Abstract
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.
Highlights
Crop residue incorporation in soils is a key practice in agricultural management
In the present incubation experiment, the average EFs for N2O (EFN2O) values for nine different crop residues were beyond the given uncertainty rage of 1.79 ± 0.3%
The N content or C/N ratio of the applied residue alone is not sufficient to explain the variations in N2O emissions
Summary
Crop residue incorporation in soils is a key practice in agricultural management. Residues provide organic C and N inputs to soils for maintaining or improving the soil stocks of these elements and, soil health and crop productivity (Lehtinen et al, 2014; Liu et al, 2014; Lugato et al, 2014). Regarding the residue N returning to soils, only two default EFN2O values for wet and dry climates (i.e., 0.6% and 0.5%, with an uncertainty range of 0.0%–1.1%) are considered when estimating N2O emissions (IPCC, 2019b). The EFN2O value only considers the amount and N content of crop residues, while neglecting the potential importance of its chemical composition and moisture content. The composition of organic N and C compounds in the soluble, cellulose, and lignin-like fractions determine the N mineralization potential of residues, and this affects the fate of the incorporated residue N, as it may be immobilized in soil fractions or lost to the environment through the gaseous and hydrological pathways (Lashermes et al, 2010). The effects of the composition of crop residues and the resulting interactions among mineralization, N dynamics, and N trace gas emissions have rarely been explored, and most relevant studies have characterized residues based solely on their N content or C:N ratio
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