Impacts of Early‐ and Late‐Terminated Cover Crops on Gas Fluxes

Abstract

Cover crops (CCs) could alter soil processes, but the effects of early versus late termination of CCs on gas fluxes are not well known. We evaluated temporal changes in fluxes of CO2, N2O, and CH4 and related soil properties in no‐till corn (Zea mays L.) with and without winter rye (Secale cereale L.) CCs that were terminated early (30 d before planting) or late (at planting) in a rainfed silty clay loam and an irrigated silt loam in Nebraska from April 2016 to June 2017. Gas fluxes, soil temperature, and soil water content were measured biweekly to monthly, and wet aggregate stability and particulate organic matter concentrations were measured seasonally. We also compared our results with a global literature review. Late‐terminated CCs did not affect CH4 fluxes but increased daily CO2 fluxes by 59% compared with no CC at both sites and N2O fluxes by 92% at the rainfed site only. Early termination did not affect gas fluxes. Termination date did not affect cumulative fluxes and had minimal effects on soil properties. The literature review supports our study results, which indicate that CC effects on (i) CO2 fluxes are driven by plant respiration during the CC growing period, and (ii) N2O and CH4 fluxes are minimal under grass CCs. Overall, under no‐till, CC termination date has small effects on N2O and CH4 fluxes, but late CC termination can increase CO2 fluxes in spring due to greater biomass yield compared with early termination. Core Ideas Early‐terminated cover crops had limited effects on CO2 fluxes in this study. Late‐terminated cover crops increased CO2 flux mainly in spring due to higher cover crop biomass yield. Cover crop termination effects on N2O and CH4 fluxes were generally nonsignificant. Our literature review showed cover crops affected CO2 mostly during their growing period. Our literature results also showed grass cover crops had limited effects on N2O.

Winter cereal rye cover crop decreased nitrous oxide emissions during early spring

“…Our findings differ from Ruis et al (2018), where rye had a minimal impact on N 2 O-N emissions. Differences between Ruis et al (2018) and our study were attributed to four factors. First, Ruis et al (2018) sampled their system 14 times from late April 2018 to June 2019 and collected point samples from the treatments biweekly between 1000 and 1400 h. In comparison, we measured emissions more than 1,100 times over 3 yr. Second, Ruis et al (2018) applied N fertilizer, whereas in our study N was not applied.…”

“…As discussed earlier, the application of N fertilizer may have placed the Ruis et al (2018) in the high emissions portion of the S-Curve where the amount of N uptake by the cover crop was not enough to affect N 2 O-N emissions. Third, Ruis et al (2018) reported that in a dryland system, the cover crop had a minimal impact on soil moisture, whereas in our study rye reduced soil moisture. Fourth, Ruis et al (2018) reported that between 6 March and 25 April an N 2 O-N flush was not observed and changes in soil inorganic N were not reported.…”

Cover crop impacts on soil physical properties: A review

“…Values above or below bars are the number of observations. Data source: Drury et al (1999); Stipesevic and Kladivko (2005); Teasdale and Daughtry (1993);Wagner-Riddle et al (1994); Kahimba et al (2008); Blanco-Canqui, Claassen, and Presley (2012); Daigh, Sauer, Xiao, and Horton (2014); Evans et al (2016);Negassa, Price, Basir, Snapp, and Kravchenko (2015); Ruis et al (2018);Vann, Reberg-Horton, Edmisten, and York (2018); Zhang et al (2009) of crops in fields with and without CCs. Few studies monitored soil temperature on a continuous basis.…”

“…The amount of CC canopy cover along CC biomass production is, however, expected to affect soil temperature, particularly near the soil surface. Indeed, when CC biomass production is low, CC effect on soil temperature can be minimal or negligible (Appelgate, Lenssen, Widenhoeft, & Kaspar, 2017;Ruis, Blanco-Canqui, Jasa, Ferguson, & Slater, 2018). However, when CCs produce large amounts of biomass (>5 Mg ha −1 ), soil temperature in spring can be reduced by as much as 4 • C (Blanco-Canqui et al, 2011).…”

“…(2016); Negassa, Price, Basir, Snapp, and Kravchenko (2015); Ruis et al. (2018); Vann, Reberg‐Horton, Edmisten, and York (2018); Zhang et al. (2009)…”