REVIEW: Do polycultures promote win‐wins or trade‐offs in agricultural ecosystem services? A meta‐analysis

Abstract

Summary1. Agriculture comprises the largest global land use, makes it a leading cause of habitat loss. It is therefore critical to identify how to best construct agricultural systems that can simultaneously provide food and other ecosystem services. This challenge requires that we determine how to maximize win-win relationships and minimize trade-offs between services. 2. Through meta-analysis, we tested whether within-field crop diversification (polyculture) can lead to win-win relationships between two ecosystem services: yield of a focal crop species and biocontrol of crop pests. We selected only studies that recorded both services (N = 26 studies; 301 observations), allowing us to better determine the underlying mechanisms of our principal findings. We calculated log-response ratios for both ecosystem services in monoand polycultures. 3. We found win-win relationships between per-plant yield of the primary crop and biocontrol in polyculture systems that minimized intraspecific competition via substitutive planting. Additionally, we found beneficial effects on biocontrol with no difference in per-unit area yield of the primary crop in polyculture fields at high cropping densities (additive planting) where legumes were used as the secondary crop. These results suggest that there is a strong potential for win-win relationships between biocontrol and per-unit area yield under certain scenarios. Our findings were consistent across geographical regions and by type of primary crop. We did not find evidence that biocontrol had an effect on yield, but rather, both were independently affected by polycultural cropping. 4. Synthesis and applications. We show that well-designed polycultures can produce win-win outcomes between per-plant, and potentially per-unit area, primary crop yield and biocontrol. Biocontrol services are consistently enhanced in polycultures, so polyculture management that focuses on yield optimization is likely to be the best strategy for maximizing both services. In doing so, we suggest that practitioners utilize polycultures that decrease plant-plant competition through a substitution of relatively large quantities of the primary crop for compatibly harvestable secondary crops. Additionally, if planting at high cropping densities, it is important that legumes be the secondary crop.

Manejo orgánico de la milpa: rendimiento de maíz, frijol y calabaza en monocultivo y policultivo

“…Para el maíz, esta sobrecosecha fue comprobada para climas tropicales y templados (Iverson et al, 2014). Esto explica por qué el rendimiento por planta del maíz fue superior al monocultivo en su asociación con el frijol y con la calabaza (Figura 1).…”

“…La milpa es además un policultivo suplementario, donde se reduce la densidad de siembra del cultivo principal (en el caso de la milpa, el maíz) para dejar espacio para uno o varios cultivos asociados. Se distingue de policultivos aditivos, donde la densidad de siembra del cultivo principal se mantiene constante (Iverson et al, 2014).…”

“…El rendimiento de un cultivo es altamente determinado por su competencia intraespecíf ica; en un policultivo suplementario, una sustitución parcial del cultivo principal por otro incrementa su nivel de producción por una reducción de la competencia intraespecíf ica (Iverson et al, 2014). Gliessman (1985) demostró que 1.73 ha de maíz en monocultivo producen tanto alimento como 1 ha de milpa; generando una cantidad adicional de 2 Mg ha -1 de residuos de cultivo (para ser incorporados al suelo) en comparación con un monocultivo.…”

A plant’s inheritance : Soil legacy effects of crops and wild relatives in relation to plant functional traits

“…Plants growing in mixtures can complement each other in the uptake of resources which enables increased plant community productivity and build-up of soil C-and N stocks, as well as reduced pathogen pressure (De Deyn et al 2009;Schnitzer et al 2011;Cong et al 2014;Iverson et al 2014). Conversely, in agro-ecosystems crops are often grown in monocultures, however these systems offer an intermediate stage towards the complexity of natural plant-and soil biodiversity as plant diversity in time is or can be easily integrated in the system (Mariotte et al 2018).…”

“…Additionally, mixtures promote the build-up of soil C-and N-stocks (De Deyn et al 2009;Cong et al 2014), and reduce pest pressure (Schnitzer et al 2011;Iverson et al 2014), forming potential feed-backs to subsequent-plant growth.…”