Nitrous oxide mitigation potential of urea co-granulated with boron sources

The application of synthetic nitrogen fertilizers accounts for 59% of global chain greenhouse gas emissions (GEE's) with direct nitrous oxide (N₂O) emissions contributing about 32% of the total anthropogenic budget. Enhanced nitrogen fertilizers (ENF) represent a strategy to mitigate N₂O emissions. This study aimed to quantify N₂O from urea (Ur) co-granulated with boron (B) sources under controlled laboratory conditions.

The experiment was conducted using static chambers containg 1 kg of soil maintained at 25ºC. Fertilizers were applied at a rate of 250 mg N kg^-1 soil. Treatments included: Ur, Ur with dicyandiamide (UrDCD), Ur with boric acid (UrAB), UrAB-DCD, Ur with ulexite (UrUL), UrUL-DCD, soil without N, and soil with DCD, with five replications. Gas samples were collected three times per week over 55 days at 0, 15 and 30 min after chambers closure using 25 mL serynges. Afterwards, samples were transferred to pre-evacuated exeteiners vials and analyzed by gas chromatograph to determine N₂O fluxes, cumulative emissions and emissions factors (EF's).

Ur and UrAB exhibited the highest peaks (~ 20 mg N-N₂O m^-2 day^-1), while UrUL and UrDCD showed intermediary fluxes (~ 10 mg N-N₂O m^-2 day^-1). UrUL-DCD and UrAB-DCD presented the lowest emissions (~ 5 mg N-N₂O m^-2 day^-1). Boron sources (without B, AB and UL) did not differ in cumulative N₂O losses (194, 167 and 100 mg m^-2) or EF's (0.42, 0.31 and 0.1). However, UrDCD (93 mg m^-2, 0.07%) significantly reduced emissions compared to Ur (215 mg m^-2, 0.49%) (p < 0.05). Field studies are required to validate these findings.