Inviting fish, crabs, and turtles into rice paddies reduces the need for fertilizers and pesticides, and even increases rice yields, a new study proves.
This discovery could be a major boon, since half the world now regularly consumes rice, which is driving the spread of monocrop fields that require heavy applications of fertilizers, pesticides and herbicides to amp up yields and deliver on this global demand.
In an attempt to change this, the researchers on the new eLife study explain that they spent four years peering beneath the surface of rice paddies in China, to study the natural habits of fish, turtles crustaceans. Setting up an experiment in which they carefully compared plots of rice that contained these animals, with paddies containing none, over the years they picked up on some striking trends.
In paddies stocked with tilapia, crabs, or soft-shelled turtles, they found that rice yields were up to 12% higher than yields from paddies without this animal menagerie. The researchers attributed this increased yield to the animals’ natural behaviors—particularly their penchant for deweeding, and depositing nutrient-rich feces, traits that also happen to deliver big sustainability benefits.
For instance, where there were animals, rice paddies were notably less troubled by weeds than in monocrops, because these provide a rich source of food for turtles, crabs, and fish. Paddies containing animals were supplied with feed to sustain them—but despite this, the researchers discovered that up to 50% of the diet in these animals was supplied by weeds, algae, and other naturally-available organic matter in the paddies, indicating their convenient appetite for agricultural ‘pests’. In the meantime, by providing this natural hoovering service tilapia, turtles, and crabs by default reduce the need for pesticides.
These paddies were also much more nitrogen-efficient, and had measurably quicker rates of organic matter decomposition, than the monoculture plots. The researchers think that’s due to aquatic animals’ critical role in enhancing nutrient cycles—which takes us back to those weeds.
Weeds growing between rice plants take up nitrogen from the soil, and when aquatic animals eat these plants, they absorb this compound and convert it into 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 in fact a rich source of natural fertilizer for rice plants, supporting their growth and yields. Animals also hasten the decomposition of organic material as they forage and consume, and by breaking down this material more swiftly, they increase the availability of nutrients to growing plants.
A bonus of all this is that in paddies stocked with these natural nutrient-providers, the need for polluting chemical fertilizers was reduced, the analysis revealed.
The takeaway? Farming more sustainably doesn’t necessarily cause trade-offs in profit and yields. In fact, the accumulating evidence suggests that by saving on inputs, boosting yields, and diversifying their produce, it benefits farmers’ bottom lines.
Rice farmers have known this for centuries in China, where it’s common practice to farm fish alongside rice to boost their yields and increase the diversity of food available to eat and sell. But these methods are giving way to the principles of monoculture, to supply a globalized food system.
By examining the interplay between animals and plants, this study helps to build the scientific case for why this age-old farming approach is one we should be championing, for nature and farmers alike. “These results enhance our understanding of the roles of animals in agricultural ecosystems, and support the view that growing crops alongside animals has a number of benefits,” the researchers write.
Guo et. al. “Using aquatic animals as partners to increase yield and maintain soil nitrogen in the paddy ecosystems.” eLife. 2022.
Image: Rice Plants Underwater/USFWS