Mixed cropping enhances beneficial bugs and reduces pests

Göttingen University agroecology researchers evaluate effects with a meta-analysis

The global decline in biodiversity is serious. Agricultural land use is a major contributor - especially farming single crops on a massive scale. Mixing crops can counteract this: in fields where different crops grow at the same time, there are more beneficial insects and spiders than in monocultures. At the same time, there are fewer pests. Researchers at the University of Göttingen show this through a systematic literature review and statistical meta-analysis. They found that it is particularly advantageous when cereals and legumes are combined and planted in strips or rows. The results were published in the journal Agriculture, Ecosystems & Environment.

The researchers evaluated 63 published articles comparing mixed crops with monocultures from 18 countries. They compared the species diversity, the number of individuals (abundance) and the density per plant of beneficial and harmful arthropods. They also looked at individual groups of beneficial arthropods: pollinators, decomposers, as well as predators and parasitoids that kill pests. In addition, they investigated how different combinations and arrangements of crops in mixed cropping influence the occurrence of these creatures.

Their findings show that the species diversity of beneficial arthropods is 27 percent higher in mixed crops than in monocultures. Their abundance is 36 percent higher and their density per plant 94 percent higher. Different groups of beneficial arthropods benefit differently from mixed cultures: the species diversity and abundance of pollinators, predators and parasitoids is greater than in monocultures, but there is no difference for decomposers. Harmful arthropods occur less in mixed crops than in monocultures: their abundance is 38 percent lower, their density per plant 41 percent. Their species diversity does not differ between the types of cultivation. Growing cereals and legumes together works better than the combination of different cereals in promoting beneficial insects and reducing pests. It is also more effective when the crops are grown in strips or rows rather than sown simply mixed together or the time of planting crops is staggered.

These findings show how sustainable agricultural practices can promote biodiversity and related ecosystem services. "Our results suggest that mixed cropping is an effective way to mitigate the adverse effects of intensive agriculture on beneficial arthropods in agroecosystems," says first author Dr Anjaharinony Rakotomalala, now a postdoctoral researcher at the University of Marburg. "The results should encourage policy-makers to provide incentives in agri-environmental programmes for the conversion of monocultures to mixed crops," add Dr Anoush Ficiciyan and Professor Dr Teja Tscharntke, from Göttingen University’s Agroecology research group.

Original publication: Anjaharinony A. N. A. Rakotomalala et al. Intercropping enhances beneficial arthropods and controls pests: A systematic review and meta-analysis. Agriculture, Ecosystems & Environment (2023). DOI: 10.1016/j.agee.2023.108617