Composting tests based on nonaerated static pile composting were conducted on a realistic scale following the agricultural habits used in Hokkaido to examine the effects on greenhouse gas emissions of controlling dairy manure moisture content by mixing the manure with wheat straw. Test plots included three different moisture contents with specific gravity levels: high, 82.3% with 888 kg m⁻³; medium, 79.1% with 796 kg m⁻³; and low, 75.9% with 679 kg m⁻³. Greenhouse gas emissions and the temperature of the compost were measured throughout the composting process (111 days). The highest temperatures were 44.7°C, 71.9°C, and 71.1°C in high, medium, and low moisture content compost, but compost temperatures were in the following order during the entire composting period: low>medium>high moisture content. The degrees of compost maturity were nearly immature and fully mature with high and low moisture content, respectively, and the degree was intermediate between the two maturities with medium moisture content. Thus, composting proceeded in a swollen/softened state and an aerobic state with low moisture content, whereas the anaerobic state was mostly found when moisture content was high. Cumulative emission rates of methane and nitrous oxide gases were in the following order: low<high<medium moisture content. This indicated that greenhouse gas emissions could be controlled by mixing a large amount of wheat straw into the compost. Cumulative greenhouse gas emissions converted to CO₂ equivalents were 572, 850, and 518 kg-CO₂eq with high, medium, and low moisture content, respectively. Thus, with low moisture content, emissions were reduced by 9.4% and 39.1% compared with those when moisture content was high and medium, respectively. These results indicate that composting by actively mixing wheat straw into dairy manure to adjust moisture content can lead to swollen and softened compost and accelerated fermentation, which could help reduce greenhouse gas emissions from dairy farms.

The 1/50,000 cultivated soil map of Japan is based on the Fundamental Soil Survey for Soil Fertility Conservation conducted during 1959–1978; it does not reflect present land-use types or recent soil survey results. Recent progress toward reformation into well-drained paddy fields may have lowered the position of the groundwater gley horizon; therefore, the distribution area of Gley Lowland soils, one of the major soil types in paddy fields in Japan, may have decreased. In this study, we conducted simple soil profile surveys at 1,474 sites in paddy fields across 12 prefectures in Japan (Hokkaido, Aomori, Iwate, Akita, Ibaraki, Chiba, Niigata, Aichi, Shiga, Hyogo, Nagasaki, and Kagoshima) and analyzed temporal differences in soil types by comparing the soil map with the present survey results, especially focusing on land-use and landform types. We found that the proportion of Gley Lowland soils had decreased from 76.4％ to 43.8％, whereas that of Gray Lowland soils had increased from 9.1％ to 32.0％. In addition, the proportion of soil groups in which the groundwater gley horizon appeared within 50 cm of the soil surface tended to have decreased to a greater extent in paddy–upland rotations or converted upland sites relative to in continuous paddy sites. Comparison by landform revealed a wide variety of trends in soil-type differences, but specific trends, similar to those detected for land use, were not found. Thus, the nationwide reformation into well-drained paddy fields has apparently lowered the position of the groundwater gley horizon, changing Gley Lowland soils into other soil types, such as Gray Lowland soils. We propose that the present land-use type is an important factor for determining the degree of soil-type change from Gley Lowland soils to other soil types in paddy fields.

In this study, soil frost depth during winter was controlled to enhance onion productivity via suppression of nitrogen leaching and improvements to physical soil properties in onion fields in the Okhotsk area of Hokkaido, Japan. In 2016 and 2017, soil frost depths under natural snow conditions measured <11 cm. We compared the conditions in controlled plots including soil frost depths of 30–40 cm with those in uncontrolled plots. The controlled plots contained higher amounts of residual inorganic nitrogen in the 0–40 cm soil layer after snowmelt and higher porosity (volume of gaseous phase at pF3.0) and saturated hydraulic conductivity in the 30–40 cm soil layer compared with the respective values in the uncontrolled plots. In addition, the average weight of onions in the controlled plot was higher than that in the uncontrolled plots, and the yield was ～10％ higher in the controlled plot. Thus, improvements in productivity were seemingly induced by the combined effects of increased nitrogen supply and improved soil physical properties, such as air permeability, water retention, and water permeability, in the main root zone (0–40 cm) of onion plants. Onion yields were increased when the soil frost depth in the study fields was 23–37 cm. Considering a possible error of several centimeters in soil frost depth control, we recommend a target frost depth of 30 cm to improve the productivity of onion fields. However, in fields with high nitrogen fertility, soil frost depth control may result in excessive nitrogen supply. In such cases, growth suppression due to salt injury and damage from diseases, such as dry and soft rot, may occur, leading to lower onion yield. Therefore, proper nitrogen management might be required in fields in which soil frost depth is controlled.

The optimum spikelet number in Oryza sativa L. “Datemasayume” cultivated in Miyagi Prefecture is 30,000–34,000 grains m⁻². This number may be obtained (within the target range) by controlling nitrogen uptake during the panicle formation and full heading stages. Thus, to control nitrogen uptake and obtain the optimum spikelet number, we designed a fertilization method wherein soil nitrogen fertility is considered. Nitrogen uptake from the transplantation to panicle formation stages could be predicted using a multiple regression equation in which the amount of nitrogen in basic fertilizer and effective accumulative temperature were explanatory variables. Furthermore, nitrogen uptake from the panicle formation to full heading stages could be predicted using a multiple regression equation in which the amount of nitrogen in topdressing fertilizer and the amount of nitrogen applied to the surface soil were explanatory variables. These multiple regression equations were adapted to calculate the optimum amounts of basic and topdressing fertilizer nitrogen. According to verification analysis conducted in a local producer’s field, the more that the amount of applied fertilizer deviated from the calculated amounts of basic and topdressing fertilizer estimated using our formula, the more that the nitrogen uptake from the transplantation to the panicle formation stage and the spikelet number deviated from the target ranges. Thus, the optimum spikelet number of Datemasayume can be obtained if the optimum nitrogen richness, calculated according to our formula, is provided using basic and topdressing fertilizers.

In a high-temperature greenhouse environment, the characteristics of the high-temperature-ripening Oryza sativa variety Fusaotome were investigated. At the full heading stage, the roots of this variety were more elongated at a depth of <5 cm than those of the normal-temperature-ripening variety Akitakomachi. During the ripening period, the sap bleeding rate of Fusaotome under high-temperature conditions was significantly higher than that of Akitakomachi, and the rice root activity of Fusaotome was higher. At high temperature, the panicle temperature of Fusaotome was significantly lower than that of Akitakomachi, whereas the relative light intensity of Fusaotome was significantly higher than that of Akitakomachi at each height from 30–80 cm. Under normal-temperature conditions, there was no significant difference in the leaf area index (LAI) between the two varieties at each height. However, at high temperature, the LAI of Fusaotome was significantly lower than that of Akitakomachi at >70 cm (top layer), 60–70 cm, and 50–60 cm. With the high-temperature treatment, the occurrence of milky white and basal white rice was significantly lower in Fusaotome than that in Akitakomachi. In contrast, there was no difference in brown rice yield between the two varieties under normal- and high-temperature conditions. These results indicate that the high-temperature-ripening O. sativa variety Fusaotome has vigorous root elongation and activity, relative to that of the conventional variety Akitakomachi, under high-temperature conditions. Moreover, it is a favorable variety for ripening with a reduced increase in LAI in the upper layers of the vegetation community.