Nitrous Oxide Emissions As Affected By the Use of Different Additives Applied with Urea for Potato Production.

Potato is a nitrogen (N) intensive crop, typically grown in sandy soils, where urea is often used as the primary N source.  These growing conditions have a high potential for N losses contributing to direct and indirect nitrous oxide (N2O) emissions. For practical use, various additives have been developed to decrease N losses and increase N efficiency. We used a combination of field and lab studies to evaluate the effects of different products designed to act as microbial inhibitors or enhancers. In a field experiment with potato grown in a Hubbard loamy sand soil, we compared the effect of split-applied urea, by itself or with the addition of the nitrification inhibitor 3,4-dimethylpyrazol phosphate (DMPP); the nitrification inhibitor dicyandiamide (DCD), DCD + the urease inhibitor N-(nbutyl) thiophosphoric triamide (NBPT), DMPP + NBPT,  and application of N-fixing microorganisms (NFM: Azotobacter vinelandii and Clostrium pasteurianum) at planting and 34 days after planting (DAP); application of a microbial enhancer (ME: L-amino acids, chitin, chitosan and glucosamine) mixed with NFM at planting, and two more applications of ME at inflorescence (63 DAP) and at mid tuber bulking period (78 DAP) on growing season soil N transformations and N₂O emissions. The N mineral forms NH₄⁺ and NO₃^- from soils sampled from the 0 - 30 cm depth were measured every two weeks, and daily N₂O flux was measured using chambers on 31 dates within the season (April 29 to October 2, 2015). In an incubation experiment with soil from the experimental field area, we compared the effect of urea with a separated addition of DMPP, DCD, NFM + ME, and ME alone on soil N transformations and N₂O emissions on 1, 4, 8, 16, 32, and 64 days after incubation.  In both the field and lab experiments, nitrification inhibitors (DCD and DMPP) maintained initial soil NH₄⁺-N concentration longer than NFM and ME and urea alone, and also maintained N₂O emissions close to the zero N control treatment. Conversely, NFM and ME did not significantly affect nitrification of NH₄⁺-N, but increased NO₂^--N and resulted in higher N₂O emissions compared to nitrification inhibitors and urea alone.