COS 312-2 - CANCELLED - Nitrogen-Enriched Organic fertilizer (NEO) elevates nitrification rates shortly after application but has no lasting effect on nitrification in agricultural soils

Abstract: In times of growing population, increasing cost of food production, scarcity of arable land, and environmental degradation of farmlands, new sustainable fertilizers are needed to enhance the resilience of global agri-food systems. Nitrogen-Enriched Organic fertilizer (NEO) is an example of a potentially sustainable bio-based fertilizer. Dinitrogen (N₂) is captured from the air by a plasma process and mixed as nitrate (NO₃^-) and nitrite (NO₂^-) with animal slurries or other liquid organic fertilizers. This process strongly acidifies the slurry, which, together with the resulting high NO₂^- content, may result in toxic inorganic or organic N compounds. Here we test the effect of NEO produced from cattle slurry and biogas digestate on soil nitrification, i.e., the conversion of NH₄⁺ to NO₂^- and NO₃^- mediated by aerobic autotrophic bacteria and archaea. We compared potential nitrification rates in soil samples from two trials (cereal and grass) fertilized with NEO and other fertilizers for two consecutive years. We also studied the immediate nitrification response to NEO in 73-hour bottle incubations. In agitated soil slurries, NEO strongly stimulated nitrification rates irrespective of feedstock (more than 2-fold), exceeding rates in ammonium controls. In loosely placed soil, a similar pattern was found, but this time ammonium chloride also resulted in high nitrification rates. By contrast, differences in nitrification rates between field-fertilized soil samples were minimal and negligible. Therefore, we conclude that despite the intense stimulation of nitrification by NEO right after application to soil, NEO has no long-lasting effects on nitrification under field conditions. This implies that NEO does not impose adverse effects on soil nitrifier communities.