APPLICATION OF DIGESTATE FROM BIOGAS PLANTS AND ORGANIC WASTE COMPOST AS BIOLOGICAL FERTILIZERS: EFFECT ON LEACHING OF AMMONIUM NITROGEN AND MICROBIAL COMMUNITY IN SOIL

Digestate can be described as the product of anaerobic organic matter transformation in order to get methane in a biogas plant. The impact of using biogas digestate as an organic fertilizer on soil fertility and microbial communities has not been sufficiently researched yet. This paper deals with the effect of compost and digestate application on leaching of ammonium nitrogen and microbial community in soil. To demonstrate the effect of these fertilizers the pot experiment was performed. Three variants with different doses of digestate, one variant with compost and control variant without added fertilizers were prepared. Lactuca sativa L. (salad) was chosen as indicator plant. Significant differences in leaching of ammonium-N, development of microbial communities and plant biomass production were found. Application of compost had a positive effect on the reduction of ammonium-N leaching and also the development of microbial communities in rhizosphere was supported by compost. Conversely the digestate addition enhanced plant biomass production, but the loss of ammonium-N was higher in digestate amended variants in comparison with variant where the compost was applied. This was caused by C/N ratio of digestate, which ranged under 10. The digestate did not contain sufficient amount of C-org, therefore the soil microbes did not have enough of energy for their metabolic processes - N compounds could not be processed and stored in their biomass. In conclusion we recommend combined applying of digestate and organic matter to get sufficient stock of organic carbon.