Denitrification in Four California Soils: Effect of Soil Profile Characteristics
1978
Gilliam, J. W. | Dasberg, S. | Lund, L. J. (Lanny J.) | Focht, D. D.
The effects of soil profile characteristics upon rate and products of denitrification were investigated using four soils in laboratory columns under steady-state water flow conditions. A general relationship existed between soil texture and amount of denitrification. Soils with heavy textured subsoils readily reduced added NO₃⁻. However, the soil with the lowest clay content had restricted water flow in the surface horizon and reduced the greatest amount of NO₃⁻. The relationship between soil texture and denitrification is a result of the relationship between water flow and denitrification. It was concluded that any soil condition which impedes water flow will be positively related to denitrification and that spatial variability in denitrification is likely to be as great as observed variability in water movement. The ratio of N₂ to N₂O found during denitrification was extremely variable with measured values from 100:1 to 1:4. The low concentrations of N₂O measured during denitrification occurred in soils where the denitrification was occurring deep in the soil profile, but there was no indication that this low concentration was a result of further reduction of N₂O as N₂O diffused through the soil profile. Our data indicate that it is currently not possible to accurately predict relative amounts of N₂ and N₂O which will be produced during most denitrification in soils, and that estimates of that N₂O produced from agricultural lands have a large uncertainty factor.
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