title: Soil nitrous oxide emissions following crop residue addition: a meta-analysis.
abstract: Annual production of crop residues has reached nearly 4 billion metric tons globally. Retention of this large amount of residues on agricultural land can be beneficial to soil C sequestration. Such potential impacts, however, may be offset if residue retention substantially increases soil emissions of N(2)O, a potent greenhouse gas and ozone depletion substance. Residue effects on soil N(2)O emissions have gained considerable attention since early 1990s; yet, it is still a great challenge to predict the magnitude and direction of soil N(2)O emissions following residue amendment. Here, we used a meta-analysis to assess residue impacts on soil N(2)O emissions in relation to soil and residue attributes, i.e., soil pH, soil texture, soil water content, residue C and N input, and residue C : N ratio. Residue effects were negatively associated with C : N ratios, but generally residue amendment could not reduce soil N(2)O emissions, even for C : N ratios well above ca. 30, the threshold for net N immobilization. Residue effects were also comparable to, if not greater than, those of synthetic N fertilizers. In addition, residue effects on soil N(2)O emissions were positively related to the amounts of residue C input as well as residue effects on soil CO(2) respiration. Furthermore, most significant and stimulatory effects occurred at 60-90% soil water-filled pore space and soil pH 7.1-7.8. Stimulatory effects were also present for all soil textures except sand or clay content ≤10%. However, inhibitory effects were found for soils with >90% water-filled pore space. Altogether, our meta-analysis suggests that crop residues played roles beyond N supply for N(2)O production. Perhaps, by stimulating microbial respiration, crop residues enhanced oxygen depletion and therefore promoted anaerobic conditions for denitrification and N(2)O production. Our meta-analysis highlights the necessity to connect the quantity and quality of crop residues with soil properties for predicting soil N(2)O emissions.
authors.affiliation: Department of Soil Science, North Carolina State University, Raleigh, NC, 27695, USA.
authors.forename: Huaihai
authors.initials: H
authors.lastname: Chen
authors.forename: Xuechao
authors.initials: X
authors.lastname: Li
authors.forename: Feng
authors.initials: F
authors.lastname: Hu
authors.forename: Wei
authors.initials: W
authors.lastname: Shi
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D002244:Carbon / Q000032:analysis; D018556:Crops, Agricultural; D005308:Fertilizers; D009584:Nitrogen / Q000032:analysis; D009609:Nitrous Oxide / Q000032:analysis*; D012987:Soil / Q000737:chemistry*
chemical_list: D000393:Air Pollutants; D005308:Fertilizers; D012987:Soil; D002244:Carbon; D009609:Nitrous Oxide; D009584:Nitrogen
keywords: C : N ratio; arable soil; crop residue; meta-analysis; nitrous oxide; soil CO2 respiration; soil pH; soil texture; water-filled pore space