Ryosuke Tajima

Although lowland rice ecosystems play a vital role in meeting the growing demand for rice in sub-Saharan Africa, the performance of New Rice for Africa (NERICA) varieties and their root traits under flooded conditions remain insufficiently characterized. We evaluated seven NERICA varieties (NERICA 1, 2, 3, 4, 7, 10, and 14) and the japonica cultivar ‘Haenuki’ as a regional reference from Japan in a two-year field trial for grain yield and in a tube-culture experiment for shoot and root traits. NERICA 1 had the numerically highest average yield among the NERICA varieties and did not differ significantly from Haenuki in either year, whereas NERICA 14 had the lowest yield in both years. The variety × year interaction was not significant. Compared with Haenuki, NERICA varieties were generally taller but produced fewer tillers and nodal roots, lower root length density (RLD), and coarser root systems, as reflected by a lower specific root length and fine-to-thick root ratio (FTR). Haenuki had greater RLD in upper soil layers, whereas no significant varietal differences were detected in deeper layers (10–20 cm). Exploratory path analysis indicated that shoot dry weight was positively associated with tiller number and RLD and negatively associated with FTR, while tiller number was positively associated with RLD. These results suggest that RLD is associated with shoot growth in tube culture, and that NERICA 1 may be a candidate for further evaluation among the tested NERICA varieties. Since this study is a preliminary screening, validation under actual field conditions in African lowland environments is needed.

Ulaanbaatar, Mongolia, relies heavily on coal for winter heating, and continued urban expansion is expected to increase heating demand. This study investigated heating demand and rooftop PV potential in Ulaanbaatar from 2016 to 2025 using Google Earth Engine. Nighttime light intensity, heating degree days (HDD), and solar radiation datasets were integrated to evaluate changes in human activity, climate-driven heating demand, and rooftop solar resources. Electricity-equivalent heating demand, rooftop PV generation, coal displacement potential, and techno-economic performance under different policy scenarios were assessed. The results reveal a clear increase in urban built-up area during the study period, accompanied by rising nighttime light intensity, indicating growing urban activity. Despite relatively stable HDD, urban expansion implies increasing potential heating demands. Under the main rooftop PV deployment scenario, surplus electricity could theoretically offset approximately 10.9% of coal-based heating demand and reduce CO₂ emissions by 1.126 MtCO₂ yr⁻¹ through resistance heating. When the same surplus was converted through heat pumps with COP = 1.86, the theoretical coal-heating offset increased to 20.3%. However, economically viable large-scale deployment remained strongly dependent on feed-in tariff support. These findings indicate that continued urban expansion may lead to higher heating demand in Ulaanbaatar and highlight both the opportunities and structural limitations of rooftop PV for decarbonizing coal-dependent heating systems in cold-climate cities.

Acidic subsoils can restrict root growth and nitrogen (N) uptake and increase the risk of N loss; however, the extent of genotypic variation remains unclear. We evaluated two bread wheat cultivars, Haruyokoi and Harukirari, and one spelt line, KU-1025, under limed and acidic subsoil treatments to clarify whether maintaining root growth in acidic subsoil contributes to greater N capture and lower N loss. After 78 days, we measured shoot dry weight, shoot N uptake, root dry weight, total root length, soil nitrate (NO₃-N) concentration, and cumulative N leaching. The acidic subsoil reduced shoot N uptake, root length in the subsoil, deep-root ratio, and NO₃-N depletion, indicating that it restricted root proliferation and N acquisition. KU-1025 showed the greatest shoot dry weight, shoot N uptake, root dry weight, and total root length under both treatments. It also maintained a high deep-root ratio under acidic subsoil conditions and showed lower soil NO₃-N concentrations and less N leaching than the two wheat cultivars. Across genotypes and treatments, shoot N uptake was positively correlated with root dry weight and total root length, whereas N leaching was negatively correlated with these traits. These results suggest that maintaining a large root system, rather than deep rooting alone, is important for improving N capture and reducing N loss under acidic subsoil conditions, and that KU-1025 may provide useful genetic variation for breeding wheat adapted to acidic subsoil environments.

Maize is a globally important staple crop, and automated monitoring of germination and seedling emergence is essential for precision agriculture, enabling timely reseeding and reducing potential yield loss. To address this need, we propose Seedling-DETR, a transformer-based model for the real-time detection of emerged and missing maize seedlings using multispectral UAV imagery in an end-to-end manner. First, we construct a multispectral UAV dataset and introduce a dedicated annotation strategy in which missing seedlings were labeled individually rather than inferred indirectly. Then, we modify the feature fusion module of RT-DETR and develop a hybrid-scale feature fusion module to obtain richer and more expressive feature representations for missing seedling detection and improve the precision of missing seedling detection. Finally, we propose a channel fusion module to incorporate multispectral images into our model without requiring a dedicated multispectral backbone or additional pretraining, thereby improving model adaptability. The results show that, under a random train–test split (8:2), when using RGB images as input, our Seedling-DETR achieves a mean average precision (mAP) of 83.1% at an IoU threshold of 0.5, outperforming YOLOv11x and RT-DETR by 2.5% and 1.1%, respectively. The proposed method achieves an AP of 69.3% at an IoU threshold of 0.5 for missing seedling detection, which increases to 71.7% when multispectral inputs are incorporated. Similar performance trends are observed on an independent validation set collected on a different date. Although the model introduces moderate computational overhead (282 GFLOPs for RGB input and 418 GFLOPs for multispectral configuration, with 84.0 M and 85.1 M parameters, respectively), it can maintain efficient detection performance suitable for actual agricultural field deployment. The method is further validated at the field scale using orthomosaic-based analysis. Overall, this study provides an effective and scalable framework for the detection of emerged and missing maize seedlings under complex field conditions. The proposed framework supports accurate reseeding decisions, and contributes to automated maize production.

Soybean (Glycine max (L.) Merr.) is a globally important economic crop, providing approximately 71% of the protein and 28.7% of the vegetable oil consumed worldwide (Soystats, 2024). Various enviro...

Accurate evaluation of plant-available phosphorus (P) in flooded paddy soils requires consideration of redox dynamics and soil-specific properties. This study evaluated five soil P extraction methods, such as Truog, Bray 2, Mehlich 3, Olsen, and ascorbic acid-reduced Bray 2 (AR Bray 2), using soils collected from 20 paddy fields in a cold region of Japan that have received long-term fertilization. All four methods, except AR Bray 2, were conducted under air-dried and flooded incubation conditions. Additionally, we conducted pot experiments with the two rice cultivars to measure P uptake. Bray 2 extracted the highest amount of P (543.6–1045.4 mg P kg⁻¹). Incubation increased extractable P by factors of 2.4–4.9 with the Mehlich 3 and Truog methods, indicating enhanced P solubility under reduced conditions. The Olsen method showed minimal sensitivity to redox changes (−31.4 mg P kg⁻¹). Principal component and cluster analyses suggested three patterns of soil P behavior under changing redox conditions: (1) stable P extractability regardless of redox status; (2) increased P availability after incubation; and (3) P extractability depending on the extraction method used. These patterns were not explained by regional or taxonomic classifications. A comparison of soil extractions and P uptake indicated that no single method consistently predicted shoot P concentrations across all soils, suggesting that conventional P extraction methods may have limited ability in long-term fertilized paddy soils. Our findings demonstrate that soil-specific redox behavior and cultivar-specific P demand critically influence the effectiveness of standard P tests. Therefore, selecting diagnostic methods tailored to soil characteristics and crop requirements is essential for accurate P evaluation and sustainable fertilizer management in rice cultivation.

根の諸形質評価のための，採取した根の洗浄作業の効率化と標準化を目的として，根洗浄機を作成して，根を含む土塊から根を分離できるかについて検証を行なった．作成した根洗浄機は塩化ビニル管等の市販の材料で構成され，スプレーノズルによるジェット水流で土壌と根を分離する構造である．コアサンプル法で取得した水稲根を含む土塊を用いた検証では，1試料あたりの平均処理時間は約5分30秒であり，試料の量が倍であってもその処理時間は変化しなかった．装置上部から排出された根と下部に残留した根についてそれぞれ根長を評価した．上部から排出された根は根長全体の90％を占めた．それらを合計して算出した全体の根長密度は既往文献の結果と比較しても高かった．これらの結果から，根洗浄機は省力的かつ再現性の高い根の洗浄装置として有用な可能性があり，今後は他の作物や土壌条件でも検証を進める必要があると考えられた．

Assessing available phosphorus (P) in paddy fields is challenging due to waterlogging-induced reducing conditions. This study tested the applicability of the Truog, Bray 2, and Mehlich 3 extraction methods in both air-dried and incubated soils, as well as the ascorbic-acid-reduced Bray 2 (AR Bray 2), which simulates reducing conditions, for evaluating rice growth under P fertilization. In addition, to investigate the chemical characteristics of the extraction methods, active Al and Fe and P sequential extractions were measured. Soil samples from four representative regions in Yamagata Prefecture were used. Pot cultivation tests using ‘Haenuki’ and ‘Tsuyahime’ cultivars were conducted with varying P fertilizer levels. Variations in P availability across soil types were influenced by levels of active Al and Fe. Sequential extractions identified NaHCO₃-P and NaOH-P fractions as important for P availability. Bray 2 in both soils and AR Bray 2 were the most effective methods, showing a strong saturating exponential correlation with rice growth and P uptake, whereas Mehlich 3 and Truog showed weaker correlations. Bray 2 and AR Bray 2 show potential but require further evaluation for practical application due to the small number of soils. Future efforts should prioritize developing methods that account for P dynamics under reducing conditions, thereby improving P management strategies and supporting sustainable rice production.