Management of cover crops in temperate climates influences soil organic carbon stocks: a meta‐analysis

Abstract

Increasing the quantity and quality of plant biomass production in space and time can improve the capacity of agroecosystems to capture and store atmospheric carbon (C) in the soil. Cover cropping is a key practice to increase system net primary productivity (NPP) and increase the quantity of high-quality plant residues available for integration into soil organic matter (SOM). Cover crop management and local environmental conditions, however, influence the magnitude of soil C stock change. Here, we used a comprehensive meta-analysis approach to quantify the effect of cover crops on soil C stocks from the 0-30 cm soil depth in temperate climates and to identify key management and ecological factors that impact variation in this response. A total of 40 publications with 181 observations were included in the meta-analysis representing six countries across three different continents. Overall, cover crops had a strong positive effect on soil C stocks (P < 0.0001) leading to a 12% increase, averaging 1.11 Mg C/ha more soil C relative to a no cover crop control. The strongest predictors of SOC response to cover cropping were planting and termination date (i.e., growing window), annual cover crop biomass production, and soil clay content. Cover crops planted as continuous cover or autumn planted and terminated led to 20-30% greater total soil C stocks relative to other cover crop growing windows. Likewise, high annual cover crop biomass production (>7 MgÁha −1 Áyr −1) resulted in 30% higher total soil C stocks than lower levels of biomass production. Managing for greater NPP by improving synchronization in cover crop growing windows and climate will enhance the capacity of this practice to drawdown carbon dioxide (CO 2) from the atmosphere across agroecosystems. The integration of growing window (potentially as a proxy for biomass growth), climate, and soil factors in decision-support tools are relevant for improving the quantification of soil C stock change under cover crops, particularly with the expansion of terrestrial soil C markets.

Cover crops and carbon sequestration: Lessons from U.S. studies

“…These review results indicate legume CCs appear to accumulate more SOC than grass CCs, particularly when legume CCs are grown in summer or in regions with both abundant precipitation and mild temperatures. Results agree with global reviews on CCs and SOC stocks indicating legume CCs either have no effect (McClelland et al., 2021; Poeplau & Don, 2015) or increase (Jian et al., 2020) SOC stock relative to nonlegume CCs.…”

“…Cover crop biomass production depends, however, on numerous factors. One such factor is the number of CC growing days (McClelland et al., 2021; Ruis et al., 2017). It is clear that the number of days when CCs are actively growing is more important than the number of days between CC planting and CC termination as CCs may not be growing during the whole period between CC planting and termination.…”

“…This finding suggests the high average SOC accumulation rate reported in global CC reviews may not be observed in all locations. Indeed, the high average SOC accumulation rates can be often driven by a few studies (Jian et al., 2020; McClelland et al., 2021; Poeplau & Don, 2015). For example, a recent global review concluded CCs can accumulate large amounts of SOC (1.11 Mg ha −1 ), but the same review discussed CCs increased SOC stock more in subtropical than in temperate cool climates (McClelland et al., 2021).…”

Seed size variability has implications for achieving cover cropping goals

“…Cover crops can help farmers adapt to the existential threats of climate change and herbicide resistance while reducing agriculture's impact on the environment (Bunchek et al., 2020; Kaye & Quemada, 2017). To advance cover cropping practices, researchers strive to elucidate relationships between cover crop management and ecosystem services including erosion prevention, nutrient cycling, weed suppression, and carbon sequestration (Blanco‐Canqui et al., 2015; Daryanto et al., 2018; McClelland et al., 2021). Despite efforts to refine recommendations including species selection and timing (Delgado & Gantzer, 2015), guidance for seeding rate—one of the most basic management decisions—remains remarkably imprecise.…”

Managing plant surplus carbon to generate soil organic matter in regenerative agriculture

“…Instead, these practices, in concert with other intensive agricultural practices such as intensive tillage, monoculture, application of pesticides, and bare fallows, have caused declines in SOM, increases in greenhouse gas emissions, and pollution of waterways (Loisel et al 2019). However, adopting regenerative agricultural practices, such as substituting chemical with organic fertilizers like compost or manure, reducing tillage, intensifying and diversifying crop rotations, and cover cropping, often increase SOM (McClelland et al 2021). The mechanisms underlying the positive effects of regenerative agricultural practices on SOM, however, are not well understood.…”