Effect of water pH on spring onion growth

Abstract

Since spring onion (Allium fistulosum) is one of the most commonly cultivated vegetables around the world (Food and Drug Administration, n.d.), it is important to understand optimal growth conditions for this crop. Despite its culinary and economic importance, there is no consensus on how the pH value of water affects spring onion growth. So, the objective of our study is to determine the effect of water pH on spring onion growth. We watered spring onion roots with water mixed with vinegar to make four different pH treatments (pH = 4, 5, 6, 7), and measured stem height over time as a proxy for growth. We hypothesized that there would be significant differences in growth heights between different pH groups, and specifically that onions in the slightly acidic treatment group pH = 6 would have optimal growth, since other crops were shown to prefer slightly acidic pH solutions, but suffer root damage at more acidic pH’s (Islam et al. 1980). After 13 days of observation, all 4 groups of spring onions grew and appeared healthy. A two-way ANOVA, with days after planting and pH as the two factors, was performed and showed there was a significant effect of time on onion growth, but no significant effect of pH on spring onion group means. This result differs from our hypothesis, but could be because other factors such as mineral content in soil, or sunlight, had a larger effect on spring onion growth and so the effect of pH was negligible in comparison to other factors.