Evaluation of Factors Affecting Nitrous Oxide Emission and N Transformation in a Sandy Loam Soil.

ABSTRACT: A better understanding of the complex factors affecting nitrous oxide (N₂O) emission and potential mitigation practices will assist in developing strategies to improve the sustainability of agricultural production systems. Using surface soil collected from a pomegranate orchard, a series of laboratory experiments were conducted to investigate the effect of nitrogen (N) application rate, soil water content, temperature, biochar amendment, and N transformation inhibitors on N₂O emission and associated N transformations. Treatments included several different urea application rates [0, 50, 100, 150 mg N kg^-1 at 10% water content (w/w)], soil water content (5%, 10%, 20% and 30% with 100 mg N kg^-1 applied), temperature (10°C, 25°C and 40°C with 150 mg N kg^-1 applied), incorporation of biochar (1%, w/w), an urease inhibitor (Agrotain® Ultra), and a nitrification inhibitor (N-Serve® 24) with 150 mg N kg^-1 applied. All soils were incubated at 25°C except for the different temperature treatments. Soil mineral N concentrations and pH as well as N₂O emissions were monitored. Total N₂O emission rose significantly with increasing N rates and temperature. Higher soil water content at 20% and 30% resulted in much higher total N₂O emission (11.59 and 10.03 mg N₂O-N kg^-1, or 11.5% and 10.0% of applied N, respectively) than that from 5% and 10% water content (0.26 and 0.32 mg N₂O-N kg^-1, respectively). Amendment with biochar, Agrotain® Ultra, and N-Serve^® 24 reduced N₂O emission by 73%, 78% and 74%, respectively, as compared with unammended soil (1.03 µg N₂O-N kg^-1). Changes in soil mineral N and pH suggested a delay in urea-N hydrolysis with Agrotain® Ultra and nitrification with N-Serve® 24. The results indicate that N₂O emission is highly affected by the environmental factors, and biochar or N transformation inhibitors can be effective in mitigating N₂O emission.