Ultra-fine bubble irrigation promotes coffee (Coffea arabica) seedling growth under repeated drought stresses

ABSTRACTCoffee plants are likely to be highly susceptible to changes in climate, and several statistical studies based on projections of altered precipitation patterns have predicted negative effects on coffee growth including the loss of suitable cultivation areas in most coffee-producing countries. Increased drought occurrences owing to climate change are expected to be a new challenge for stable coffee production, because coffee production relies heavily on stable rainfall conditions. In recent years, ultra-fine bubble (UFB) water has been reported to be effective in alleviating environmental stresses for plant growth, especially drought stress. The objective of the present study was to determine the effect of UFB water irrigation on the growth of coffee seedlings to mitigate the stress of repeated droughts. To simulate an environment with frequent droughts, six pot experiments were conducted over 3 years by applying repeated drought stress to coffee plants in a greenhouse. The results showed that UFB water had a remarkable growth-promoting effect on coffee seedlings under drought conditions. In contrast, no significant effect on coffee growth was observed in the environment with sufficient nutrients, in which additional fertilizer was used. UFB water significantly increases the root length and surface area of coffee plants, which may promote water absorption and prevent leaf senescence (leaf cell collapse) under drought conditions. This leads to coffee plants adapting to drought conditions. Therefore, UFB water irrigation may be an effective measure to promote coffee growth in drought conditions.