Pea-based cover crop mixtures have greater plant belowground biomass, but lower plant aboveground biomass than a pure stand of pea
Lavergne, S., Vanasse, A., Thivierge, M.N., Halde, C. (2021). Pea-based cover crop mixtures have greater plant belowground biomass, but lower plant aboveground biomass than a pure stand of pea. Agriculture, Ecosystems and Environment, [online] 322 http://dx.doi.org/10.1016/j.agee.2021.107657
Plain language summary
In organic cash crop rotations, there is a rising interest in using multi-species cover crop mixtures instead of pure stands. These mixtures are believed to provide a wider range of ecosystem services than the use of a single species. The purpose of this study was to compare the performance of a single cover crop species (field pea) to pea-based mixtures of 2, 6 or 12 species. Aboveground biomass and root biomass production and stability were compared at 3 sites in Quebec, Canada. At all sites, the pure stand of field pea led to the greatest aboveground biomass yield, followed by the 2-species mixture, and finally by the multi-species mixtures (6 and 12 species). However, the mixtures had a greater root biomass, compared to a pure stand of field pea, indicating a potential to enhance some ecosystem services such as nutrient cycling, soil structure maintenance or carbon sequestration. Root biomass of species mixtures was also more stable between sites and years than that of the pure stand of field pea, implying more consistent provision of ecosystem services under varying soil and climate conditions. The benefits of pea-based mixtures, compared to a pure stand of field pea, lie mainly below the soil surface rather than above it.
In eastern Canada, organic grain producers have a rising interest in using cover crop mixtures instead of pure stands to maximize ecosystem services. Yield stability and belowground biomass of cover crop mixtures have however received limited attention in the scientific literature, although they do affect ecosystem services. The aims of this study were to evaluate the aboveground and belowground biomass and yield stability of pea-based cover crop mixtures, and to assess species-specific contributions to aboveground biomass. In a field experiment conducted at three site-years in Quebec, Canada, a pure stand of field pea (Pisum sativum L.) and cover crop mixtures of 2, 6, and 12 species, all including field pea, were compared to a weedy control (without cover crop). The mixtures were seeded according to a substitutive unbalanced design. The proportion of field pea ranged from 45% to 93% of the aboveground plant biomass within all mixtures. Among all site-years, pure stand of field pea provided the highest aboveground biomass (2636 kg ha−1), followed by the 2-species mixture (2320 kg ha−1) and both multi-species cover crop mixtures (mean of 1849 kg ha−1). Aboveground biomass was inversely correlated to cover crop diversity (Pearson coefficient of −0.73), and inversely correlated to weed biomass (Pearson coefficient of −0.54). Pure stand of field pea had the lowest belowground biomass and stability (693 kg ha−1, CV of 28%) when compared to mixtures (886 kg ha−1, CV of 14% on average). This study confirms that the value of pea-based mixtures, compared to a pure stand of field pea, lies mainly below the soil surface rather than above it. This could likely enhance many soil-related ecosystem services.