Resource acquisition, one of the major functions of roots, can contribute to crop growth and mitigating environmental impacts. The spatio-temporal distribution of roots in the soil in relation to the dynamics of the soil resources is critical in resource acquisition. Root distribution is determined by root system development. The root system consists of many individual roots of different types and ages. Each individual root has specific development, resource acquisition, and transport traits, which change with root growth. The integration of individual root traits in the root system could exhibit crop performance in the various environments via root distribution in the soil. However, the relationship between individual root traits and the pattern of root distribution is complicated. To understand this complicated relationship, we need to evaluate enormous numbers of individual root traits and understand the relationship between individual root development and root distribution as well as the integrated functions of individual root traits along with dynamics of resources in the soil.

Winter flooding of paddy rice production is characterized by flooding of paddy fields during the winter fallow season. It has attracted attention in terms of its ecological function, supporting the biodiversity of paddy field ecosystems. Therefore, recent winter flooding in Japan has been conducted by organic farming. However, it is not well documented how organic farming with winter flooding affect the productivity of rice. We conducted field experiments to examine changes in rice yield in organic farming with winter flooding compared with those in conventional and organic farming over the period of 5 and 9 years. The yields in organic farming with winter flooding were lower than those in conventional farming but were almost the same as those in organic farming. We found a trend that shows the relative yield of organic farming with winter flooding compared to that of conventional farming increased during the first several years after the conversion from conventional farming to organic farming with winter flooding, but that it decreased after several years. This trend may be caused by the flourishing of weeds during continuous organic farming with winter flooding. Therefore, we tested four weed control methods: rice bran application, mechanical weeding, repeated puddling, and side-row fertilizer application. Although each method suppressed weeds to certain extents, some combinations of different weeding methods more effectively suppressed weed growth, thereby resulting in enhanced rice yields. We found a trend in rice yield and a possibility of combining several weed control methods in organic farming with winter flooding.

Andosols are characterized by high organic matter content and play a significant role in carbon storage. However, they have low phosphorus fertility because of the high phosphate-fixing capacity of active aluminum. For agricultural use of Andosols, it is necessary to ameliorate its poor phosphorus fertility by applying lime and high doses of phosphate fertilizers. The objective of the present study was to clarify how such soil amendments affect the mineralization of soil organic carbon (C) and nitrogen (N) in allophanic Andosols under different temperature regimes. The soil was treated using combinations of liming and heavy phosphate application, followed by incubation under different temperature conditions. The N mineralization and the soil CO₂ evolution rate were measured periodically. The patterns of N mineralization were analyzed by fitting them to first-order kinetics. Liming increased C and N mineralization irrespective of temperature, and the increase was further enhanced by phosphate application. Kinetic analysis of the N mineralization curve indicated lowering of the activation energy of N mineralization reactions with phosphate application, suggesting that P application may accelerate N mineralization at lower temperatures. These findings provide a basis for developing soil management strategies to reduce the loss of soil organic matter.

In crop production, which is largely dependent on environmental conditions, various attempts at environmental or social changes have been highlighted, and many field experiments are needed for them. However, since field experiments in agricultural production are constrained by high labor and time consumption, alternative methods to respond to these constraints are required. In this study, to establish a new method for application to field experiments, we proposed the evaluation of the leaf area index (LAI) of all individual plants in an experimental sweetcorn field using an unmanned aerial vehicle (UAV). Small-scale field experiments were conducted over two years. In the first year, the nitrogen fertilizer level was changed, and the plant density and additional nitrogen fertilizer application time were changed in the next year. Three vegetation indices (VIs), namely, the normalized difference vegetation index (NDVI), enhanced vegetation index 2 (EVI2), and simple ratio (SR), were validated to quantify the LAI estimation using a UAV for individual plants. For the evaluation of the individual plants, we used a plant-based method, which created all of the plant buffers based on the points of existing plants and the plant distance. To confirm the impact of the method, we additionally demonstrated the relationship between the LAI and yield, the results of statical analyses, and the difference of the center and the border of the field. Among the three VIs, index SR was found the most promising in the estimation of the LAI of the individual sweetcorn plants, providing the strongest correlation of yield with SR. Because a lot of data were obtained using the plant-based method, the statical differences in the LAI and yield were more easily detected for the plant density and fertilizer treatments. Furthermore, interesting differences between the center and the border of the field were found. These results indicate the availability and impact of plant-based evaluations using UAVs in near future field experiments.

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.

Phosphorus (P) availability in soils is often constrained by its accumulation in non-labile phosphorus (NLP) forms, limiting its accessibility to plants. This study examines how soil physical properties, chemical characteristics, and climatic conditions influence phosphorus fractionation and the transformation of NLP into plant-available labile phosphorus (LP). Utilizing global structural equation modeling (SEM), we found that silt content enhances organic phosphorus fractions, including NaHCO₃-Po and NaOH-Po. In the upper 30 cm of soil, pH decreases the availability of NaHCO₃-Po and NaOH-Po while stabilizing NLP, highlighting its essential role in phosphorus cycling under acidic conditions. In deeper soil layers, pH facilitates phosphorus mobilization from NLP pools, with effects varying across fractions. Long-term studies on Japanese Vaccinium soils reveal that pH and electrical conductivity (EC) management significantly promote NLP-to-LP conversion, primarily through NaOH-Po, thereby improving phosphorus use efficiency. These findings underscore the critical importance of prioritizing chemical property management over physical modifications to optimize nutrient cycling, preserve soil fertility, and reduce reliance on external phosphorus inputs in agricultural systems. Our study emphasizes the need for integrated approaches to achieve sustainable phosphorus management in both natural and managed ecosystems.