Altering the rhizosphere of crops to reduce greenhouse gas (GHG) emissions and enhance carbon sequestration can be an effective strategy for combating global warming. However, research on the relationship between crop root traits and GHG emissions is limited and lacks comprehensive understanding. This review outlines the general mechanisms of GHG production and emission, summarizes the sensing technologies for the rhizosphere and GHGs along with their challenges, and discusses the potential of altering crop root traits to reduce GHG emissions based on the latest research to facilitate advancements in this field. Additionally, the trade-offs between GHG emission reduction and carbon sequestration are shown and the practical measures for global warming prevention are discussed.

In western Japan, wheat is generally sown on 1.5 to 2 m wide ridges with rows 0.3 m apart, but this cultivation method does not fully use the sunlight irradiated on the drainage furrows. In this study, we examined whether a combination of 4.5 m ridge width omitting two drainage furrows and double the number of rows without changing sowing density (WR-NR) could improve light use efficiency, yield and grain quality of wheat cultivar for bread ‘Setokirara’ for four seasons. WR-NR showed a similar or higher yield than the conventional method in all four seasons. The higher yield in WR-NR was due to the higher crop growth rate from heading to maturity. The grain protein content in WR-NR was maintained high due to high aboveground nitrogen accumulation at maturity even when yield increased. We measured the changes in plant height and culm length, internode length and internode dry weight per unit length at two weeks after anthesis in the fourth season. The results showed that plant height in WR-NR remained lower than that in the conventional from the fourth leaf appearance to two weeks after anthesis. Also, WR-NR produced heavier internode dry weight per unit length, both in the main stems and tillers, thus reducing the risk of lodging. WR-NR was an effective cultivation method to increase wheat yield and grain quality in western Japan while reducing the risk of lodging.

Using brown rice of the brewer’s rice cultivar “Ginnoyume” produced in 11 regions of Kochi Prefecture during the five-year period from 2016 to 2020 and its production log, We investigated the actual situation of the regional and yearly differences in brown rice quality in“Ginnoyume” and the causal factors. Between regions, significant differences were observed in 1000-grain weight, percentage of whole grains, white-core grains,inspection grade and alkali solubility; and the coefficients of variation were relatively large (more than 10) for percentage of whole grains, white-core grains,inspection grade and alkali solubility.Between years, significant differences were observed in 1000-grain weight, percentage of whole grains, protein content and alkali solubility, and the coefficients of variation for percentage of whole grains and alkali solubility were greater than 10. The maximum and minimum differences in brown rice quality traits found to be significantly different between regions and between years, respectively, were 1.5g and 1.2g for 1000-grain weight, 32.5% and 15.4% for percentage of whole grains, and 0.49 and 0.24 for alkali solubility.Similarly, the coefficients of variation were 1.9 and 2.2 for 1000-grain weight, 14.5 and 10.1 for percentage of whole grains, and 19.7 and 11.7 for alkali solubility, between regions and between years, respectively.Therefore, the differences in 1000-grain weight between regions and between years were similar, and the differences in percentage of whole grains and alkali solubility between regions were larger than those between years. Between regions,the significant correlations were as follows.The percentage of whole grains was positively correlated with elevation; and, negatively correlated with average temperature and solar radiation during the ripening period. The percentage of white-core grains was positively correlated with average solar radiation during the ripening period; and, negatively correlated with maturity time. The inspection grade was positively correlated with average temperature and solar radiation during the ripening period; and, negatively correlated with elevation. The alkali solubility was positively correlated with elevation and maturity time; and, negatively correlated with average temperature and solar radiation during the ripening period. Therefore, the regional differences in the percentage of whole and white-core grains,the inspection grade and the alkali solubility need to be reduced in order to achieve a high brown rice quality in “Ginnoyume”.The regional differences in the percentage of whole and white-core grains, the inspection grade and the alkali solubility were affected by the average temperature and solar radiation during the ripening period through elevation and maturity time. Therefore it is important to develop a cultivation method that provides appropriate meteorological conditions for the ripening period in each production region.

Perilla is an important local resource that can attract people to mountainous areas. In Shitara-town, a mountainous area in Aichi Perefecture, perilla seeds from a native line are processed into gohei-mochi(rice cake) sauce and oil, which are sold locally. However, production is declining with theadvance in age of the producer. In this region the native lineis planted in early July and harvested in late October or early November. Because of the short harvest season, it is difficult for the same grower to expand the cultivation area for production. Early frosts in October lower yield and quality. We studied the effects of planting time on flowering, harvest time, growth, and yield in 2017 and 2018, using the local native line ‘Nagura’. We also used Line ‘No.1’ obtained by crossing the native line ‘Nagura’ with an early flowering line. The later the planting time of ‘Nagura’, the slower the growth and lower the yield were. The harvest time of ‘Nagura’ could not be dispersed by changing the planting time. On the other hand, the harvest time of ‘No.1’ varied with the planting time. Therefore, it may be possible to increase production by planned planting of new lines with adjusted flowering and harvesting times in combination with conventional lines.

Plant emergence isinhibited by factors such as drought and soil crust. These factors vary depending on weather conditions. Emergence rate and proper seeding depth are significantly affected by precipitation conditions before and after seeding.The method of sowing more seed and manually thinning as a countermeasure is labor-intensive and difficult for field crops. Sincesmall-seeded crops are particularly susceptible to emergence inhibition, setting proper seeding depth based on weather conditions is important. However,prediction of post-seeding weather conditions is difficult. Therefore, I inventedthe “double depth seeding method.” In this method, seeds are sownalternately in shallowand deep soil with half the space of the rows to be cultivated, and then the rows with poorer plantemergence are thinned out by intertillage.In this study,double depth seeding of sesame was conducted 38 times under various weather conditions in the field and emergence rateswere investigated.As a result, there were three different patterns depending on weather conditions:1) only the emergence rate in the shallow plot was high, 2) only the emergence rate in the deep plot was high, and 3) there was little if any difference.Based on the posterior distribution of emergence rate and the occurrence rate of weather pattern, the emergence ratein the test area was simulated. The results showed that the probability of achieving the target value (45% to 75%)was 59% for the shallow sowing only and 54% for the deep sowing only, while it was 81% for the doubledepth seeding, indicating the practicality of the method.

In Chiba prefecture, short storage root (length/width<2.5) occurred frequently in sweet potato (Ipomoea batatas (L.) Lam.) cultivar “Beniazuma”. As this was considered to be an effect of dryness in the early developmental stage, which determines the length of the storage root, we clarified the effects of watering in the early developmental stage on the growth, yield and occurrence of the short storage root. In this study, experimental plots were set up without irrigation, immediately after planting, 10 days after planting, and 10 days plus 30 days after planting. As a result, in the two plots that were irrigated 10 days after planting, compared to the non-irrigated plot, occurrence of the short storage root decreased due to the lengthening of thestorage root. This indicated that the dryness in the early developmental stage may cause short storage root and thatirrigation10 days after planting was effective for reducing occurrence ofshort storage root.

The effect of sowing time (mid-October, early November, and mid-November), seed production year and seed chemical treatment on emergence rate of the following spring were evaluated to clarify the early sowing limit for early-winter direct-sowing cultivation of rice in the Hokuriku region. Seeds of cultivar “Tsukiakari” and “Nijinokirameki” were sown in Joetsu City, Niigata Prefecture in early winter of 2021 and 2022. The emergence rates of the seeds produced the previous year and sowed in mid-October were less than 3% regardless of whether the seeds were smeared with thiuram hydrating agent. On the other hand, the emergence rate of the seeds produced the current year and sowed in the same period was 31-65%, and the rate was increased by treatment with thiuram hydrating powder. The emergence rate increased with the delay of sowing time. Seeds producedthe previous year, had the emergence rate of 36-62% when sown in mid-November, assuming low temperature storage at around 10°C and treatment of the seeds with thiuram hydrating agent. Differences in emergence rates depending on sowing time and seed production year were thought to be due to seed dormancy at the time of sowing. For the cultivars “Tsukiakari” and “Nijinokirameki” in each seed production year, the seeding amount for each sowing time and the early sowing limits based on the effective accumulated soil temperature and air temperature within the year werediscussed.

This study investigated typhoon damage due to strong winds and saltwater splash in three green manure crops (Crotalaria juncea, C. spectabillis and Sesbania rostrata) in Okinawa, assessed as stem breakage, leaf wilt, and survival at harvest. Stem breakage due to strong winds was significantly higher in C. juncea and leaf wilt due to saltwater splash was significantly higher in C. juncea and C. spectabillis than in S. rostrata, which had almost no damage. Some damaged C. juncea plants regenerated, but C. spectabillis did not, and most plants withered before July 21st after passage of the typhoon 10. At harvest, the plant survival rate was 49% in C. juncea and 87% in S. rostrata. Thus, S. rostrata was the most resistant to strong winds and saltwater splash. It had a somewhat higher biomass and N content than C. juncea but a comparable P content. The amount of regrowth per remaining plant was greater in C. juncea than in S. rostrata owing to the greater loss of C. juncea plants, and the CN ratio was significantly higher in C. juncea stems, suggesting a decrease in the rate of stem decomposition.

While productivity in converted paddy fields in hilly and semi-mountainous areas is important, excess moisture damage due to poor drainage is a serious problem in Japan. The objective of this study was to develop an effective drainage method for farmers, by focusing on the artificial landform transformation history of the fields.The experiment was conducted from 2020 to 2022 at fields in a hilly and semi-mountainous area in Higashi-Hiroshima, Hiroshima Prefecture, using a rice husk underdrain construction machine and a bullet underdrain construction machine for upland farming in a paddy field rotation. A construction map was created using past aerial photographs, and the underdrain was settled in the direction connecting the leveled and reclaimed areas. Subsidence of the ground surface was observed at the reclaimed area, and water was found to be collected in the reclaimed area. In 2022, the soybean seedlings and yields were improved by installing a drainage outlet in the reclaimed areas and by connecting the leveled and reclaimed areas through underdrains. Taking into consideration the location of the drainage outlet, a significant increase in the seed yield was observed. These results suggest that in hilly and semi-mountainous areas, the effect of drainage methods can be enhanced by focusing on the artificial developmental history of the fields.