Non-legume cover crops can increase non-growing season nitrous oxide emissions

Citation

Thomas, B.W., Hao, X., Larney, F.J., Goyer, C., Chantigny, M.H., Charles, A. (2017). Non-legume cover crops can increase non-growing season nitrous oxide emissions, 81(1), 189-199. http://dx.doi.org/10.2136/sssaj2016.08.0269

Plain language summary

Cover crops retain post-harvest nutrients will impact non-growing
season nitrous oxide (N2O) emissions .
• Nitrous oxide emissions were greater in winter than spring or fall.
• Tillage radish increased over-winter N2O fluxes.
• Non-legume cover crops increased

• N2O fluxes under apparent NO3 limiting conditions

Abstract

Cover crops retain post-harvest nutrients but how they impact non-growing season nitrous oxide (N O) emissions is unclear. Therefore, we quantified how cover crop type (fall rye [Secale cereale L.] or oilseed radish [Raphanus sativus L.]) and fertilizer source (compost or inorganic fertilizer) affected N OO emissions, soil water-extractable organic C (WEOC) and nitrate (N O) dynamics over two non-growing seasons. A treatment with no fertilizer or cover crop was also included. Weekly, N O fluxes were determined using vented static chambers; soil WEOC and N O-N concentrations were measured monthly. Each non-growing season, mean N O fluxes were 74 to 450% greater in the winter (21 December-20 March) than spring (21 March-20 June) or fall (22 September-20 December). In winter 2014-2015, oilseed radish increased the mean N O flux by 39 and 323% compared with fall rye and no cover crop, respectively, while the mean N O fluxes were strongly correlated to the pre-winter (16 Dec. 2014) N O concentrations (r = 0.96; P < 0.001), indicating N O levels < 6 mg N O-N kg-1 limited N O fluxes. In 2014-2015, fall rye and oilseed radish had 76 and 154% greater cumulative N O emissions than amended soils with no cover crop, respectively. Across both winters, an exponential model explained 67% of variability between the pre-winter WEOC to N O ratio and N O fluxes, indicating that organic C and N O controlled over-winter N O fluxes. Non-legume cover crops increased non-growing season N O emissions, suggesting that cover crops concentrate denitrification substrates in root-Associated soil to enhance N O fluxes. 2 2 3 2 3 2 2 2 3 3 3 2 2 3 2 3 2 2 2