Abstract
1. Vine growth and nutrient absorption of Delaware grapes were observed in soils of different moistures as“High”83-72% of water holding capacity, “Medium”65-55%, “Low”55-50% and“Very low”48-35%. As a result, apparent assimilation, shoot elongation, weight growth of a plant, blooming rate of flowerlets per cluster and berry development were all inferior with decreasing soil moisture.
2. When temperatures rose rapidly after the end of the rainy season, several leaves at the base of the shoots were discolored and shed early. Except for the“Very low” plot where the leaves dropped least, the lower the soil moisture, the more severe was the defoliation. Particularly, the damage was greatest in the“High-Very low”plot where the soil moisture was changed from“High”to“Very low”in early July.
3. Leaf content of Mg was markedly influenced as compared with those of N, P, K, and Ca when the soil moisture was reduced. It decreased so much as to reach a level of deficiency with fruiting vines both in the plots of“High-Very low”and“Very low”Therefore, most severe defoliation in the“High-Very low”plot might have been induced by the rapid change of water condition as well as Mg deficiency due to drought.
4. In the measurement of the daily change of berry size, the berries shrunk during the day and enlarged again at night in summer. The difference of berry size between day and night became greater with decreased soil moisture.
