Episodic N 2 O emissions following tillage of a legume–grass cover crop mixture

[摘要] Nitrogen (N) fertilizer inputs to agricultural soils area leading cause of nitrous oxide ( N 2 O ) emissions. Legume cover cropsare an alternative N source that can reduce agricultural N 2 O emissionscompared to fertilizer N. However, our understanding of episodic N 2 O flux following cover crop incorporation by tillage is limited and hasfocused on single-species cover crops. Our study explores whether increasingcover crop functional diversity with a legume–grass mixture can reduce pulseemissions of N 2 O following tillage. In a field experiment, we plantedcrimson clover ( Trifolium incarnatum  L.), cereal rye ( Secale cereal L.), a clover–rye mixture, and a no-covercontrol at two field sites with contrasting soil fertility properties inMichigan. We hypothesized that N 2 O flux following tillage of the covercrops would be lower in the mixture and rye compared to the clovertreatment because rye litter can decrease N mineralization rates. Wemeasured N 2 O for approximately 2 weeks following tillage to capturethe first peak in N 2 O emissions in each site. Across cover croptreatments, the higher-fertility site, CF, had greater cover crop biomass,2-fold-higher aboveground biomass N, and higher cumulative N 2 O emissions than the lower-fertility site, KBS ( 413.4±67.5 vs. 230.8±42.5  g N 2 O-N ha −1 ; P =0.004 ). Therewas a significant treatment effect on daily emissions at both sites. AtCF, N 2 O fluxes were higher following clover than the control 6 d aftertillage. At KBS, fluxes from the mixture were higher than rye 8 and 11 dafter tillage. When controlling for soil fertility differences betweensites, clover and mixture led to approximately 2-fold-higher N 2 O emissions compared to rye and fallow treatments. We found partial supportfor our hypothesis that N 2 O would be lower following incorporation ofthe mixture than clover. However, treatment patterns differed by site,suggesting that interactions between cover crop functional types andbackground soil fertility influence N 2 O emissions during cover cropdecomposition.

[学科分类] 大气科学