Effect of vermicompost tea on rooibos (Aspalathus linearis) growth and rhizosphere microbial diversity under field conditions

Abstract

Increasing demand for rooibos tea (Aspalathus linearis) requires producers to increase production in a sustainable manner. The aim of the study was to examine the effect of applying vermicompost tea (VCT) (100 and 500 L ha^–1 month^–1) and tap water drenches on one-year old rooibos nutrient uptake, and tea yields and rhizosphere microbial diversity under field conditions in the Nieuwoudtville region. The application of VCT solutions had no significant effect on rooibos survival or tea yields compared to the same volume of tap water. The application of tap water with or without VCT resulted in significant increases in plant survival (23–31% higher), resulting in lower tea yields (38–66% lower) likely due to increased plant competition. The application of VCT drench applied at 5 times the supplier’s recommendations (500 L ha^–1 month^–1) significantly enhanced foliar P and Fe and reduced foliar Al, attributed to the organic acids in VCT. VCT application at 100 L ha^–1 significantly enhanced bacterial species diversity and decreased dominance. Further research is needed to identify which bacterial species are increasing with addition of vermicompost tea. Application of compost tea with higher mineral N content would likely be more beneficial for enhancing yields.