Rice-fish system

A rice-fish system is a polyculture practice that integrates rice agriculture with aquaculture, most commonly with freshwater fish. It is based on a mutually beneficial relationship between rice and fish in the same agroecosystem.

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, increased food security, and reduced need for inputs of fertilizer and pesticide. Because fish eat insects and snails, the systems may reduce mosquito-borne diseases such as malaria and dengue fever, and snail-born parasites such as the trematodes which cause schistosomiasis. The reduction in chemical inputs may reduce environmental harms caused by their release into the environment. The increased biodiversity may reduce methane emissions from rice fields.

History

The simultaneous cultivation of rice and fish is thought to be over 2,000 years old. Ancient clay models of rice fields, containing miniature models of fish such as the common carp, have been found in Han dynasty tombs in China.^[1] The system originated somewhere in continental Asia such as in India, Thailand, northern Vietnam and southern China. The practice likely started in China since they were early practitioners of aquaculture.^[2]

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 of Pi County northeast of Chengdu, Sichuan Province, can be used for making sauce".^[2] Liu Xun wrote the first descriptions of the system, with texts written during 900 AD during the Tang 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 excess fry in their ponds and found the results beneficial.^[1]

It is possible that the practice developed independently from China in other Asian countries. It appears to have 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 the Mozambique tilapia (Oreochromis mossambicus) in second place.^[2] As the practice spread throughout the world, new species were adopted. For example, Malaysia introduced the snakeskin gourami (Trichogaster pectoralis) and Egypt used the Nile tilapia (Oreochromis niloticus).^[2]

An early study, in Jiangsu Province in 1935, found that growing black 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 animal protein alongside the staple food, rice.^[3] From the 1980s on, Chinese systems developed rapidly with new species such as the Chinese mitten crab, the red swamp crayfish, and softshell turtles.^[3] The space used for fish-rice systems in China grew from 441,027 hectares (1,089,800 acres) 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]

Principle

Rice-fish systems are polycultures based on the concept of mutual benefit. Both rice (a semiaquatic wetland crop) and fish are grown in the same aquatic ecosystem and both benefit from this, creating a mutualistic relationship. The principle has evolved through the years and major technological advances allowed for the popularisation of the practice. A notable improvement was the addition of channels in the previously flat rice fields that allowed for the fish to continue growing even during rice harvest and dry seasons.^[3][4]

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 organic manure.^[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 of plankton and benthos 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 include fish meal, soybean cake, rice bran and wheat bran.^[3] Fish are stocked at a rate between 0.25 and 1 per square metre (1,000–4,000/acre).^[4]

Unwanted fish or invasive species can threaten the mutualistic relationship between rice and fish, and therefore reduce the food production. For example, in the integrated Rice-Swamp Loach Aquaculture Model, catfish, snakeheads (Channa argus) and paddy eels (Monopterus albus) are considered as unwanted species.^[3] Predatory birds can be considered a threat: adding nets to the rice fields can prevent these birds from eating the wanted fish.^[3]

Rice-fish systems are the most common type of integrated rice-field system. However, some 19 other models exist, including rice-crayfish, rice-crab and rice-turtle.^[3]

Rice-fish mutualism

Rice and fish form a mutualistic 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 as brown planthoppers, diseases such as sheath blight of rice, and weeds.^[7] By controlling weeds, competition for nutrients is decreased. CO₂ released by the fish may be used in photosynthesis by the rice.^[5]

The constant fish movements allow for the loosening of the surface soil which can:

• Improve oxygen levels by increasing the amount of dissolved oxygen.^[8] Consequently, the activity of microorganisms is increased and they generate more usable nutrients, which will allow an increased nutrient uptake for the rice.^[8]

• Increase mineralization of the organic matter.^[5]
• Optimization of nutrient release in the soil.
• Promote fertilizer decomposition and therefore fertilizer effectiveness.^[5]
• Better root development of the rice.^[5]

Soil fertility is improved by the integration of fish, whose manure is a fertilizer recycling organic matter, nitrogen, phosphorus and potassium.^[5] The inclusion of fish in rice-fields helps to maintain soil health, biodiversity, and productivity.^[7]

The aquatic diversity in rice-fish systems includes plankton (both phytoplankton and zooplankton), soil benthic fauna and microbial populations that all play a role in the enhanced soil fertility and the sustainability of production.^[5] However, benthic communities may be disturbed by constant grazing from the fish.^[5]

Benefits

Economic

Net gains vary between and within countries. Overall, integrated rice-fish fields have a positive impact on net returns. In Bangladesh, 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.^[9] This might be caused by the initial investment needed when starting the system.^[9][10] The use of rice-fish systems has resulted in an increase in rice yields and productivity from 6.7 tons to 7.5 tons of rice per hectare and simultaneously also from 0.75 tons to 2.25 tons of fish per hectare.^[11] The landscapes created by rice-fish systems form a possible tourist attraction, as it creates a distinctive landscape.^[10]

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]".^[12]

Rice-fish farming was one of the first systems to be considered as a "Globally Important Agricultural Heritage System" according to the FAO's Global Environment Facility.^[3]

Public health

In 1981, the Health Commission of China recognised integrated rice fields as a possible measure to decrease the population of mosquitoes, which carry diseases such as malaria and dengue fever.^[3] The larvae density is reduced in integrated rice fields since freshwater fishes routinely prey on the larvae.^[13] Rice-fish systems may decrease the number of snails, known to carry trematodes which in turn cause schistosomiasis.^[14] Farmers' diets may improve with the addition of fish protein.^[10] Reduced antibiotic resistance is another possible benefit. Rice-crayfish systems have lower abundance and diversity of antibiotic resistance genes in bacteria than aquaculture systems without rice.^[15]

Environmental

As fish control pests and weeds, fewer chemicals (such as pesticides and herbicides) are used, reducing the release of these agricultural chemicals into the environment.^[10] In addition, farmers often choose not to use pesticides, to avoid harming the fish.^[16] In turn, biodiversity is increased. Rice-fish systems can reduce methane emissions compared to rice monoculture.^[17]

Applications

Developing countries

Rice-fish systems are being exported to less developed countries with the FAO/China Trust fund.^[11] 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 the South Pacific to implement the rice-fish systems and their benefits as well as share their agriculture knowledge.^[11] For example, the China-Nigeria South-South Cooperation programme integrated over 10,000 hectares of rice-fish fields in Nigeria, which has allowed for the production of rice and tilapia to almost double.^[11]

Climate change

Climate change threatens global food production as it creates numerous changes to regional weather, such as higher temperatures, heavy rainfall, and storms. These changes may cause outbreaks of pests with, for example, an increase in the number of plant hoppers and stem borers.^[18] Rice-fish systems should be beneficial in future climates because they have higher reliability and stability than rice monoculture.^[18]

See also

• Rice-duck farming

References

Sources

• Halwart, Matthias; Gupta, Modadugu Vijay (2004). Culture of fish in rice fields. Food and Agriculture Organization and WorldFish Center, Penang, Malaysia. ISBN 983-2346-33-9.