Leaf removal is a commonly applied canopy management in vineyards as it has a significant impact on the microclimate around grape clusters and canopy photosynthetic efficiency. This effect is observed within the complex radiative and thermal dynamics associated with hedgerow environments. We evaluated the effects of leaf removal on cluster-zone microclimate during an extraordinarily hot 2023 summer in central Hokkaido. The surface temperature of east-facing clusters was up to 10°C higher than ambient temperatures when the clusters were exposed to sunlight by leaf removal. The temperature increase of east-facing clusters covered by leaves (i.e., without leaf removal) was significantly suppressed. Such radiation-dependent heating was hardly observed in west-facing clusters during the afternoon when wind speeds were highest. Effective cumulative cluster temperatures above 25°C were higher for east-facing clusters with leaf removal than east-facing clusters without leaf removal and west-facing clusters with and without leaf removal. Although the relative humidity in the middle of canopy decreased slightly faster in the morning when the east-side leaves were removed, no marked difference was observed under high humidity conditions. Further, diurnal patterns in net photosynthetic rates for leaves from the upper, middle, and lower canopy were measured on both sides of hedges to assess their contributions to canopy photosynthetic gain on two hot and sunny days. Despite record high air temperatures, the photosynthetic rates for leaves on both sides of hedgerows did not decrease at midday. East-side leaves in the upper canopy tended to show higher photosynthetic rates, likely due to increased light interception and atmospheric CO₂ concentrations during the morning. Our results suggest that removing east-side leaves, a conventional practice aimed at suppressing cluster temperature, is not always effective for this purpose, and that canopy photosynthetic gain does not differ markedly between the sides of hedgerows and within the canopy, even during heatwaves.

　To implement greenhouse environmental controls that maximize profit, it is necessary to monitor photosynthesis of plants. While some methods estimate canopy photosynthesis based on light-response curve of single leaf (EST), real-time photosynthesis and transpiration monitoring system that is an open-chamber system for whole plants can be used for measurement of canopy photosynthesis (MEAS). In this study, we compared the results obtained by the two methods on the same tomato plants under water stress to clarify the characteristics of these two methods for practical monitoring of canopy photosynthesis in a greenhouse. In MEAS, the canopy net photosynthesis rate in the first week after stress treatment (S1W) was 25% of that in the pre-stress treatment (NS). The canopy net photosynthetic rate in MEAS was positively proportional to total conductance with almost constant slope regardless of the periods. On the other hand, in EST, the canopy net photosynthetic rate at S1W was 68% of that at NS. It was not as much reduction as observed in MEAS. Since EST used in this study only incorporated the response of total conductance in a plant condition assumed to be the absence of water stress, it was inferred that EST overestimated total conductance and canopy photosynthesis of plants under water stress. Based on these results, we believe that at a minimum, total conductance measurement is necessary to monitor the canopy net photosynthetic rate under greenhouse conditions.

　This study evaluates the effect of the agricultural covering material thickness on the overall heat transfer coefficient in developing covering materials with high heat insulation. The thickness of a thin film, such as the covering material, minimally impacts conductive and convective heat transfer within and outside the greenhouse. Nevertheless, the effect of covering material thickness on radiative heat transfer remains unexplored. The higher the longwave radiation absorptance of the covering material, the lower the overall heat transfer coefficient due to the suppression of radiative heat transfer through the material. This study examined the relationship between the covering material thickness and the overall heat transfer coefficient for 24 types of polyolefin (PO) films in the market. An equation was used to estimate the overall heat transfer coefficients based on the longwave radiation absorptance of each covering material, which was measured using an emissivity meter. The tested PO films’ maximum, minimum, and average thicknesses were 0.16, 0.06, and 0.12 mm, respectively, with a standard deviation (SD) of 0.03 mm. The longwave radiation absorptance’s maximum, minimum, and average values were 0.74, 0.37, and 0.63, respectively, with an SD of 0.08. The maximum, minimum, and average values of the overall heat transfer coefficients were 7.22, 6.19, and 6.56 W m^-2 K^-1, respectively with an SD of 0.24 W m^-2 K^-1. A significant positive correlation was observed between film thickness and longwave radiation absorptance (R = 0.6468). There was a significant negative correlation between film thickness and the overall heat transfer coefficient (R = -0.6642). As film thickness increased, longwave radiation absorptance increased, suppressing radiative heat transfer through the covering material and decreasing the overall heat transfer coefficient. This study clarifies the mechanism by which the thickness of the covering material affects the overall heat transfer coefficient.

　In greenhouse cultivation, CO₂ enrichment enhances the net photosynthetic rate (P_n) of the plant canopy. Null balance CO₂ enrichment (NB-CE) maintains equal CO₂ concentrations inside and outside the greenhouse (C_in and C_out), limiting CO₂ leakage; however, there may be more cost-effective strategies. This study proposes an alternative strategy termed CO₂ enrichment only for high photosynthetic photon flux density (PPFD) hours (HP-CE). In this strategy, C_in is maintained slightly above C_out when P_n is expected to be high, aiming to improve cost-effectiveness. We defined the cost-effectiveness of CO₂ enrichment as the increase in integrated P_n over a photoperiod compared to non-CO₂ enrichment, divided by the CO₂ supply rate (S) integrated over the same period. Since CO₂ leakage increases with the number of air exchanges per hour (N), we evaluated the cost-effectiveness of HP-CE at several N levels. In this study, the integrated S of HP-CE was set equivalent to that of NB-CE, and the CO₂ supply period of HP-CE was adjusted based on the target C_in (450-700 µmol mol^-1) at N of 4, 6, 8, and 10 h^-1. Using an open-type assimilation chamber to reproduce ventilated greenhouse environments, we measured the PPFD-P_n and PPFD-S curves of cucumber seedlings. We then estimated the P_n and S over a 12-hour photoperiod for NB-CE and several HP-CE scenarios. The estimation revealed that HP-CE could be more cost-effective than NB-CE for C_in 450-700 µmol mol^-1 at N of 4, 6, and 8 h^-1. HP-CE was less cost-effective than NB-CE at N of 10 h^-1 due to significant CO₂ leakage at increased target C_in. These findings suggest that for ventilated greenhouses with relatively low N, CO₂ enrichment can be more cost-effective than NB-CE by slightly elevating C_in above C_out only for high PPFD hours.

　Ethiopia, a tropical highland region, is an important cool-climate rice-production region. Limited information is available on rice yield potential in Ethiopia. This study aimed to compare rice yield potential from experimental and modeling studies in Ethiopia and Japan. Experimental potential yield (PY_E) was evaluated from field trials in the Fogera plain in Ethiopia and in northern Japan, both cool-climate regions, using the same two cultivars under optimal conditions during the 2023 cropping season. Climatic potential yield (PY_C) was estimated by a weather-driven crop growth model. The gap between experimental and national yields was estimated. The PY_E in Ethiopia was 30% lower than that in northern Japan. This decrease was similar to the difference in PY_C between Ethiopia and northern Japan. The national yield, relative to PY_E, was 56% in Ethiopia, versus 90% in Japan. It was concluded that lower national yield in Ethiopia than Japan can be attributed to PY_C and the gap from PY_E. The combined use of experimental and modeling studies represents a useful approach for evaluating the national crop productivity from a climate perspective. Our results will support future strategies to improve rice productivity in Ethiopia.

　We propose a model to predict winter wheat developmental stages in Hokkaido, a snowy region in Japan. The model uses regression equations incorporating day of the year (DOY) data of multiple developmental stages preceding the prediction target stage and air temperature. Using DOY of snow melting dates, the timing of snow disappearance is considered explicitly. We predicted dates of panicle formation, heading, flowering, and maturity of winter wheat ‘Kitahonami’. We also applied the conventional developmental rate (DVR) model, which considers the vernalization requirement of winter wheat, and compared the obtained prediction accuracy against that of our proposed model. For the DVR model, the root mean square errors (RMSEs) were, respectively, 3.6, 1.9, 2.5, and 3.1 days for panicle formation, heading, flowering, and maturity. By contrast, for the proposed model, they were 2.8, 1.9, 1.9, and 2.6 days, respectively. Mean absolute errors (MAEs) for the proposed model were also smaller than those for the DVR model. The proposed model shows improved prediction accuracy, indicating that the use of DOYs of multiple stages and air temperature is beneficial for predicting various developmental stages.