Delayed early growth, mainly due to excess water stress, can be a critical cause of low soybean yield in Japan. However, effective treatment for improving early growth, such as drainage improvement, would be difficult to conduct in all the fields, especially in those covering hundreds of hectares of land. Under such situations, the sowing date can differ among fields and the plant population may vary with the number of deaths. Therefore, we aimed to develop a method for scoring early growth in soybean available under different sowing dates and plant populations. First, the parameters of the leaf area model in a cultivar ‘Ryuho’ were acquired from the cultivation at 3 planting densities and 4 sowings, which enabled calculation of leaf area based on the accumulated temperature. The growth score was calculated as the ratio of the remotely-sensed leaf area to the values calculated from the leaf area development model. Second, the formula for calculating days from sowing to the start of the leaf area model was acquired from the experiment of 5 sowings. Finally, the relationship between the growth score and final grain yield was evaluated in the actual farmer’s field, where there was a significant correlation (r = 0.70, p < 0.01). Adjustment of our method to other cultivars, locations, and cultivating methods is a future task for realizing stable production of soybean in the farmer’s fields.

A high steely grain rate lowers the quality of hulless barley. However, the mechanism of the occurrence of steely grain is not clear. In this study, we investigated the occurrence of steely grains in each tiller and each spikelet position and analyzed the related causes. Steely grains occurred more frequently at higher nodal tillers and lower spikelet position. Interestingly, the steely grain rate was correlated positively with the flowering date. Therefore, the difference in the steely grain rate among tillers is attributed to the variation in flowering date. The steely grain rate markedly decreased during the later ripening stage at the same time as rainfall. Also, by soaking in water the grains that had a moisture rate under 22%, the steely rate decreased, which suggested that water absorption of grains by rainfall was involved in the decrease. On the other hand, the steely grain rate did not decrease when the grains with more than 30% moisture were soaked. The period from flowering to rainfall was shorter for the grains at the higher nodal tillers and the steely grain rate was not decreased by soaking because of the high water content of the grains. In addition, it was considered that the grains in the lower position of the panicle had a higher water content than those in the higher position at 35 to 40 days after flowering, resulting in the frequent occurrence of steely grains.

In the Hokuriku region of Japan, sterile spikelets of barley are known to occur in the lower part of the ear, and this is considered one of the reasons for the reduced yields in this region. The ear formation period in barley begins during winter. In areas subject to snowfall, the environment during ear formation varies greatly depending on the presence or absence of snow cover. This study aimed to confirm that the ear characteristics of barley plants grown in different environments differ at maturity and to examine the factors involved in sterile spikelet formation, focusing on the maximum number of spikelet primordia and the spikelet survival rate. The test was conducted in fields in the cities of Joetsu and Morioka over three cropping seasons. Ears of barley grown in the six different environments differed significantly in spike morphology, such as in the total numbers of spikelets and lower sterile spikelets and the maximum number of spikelet primordia. The number of lower sterile spikelets was higher in Joetsu than in Morioka in all three years. The maximum number of spikelet primordia was significantly positively correlated with the cumulative temperature in the spikelet-differentiation period and negatively correlated with the rate of spikelet differentiation. The spikelet survival rate was negatively correlated with the maximum number of spikelet primordia. Higher temperatures during the ear-formation period increased the maximum number of ear primordia but decreased the spikelet survival rate, resulting in the formation of ears with greater numbers of lower sterile spikelets.

In Japan, farmland accumulation has led to the development of large-scale farms that manage numerous soybean fields together. Excess-moisture injury during the early growth stages of soybean cultivation can reduce the yield. Thus, to enhance the soybean productivity, we need to identify the fields where soybean growth is severely suppressed through satellite-based sensing and constructing drainage. However, weather conditions complicate satellite-based sensing. The early growth stages of soybeans coincide with the rainy season, and cloud cover hinders satellite-based sensing. This study evaluated the practicality of sensing vegetation sensing using Sentinel-2, PlanetScope, and Sentinel-1 satellites. Investigations were conducted from 2021 to 2023 to compare the soybean coverage rate estimation accuracy and the number of fields where sensing was successful. The results indicate that Sentinel-2 and PlanetScope accurately estimate the coverage rate. However, the number of fields in which these satellites were used for sensing successfully varied annually. Conversely, although Sentinel-1 had lower accuracy in estimating coverage rates, Sentinel-1 allowed for assessment across more fields than Sentinel-2. According to our results, effective utilization of satellite-based sensing on large-scale farms requires improvement of the success rate of sensing using Sentinel-2 and PlanetScope or enhancing the accuracy of cover rate estimation using Sentinel-1.

We investigated the yield increase under twin-row cultivation of soybean cultivars differing in stem growth habit and high-yield factors among yield components measured in two consecutive years. ‘Toyomusume’ (determinate type) and ‘Brock’ (indeterminate type), both medium-maturing cultivars (MGI), were sown at five planting densities ranging from 8.3 to 55.6 plants/m² with conventional row (CR) and twin-row (TR) planting patterns. The seed yield for both cultivars in the 2 years was TR ≧ CR at all planting densities. The mean yield increase of TR vs CR for Toyomusume and Brock was estimated 107% and 111%, respectively, for the 2-year period. A quadratic regression equation best fit the relationship between planting density and seed yield for both cultivars and planting patterns. The optimal planting density with the highest yield increase was 27–31 plants/m², The yield increase at the optimal planting density for Toyomusume and Brock was 110% and 120%, respectively, and it tended to be higher for the indeterminate cultivar than the determinate cultivar. The greater yield increase of indeterminate cultivars with dense planting reflected the suppression of the decrease in branch yield associated with dense planting. This suppression of the decrease in branch yield was thought to be due to the increase in the number of branches and the small decrease in the number of pods per node on each branch with dense planting.

In the Tohoku region, the cultivation of maize in upland fields converted from paddy fields benefits significantly from plowing, and proved to be an effective method for the farmers. This study evaluated seeder settings for achieving a plant density of 7000 plants 10 a^-1, yield-related traits, soil pulverization rates, and seedling establishment rates to obtain a combined yield of 800 kg 10 a^-1 under plowing conditions in converted paddy fields in central Iwate Prefecture, Japan. A density of 7000 plants 10 a^-1 was achieved by increasing the setting of pneumatic seeders by approximately 5% above the target density. The desired combined yield of 800 kg 10 a^-1 was obtained only in fields with good drainage. The crop yield per unit area should be set at 900 g m^-2, requiring 3161 kernels m^-2, a seedling establishment rate of 91%, and a soil pulverization rate of at least 66% to achieve a combined yield of 800 kg 10 a^-1 in a well-drained. These results indicate that achievement of a combined yield of 800 kg 10 a^-1 with plowing in converted paddy fields depends on sufficient seedling establishment rate and soil pulverization rate, with adequate drainage ensured by appropriate measures. Furthermore, the planting density setting of the seeding machine must exceed the target density to ensure optimal planting density.

To expand the cultivars applicable as a soybean crop model, we evaluated the accuracy of the model predicted yield for three cultivars: ‘Yukihomare’, ‘Satonohohoemi’ and ‘Sachiyutaka’. Varietal differences were incorporated into the genetic parameters of the phenological model as differences in earliness. The five major domestic cultivars, including the three newly applied cultivars, were grown by sowing in 2017 and 2018 in Tsukubamirai, Ibaraki, Japan. We measured the above-ground biomass at the beginning of seed filling (R5), as well as the seed yield and stem and pod biomass at maturity (R8) to evaluate the model outputs. The average of canopy cover ratio and radiation use efficiency from germination (VE) to R5 and the harvest index at R8 were also calculated. The relative root mean square error (rRMSE) for the seed yield of the three newly applied cultivars in 2017 was 15.8%, which is more accurate than previous calculations. However, the model overestimated the above-ground biomass at R5 and underestimated the harvest index at R8 for ‘Yukihomare’. In 2018, when there was little rainfall during the soybean growing period, the model severely overestimated the seed yield, with an rRMSE of 60.1%. This overestimation is attributed to the overestimations of the canopy cover ratio and the harvest index. For these traits, we need to account for the impacts of drought to improve the model performance.

The characteristics and temperature responses of sparsely sown rice seedlings were investigated using leading rice cultivars in the Tohoku region. In experiment 1, ‘Akitakomachi’ seedlings were investigated under three sowing conditions: sparse (60 g box^-1 of dry seed), standard (120 g box^-1), and dense (240 g box^-1), at Iwate University in 2020. Compared to the standard and dense sowing conditions, the sparse sowing condition produced seedlings with more vigorous leaf age development and higher dry matter weight with increasing accumulated soil temperature. In addition, sparsely sown seedlings had higher dry matter weight per plant length than those sown under other densities. In experiment 2, the seedling quality of leading cultivars such as ‘Masshigura’, ‘Akitakomachi’, ‘Ginganoshizuku’, ‘Haenuki’, ‘Hitomebore’ and ‘Tennotsubu’ was investigated at each experimental site in the Tohoku region in 2023 and 2024 under sparse sowing (65–80 g box^-1) and standard sowing conditions (120–160 g box^-1). The sparsely sown seedlings had higher dry matter weight and more seedling vigor than standard seedlings under an accumulated air temperature range of 400–700°C-day, regardless of the experimental site and cultivar. This is attributed to the larger dry matter per unit air temperature of the sparsely sown seedlings. Sparse sowing can maintain superior seedling quality over a wide temperature range; therefore, it is not only beneficial for large-scale operations with long transplanting periods but also helps to prevent the decline of seedling quality under the global warming environmental situation.

In the Tohoku region, an increasing area is dedicated to dry direct seeding (DS) cultivation of rice using plowing and compaction. However, the widespread use of controlled-release fertilizer (CRF) in DS poses future challenges due to its detrimental environmental impact. Consequently, this study investigated the effects of using nitrogen only (urea) combined with manure (NOM) on rice growth and yield in DS in cold-climate regions. Comparative analyses were conducted between the conventional fertilizer system employing CRF and the NOM strategy. The findings showed no significant differences in seedling establishment, growth, or yield of the ‘Akitakomachi’ cultivar between CRF and NOM in Andosol. In trials conducted in farmers’ fields in Iwate and Miyagi prefectures using the ‘Tsukiakari’ cultivar, the number of seedlings established exceeded 100 plants m^-2, with combined yields averaging more than 600 kg 10 a^-1. In ‘Tsukiakari’, a positive correlation was observed between the combined yield and the number of spikelets per panicle and the percentage of ripened grains. In addition, a positive correlation was observed between the total number of spikelets and thousand-grain weight. The results showed that NOM in DS under cold climate conditions produced comparable growth and yields to conventional practices in Andosol. The field trials highlighted the importance of optimizing spikelet number and thousand-grain weight to stabilize yields while maintaining the ripening rate, with recorded yields exceeding 600 kg 10 a^-1.

To clarify the optimal application of trace elements to Adzuki bean, the effect of fertilizers containing boron, zinc and manganese (Experiment 1); and, that containing iron and zinc (Experiment 2) on the yield of two Adzuki cultivars was investigated. The cultivars were grown in Hokkaido at Ebetsu on gray upland soil and at Obihiro on volcanic ash soil. At both sites, the pre-experiment soil contents of boron, zinc, and iron were near the lower limit of the soil diagnostic standard. Application of fritted trace elements, Agri-Ace (citric acid-soluble boron , zinc and manganese), and water soluble fertilizer (water-soluble boron, zinc and manganese) increased yield by 19%, 13%, and 8%, respectively, in Experiment 1. The yield increase reflected increased absorption of boron. In Experiment 2, soil application and foliar application of soluble iron and zinc increased yield by 20% and 38%, respectively. Zinc and iron absorption from the foliar application was expected to be higher than that from the soil application. The maximum increase in the soil concentration of boron, zinc, and iron after harvest was 0.2, 1, 5 ppm, respectively, and none of the trace elements accumulated to toxic concentrations. The two experiments indicated that application of boron at 360 g/10 a and zinc at 900 g/10 a was effective in increasing Adzuki bean yield.

The yield components of potato are number of tubers and average tuber weight, and these yield components need to be increased to improve yield. Gibberellin treatment of seed potatoes prior to planting is known to increase the number of tubers at harvest time, but does not increase yield because the average tuber weight is reduced. On the other hand, jasmonic acid is known to promote tuber formation and enlargement. Therefore, the present study investigated whether treatment with prohydrojasmon, a derivative of jasmonic acid, in addition to gibberellin treatment would increase the yield of potato. Gibberellin treatment was done by soaking seed tubers before planting, while prohydrojasmon treatment was done by foliar spray at 100 ppm to 200 ppm at the tuber initiation stage. The results showed that the combined gibberellin and prohydrojasmon treatment increased yield to the same extent as the top-dressing treatments. In particular, the yield increase in the combined gibberellin and prohydrojasmon treatment was more stable than that in the prohydrojasmon alone treatment or the combined gibberellin and top-dressing treatment, suggesting a synergistic effect of gibberellin and prohydrojasmon on tuber growth. The gibberellin and prohydrojasmon treatment also resulted in less reduction in starch content loss than the top-dressing treatment. In summary, the combined gibberellin and prohydrojasmon treatment could be an alternative to chemical fertilizers for increasing potato yield.