title: Climate, duration, and N placement determine N2 O emissions in reduced tillage systems: a meta-analysis.
abstract: No-tillage and reduced tillage (NT/RT) management practices are being promoted in agroecosystems to reduce erosion, sequester additional soil C and reduce production costs. The impact of NT/RT on N2 O emissions, however, has been variable with both increases and decreases in emissions reported. Herein, we quantitatively synthesize studies on the short- and long-term impact of NT/RT on N2 O emissions in humid and dry climatic zones with emissions expressed on both an area- and crop yield-scaled basis. A meta-analysis was conducted on 239 direct comparisons between conventional tillage (CT) and NT/RT. In contrast to earlier studies, averaged across all comparisons, NT/RT did not alter N2 O emissions compared with CT. However, NT/RT significantly reduced N2 O emissions in experiments >10 years, especially in dry climates. No significant correlation was found between soil texture and the effect of NT/RT on N2 O emissions. When fertilizer-N was placed at ≥5 cm depth, NT/RT significantly reduced area-scaled N2 O emissions, in particular under humid climatic conditions. Compared to CT under dry climatic conditions, yield-scaled N2 O increased significantly (57%) when NT/RT was implemented <10 years, but decreased significantly (27%) after ≥10 years of NT/RT. There was a significant decrease in yield-scaled N2 O emissions in humid climates when fertilizer-N was placed at ≥5 cm depth. Therefore, in humid climates, deep placement of fertilizer-N is recommended when implementing NT/RT. In addition, NT/RT practices need to be sustained for a prolonged time, particularly in dry climates, to become an effective mitigation strategy for reducing N2 O emissions.
authors.affiliation: Department of Plant Sciences, University of California, Davis, CA 95616, USA. cvankessel@ucdavis.edu
authors.forename: Chris
authors.initials: C
authors.lastname: van Kessel
authors.forename: Rodney
authors.initials: R
authors.lastname: Venterea
authors.forename: Johan
authors.initials: J
authors.lastname: Six
authors.forename: Maria Arlene
authors.initials: MA
authors.lastname: Adviento-Borbe
authors.forename: Bruce
authors.initials: B
authors.lastname: Linquist
authors.forename: Kees Jan
authors.initials: KJ
authors.lastname: van Groenigen
mesh_terms: D000383:Agriculture; D002980:Climate; D009584:Nitrogen / Q000032:analysis*; D009609:Nitrous Oxide / Q000032:analysis*
chemical_list: D009609:Nitrous Oxide; D009584:Nitrogen