Non‐Legume Cover Crops Can Increase Non‐Growing Season Nitrous Oxide Emissions

Abstract

Abbreviations: FRC, fall rye with compost; FRF, fall rye with inorganic fertilizer; MDL, minimum detection limit; ORC, oilseed radish with compost; ORF, oilseed radish with inorganic fertilizer; NCC, no cover crop with compost; NCF, no cover crop with inorganic fertilizer; CON, nonamended soil with no cover crop; WEOC, water-extractable organic carbon. P ost-harvest seeding of cover crops reduces the risk of wind erosion and nutrient loss through leaching and runoff during the non-growing season, but how cover crops affect C and N transformations during this time is poorly understood. Although soil microbial activity slows during the non-growing season, this period is particularly prone to N 2 O emissions in temperate regions (Wagner-Riddle and Thurtell, 1998;Dörsch et al., 2004;Ellert and Janzen, 2008;Hao, 2015). Whether cover crops reduce N 2 O emissions during the non-growing season by assimilating ammonium (NH 4 ) and NO 3 is uncertain. In part, this is because cover crops release labile C and N through root exudates and rhizodeposition during their growth phase and freeze-thaw cycles, which can stimulate microbial activity and increase N 2 O emissions (Petersen et al., 2011;Gul and Whalen, 2013;Mitchell et al., 2013). This may counter the crop N uptake and explain why there is no clear consensus on how non-legume cover crops effect N 2 O emissions (Basche et al., 2014 Core Ideas• Nitrous oxide emissions were greater in winter than spring or fall.• Tillage radish increased over-winter N 2 o fluxes.• Non-legume cover crops increased N 2 o fluxes under apparent No 3 limiting conditions.

Cover Crop Biomass Production in Temperate Agroecozones

“…While many reviewed CC effects on soil properties (Blanco-Canqui et al, 2015), C sequestration (Poeplau and Don, 2015;, soil biology (Vukicevich et al, 2016;Finney et al, 2017), and other topics, an overall synthesis of CC biomass production under different cropping systems, management systems, CC species, and climatic conditions across temperate regions worldwide is not available. Individual studies suggest that CC biomass production can be highly variable, even within the same region (Finney et al, 2016;Thomas et al, 2016Thomas et al, , 2017.…”

Fertilizer timing affects nitrous oxide, carbon dioxide, and ammonia emissions from soil

“…Based on these amounts, nitrate-N concentration in the surface 30 cm in the early fall, mid-spring, early winter, early spring, mid-spring, and early summer were 9.09, 10.24, 6.76, 6.55, 0.91, and 10.66 mg NO 3 -N kg −1 , respectively. For some of the application dates, the NO 3 -N concentrations may have been low enough in the unfertilized treatments to increase the conversion of N 2 O to N 2 (Blackmer & Bremner, 1979;Thomas et al, 2017).…”

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

“…Studies investigating gas fluxes under different CC termination dates are very few. In many studies, CCs are terminated early with low biomass production (<1 Mg ha −1 ), which may reduce gas fluxes (Negassa et al, 2015; Thomas et al, 2017). For example, Negassa et al (2015) showed that CO 2 and N 2 O fluxes were not affected when CC biomass yield was below 0.5 Mg ha −1 .…”

“…For example, Negassa et al (2015) showed that CO 2 and N 2 O fluxes were not affected when CC biomass yield was below 0.5 Mg ha −1 . Similarly, CO 2, N 2 O, and CH 4 fluxes were unaffected when CC biomass yield was 0.5 to 1.11 Mg ha −1 (Guardia et al, 2016; Thomas et al, 2017). However, CO 2 fluxes, but not N 2 O and CH 4 fluxes, were affected by larger quantities of CC biomass yield, such as 4.11 Mg ha −1 (Sanz‐Cobena et al, 2014).…”