Study of Total Bacteria and Ammonia-Oxidizing Bacteria and Ammonia-Oxidizing Archaea in Response to Irrigation with Sewage Sludge Compost Tea in Agricultural Soil

Organic amendments have been shown to improve the quality of agricultural soils. Thus, the use of sewage sludge compost tea as a fertilizer can be considered a worthy and environmentally friendly alternative as it also offers the option of recycling sludge at the same time. However, an in-depth knowledge of how the addition of this product affects soil microbial diversity is still necessary. As such, the main objective of this study was to evaluate, at a microcosm level, the effects of irrigation with sewage sludge compost tea in an olive grove soil, focusing on the changes in the total bacteria, ammonia-oxidizing bacteria (AOB), and ammonia-oxidizing archaea (AOA). For this purpose plastic pots were filled with olive grove soil, watered with different amounts of water and/or compost tea, and incubated at 21 and 35 degrees C for a period of 90days. Denaturing gradient gel electrophoresis (DGGE) fingerprinting, real-time PCR, and 454-pyrosequencing analysis were performed. Our results suggested that the addition of sewage sludge compost tea (liquid fertilizer) slightly increased the soil biological diversity during the incubation time which suggests that sewage sludge compost tea did not have any negative effects in the soil microbiota. Accordingly and regardless of the incubation temperature, significant changes in the soil community structure were not observed throughout the experiment, suggesting that the treated soils maintained their microbiological stability.