Effect of of incorporation techniques and soil properties on NH₃ and N₂O emissions after urea application

Ammonia (NH₃) emissions affect the environment, the climate, and human health and originate mainly from agricultural sources like urea fertilizers. Such losses from urea fertilizer can be avoided by different application techniques like incorporation. However, the knowledge of the effect of these techniques on NH₃ emissions is very limited and ambiguous since incorporation can also promote nitrous oxide (N₂O) emissions. Three different principles of fertilizer incorporation methods were compared in three different soils (sandy, loamy, and clayey) at two moisture levels of 70% and 30% water-holding capacity (WHC), shallow mixing at 2 cm, injection with the slit technique at 5 cm, and deep complete incorporation at 5 cm simulating plow incorporation. The laboratory study was conducted with open dynamic incubation chambers where NH₃ emissions were monitored with washing bottles while N₂O emissions were studied with gas chromatographic (GC) measurements. The highest cumulative NH₃ emissions occurred at low soil moisture levels in sandy soil (34% of the N applied). A maximum reduction in emissions by 87% was achieved with slit injection and 82% with deep injection compared to standard surface application. The reduction effect was positively related to increasing clay content. N₂O emissions were delayed and highest from sandy soil. Overall, all urea incorporation techniques showed great potential for mitigating NH₃ emissions on the clayey soil; for sandy and drier soils, only deeper or closed slot injection were consistently effective. However, connected to the surface incorporation at the higher moisture level, a relevant increase in N₂O emissions compared to surface application was observed. Therefore, an increase in N₂O emissions by urea incorporation may rule out specific incorporation techniques for NH₃ emissions reduction from field-applied urea. In agricultural practice, a lower reduction in NH₃ by fertilizer incorporation can be assumed in sandy soils or under dry soil conditions, as well as a more challenging technical implementation.