Co-Cultures: Growing together gives more rice and aquatic food

Allowing aquatic organisms to grow in rice fields – a practice called co-culture – increases rice yields while maintaining soil fertility and reducing weeds.
  1. Jian Liu
  2. Siri Caspersen
  3. Jean WH Yong  Is a corresponding author
  1. School of Environment and Sustainability, Global Institute for Water Security, University of Saskatchewan, Canada
  2. Department of Biosystems and Technology, Swedish University of Agricultural Sciences, Sweden

When you eat rice with fish – or rice with crab or shrimp – you probably do not think about where the food came from. And if you do, you probably think that the rice grew in a paddy field, while the fish, crab or shrimp were caught in the sea. However, this may only be partially true. Systems for growing rice and various aquatic animals together have existed for over 1,200 years, but the practice of ‘co-culture’ has only recently gained the attention of the major rice-producing nations and the scientific community (Xie et al., 2011).

Rice is one of the most widely consumed grains in the world and is grown in more than 100 countries. It is a staple food source for over half of the world’s population and of upmost importance for lower income countries in Asia, Latin America and Africa (Bashir et al., 2020). Climate change, declining natural resources and an ever-growing population put immense pressure on both increasing yields and reducing the environmental footprint of rice (Hu et al., 2016; Ahmed and Turchini, 2021). Global trends are thus moving towards sustainable and organic management of biological resources (Chen et al., 2014; Muller et al., 2017). Strategic coupling of terrestrial and aquatic ecosystems, such as growing crops and aquatic animals together, could help meet this target (Ahmed and Turchini, 2021).

Previous research has shown that co-cultures can boost yields, improve soil health and enhance ecosystem services (Mueller et al., 2012; Campanhola and Pandey, 2019). But even though co-culture systems would help optimise the use of land and water resources to produce food – while reducing the environmental impacts associated with rice monocultures – large-scale and long-term data are lacking (Bashir et al., 2020).

Now, in eLife, Xin Chen and colleagues at Zhejiang University and Bioversity International – including Liang Guo and Lufeng Zhao as joint first authors – report new evidence in support of co-cultures with aquatic animals and rice crops (Guo et al., 2022). Between 2017 and 2020, the team conducted three separate field experiments in which rice was grown with either fish, crabs or soft-shelled turtles. Each set-up also included a control experiment, where rice was grown as a monoculture. No agrochemicals were used to control weeds, pests or diseases during the field trials.

Over the four years, the co-cultures demonstrated multiple benefits (Figure 1). Rice yield was consistently higher in fields containing aquatic animals (between 8.7% and 12.1%). Moreover, the team was also able to harvest significant amounts of fish, crab and turtle as food (between 560 and 2660 kg/ha). Co-cultures also had fewer weeds and maintained consistent levels of mineral nutrients (nitrogen and phosphorus) in the soil. Moreover, the breakdown of organic matter happened faster in the co-cultures.

The benefits of co-culture for growing rice.

Guo et al. showed that growing rice with aquatic animals (fish, crabs or turtles) increases rice yield, suppresses the growth of weeds, and maintains the levels of nitrogen and phosphorus in the soil. Growing rice with crabs or turtles was also shown to promote a more efficient use of nitrogen. The photographs show the field before (left) and after (middle) the rice plants were transplanted, and near harvest time (right). The aquatic animals were introduced as juveniles about a week after transplanting and lived with the rice plants throughout the experimental periods.

Animals are instrumental in moving elements, such as carbon, nitrogen and phosphorus, in the environment (Schmitz et al., 2018). To find out whether the biology of a co-cultured animal would affect the growth of rice, Guo et al. carried out three additional, controlled experiments to trace the movement of nitrogen from feed (labelled with stable isotopes) to aquatic animals and the environment.

Analyses of the animal’s food intake revealed that fish and crabs obtained up to half of their diet (50% and 35%, respectively) from the rice fields, consuming algae, phytoplankton or weeds. Turtles relied more on additional feed, and only derived 16% of their food intake naturally. The animals’ wastes and any uneaten feed also increased the nutrient availability for the rice plants: rice plants used up to a third of the nitrogen from the animal feed.

The work of Guo et al. demonstrates clearly how co-cultures could make agriculture more sustainable, by increasing soil fertility and reducing the need for fertilizers or pesticides. Moreover, these coupled systems could also help fight the spread of malaria by introducing natural, co-culturing predators, such as frogs (which eat the mosquitos) and fish (which eat the mosquito larvae), and so contribute towards several ‘Sustainable Development Goals’ of the United Nations (Khatiwada et al., 2016; Campanhola and Pandey, 2019).

More research is needed to better understand the impact of co-culture on greenhouse gas emissions and nutrient pollution (Bashir et al., 2020). Nevertheless, these experiments provide a good foundation for further studies to explore how agriculture can be made more sustainable.

References

Article and author information

Author details

  1. Jian Liu

    Jian Liu is in the School of Environment and Sustainability, Global Institute for Water Security, University of Saskatchewan, Saskatoon, Canada

    Competing interests
    No competing interests declared
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-4199-1296
  2. Siri Caspersen

    Siri Caspersen is in the Department of Biosystems and Technology, Swedish University of Agricultural Sciences, Alnarp, Sweden

    Competing interests
    No competing interests declared
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-1033-5483
  3. Jean WH Yong

    Jean WH Yong is in the Department of Biosystems and Technology, Swedish University of Agricultural Sciences, Alnarp, Sweden

    For correspondence
    jean.yong@slu.se
    Competing interests
    No competing interests declared
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-3325-8254

Acknowledgements

The authors would like to thank SLU Aquaculture and Jordbruksverket for financial support.

Publication history

  1. Version of Record published: February 22, 2022 (version 1)

Copyright

© 2022, Liu et al.

This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited.

Metrics

  • 1,143
    Page views
  • 124
    Downloads
  • 2
    Citations

Article citation count generated by polling the highest count across the following sources: Crossref, PubMed Central, Scopus.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Open citations (links to open the citations from this article in various online reference manager services)

Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)

  1. Jian Liu
  2. Siri Caspersen
  3. Jean WH Yong
(2022)
Co-Cultures: Growing together gives more rice and aquatic food
eLife 11:e77202.
https://doi.org/10.7554/eLife.77202

Further reading

    1. Ecology
    Luca Casiraghi, Francesco Mambretti ... Tommaso Bellini
    Research Article

    The understanding of eco-evolutionary dynamics, and in particular the mechanism of coexistence of species, is still fragmentary and in need of test bench model systems. To this aim we developed a variant of SELEX in vitro selection to study the evolution of a population of ∼1015 single-strand DNA oligonucleotide ‘individuals’. We begin with a seed of random sequences which we select via affinity capture from ∼1012 DNA oligomers of fixed sequence (‘resources’) over which they compete. At each cycle (‘generation’), the ecosystem is replenished via PCR amplification of survivors. Massive parallel sequencing indicates that across generations the variety of sequences (‘species’) drastically decreases, while some of them become populous and dominate the ecosystem. The simplicity of our approach, in which survival is granted by hybridization, enables a quantitative investigation of fitness through a statistical analysis of binding energies. We find that the strength of individual resource binding dominates the selection in the first generations, while inter- and intra-individual interactions become important in later stages, in parallel with the emergence of prototypical forms of mutualism and parasitism.

    1. Ecology
    Yongzhi Yan, Scott Jarvie, Qing Zhang
    Research Article

    Habitat loss and fragmentation per se have been shown to be a major threat to global biodiversity and ecosystem function. However, little is known about how habitat loss and fragmentation per se alters the relationship between biodiversity and ecosystem function (BEF relationship) in the natural landscape context. Based on 130 landscapes identified by a stratified random sampling in the agro-pastoral ecotone of northern China, we investigated the effects of landscape context (habitat loss and fragmentation per se) on plant richness, above-ground biomass, and the relationship between them in grassland communities using a structural equation model. We found that habitat loss directly decreased plant richness and hence decreased above-ground biomass, while fragmentation per se directly increased plant richness and hence increased above-ground biomass. Fragmentation per se also directly decreased soil water content and hence decreased above-ground biomass. Meanwhile, habitat loss decreased the magnitude of the positive relationship between plant richness and above-ground biomass by reducing the percentage of grassland specialists in the community, while fragmentation per se had no significant modulating effect on this relationship. These results demonstrate that habitat loss and fragmentation per se have inconsistent effects on BEF, with the BEF relationship being modulated by landscape context. Our findings emphasise that habitat loss rather than fragmentation per se can weaken the positive BEF relationship by decreasing the degree of habitat specialisation of the community.