Temperatures higher than 8℃ are commonly used when forcing cultured Japanese persimmon (Diospyros Kaki Thunb.) 'Tone-wase', without consideration of the rest completion time that the trees require. For that reason, we investigated the relation between the period of temperatures less than 7.2℃ and the Development Index (DVI), sprouting and full bloom, and cumulative temperatures for developing leaves and buds afterward. Sprouting and full bloom occurred sooner following heating initiation when DVI was over 0.7. But growth days from heating initiation to sprouting increased by advancing of heating initiation if DVI was less than 1 when the maximum temperature was managed at 30℃ and the minimum temperature was managed at 15℃. When heating was performed from the end of December, the DVI was often less than 1. Therefore, it is appropriate to set a minimum temperature at the start as 8℃, then raise it 2℃ every about 10 days. Consequently, we should set the highest temperature as 30℃. Cumulative temperatures from sprouting to full bloom were about 700℃.

View full abstract

Tomato fruits (Lycopersicon esculentum cv. Momotaro) at turning stage were treated by hot air at 38℃ for various exposure times from 6 hrs to 6 days and then stored at 20℃ for ripening. The weight loss, total sugar, titratable acidity and firmness were measured at the red-ripe stage as well as the subsequent 3 and 6 days. The surface color development was delayed in fruits exposed to hot air for 1 day or over, and the extent of delay was enhanced with an increase in exposure time. Ethylene production was inhibited during hot air treatment and recovered after transfer to 20℃. A significantly high weight loss was observed in fruits exposed to hot air for 2 or more days, but did not affect the external quality. Total sugar, titratable acidity and firmness of fruits treated for up to 3 days were similar to those of the control. The hot air treatments for duration of 1 to 3 days were found to be effective in delaying the ripening and maintaining the quality of tomato fruits. Such treatments would be usefully applied in the postharvest quality management of tomato fruits.

View full abstract

An experiment was conducted to clarify the changes of the physical and chemical properties of organic substrates with different mixing ratios of coir and peat mixture (3:7, 5:5, 7:3 and 10:0) at different times of cultivation, and the relationship between physical and chemical properties of the substrates and growth and yield of strawberries grown in soilless culture. As for the chemical properties, nutrient fixation and leaching of new substrates changed greatly in the first cultivation, although there was little change afterwards. The water holding capacity of substrate at higher coir ratios increased with increasing times of cultivation. However, there was no change in the water holding capacity with increasing times of cultivation in the substrates at higher peat mixture ratios. The C/N ratio of substrates at higher coir ratios decreased with increasing times of cultivation, although there was no change in the substrate at higher peat mixture ratios. Therefore, it was considered that the increasing water holding capacity of substrate at higher coir ratios was caused by the decomposition of substrate. The yield of strawberries during the February-March period only decreased with increasing coir ratios regardless of times of cultivation. There was no difference in the yield of strawberries grown in substrate at higher peat mixture ratios irrespective of times of cultivation. However, the yield of strawberries grown in substrate at higher coir ratio increased with increasing times of cultivation. There was highly correlation between the yield of strawberries and water content of substrate during the February-March period (r=0.74) regardless of coir ratios or times of cultivation.

View full abstract

Effects of low shading grade white cheesecloth cover (giving 10% shade) on the shoot growth and fruit quality of peach (Prunus persica Batsch cv. 'Hikawahakuho') trees were investigated. The covering greatly reduced terminal shoot growth and their contact with cheesecloth caused shoot bending resulting in mutual shading with shoots. It seemed that this delayed fruit maturation and slightly lowered fruit quality when harvested at the same time as the control. The leaf drop of covered trees was one-fifth that of the control when the trees were affected by a typhoon. The ethylene production and abscisic acid (ABA) content of the shoot tips of covered trees tended to be higher than those of the control ones. Therefore, the inhibition of shoot growth by low grade shading white cheesecloth covering may be caused by promotion of ethylene production and ABA accumulation in the shoot tips.

View full abstract

On the melting snow system using heated air onto the internal roof of a four-span greenhouse, the maximum melting rate of snow was measured in a field experimentation, and was estimated individually for the forced convection area and the natural convection area. The measured melting rate of snow fluctuated with snowfall. The maximum measured melting rate of snow was 1.6kg・m^<-2>・h^<-1>. However, the estimated melting rate of snow was 2.0kg・m^<-2>・h^<-1>. The amount of heat transfer in the forced convection area was 75% of the total heat. This suggests that optimization of ducts providing heated air onto the internal roof may increase the melting rate of snow. It was shown that the double ducts increased the heat transfer up to 18% compared with the single duct. On the other hand, the heat transfer in the natural convection area was small. Opening the thermal screens to raise the air temperature close to the roof surfaces may not work effectively on the melting performance.

View full abstract