Short term N2O, CH4 and CO2 production from soil sampled at different depths and amended with a fine sized slurry fraction1

Little is known about the interaction of the soil’s physicochemical environment and livestock slurry throughout the soil profile. In this study, five soil layers (2–6, 6–10, 10–14, 14–18, 18–22 cm) amended with a < 45 μm slurry fraction (FS) or water (control) were incubated for 58 d at 20 °C to determine the effect of the slurry position in the soil profile on the production of CO2, N2O, CH4 and total greenhouse gas (GHG) expressed as CO2 equivalent.

FS application increased the CO2 production in all soil layers by 3–8 times compared to the controls. The total CO2 produced during the incubation in the 2–6 cm amended soil layer (>1600 mg CO2–C kg−1 dry soil) was significantly greater (P < 0.05) than in other amended layers (<800 mg CO2–C kg−1 dry soil).

No detectable N2O production was observed from control treatments, and application of FS induced a slow increase in N2O production. N2O production occurred earlier and at a higher rate in deeper soil layers. Furthermore, a good correlation (r = 0.899, P < 0.05) was observed between N2O production and soil depth. The higher N2O production in the deeper soil layers could have been due to enhanced denitrification promoted by a lower aeration and low soil respiration in the deep soil. At the end of the incubation, >11% of the total applied N was lost as N2O from the two deeper soil layers against 2.5–5% in all other soil layers. Methane production was only observed from FS amended treatments within the first 7 d (range 0.02–0.41 mg C kg−1 soil d−1).

The greatest net production of GHGs, expressed as CO2 equivalents, was observed from the two deeper soil layers (≈4.5 g CO2 eq kg−1 soil). N2O and CO2 contributed equally (50%) to the total GHG production in 2–14 cm soil layers, whereas N2O contributed reached 80% to the total GHG production in the deeper soil layers. The CH4 contribution was not significant in any treatment.