Use of Agro-Energy Waste as Agricultural Inputs: Impact on Soil Bacterial Diversity

Waste reuse is a very interesting option from an economic, environmental, and often a social point of view. However, it is important to assess the impact of their use on soil characteristics to optimize proper dosages. Because microbial diversity can be used as one of the indicators of soil quality; we aimed to evaluate soil bacterial diversity after using combinations of gravel (waste from drilling in the petroleum industry) and Crambe press-cake (a by-product of biodiesel production) in haplic planosol cultivated with sunflowers (Helianthus annus l.) using a culture-independent technique, Denaturing Gradient Gel Electrophoresis (DGGE). Analysis of variance showed that the use of gravel and Crambe press cake at doses tested in haplic planosol did not significantly affect soil microbial diversity. This wastes had no significant effect on the number of bands obtained using DGGE. Besides, dynamics of the bacterial population did not follow any other parameter, such as chemical parameters, evaluated in the study, confirming that changes in the chemical characteristics of the soil due to the application of the wastes did not affect bacterial diversity. The results indicate that the use of these wastes is environmentally safe and that higher sodium content did not affect soil bacteria diversity.