Dry direct-seeding rice cultivation requires less labor than traditional transplanting cultivation, as there is no need for seedling production, the puddling process, and the transfer of seedling trays. In northern Kyushu, a double-cropping area in southern Japan, dry direct-seeding rice cultivation has generally not been adopted due to water leakage and the accompanying weed overgrowth. This situation prompted the authors to devise a water leakage prevention technique that can be rapidly implemented after winter cropping, with the aim of guaranteeing a reliable rice harvest. In this study, we use a vibratory roller to compact the soil, investigate the optimal conditions for effective compaction, and demonstrate the procedures for confirming these conditions on-site. This article provides an overview of the research process used to develop this water leakage prevention technique and an outline of our dry direct-seeding rice cultivation method for double-cropping areas, including weed control during the dry period.
Small-scale protected horticulture is carried out in mountainous areas, such as in the sloping terrain and highlands of Japan. Given the cooler climate in mountainous areas, agricultural products can be produced there during summer, which is the off-crop season in the flatlands. However, the effects of global warming are making it harder to produce vegetables in summer, even in mountainous areas. Therefore, cooling techniques have been developed and improved for small-scale protected horticulture in mountainous areas. Intercepting solar radiation is an effective way to limit temperature rise in greenhouses. By using a computer program responsive to solar radiation intensity controlling a motorized movable shaft system with a shading material, it is possible to reduce the temperature in greenhouses caused by excessive-solar radiation without affecting photosynthesis. Such evaporative cooling techniques as the fog cooling and the pad and fan cooling systems were previously too expensive and complex to install in small-scale greenhouses. These systems have now been simplified with the costs reduced. Local cooling techniques are efficient for summer production. These techniques can locally and directly cool the specific parts and ambient temperature of a plant. In strawberries, for example, the formation of flower buds will be accelerated by locally cooling the crown or the root zone, thereby accelerating the harvest period.
Rice necrosis mosaic virus (RNMV) is a fungus-transmitted bymovirus that leads to losses in rice yield. This research tested ten rice cultivars (cvs) with different levels of resistance to RNMV. The lowest levels of RNMV RNA were found in two high-resistance cvs; the highest levels were found in the two low-resistance cvs. The RNA-dependent RNA polymerase 6 gene in rice (OsRDR6) was found to be the most highly expressed in two high-resistance cvs and the least expressed in two low-resistance cvs although its basal level of constitutive expression was similar among cvs. Plant growth and yields were also tested. The extent of RNMV RNA accumulation affected plant height, panicle/tiller numbers, and seed weight. The RNMV induced OsRDR6 expression level in the rest of cvs was more or less inversely correlated to RNMV RNA accumulation. The observed results suggest a close relationship between RNMV resistance and RNMV induced OsRDR6 expression level in these cvs.
Massive freshwater discharges due to heavy rainfall have recently caused negative changes to coastal waters, such as red tides and anoxic water masses. In this research, a salinity analysis was conducted using a three-dimensional σ-coordinate model to evaluate the impact of large freshwater discharges on the horizontal and vertical distribution of salinity. Specifically, Hakata Bay was examined after a heavy rainfall with a six-year return period, beginning 16 September 2002, a common recurrence interval. The data were calculated for 11-27 September 2002. Tank models were applied to calculate river inflow discharges, which were considered river inflow in the hydrodynamic and salinity diffusion model for Hakata Bay. Model validation results showed high reproducibility, and the calculated tidal current and salinity agreed well with observed data. Results also showed that: (1) salinity was less than 15.0 psu at the river mouths about one day after heavy rainfall; (2) low-salinity water (< 28.0 psu) spread across the surface of the inner part of the bay; and (3) salinity differences between the surface and bottom were large (approximately 4 psu) and lasted three days after the heavy rainfall. It was concluded that red tides and anoxic water masses could be induced in the inner part of the bay.
Hanoi, the capital city of Vietnam, is highly vulnerable to flooding from the Red River. A flood disaster in 1971 devastated the river basin and claimed the lives of 100,000 people. The Red River dike system was built to protect Hanoi from flooding of the Red River; however, thousands of households are outside the protected area inside the dike system and are highly vulnerable to flooding. Hanoi’s flood protection measures are classified according to the water level of the Red River at Long Bien station: warning levels 1, 2, and 3 correspond to water levels of 9.5 m, 10.5 m, and 11.5 m, respectively. However, risk-reduction strategies for residential areas based on a flood hazard assessment are still inadequate. This study modeled floods and mapped them using a two-dimensional depth-averaged hydrodynamic model to show the inundation depth levels for the entire area in high resolution. Residential areas were found to be highly vulnerable to flooding at all warning levels. Outside the area protected by the dike system, 40.17% (15.94 km2), 54.08% (21.44 km2), and 79.75% (31.60 km2) of the study area were inundated at warning levels 1, 2, and 3, respectively, and these areas contain a small number of households. These results can be used to develop flood prevention and mitigation plans for Hanoi.
Indica and japonica rice are subject to different market structures, and the international prices of both varieties display different trends. We project and simulate the future global indica and japonica rice markets under climate change in the mid- and long-term, developing a partial equilibrium model, the Rice Economy Climate Change (RECC) model that covers the indica and japonica rice markets in 24 countries and regions. The simulation results suggest that public agricultural knowledge and innovation system in Vietnam and China play a crucial role in stabilizing the international prices of indica and japonica in the mid- to long-term in target countries, as both rice production markets become increasingly affected by climate change.
Long-term field observation was clarified over ten years for the water budget of Cambodia’s forest watershed, one of the world’s most data-sparce areas. The La Niña years had large amounts of annual rainfall exceeding 1,800 mm, often marked by monsoon breaks during the rainy season. The El Niño years had smaller amounts of annual rainfall between 1,100 mm and 1,200 mm, aside from that in 2016. The strong El Niño during 2015-2016 caused large drops in both river and groundwater levels in the Cambodian forest catchment. However, the former levels of groundwater and river water were restored by 953.4 mm of rain received during the second half of the rainy season in 2016. Thus, the monsoon breaks may be correlated with the increased amount of rainfall in the second half of the rainy season.
The growth performance and condition factor (CF) of milkfish (Chanos chanos) in relation to body size and temperature were investigated in a shallow marine pen culture system in coastal waters of the Philippines. Three common models were tested to determine the best-fit model for the growth of milkfish, and the logistic model was found to be best for both weight-based and length-based growth. Daily specific growth rate in weight (DSGRw) and length (DSGRL) were positively correlated with water temperature, while both DSGRw and DSGRL were correlated negatively with the size of the fish, which supported the fit of the growth model. CF of milkfish exhibited a positive correlation with the feed conversion ratio and significant seasonal variations. The ratio was lower in the fast growth season (dry season) than in the slow growth season (rainy season). By integrating these controversial findings, we were able to posit that low temperature and inefficient feeding makes ‘fat’ fish and vice versa. This may be explained by changes in proximate body composition (e.g., protein and water content) and the change in metabolic rate brought about by different water temperatures.