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Arice-fish system is arice polyculture, a practice that integratesriceagriculture withaquaculture, most commonly withfreshwater fish. It is based on amutually beneficial relationship between rice and fish in the sameagroecosystem. The system was recognized by theFAO in 2002 as one of the firstGlobally Important Agricultural Heritage Systems.
The benefits of rice-fish systems include increased rice yield, the production of an additional (fish) crop on the same land,diversification of farm production, increasedfood security, and reduced need for inputs offertilizer andpesticide. Because fish eat insects and snails, the systems may reducemosquito-borne diseases such asmalaria anddengue fever, and snail-bornparasites such as thetrematodes which causeschistosomiasis. The reduction in chemical inputs may reduce environmental harms caused by their release into the environment. The increasedbiodiversity may reducemethane emissions from rice fields.
The simultaneous cultivation of rice and fish is thought to be over 2,000 years old. Ancient clay models ofrice fields, containing miniature models of fish such as thecommon carp, have been found inHan dynasty tombs inChina.[1] The system originated somewhere in continental Asia such as inIndia,Thailand,northern Vietnam andsouthern China. The practice likely started in China since they were early practitioners of aquaculture.[2]
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Common carp were probably among the first fish used in rice-fish systems.Wei dynasty records from 220 to 265 AD mention that "a small fish with yellow scales and a red tail, grown in the rice fields ofPi County northeast ofChengdu,Sichuan Province, can be used for making sauce".[2]Liu Xun wrote the first descriptions of the system, with texts written during 900 AD in theTang dynasty.[1] Rice-fish systems may have evolved from pond culture in China; one theory proposes that the practice started when farmers decided to place excessfry in their ponds and found the results beneficial.[1] The practice may have developed independently from China in other Asian countries; there is evidence that it spread from India to neighbouring Asian countries over 1500 years ago.[2]
The practice slowly gained popularity among farmers, and by the mid-1900s, over 28 countries on all continents except Antarctica used rice-fish systems.[2] Historically, the common carp was the most commonly used fish, with theMozambique tilapia (Oreochromis mossambicus) in second place.[2] As the practice spread throughout the world, new species were adopted. For example, Malaysia introduced thesnakeskin gourami (Trichogaster pectoralis) and Egypt used theNile tilapia (Oreochromis niloticus).[2] An early study, inJiangsu Province in 1935, found that growingblack carp (Mylopharyngodon piceus),grass carp,silver carp,bighead carp (Aristichthys nobilis) and common carp together with rice was beneficial.[1] Rice-fish systems were traditionally low maintenance, growing additional animalprotein alongside thestaple food, rice.[3] The space used for fish-rice systems in China grew from 441,027hectares (1,089,800acres) to 853,150 hectares (2,108,200 acres) and the production increased dramatically, going from 36,330 tonnes to 206,915 tonnes between 1983 and 1994.[3]In 2002, the rice-fish system became one of the firstGlobally Important Agricultural Heritage Systems to be recognized by theFAO.[4][3]
Rice and fish form amutualistic relationship: they both benefit from growing together. The rice provides the fish with shelter and shade and a reduced water temperature, along with herbivorous insects and other small animals that feed on the rice.[7] Rice benefits from nitrogenous waste from the fish, while the fish reduce insect pests such asbrown planthoppers, diseases such assheath blight of rice, and weeds.[7] By controlling weeds, competition for nutrients is decreased. CO2 released by the fish may be used inphotosynthesis by the rice.[5]
The constant fish movements allow for the loosening of the surface soil which can:
Soil fertility is improved by the integration of fish, whose manure is a fertilizer recycling organic matter, nitrogen,phosphorus andpotassium.[5] The inclusion of fish in rice-fields helps to maintainsoil health, biodiversity, and productivity.[7]
The aquatic diversity in rice-fish systems includesphytoplankton,zooplankton), soilbenthic fauna andmicrobial populations; all of these play a role in enhancing soil fertility and sustaining long-term production.[5] However, benthic communities may be disturbed by constant grazing by the fish.[5]
Rice-fish systems arepolycultures based on the potential for mutual benefit. To put this into practice, channels are added in the previously flat rice fields to allow the fish to continue growing even during rice harvest and dry seasons.[3][9]
Before creating the rice field, the field is treated with 4.5–5.25 tonnes per hectare (2.0–2.3 short ton/acre) of organicmanure.[3] Organic manure is applied again during the main growing season, with about 1.5 tonnes per hectare (0.7 short ton/acre) applied every 15 days.[3] This provides nutrients for rice and the added cultures ofplankton andbenthos that feed the fish.[3] During the main growing season, supplementary feeds complement the plankton and benthos culture and are used once or twice a day.[3] The supplementary feeds includefish meal,soybean cake,rice bran andwheat bran.[3] Fish are stocked at a rate between 0.25 and 1 per square metre (1,000–4,000/acre).[9]
Unwanted fish orinvasive species can threaten the mutualistic relationship between rice and fish, and therefore reduce productivity. For example, in the integrated Rice-Swamp Loach Aquaculture Model,catfish,snakeheads (Channa argus) andpaddy eels (Monopterus albus) are considered as unwanted species.[3]Predatory birds are a threat;bird netting can be used to protect the fish.[3]
Net gains vary between and within countries. Overall, integrated rice-fish fields have a positive impact on net returns. InBangladesh, net returns are over 50% greater than in rice monocultures.[6] In China, the net return by region is between 45 and 270% greater.[6] A case of loss in net returns was found in Thailand with only 80% of the profitability of rice monocultures.[10] This might be caused by the initial investment needed when starting the system.[10][11] The use of rice-fish systems has resulted in an increase in rice yields and productivity from 6.7–7.5 tonnes per hectare (3.0–3.3 short ton/acre) and simultaneously also from 0.75–2.25 tonnes per hectare (0.3–1.0 short ton/acre) of fish.[12] Rice-fish systems form a possible tourist attraction, as the practice creates a distinctive landscape.[11] The addition of fish diversifies the farm's production, increases food security, and generates income; Halwart and Gupta comment that if it also increases rice yield and cuts the need for fertilizer and pesticide inputs, these are "added bonus[es]".[13]
In 1981, the Health Commission of China recognised integrated rice fields as a possible measure to decrease the population ofmosquitoes, which carry diseases such asmalaria anddengue fever.[3] Thelarvae density is reduced in integrated rice fields sincefreshwater fishes routinely prey on the larvae.[14] Rice-fish systems may decrease the number ofsnails, known to carrytrematodes which in turn causeschistosomiasis.[15] Farmers' diets may improve with the addition of fish protein.[11] Reducedantibiotic resistance is another possible benefit; bacteria in rice-crayfish systems have a lower frequency and a lower diversity of antibiotic resistance genes than aquaculture systems without rice.[16]
As fish control pests and weeds, fewer chemicals (such aspesticides andherbicides) are used, reducing the release of these agricultural chemicals into the environment.[11] Paddies with fish have been measured to require 24% less fertilizer input and 68% less pesticide usage than rice grown alone.[4] In addition, farmers often choose not to use pesticides, to avoid harming the fish.[17]
In turn,biodiversity is increased.[18] For example, the addition of common carp (Cyprinus carpio) to a rice monoculture increased the number of energy transfer pathways by 78.69%, while the energy transfer efficiency increased by 67.86%.[19]
In addition, rice-fish systems can reducemethane emissions compared to rice monoculture.[18] Rice paddyfields are agriculture's main contributors togreenhouse gases, which contribute toclimate change, mainly because when flooded, as they often are on a regular cycle, they supportmethanogenic bacteria; overall, paddyfields contribute around 10% of the global greenhouse effect. Rice-fish systems may be able to contribute to global-scale reduction of methane emissions.[4]
In the 2010s, rice-fish systems were exported to less developed countries with the FAO/China Trust fund.[12] About 80 Chinese rice-fish experts were sent to underdeveloped countries in diverse regions of the world such as certain African countries, other parts of Asia and in theSouth Pacific to implement the rice-fish systems and their benefits as well as share their agriculture knowledge.[12] For example, the China-Nigeria South-South Cooperation programme integrated over 10,000 hectares (25,000 acres) of rice-fish fields inNigeria, which has allowed for the production of rice and tilapia to almost double.[12]
Climate change threatens global food production as it creates numerous changes to regional weather, such as higher temperatures, heavy rainfall, and storms.[20][21] These changes may cause outbreaks of pests with, for example, an increase in the number ofplant hoppers andstem borers.[21] Rice-fish systems offer the potential for benefit in future climates because they have higher reliability and stability than rice monoculture in the face of changing weather patterns.[21] The diversifiedagroecosystem is likely to be more resilient to climate change, making better use of resources and supporting a range of ecosystem services.[22]
Rice-fish systems are the most common type ofintegrated rice-field polyculture. However, some 19 other models exist, includingrice-duck, rice-crayfish, rice-crab and rice-turtle.[3] From the 1980s on, the diversity of Chinese rice polycultures developed rapidly, involving new species such as theChinese mitten crab, thered swamp crayfish, andsoftshell turtles.[3]
