Short-Term Effects of Crude Botanical Extracts and Rhizosphere Soils on Soil Respiration and β-Glucosidase Activity

Plant-derived compounds may modify microbial carbon turnover, but their effects on soil respiration and enzyme activity are poorly documented. This laboratory study compared crude ethanolic extracts and rhizosphere soils of garlic, ginger, turmeric, moringa and aloe vera with untreated soil during a 5-week incubation (n = 3). Extracts reduced basal respiration and cumulative CO2-C relative to the control, with garlic extract giving the most persistent reduction, whereas rhizosphere soils showed stimulated CO2-C release from week 2 onward. Beta-Glucosidase activity was 4.3 percent lower under garlic extract, 14.0 percent lower under aloe vera extract and 57.4 percent lower in garlic rhizosphere soil, whereas turmeric extract and ginger rhizosphere soil increased it. Extracts also reduced culturable bacterial, yeast and mold counts. Apparent soil organic matter was higher under several treatments but cannot be separated from added carbon. These preliminary results show treatment-specific responses; their field relevance requires characterized extracts, appropriate controls and longer studies.