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

Amidst population growth, escalating food costs, limited arable land, and farmland degradation, the adoption of innovative technologies—like organic waste recycling and nutrient recovery—is crucial for enhancing the resilience of global agri-food systems. Nitrogen-Enriched Organic fertilizer (NEO) is produced using a new method, where dinitrogen (N2) is captured from the air through a plasma process and mixed with slurries or digestates as nitrate (NO3-) and nitrite (NO2-). This process leads to solid slurry acidification and a high NO2- content, potentially yielding toxic inorganic or organic N compounds. This study investigated the impact of NEO derived from cattle slurry and biogas digestate on soil nitrification—conversion of NH4+ to NO2- and NO3- by aerobic autotrophic bacteria and archaea. We investigated and compared the potential nitrification rates in soil samples from two agricultural trials (cereal and grass) treated with NEO and other fertilizers after two consecutive fertilization years. Additionally, we examined the immediate nitrification response to NEO through 73-hour soil incubations. Our results revealed that NEO significantly stimulated nitrification rates in agitated soil slurries, regardless of the feedstock used, surpassing rates observed in ammonium controls. Similarly, this pattern was also observed in loosely placed soil samples, with high nitrification rates occurring with NEO and ammonium chloride. Interestingly, the differences in nitrification rates between field-fertilized soil samples were minimal and inconsequential, suggesting that while NEO exhibits a rapid boost in nitrification rates shortly after application, this effect is not sustained ≈ six months after fertilization under field conditions. Consequently, NEO indicates its potential as an environmentally benign fertilizer without adversely affecting soil nitrification.