Will aquaponics work in India?
Fish on rice plantations to save the climate. Can it work?
When it comes to combining rice and fish, most people think of sushi or an Asian curry pan, but not of a recipe for combating climate change. Still, it can be one. In this country, an average of five kilograms of rice are consumed per person each year. In China and India, where rice is the staple food, an average of more than 100 kilograms of rice is consumed per person per year. Rice feeds two thirds of the world's population and accounts for a fifth of the world's calorie intake.
Rice cultivation naturally has an ecological footprint - and contrary to expectations, not a good one. Although rice performs many times better in terms of emissions per calorie than meat, vegetables or wheat, for example, the enormous quantities produced make up for the lead in absolute terms. We consume a lot, so we also need to be aware of the consequences.
The methane gas that vapors from the flooded rice fields, for example, is around 25 times stronger than carbon dioxide. Between ten and 20 percent of the methane in our atmosphere comes from growing rice. Not least because of this, researchers have been experimenting for years with methods of how rice could be grown in a more climate-friendly way. This is exactly where the fish come into play. They should be released on the watered rice plantations, eat plankton and thus indirectly reduce methane emissions.
The idea of breeding rice and fish together came up earlier. In China, for example, farmers have relied on this symbiosis for thousands of years. While the rice provided shelter for carp, they ate annoying insects, seaweed and pathogens out of the way. That brought bigger yields, more income, less pesticides and additional food.
Plankton for the perch
The climate aspect was not so well known for a long time. The US NGO Resource Renewal Institute has been preparing to change that for around five years now. The first tests were started together with the ecologist Shawn Devlin, who found out in a study lasting several years that adding perch to a Finnish lake could reduce methane emissions many times over.
The research in Finland had shown that perch mainly eats zooplankton. This in turn usually feeds on small bacteria, which in turn feed on methane. As the bacteria had fewer predators, their population increased, and at the same time the amount of "exterminated" methane increased.
The manipulation of the food chain ultimately resulted in less environmentally harmful methane being released into the atmosphere. At first glance, one might think of a trick as ingenious as it is banal.
More income for farmers
Devlin and the NGO have since tested the method on dozens of rice fields in the US state of California - including sea bream. There were experiments all over the world not only with fish, but also with crabs, crayfish, shrimp and ducks. Because the food chain is always such a thing, nets in many places have to protect the Reissee residents from hungry birds.
In the US experiment, methane emissions are said to have been reduced by more than half. Not only the methane, but also the CO2 content in the air could be improved with this: Because the plankton, which the fish feeds, absorbs CO2 from the atmosphere and thus serves as a carbon store, according to the NGO.
How profitable the fish and rice concept can be was shown in Bangladesh. There, farmers could look forward to a 50 percent increase in income.
Many critical voices
However, the researchers are still a long way from using the method worldwide. Of the approximately 20 million hectares that would be suitable for rice-fish cultivation in India, just 0.23 million hectares are used accordingly. So are resources being wasted here?
This question is not that easy to answer. Quite a few experts are actually quite skeptical of the idea. "The cultivation area of the rice-fish systems is very limited globally," says Reiner Wassmann, emeritus scientist at the International Rice Research Institute. Study results show that many farmers use far cheaper pesticides to produce rice instead of fish. The acute worsening water shortage in many rice-growing regions is another problem.
The most successful strategies to date for reducing emissions are therefore those that target shorter flooding periods, according to the expert. The fields are alternately dried and flooded, which almost halves methane emissions.
"Cultivating fish together with rice is certainly not the big game changer for climate change," says Steven Weiss, biologist at the University of Graz. Much depends on how the fish are raised and what they get to eat. "It cannot be ruled out that some farmers will breed more fish to meet the increasing demand and then feed them with additives such as fishmeal, which would be nonsense for the climate," says Weiss.
There is a lack of money
Another problem: it will take years for fish and rice production to be perfectly matched to the region and its climatic conditions, according to the expert. "Most farmers simply cannot afford such a break from normal operations." In order to experiment with the new methods, new support and funding models are needed for farmers.
It would be almost too nice if a concept that is thousands of years old suddenly found a simple solution in the fight against global warming. However, at least as many parameters depend on the consequences for the climate as there are links in the animal food chain. That doesn't mean that the ancient Chinese didn't have a great premonition after all. Used correctly, it could contribute to an environment worth living in for people, fish and rice. (Jakob Pallinger, Fabian Sommavilla, 7.3.2021)
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