Short term N 2O, CH 4 and CO 2 production from soil sampled at different depths and amended with a fine sized slurry fraction

Abstract

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 CO 2, N 2O, CH 4 and total greenhouse gas (GHG) expressed as CO 2 equivalent. FS application increased the CO 2 production in all soil layers by 3–8 times compared to the controls. The total CO 2 produced during the incubation in the 2–6 cm amended soil layer (>1600 mg CO 2–C kg −1 dry soil) was significantly greater ( P < 0.05) than in other amended layers (<800 mg CO 2–C kg −1 dry soil). No detectable N 2O production was observed from control treatments, and application of FS induced a slow increase in N 2O production. N 2O 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 N 2O production and soil depth. The higher N 2O 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 N 2O 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 CO 2 equivalents, was observed from the two deeper soil layers (≈4.5 g CO 2 eq kg −1 soil). N 2O and CO 2 contributed equally (50%) to the total GHG production in 2–14 cm soil layers, whereas N 2O contributed reached 80% to the total GHG production in the deeper soil layers. The CH 4 contribution was not significant in any treatment.