Microbial transport of aerated compost tea organisms in clay loam and sandy loam – A soil column study

• Use of aerated compost tea is a novel approach for bioaugmentation/bioremediation.
• We investigate rate of vertical migration of added microorganisms in soil.
• High bulk density is a limiting factor for vertical migration of bacteria and yeasts.
• Bulk density, SOM and soil texture are critical factors.
• Bioaugmentation for soil remediation may be inefficient below 2 cm in dense soils.

Soil bioaugmentation is a promising approach with applications in agriculture and in bioremediation of polluted soil. One way of supplying microorganisms to the soil that has received increasing attention during the last decade is by the addition of compost teas. The success of such strategies depends on whether the organisms are capable of migrating through the soil and reaching its target, i.e. the pollutants or soil pathogens. The structural conditions of the soil affect the microbial migration rate and this study aims to determine the migration rates of microorganisms found in aerated compost tea through both a sandy loam and a clay loam in soil columns. A considerably higher proportion of the microorganisms from the aerated compost tea were deposited at 2 cm in the sandy loam compared to the clay loam. Microbial deposition was concentrated to the top 2 cm in the sandy loam and then decreased abruptly at 10 cm whereas the clay loam presented an irregular pattern. Despite a favourable particle size distribution for microbial transport, the sandy loam retained a greater proportion of the microorganisms present in the aerated compost tea in the top 2 cm, presumably because the lower bulk density and higher soil organic matter in the clay loam aided transport and growth of microorganisms. The limited migration of aerated compost tea microorganisms in sandy soil suggests that its efficiency for bioremediation or pathogen control may be limited below 2 cm depth in similar soils. Our results indicate that in less dense soil with higher soil organic matter content the efficiency may be higher.