We constructed a simplified method to estimate first flowering dates of cherry tree (Prunus×yedoensis), considering temperature conditions in endodormancy process. We adopted the DTS method, which is an accumulation model of forcing effect of temperatures during developing process, as an estimation model of cherry blossom phenology in this study. In our previous studies, DTS method with fixed (pre-determined) starting dates for each site showed high accuracies for cold regions, whereas low accuracies for warm regions. Such accuracy drop was attributed to the volatility in endodormancy completion in warmer region of Japan, affected by inter-annual variation in chilling temperature during winter season. In order to reduce such error, it had been necessary to calculate chilling hours from hourly temperature data and evaluate the progress in endodormancy releasing process, with complicated conventional procedures. In our new model, an annual discrepancy in starting date of forcing effect from the pre-determined dates, calculated from a simplified procedure in our previous model, were calculated as the product of the correction coefficient, Ci, for each year and a winter temperature normal value above a threshold of chilling effect for endodormancy release, (TDJ-1.5), for each site. Annual correlation coefficient Ci was calculated from averaged winter temperatures at 7 secular observatories in warm region in Japan. Estimated first flowering dates with and without correction of starting dates were compared each other. The estimations by new method kept under about 3.2 days of RMSE. The introduction of new method also reduced RMSE within 3 days into approximately half of stations, applied to verification of new method with relatively long (50-year) period.
Although climatic conditions had hindered the introduction of Pinot Noir, a cultivar of wine grape (Vitis vinifera), to areas such as Yoichi and Sorachi, Hokkaido, northernmost Japan, the growing region of the cultivar has recently extended. We analyzed meteorological data to obtain the rationale for the successful cultivation of Pinot Noir in Hokkaido; climate shift since 1998 pointed by Kanno (2013), i.e., rise in summer temperature, facilitated cultivation of the variety. Today, Yoich and Sorachi have become the right locations for growing the cultivar, and it has also been grown in other areas. Indeed, the vintage chart in Tokachi indicated the consistent, good harvest of grape since 1998. There is negative correlation in the average monthly temperature between April and August, and positive correlation between August and September ever since the climate shift. We hypothesize the benefits of the climate shift in terms of wine production as follows: 1) in years with low April temperature and high summer temperature, the growth rate in early stage delays, but the temperature required for grape maturation is secured by high temperature in August and September; and 2) in years with warm April and subsequent cool summer, early growth start keeps the growing season long enough, which may have compensated the risk of poor grape maturation in cool summer. Thus, climate change is considered to have favored the cultivation of Pinot Noir in Hokkaido.
In this study, we aimed to estimate the drought vulnerability of soybeans in Japan based on meteorological factors in order to alleviate drought stress by introducing farm-oriented enhancement for aquatic-system (FOEAS). The differences between precipitation and crop evapotranspiration during the period from flowering (R2) to thirty days after the beginning of seed filling (R5) (WD) could be used to estimate decreases in the harvest index and seed yield with drought stress. This WD index was calculated to assess the occurrence of drought stress by considering the cultivars and cropping season in each region using long term (1980-2013) meteorological data and a phenological development model. The WD index was below zero about 50% of the time in the northern part of Fukui Prefecture with the assumption of Enrei cultivation. Moreover, our data showed that the WD index tended to decrease in northwestern Kyushu, where the Fukuyutaka cultivar predominated. Reference evapotranspiration tended to increase in many regions; however, in Saga City, located in northwestern Kyushu, precipitation tended to decrease, resulting in the decrease in the WD index in this region.
An alternative approach for predicting the heading date of rice plants was developed by using the 30-yr averaged normal heading date for the input of a developmental index model instead of using the information on the rice transplanting date and the developmental index on that date. This approach is based on the fact that the normal heading date has less spatial heterogeneity compared with the standard input variables and facilitates prediction of the spatial variation of the heading date. The model predicted the inter-regional variation of the heading date in the Tohoku district of Japan within 2 days for its root mean square errors (RMSE), which is similar to that of the traditional developmental index (DVI) model, and well reproduced spatial variation of the heading date over Tohoku district in extremely hot/cold years, although further validation is needed to prove the model accuracy.
To clarify the effect of water stress after reproductive growth stage on the seed size (weight of 100 seeds) and the seed coat cracking ratio (percentage of the seeds that have cracked seed coat) of soybean, we conducted pot experiments. Soybeans were direct-seeded (cv. ‘Shurei’ in late June in 2013 and 2014, and cv. ‘Sato-no-hohoemi’ in late May and late June in 2015) to 1/5000 a plastic pots filled with heavy clayey soil in a plastic film house. Water was automatically supplied to the soil surface of each pot by drip irrigation and, in the control plot, soil water was kept to the level which was lower than the field capacity but applied no water stress to the plants. Irrigation amount at a time was set to 0.1 L/pot in all plots before flowering. After flowering, water stress treatments were incorporated by reducing single irrigation amount to 0.07 L/pot. The treatments were incorporated from flowering to early seed filling stage in a ‘former stress (FS) plot’ and from early seed filling stage to harvesting in a ‘latter stress (LS) plot’. As little drainage from pot was occurred, the amount irrigated should be nearly equal to evapotranspiration amount. Seed size was largest in the FS plot and smallest in the LS plot. The seed coat cracking ratio did not significantly differ among plots, but differ among cultivations for each cultivar. The seed coat cracking ratio was not significantly correlated with the average seed size of each plot. The seed coat cracking ratio was smaller in 2014 for ‘Shurei’ and in later seeding in 2015 for ‘Sato-no-hohoemi’, possibly because temperature, vapor pressure deficit, solar radiation and transpiration requirement after pod setting were smaller in those cultivation periods compared with the other cultivation periods for each cultivar.
We investigated the light and temperature dependence of photosynthesis and its seasonal variations in the loquat cultivar ‘Mogi’ grown in a pot in an orchard. Leaf photosynthesis was light saturated in each season. The optimum temperature, at which net photosynthetic rate (Pn) was maximal, varied seasonally: 15°C in the fall, 5°C in winter, 20°C in spring, 25°C in the rainy season, and 30°C in summer. Maximum Pn value was 11-12 μmol CO2 m−2 s−1 in the fall and summer, 2 μmol CO2 m−2 s−1 in winter, and 6-10 μmol CO2 m−2 s−1 in spring and rainy season. Thus, our results suggested that loquat photosynthesis is temperature dependent. When loquat was moved to a phytotron in winter and kept at 13°C for 2 weeks, its maximum Pn increased considerably and almost reached the value of loquat that was continuously cultivated in the phytotron at 13°C during winter.
We developed a greenhouse with an inclined-ridge roof designed to accelerate the movement of rising air across the roof slope, and to enhance greenhouse ventilation. In this study, distributions of air temperatures of 3 m wide and 10.8 m long plastic greenhouses with different ridge-roof inclinations (horizontal ridges, inclined-ridge of 2.7°, 5.3° or 7.9°) were investigated. The upper parts of the two gable-ends on each greenhouse were opened for ventilation. The average air temperature was the highest in the greenhouses with horizontal ridges, and gradually decreased as the ridge inclination increased. An air temperature gradient was clearly observed along the long axis in the inclined-ridge greenhouses; the air temperature was lower on the lower roof side. This temperature gradient is probably due to air movement from the lower to the higher-roof side caused by natural ventilation, which can be enhanced by the ridge inclination.
Monthly averaged temperature and precipitation of climatological Normals from 1981 to 2010 at 158 points provided by Japan Meteorological Agency are applied for statistical classifying Hokkaido climate. These points are divided into 5 clusters based on the shape of dendrogram. The results show that clusters A and B are located along the coast of the Sea of Japan with their heavy rain and snow in fall/winter. Rain and snow in Cluster A is heavier than in Cluster B. Cluster D and E are located along the coast of the Pacific with their heavy rain in summer. Rain in cluster E is heavier than in Cluster D. Cluster C has no heavy precipitation season through a year. It corresponds to the climate of the Sea of Okhotsk. It prevails not only along the Sea of Okhotsk but also inland of Hokkaido. These classifications are assumed to be used for application of results of crop adaptation test at an experimental station to the area of same cluster. The attribution to cluster on the required spot needs to be considered not from the nearest neighbor but synthetic judgment in a surrounding region.
In conventional greenhouse hybrid heating systems, a non-oil heating device such as a heat pump or a wood-pellet heater is used in combination with an oil heater. The system needs to be designed not only to minimize the installation cost of the expensive non-oil device but also to efficiently reduce the use of fossil oils. Herein, we propose an approach to estimate the percentage of seasonal heat supplied by a non-oil heating device. By assuming that heat loss from a greenhouse is proportional to the difference between the inside and outside air temperatures, we determined the ratios of the heating capacity of a non-oil and an oil device to achieve maximum heating load. We also determined the percentages of total seasonal heat supplied by the two devices, assuming that the total heat consumption is proportional to heating degree hours. The percentage of the heat supply calculated using hourly temperature records at 11 locations in Japan was linearly related to the mean difference between inside and outside temperatures, and this relationship was consistent across the selected locations. Using these results, we derived equations that enable the estimation of the percentage of seasonal heat supplied from a non-oil heating device.