Dinitrogen and N 2O emissions in arable soils: Effect of tillage, N source and soil moisture

Abstract

A laboratory investigation was performed to compare the fluxes of dinitrogen (N 2), N 2O and carbon dioxide (CO 2) from no-till (NT) and conventional till (CT) soils under the same water, mineral nitrogen and temperature status. Intact soil cores (0–10 cm) were incubated for 2 weeks at 25 °C at either 75% or 60% water-filled pore space (WFPS) with 15N-labeled fertilizers (100 mg N kg −1 soil). Gas and soil samples were collected at 1–4 day intervals during the incubation period. The N 2O and CO 2 fluxes were measured by a gas chromatography (GC) system while total N 2 and N 2O losses and their 15N mole fractions in the soil mineral N pool were determined by a mass spectrometer. The daily accumulative fluxes of N 2 and N 2O were significantly affected by tillage, N source and soil moisture. We observed higher ( P<0.05) fluxes of N 2+N 2O, N 2O and CO 2 from the NT soils than from the CT soils. Compared with the addition of nitrate (NO 3 −), the addition of ammonium (NH 4 +) enhanced the emissions of these N and C gases in the CT and NT soils, but the effect of NH 4 + on the N 2 and/or N 2O fluxes was evident only at 60% WFPS, indicating that nitrification and subsequent denitrification contributed largely to the gaseous N losses and N 2O emission under the lower moisture condition. Total and fertilizer-induced emissions of N 2 and/or N 2O were higher ( P<0.05) at 75% WFPS than with 60% WFPS, while CO 2 fluxes were not influenced by the two moisture levels. These laboratory results indicate that there is greater potential for N 2O loss from NT soils than CT soils. Avoiding wet soil conditions (>60% WFPS) and applying a NO 3 − form of N fertilizer would reduce potential N 2O emissions from arable soils.