Relationship between soil profile accumulation and surface emission of N2O: effects of soil moisture and fertilizer nitrogen

Abstract

A soil column experiment was conducted to examine the effects of fertilizer N source and depth of placement on soil profile N2O accumulation and surface emissions at 44% and 77% water-filled pore space (WFPS). The used N fertilizers were polymer-coated urea, stabilized urea with urease and nitrification inhibitors, and conventional granular urea. Conventional urea and stabilized urea were applied either uniformly at 0–65 cm or deeply at a 40- to 65-cm depth of 65 cm repacked soil columns, whereas polymer-coated urea was subsurface banded at a 10-cm depth to reflect fertilizer application practices at a field scale. Profile N2O concentrations at 5, 15, 30, and 60 cm and surface flux were monitored over 3 months. Compared to conventional urea, stabilized urea and polymer-coated urea generally reduced N2O accumulation in the column, but not cumulative emissions. Across fertilizer sources, compared with uniform addition, deep placement reduced column N2O accumulation at 44% but not at 77% WFPS. Deep placement also reduced emissions 56–71% than for uniform placement. Column N2O accumulation doubled at 77% than 44% WFPS, whereas cumulative emissions and applied N–based emission factors were lower at the former WFPS value. Cumulative N2O emissions increased exponentially with total accumulation at 44% but not 77% WFPS. Reduced N2O emissions at high WFPS were likely due to consumption and low diffusivity of the gas in the soil profile, rather than low production by denitrification. These results suggest fertilizer N leached down the profile is less prone to N2O loss while emission reductions by using more efficient fertilizers may be limited.