FIELD EVALUATION OF NITRATE LEACHING: THE ROLE OF FERTILIZERS AND SOIL MICROORGANISMS Bruno Rizzi, Massimo Zilio, Fulvia Tambone, Piergiorgio Stevanato, Andrea Squartini, Fabrizio Adani

Bruno Rizzi 1 , Massimo Zilio 1 , Fulvia Tambone 1 , Piergiorgio Stevanato 2 , Andrea Squartini 2 , Fabrizio Adani 1

1 Dipartimento di Scienze Agrarie e Ambientali –DISAA, Università degli Studi di Milano, Italia 2 Dipartimento di Agronomia, Animali, Alimenti, Risorse naturali e Ambiente –DAFNAE, Università degli Studi di Padova, Italia

Nitrate (NO3-) pollution of groundwater and surface water bodies is a widespread threat in developed countries, causing contamination of drinking waters and eutrophication of surface water bodies. Agriculture has been addressed as one of the main contributors to this phaenomena, due to the use of high nitrogen inputs of intensive agriculture and subsequent risk of leaching. The fate of nitrogen based fertilizers in field applications, both organic and inorganic, actually depends on a wide range of factors (chemical form of fertilizer, climate, metabolism of microbial communities, soil characteristics), so further studies are necessary to better clarify the speciation of nitrogen in the profile of agricultural soils.

Our study aims to the description of nitrogen speciation in different agricultural scenarios, during all the year, and on the correlation of such speciation with microbial metabolic activity; particular attention is given to the environmental fate of nitrate.

Experiment consists in a field cultivation of two crops, corn and rice, which differ from each other for growing season and cultivation technique. For each crop three treatments (high solids sewage sludge digestate fertilization, mineral fertilization and a non-fertilized control) are compared in triplicate.

Soil profile is investigated from surface to 100 cm depth, in 5 sampling times distributed during the agricultural season. Each layer of the soil profile is characterized in terms of nitrogen speciation (Ammonia, Nitrate, Total Kjeldahl Nitrogen, Organic Nitrogen), analysis which are integrated by a complete description by a chemical and physical point of view (Soil Texture, Water Content, temperature, pH, ORP, TOC, Assimilable Phosphorus).

Microbial activity in the soil profile is investigated using molecular-based approaches: quantitative polymerase chain reaction (qPCR) is used for the quantification of microbial genes, in particular those that are correlated with the transformations of nitrogen in soils.

Results by now shows that there is a possible risk of nitrate leaching only after fertilizations; however, nitrate concentrations in deeper layers of soil profile are very low (< 20 mg kg-1), with no differences between digestate, mineral fertilization and unfertilized soil.

The use of different fertilizations seems to have not an influence on the metabolic activity of soil microorganisms, but analysis are still ongoing, and will be integrated with studies of metagenomics to better describe the structure of soil microbial communities.

Described research work is funded and integrating part of Horizon 2020 Nutri2Cycle project (Grant Agreement no. 773682, https://www.nutri2cycle.eu/).

Data presented also affer to Horizon 2020 Systemic project (Grant Agreement no. 730400, https://systemicproject.eu/).

Special thanks to Acqua & Sole s.r.l., partners in Nutri2Cycle project, for their support in experimental fields management, and to University of Padua, DAFNAE, for their precious collaboration on molecular microbiology.