and nitrogen mineralization characteristics of organic fertilizer, we examined the influence that topdressing had on yield determined based on the growth diagnosis. The tiller number of organically grown rice was smaller than that of conventionally grown rice throughout the growth period. However, the percentage of productive tillers in organically grown rice was higher than that in conventionally grown rice. The panicle number in organically grown rice was almost the same as that in conventionally grown rice. Furthermore, as compared with conventionally grown rice, the leaf color score of organically grown rice was lower until the beginning of July and was higher after the panicle formation stage. Rate of nitrogen uptake from five types of organic fertilizers ranged from 40 to 80%, with an average of 69%. Kinetics analysis showed that the nitrogen mineralization rate of organic fertilizer was 20 to 60%, and the rate showed a significant positive correlation with the nitrogen uptake rate. Topdressing based on the growth diagnosis produced the target number of panicles and color score in organically grown rice to obtain the target yield of 550–600 g m^–2. Thus, the target grain yield can be obtained by topdressing determined based on the growth diagnosis in organically grown rice.

In order to establish a cultivation method to obtain a stable yield of black-seeded soybean ‘Tambaguro’ for Edamame (green soybean) cv. ‘Murasakizukin 2’ in Kyoto prefecture,we investigated the effect of sowing time, planting density, fertilizer type and amount of nitrogen topdressing at the molding time on pod yield of ‘Murasakizukin’. The harvesting time was shifted by changing sowing time, but the shift of harvesting time was shorter than that of sowing time. The optimal sowing time was from mid to late June because by delaying the sowing time, the havesting time was shifted to almost the same time as that in ‘Murasakizukin’, and by advancing sowing time, the yield and the ratio of pods more than 11 mm in thickness to total pod weight was decreased. The total number of pods and total pod weight per m² increased with increasing planting density, but the weight ratio of pods more than 11 mm in thickness to that of total pods was decreased by decreasing the hill distance to 20 cm. Therefore, the planting density suitable for ‘Murasakizukin 2’ was considered to be 30–40 cm in hill distance and 90 cm in row spacing. Top dressing with 40-day sigmoidial-releasing type coated urea (CUS40), controlled release fertilizer, at the molding time, increased the total pod weight and weight of pods more than 11 mm in thickness in a low yield year, such as 2008, but not in a high yield year such as 2009.