RESUMO
Crop residues may serve as a significant source of soil emissions of N2O and other trace gases. According to the emission factors (EFs) set by the Intergovernmental Panel on Climate Change (IPCC), N2O emission is proportional to the amount of N added by residues to the soil. However, the effects of crop residues on the source and sink strength of agroecosystems for trace gases are regulated by their properties, such as the C and N content; C/N ratio; lignin, cellulose, and soluble fractions; and residue humidity. In the present study, an automated dynamic chamber method was used in combination with soil mesocosms to simultaneously measure the effects of nine different crop residues (oilseed rape, winter wheat, field pea, maize, potato, mustard, red clover, sugar beet, and ryegrass) on soil respiration (CO2) and reactive N fluxes (N2O, NO, and NH3) at a high temporal resolution. Specifically, crop residues were incorporated in the 0-4 cm topsoil layer and incubated for 60 days at a constant temperature (15 °C) and water-filled pore space (60% WFPS). Residue incorporation immediately and sharply increased soil N2O and CO2 emissions, but these were short-lived and returned to background levels within respectively 10 and 30 days. The magnitude of increase in soil NO flux following residue incorporation was lower than that in CO2 and N2O fluxes, with peak emissions observed around day 20. Overall, the N content or C/N ratio of the applied residue could not sufficiently explain the variation in soil N2O and NO emissions. The range of the calculated N2O EFs over a 60-day period was -0.17 to +4.5, being wider than that proposed by the IPCC (+0.01 to +1.1). Therefore, the residue maturity stage may be used as a simple proxy to estimate the N2O + NO emissions from incorporated residue.
