Abstract

Compost tea is gaining much interest due to its nutritional, biostimulation and disease suppression benefits to the plants. Four experiments were carried out to determine the effect of incubation temperature, incubation periods, dilution rate and nutritional sources on the microbial populations, physico-chemical properties and indole acetic acid (IAA) levels. Incubation at 28°C showed the highest number of bacteria and aerobic N₂-fixing bacteria (ANFB), along with the highest levels of total nitrogen and IAA. All the microbial populations increased in proportion with increase in the incubation period; however, increasing the incubation more than 48 h did not show any significant improvement (P ≤ 0.05) in the physico-chemical properties or IAA levels. All microbial numbers and chemical properties decreased by increasing the dilution rate. Adding a mixture of the three used nutrients (molasses "0.5% v/v", ammonium nitrate "0.5 g/L" and di-potassium phosphate "0.5 g/L") resulted in the highest microbial populations (except for ANFB) as compared to the molasses, or double the amount of each other chemical alone. This study show the optimum conditions for preparing compost tea with high microbiological and physico-chemical properties. The study includes ANFB, important for soil application, and IAA, important for foliar application, which have not been studied before in compost tea.

Key words: Compost tea extraction, factors, microbiology, physico-chemical, indole acetic acid (IAA), aerobic N₂-fixing bacteria (ANFB).