Diversification of intensive maize production with undersowings reveals taxon-specific biodiversity-yield trade-offs

Diversified cropping systems are an important strategy in the agro-ecological transformation process to increase biodiversity and agricultural productivity. Maize ( Zea mays L.) is an economically important crop, but is associated with high environmental costs and low biodiversity. Undersowing maize can mitigate the effects of intensive maize cultivation and provide additional resources for arthropods. However, competition between maize and undersowings can reduce maize yield substantially. In a field experiment, we investigated how diversifying maize with six different undersowings (fescue, cress, clover, vetch, mallow, marigold-borage) effects pollinating insects, predatory arthropods, potential pest control and yield compared to mono-maize and mono-undersowings. Undersowing maize showed clear improvements over mono-maize with up to 10 times more pollinator individuals and up to two times more predatory arthropods, but there was no single undersown species that benefited all groups equally. Yield reductions ranged from 15 – 65 % in mixed versus mono-maize. Undersowing maize with flowering species promoted pollinating insects but at high cost to yield, displaying a high biodiversity yield trade-off, while pest predation was maintained across the observed yield range. Thus, pollinators may be more effectively supported by measures outside the maize field while predatory arthropods benefit from within-field diversification with small-growing legumes and grasses, which caused less yield reduction. Considering the biodiversity-yield trade-off is an important aspect to increase farmers’ acceptance to diversify high performing maize. Among several innovative tools to promote agro-ecological transformation at the landscape scale, undersowing in maize may be an important one, but validation across multiple independent sites should be pursued. • Undersowings support biodiversity but reduce maize yields by 15 – 65 %. • Flowering undersowings benefit pollinating insects but at a high costs to yield. • Predatory arthropods benefit from within-field diversification through undersowing. • Pest predation potential can be maintained over the observed yield range. • Undersowing maize may promote agro-ecological transformation at the landscape scale.