Diverse crop rotations can give greater cereal yields in a changing climate

The studies were led by researchers at the Swedish University of Agricultural Sciences, in collaboration with researchers across Europe and North America. The results are now published in the scientific journals of Communications Earth & Environment and Global Change Biology.

Diversifying farming by growing several different crops in sequence, instead of growing the same or very few crops year after year, can render agriculture more sustainable. Current commodity cropping is often simplified, relying mainly on a few cereal species grown in sequence in a field year after year. To maintain yields, this form of cropping is dependent on high inputs of mineral fertilisers and pesticides that contribute to environmental degradation, climate change and biodiversity loss. Moreover, to rely on few crops means the farmer is more vulnerable to adverse climatic conditions.

It is known that diversifying agriculture by rotating a greater number of crop species in sequence one growing season after the other can benefit yields. But this study contributes to a deeper understanding of the long-term effects of more diversified crop rotations and how this can help agriculture better adapt to a changing climate.

“Earlier studies have compared monoculture cropping against all forms of diverse rotations, irrespective of the level of diversity, and with less data. We wished to explore how increasing crop rotational diversity from one to two, three and more species in sequence, gradually enhances yields and when the maximum benefit is reached. We also wanted to know how such benefits might develop over time”, explains Riccardo Bommarco, Swedish University of Agricultural Sciences, and one of the co-authors.

“We also wished to explore whether more diverse rotations can compensate losses caused by detrimental climatic conditions, such as warm and dry conditions”, says Giulia Vico from the Swedish University of Agricultural Sciences and co-author of the studies.

Fortunately, agricultural researchers have maintained long-term field experiments testing yields from different crop rotations in many places over decades, some even since the late 1950s.

“We were very excited to delve into such a rich source of detailed data, covering a huge geographic range over such long periods, including many soil types, climatic conditions, and management approaches. Without the persistence and collaborative spirit of the many researchers that have managed these experiments all these years, it would have been impossible to explore these long-term benefits and effects of extreme climatic conditions”, says Monique Smith at the Swedish University of Agricultural Sciences, lead author of one of the studies.

Yields of the cereal crops increased as the number of crop species in the rotation increased, peaking at around four crops in a rotation. However, crop yields of especially winter-sown cereals declined when the diversity exceeded this number of crops in the rotation. This happened because more cereal species were included, possibly because of a lack of locally-adapted alternatives from additional crop types. The number of species that maximized yields depended on climatic conditions.

Increasing the number of non-cereal crop groups, such as legumes and broadleaves, showed no yield decline. This suggests that combining crop types with different attributes is important across many environments. Yield benefits of crop rotation diversity increased over-time for all cereals, maize and small-grains alike.

Adding a single non-cereal crop to a cereal only rotation could compensate the losses caused by warming, dry periods, and, for small grains, wet conditions. But an even more diverse rotation, with cereals plus two among broadleaves, annual legumes, or leys, could provide cereal yields on par with those of cereal only rotations in a “good year”. Diversifying rotations is thus a way to adapt our cropping systems to climate change.

The benefits of diverse crop rotations were especially large at low nitrogen fertilisation which is interesting considering the enormous environmental impact that nitrogen fertilisers have on the climate, water quality and ecosystems.

The yield benefits of diversifying crop rotations likely stem from a number of factors. Regulation of pests and weeds is enhanced. Pest life cycles are interrupted when a different crop is grown after another. Pest antagonists are introduced into the rotation. Enhanced soil health improve nitrogen availability and water holding capacity which can have long-term effects on yield, in particular in the face of excessive or insufficient precipitation and high temperatures.

“The long-term results were really encouraging because they demonstrated that switching to carefully designed and managed rotations can increase yields beyond 30 years while reducing the need for fertilisers and the vulnerability to climate change”, says Alessio Costa, Swedish University of Agricultural Sciences, lead author of the other study.

This comprehensive dataset allows tackling additional questions.

“We are now assessing if specific diversity levels can support a diverse human diet or enhance nitrogen use efficiency”, says Alessio Costa.

Contacts at SLU

Riccardo Bommarco, Professor
Department of Ecology, Swedish University of Agricultural Sciences
Riccardo.Bommarco@slu.se
+46-18-672423
https://www.slu.se/en/ew-cv/riccardo-bommarco/ 

Giulia Vico, Professor
Department of Ecology, Swedish University of Agricultural Sciences
Giulia.Vico@slu.se, +46-18-671418
https://www.slu.se/en/ew-cv/giulia-vico/

Alessio Costa, PhD student
Alessio.Costa@slu.se
https://www.slu.se/en/ew-cv/alessio-costa/

Monique Smith, Postdoctoral researcher
Monique.Smith@slu.se
https://www.slu.se/en/ew-cv/monique-smith2/

Beyond the core SLU team, this was an international collaboration with Timothy Bowles, Amélie C.M. Gaudin, Sara Hallin, Christine A. Watson, Remedios Alarcòn, Antonio Berti, Andrzej Blecharczyk, Francisco J. Calderon, Steve Culman, William Deen, Craig F. Drury, Axel Garcia y Garcia, Andrés García-Díaz, Eva Hernández Plaza, Krzysztof Jonczyk, Ortrud Jäck, R. Michael Lehman, Francesco Montemurro, Francesco Morari, Andrea Onofri, Shannon L. Osborne, José Luis Tenorio Pasamón, Boël Sandström, Inés Santín-Montanyá, Zuzanna Sawinska, Marty R. Schmer, Jaroslaw Stalenga, Jeffrey Strock, Francesco Tei, Cairistiona FE Topp, Domenico Ventrella, Robin L Walker, see publications for their affiliations.

Publications

Smith, M.E., Vico, G., Costa, A. …, Bommarco R. Increasing crop rotational diversity can enhance cereal yields. Commun Earth Environ 4, 89 (2023). https://doi.org/10.1038/s43247-023-00746-0

Costa A, Bommarco R, Smith ME, …, Vico G. Crop rotational diversity can mitigate climate-induced grain yield losses, Global Change Biology, 30, 5 (2024). https://doi.org/10.1111/gcb.17298