A modern study of the ancient practice of mixing rice and fish farming reveals striking trends

Inviting fish, crabs and turtles to rice paddies reduces the need for fertilizers and pesticides, and even increases rice yields, according to a new study.

This discovery could be a major boon, since half the world now regularly consumes rice, leading to the spread of monoculture fields that require heavy applications of fertilizers, pesticides and herbicides to increase yields and meet this global demand.

In an attempt to change that, researchers of the new eLife explain that they spent four years peering beneath the surface of rice paddies in China, study the natural habits of fish, shellfish turtles. By setting up an experiment in which they carefully compared rice plots containing these animals with rice paddies that did not, they found some striking trends over the years.

In paddies populated with tilapia, crabs or soft-shelled turtles, they found that rice yields were up to 12% higher than in paddies without this animal menagerie. The researchers attributed this increase in yield to the animals’ natural behaviors, particularly their penchant for weeding and depositing nutrient-rich dung, traits that also offer great sustainability benefits.

For example, where there were animals, the paddy fields were much less bothered by weeds than in monocultures, as these provide a rich food source for turtles, crabs and fish. Rice paddies containing animals received food to sustain them, but despite this, researchers found that up to 50% of the animals’ diet was provided by weeds, algae and other naturally available organic matter. in the paddy fields, indicating their convenience. appetite for agricultural “pests”.

Meanwhile, by providing this natural suction service, tilapias, turtles and crabs reduced the amount of pesticides needed on these more diverse rice paddies, the researchers found.

These paddies were also much more nitrogen-efficient and had significantly faster rates of organic matter decomposition than monoculture plots. Researchers believe this is due to the essential role of aquatic animals in enhancing nutrient cycles, which brings us back to these weeds.

Weeds growing between rice plants absorb nitrogen from the soil, and when aquatic animals eat these plants, they absorb this compound and convert it to ammonia, turning it back into a form that plants can use. In fact, studies show that aquatic animals convert up to 85% of the nitrogen they consume into ammonia. So when they excrete waste, it is actually a rich source of natural fertilizer for rice plants, supporting their growth and yields. Animals also speed up the decomposition of organic matter when they feed and consume, and by breaking down this material faster, they increase the availability of nutrients to growing plants.

A bonus of all this is that in paddy fields filled with these natural nutrient providers, the need for polluting chemical fertilizers has been reduced, the analysis found.

Take-out? More sustainable agriculture does not necessarily entail trade-offs in terms of profits and yields. In fact, accumulating evidence suggests that by saving on inputs, increasing yields and diversifying their products, it benefits farmers’ bottom lines.

Rice farmers have known this for centuries in China, where it is common to raise fish alongside rice to increase their yields and increase the diversity of foods available to eat and sell. But these methods are giving way to the principles of monoculture, to feed a globalized food system.

By examining the interaction between animals and plants, this study helps scientifically substantiate why this age-old agricultural approach is the one we should champion, for nature and for farmers alike. “These findings improve our understanding of the roles of animals in agricultural ecosystems and support the idea that growing crops alongside animals has a number of benefits,” the researchers write.

Guo and. al. “Using aquatic animals as partners to increase yield and maintain soil nitrogen in paddy ecosystems.” eLife. 2022.

Image: Rice plants underwater/USFWS