Plasma treated cattle slurry with modest fertilizer effect on grass

Plasma-based nitrogen (N) enrichment of organic fertilizers is a process that utilizes plasma technology and electricity to infuse liquid biobased fertilizers with atmospheric N, doubling plant-available N content. The final product is labeled as Nitrogen-Enriched Organic Fertilizer (NEO). This study investigates and compares the applicability of NEO against conventional fertilizers in grass production during 2020–2023 across two regions in Norway. Regarding different fertilizers' N efficacy, in the trials featuring only grasses, applying 210 kg N ha⁻¹ in NEO yielded dry matter (DM) and N yield comparable to those achieved with 149 and 154 kg N ha⁻¹ in mineral fertilizer, respectively. Besides, the untreated cattle slurry and mineral fertilizer combination containing 210 kg N ha⁻¹ resulted in a DM and N yield equivalent to 178 and 180 kg N ha⁻¹ in mineral fertilizer. In the grass-clover mixture trials, NEO and mineral fertilizers reduced the clover proportion, significantly influencing the overall yield. Merging the results from all trials (2021–2022), it was found that given identical N-min content, standalone mineral fertilizer, and the untreated slurry and mineral fertilizer combination resulted in ∼19 % and ∼28 %, and ∼14 % and ∼13.5 % higher DM and N yields than NEO, respectively. Further, NEO provided ∼9 % and ∼25 % higher DM and N yields than untreated slurry. Notably, NEO's N-min content was nearly double that of untreated slurry (210 vs. 107 kg N ha⁻¹). Nonetheless, a supplementary trial (2023) employing different NEO variants with reduced nitrite and elevated nitrate levels returned more promising results than those examined in prior years. Still, ∼9 % and ∼6 % less DM and N yield than mineral fertilizer with identical 210 kg N ha⁻¹ content. Our findings suggest that although a considerable N fraction of NEO did not translate to yields compared to other fertilization treatments, and given that NEO is an evolving product, the NEO's enhanced performance in the final study year highlights the necessity for continued research and optimization to fully unlock and utilize the potential advantages of NEO in future agriculture.