A. G. Cagauan, R. D. S. Branckaert and C. Van Hove

Several countries in Asia practice integrated rice-duck farming. The benefits and limitations of this system are discussed. It is noteworthy that on-farm resources such as duck manure and feed waste are not adequately used and recycled in the system. There is a great potential for increasing the productivity of the integrated system which offers research opportunities. The integration of fish and the nitrogen-fixing aquatic fern Azolla are promising approaches for increasing the production potential of the rice-duck system. Fish, Azolla and ducks integrated with rice can result in nutrient enhancement, pests (weeds, insects and golden apple snails) control, feed supplementation and biological control. Some of the results of a case study on integrated rice-fish-Azolla-duck farming system conducted in the Philippines are presented.

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In the Asian region, the majority of duck production is closely associated with wet-land rice farming, particularly in the humid tropics and sub-tropics (Farrell, 1997). The traditional practice of duck raising in ricefields in the Philippines, Thailand, Vietnam and Indonesia involves herding the birds in paddy fields after the rice harvest. In the Philippines, duck herders transfer their flocks from one farm to another depending on food availability. Herders house their flocks in sheds usually along irrigation canals where water is available for the duck. Duck pasture in ricefields after rice harvest helps economize on the high cost of feed. In the Southeastern part of the Philippines, particularly Bukidnon, Agusan and Capiz, ducks are introduced in lowland ricefields during the maximum tillering to get rid of some weeds and insects (Quisumbing, 1983) and there has been no reported damage to rice. In the central province of Thailand, enterprising duck raisers contract the care for fattening ducks to rice farmer in the area (Chandrapanya and Pantastico, 1983). After a month or so, the duck raiser comes back and pays the farmers for his services. In Taiwan, Republic of China, ducks are released in ricefields mainly to control large mud snails and weed (AICAF, 1988). Since the dramatic introduction in Southeast Asia of the herbivorous snail Pomacea canaliculata Lamarck during the early eighties, ducks can be assigned a new function in the ricefields, the control of this exotic pest.

In Japan, rice-duck farming practice was promoted 400 years ago by allowing wild ducks into ricefields (Manda, 1992). In the late 1980s, the practice was revived to fit modern agriculture by Takao Furuno, a farmer in Fukuoka prefecture, Kyushu, Japan, who has practiced organic farming for the last 12 years (Furuno, 1996). Furuno integrates rice farming with aigamo duck, a crossbred between wild and domestic duck. About seven-day old aigamo duck at 400 ducklings per ha are released in ricefields within 10 days after rice transplanting for two months. Simultaneous raising of ducks with rice helps control weeds and insects that leads to the non-application of pesticides (Furuno, 1996; Manda, 1992). Ricefields are fenced with low-voltage electric wire to keep the ducks from escaping and to protect them from intruding outside animals. Ducks are housed near the ricefield where they can freely forage. Presently, organic farming such as rice-duck system is being advocated in Kyushu, Japan.

In South Korea, organic farming such as rice-duck raising is being promoted by the Korean Rice Farming Association (Kim Bok Kwan, personal communication). Rice grown organically without pesticides commands a higher market price per kg, about 40-60 %, compared to rice grown with chemicals. According to Kim (1997), the number of rice-duck farmers and areas being farmed in South Korea showed an increasing trend from 1993 to 1997. South Korea's rice-duck cultivation is basically patterned from the Japanese practice. Farmers raise a hybrid meat type duck at a density of 200-350 birds/ha released in the ricefields two weeks after rice transplanting. Azolla growing naturally in ricefields serves as food for the ducks. Apart from the on-farm feed resources consumed by ducks, supplements in the form of commercial feed, rice bran and vegetable scraps, and kitchen scraps are fed to the ducks in sheds built near the ricefields. There is a great demand for ducks in November when the weather becomes cold.

In Vietnam, there are about 10 million ducks raised annually in two ways: seasonally in ricefields and throughout the year in backyards of farm households (Men, 1997). Ducks are integrated with the growing rice and after rice harvest. Ducklings (7-day old) are driven into the ricefields at 20 days after rice transplanting until the start of flowering. Supplementary feeds consisting of rice by-products or rice grain are supplied to the ducks 3-4 times a day, depending on the availability of food in the ricefields. At the start of rice flowering, the ducks are driven out of the ricefields to canals, ditches, lakes, swamps to forage in water. Duck raising after rice harvest is for larger birds i.e. about 3-week old. During the day, the ducks are herded in the paddy fields where they forage on left-over rice grains, insects, fish, shrimps, snails and water plants. They are then driven to pens or sheds near the households for the birds to stay at night. For meat-type duck, the fallow period (time between rice harvest and next transplanting) involves limited time for the birds to forage.

Indonesia is considered as one of the countries in the world having the largest duck population with more than 30 million ducks; their contribution to the total poultry egg production is about 25 % as compared to that of native chickens (15 %) and improved breeds of chicken (60 %) (Setioko, 1997). The traditional system of raising ducks which is most widely employed is the herding system similar to that of the Philippines.

The use of agro-chemicals in modern rice farming represents an important threat to traditional rice-duck farming (Manda, 1996; Farrell, 1997). Manda (1996) observed that there is a rapid decline in traditional rice-duck farming in Southeast and East Asia due to the introduction of western style agriculture that implies the use of chemicals and pesticides leading to environmental pollution and health hazards.

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Ducks can be raised for meat and egg production. Most common meat-type duck breeds are Beijing (or Peking), Rouen and Muscovy. Muscovy (Carina moschata) is more often considered as a different species. Crossbreds like aigamo, hybrids such as mule duck (Muscovy male x Mallard female) and commercial strains e.g. Cherry Valley or Grimaud are commonly used. Egg-type ducks are Mallard, Khaki Campbell, Indian Runner and commercial Hybrid strains. Meat-type ducks are popular in China, Japan, South Korea, Vietnam and Thailand. In Bangladesh and Indonesia, egg production from egg-type breeds are prevalent. The meat and egg-type ducks are raised in the Philippines but the latter is more popular. Mallard duck locally known as 'Pateros itik' (Anas platyrynchos) is commonly used by duck farmers in the Philippines. The eggs from this duck are processed to "balut" and salted eggs. "Balut" is an incubated egg with developed embryo of 17 to 19 days which is boiled and eaten with or without salt. It is a Filipino delicacy that commands a good price. Fresh duck eggs are also used to prepare a dessert called "leche flan" (egg custard).

In the Philippines, ducks rank next to chickens for egg and meat production (PCARRD, 1991). There were more than 10 million ducks in the country in 1991 (Anonymous, 1991). Some of the advantages of duck raising are as follows: they require inexpensive, non-elaborate housing facilities, little attention and less space for rearing compared to chickens. These animals are hardy and resistant to common avian diseases and feed on a variety of foods. Duck eggs are larger and more nutritious than chicken eggs as shown in Table 1.

Table 1: Comparison of chemical composition of chicken and duck eggs (Source: Bird, 1986)

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In aigamo duck-rice cultivation in Japan, total weed biomass was controlled better in aigamo plots compared to plots applied with agrochemical (Furuno, 1996; Manda, 1992). From on-station research in the Philippines, it was observed by Cagauan (1997) that the total weed biomass in the ricefield was reduced by mallard ducks by rates ranging from 52-58 %. The mechanism of weed control by ducks is direct consumption of plant parts and seeds and disturbance of weed growth brought about by their feeding activity.

In Japan, the numbers of planthoppers in rice plots with aigamo ducks were observed to decrease during the early stage of rice (Manda, 1992; Furuno, 1996). In the Philippines, ducks have been reported as effective biological control for the herbivorous golden apple snail (GAS) (Rice IPM Network, 1991). Rosales and Sagun (1997) reported a decrease in the GAS abundance from 4.6 snails/m2 in the first year of cropping to 0.8-1.6 snails/m2 in the second year as a result of the continuous duck pastures in the ricefields after every rice harvest. Using 900 ducks per ha, Vega (1991) reported a 74-84 % decrease of GAS abundance in ricefields, hence, less rice missing hills, due to duck pasture. However, the economic suitability of the use of such high duck density should be worth investigating.

Ducks' movements and feeding activity in the ricefields disturb the soil resulting in improvement of soil physical property, hence, better rice root systems and enhanced tillering as observed in the farm of Furuno (1996). Duck manure contributes to the fertility of the soil.

Reported improved rice grain yield from duck raising in ricefields can be attributed to the benefits previously discussed. Higher grain yield and reduced labor costs due to weeding, spraying and fertilizing contribute to better economic benefits derived from rice-duck farming. In South Korea, the increase in income derived from rice-duck farming ranged from 73-77 % compared to conventional rice farming (Kim, 1997).

Duck raising in ricefields leads to organic farming with the benefits of reducing costs of fertilizers, pesticide and labour. 'Organic rice' has a higher price than ordinary rice in some Asian countries like Japan and South Korea.

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Duck raising in integration with rice is limited to transplanted rice. Ducks have indeed more space to move around in transplanted ricefields than in direct seeded rice. Ducks can be affected by pesticides applied from neighbouring farms, particularly when water comes from communal irrigation canals. Ducks can either be stolen or killed by outside animals if ricefields are not fenced. Fencing adds to the high initial capital investment. Vietnamese farmers observed that ducks do not only eat harmful insects but also friendly ones.

In the Philippines, China and Vietnam, duck pasture has been implicated in paddy field dermatitis. In the Philippines, rice transplanters hesitate to enter ricefields pastured with ducks for fear of skin itchiness. In some areas of Guangxi in China, field investigations and experimental observations between 1984 and 1990 indicated that the cercaria of Trichobilharzia paoi was the only aetiological agent of paddy field dermatitis found (Hu et al., 1994). The authors reported that the natural final host of adult flukes is the domestic duck (Anas platyrynchos) while the intermediate hosts are the snails Radix (Lymnaea) swimhoei and Galba pervia. They further reported that the dermatitis is usually associated with such factors as duck rearing methods, seasonality, kind of paddy field and chemical fertilizer applied. The prevalence of dermatitis is during April to September, and the highest incidence occurs from April to May. Farmers in the Philippines protect their feet with automotive oil or grease while Vietnamese farmers cover their feet with plastic whenever they get into the ricefield pastured with ducks.

The practice of duck raising with rice, common to all the Asian countries, involves housing the birds in sheds near the ricefields. In this practice, there is an accumulation of duck manure and uneaten feed resulting in the fouling of the sheds. This develops an unpleasant odour and attracts flies and eventually becomes unhygienic for raising ducks. Disposal of accumulated organic matter in the ducks' sheds could be an additional labor cost. In the present practice of rice-duck raising, duck manure and spilled feed in ducks' sheds appear as wasted on-farm resources as they are not recycled.

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The production from the present practice of rice-duck farming in Asia has great potential to be maximized. Rice-duck farming can be integrated with fish and the nitrogen-fixing aquatic fern Azolla. Fish is a cheap source of protein that can be grown in ricefields while the aquatic fern Azolla naturally grows in the same place. Fish, Azolla and ducks integrated with a rice farming system could result in nutrient enhancement, pests (weed, insects, golden apple snails) control, feed supplementation and biological control (Figure 1). Nutrient recycling in an integrated rice-fish-Azolla-duck farming system is better and more efficient compared to rice-duck or rice-fish farming systems (Cagauan et al., 1996) resulting in higher productivity.

In rice-fish-Azolla-duck integration, duck houses must be constructed over the fish pond refuge which is a contiguous part of the ricefield. The floor of the duck house should have some spaces to allow the manure and spilled feed to fall directly to the fish pond. The duck manure serves as an organic fertilizer for plankton production while the spilled feed can be directly consumed by the fish. Any nutrients from the fish pond refuge may be dispersed to the ricefields by irrigation water or by the movement of fish and ducks.

The ducks can be pastured in the paddy fields after rice harvest. They should be confined in their house during land preparation until the fish is at least 2-3 weeks from stocking. In this way, any toxicity of pesticides applied at rice transplanting would have dissipated and the size of fish would be large enough to prevent predation by ducks. Ducks can either be confined or allowed to move around the ricefields until rice harvest. The animals are confined at the on-set of rice flowering to prevent any damage the ducks activity can cause the rice. The damage to rice may depend on the size and density of the ducks introduced initially and the rice variety used. During confinement, ducks should be fed with supplemental feed. In cases, when the ricefield becomes insufficient with natural food due to continuous duck foraging, supplementary feeds can also be given.

Integrated rice-fish culture has a long history in the rice growing areas of Southeast Asia. Fishes that are trapped in ricefields grow simultaneously with rice until harvesting. This traditional practice of captural rice-fish culture has evolved into an aquaculture farming system. Fish production in such a system can be augmented by naturally growing in situ Azolla feed and spilled duck feeds which fall directly to the pond. Moreover, the duck manure serves as an organic fertilizer for plankton production for the fish. For precocious spawners such as Nile tilapia (Oreochromis niloticus L.), the overpopulation results in small size fish at harvest. Ducks may serve as a biological control for tilapia reproduction if the birds are allowed to forage in the ricefield throughout the culture period.

Azolla can be utilized not only as organic fertilizer for crops but also as feed for livestock and fish (Van Hove, 1989; Van Hove and Lejeune, 1996). The utilization of this aquatic plant in aquaculture was reviewed by Cagauan and Pullin (1994). Azolla can be an inexpensive feed for tilapia grown in ricefields. Increased fish production has been demonstrated in integrated rice-fish-Azolla production systems where Azolla served as an in situ fresh feed for the macrophytophagous fish (Anonymous, 1988; Liu and Liu, 1995; Cagauan, 1995). Azolla as fresh feed in combination with a good level of natural feeding could be beneficial to fish production (Cagauan and Pullin, 1994).

Azolla was reported to be a partial replacement for rice grain-snail-shrimp basal ration for mallard duck (Alejar and Aragones, 1989). The authors added that the egg production of mallard duck fed with 20 % Azolla in the ration was similar to those fed with commercial feed and the rice grain-snail-shrimp feed. Reports on the effect of Azolla on egg shell thickness of mallard duck eggs (Alejar and Aragones, 1989; Joome, 1996) are controversial. Egg shell thickness is a very important factor in the handling and processing of "balut" and salted eggs. Egg yolk coloration in mallard duck eggs (Alejar and Aragones, 1989; Joome, 1996) and chicken eggs (Anonymous, 1985) has been observed to be intensified with Azolla in the diet. The carotene content of Azolla as observed by Becerra (1994) was 366 mg/kg on a dry matter basis.

Azolla, as any other production, is submitted to various constraints depending on local ecological and socio-economic factors. Often emphasized, these constraints have been critically reviewed by Van Hove and Lejeune (1996).

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A research project on integrated rice-fish-Azolla-duck farming system was conducted on-station in 1995-1996 at the Freshwater Aquaculture Center, Central Luzon State University, Philippines, supported by the Food and Agriculture Organization, the Catholic University of Louvain, Belgium, and the Philippine institution (Cagauan, 1997). The research investigated the production, economics and pests control (weed and golden apple snails) aspects of the integrated system. High yielding rice variety (IR 64), genetically improved Nile tilapia (GIFT strain, GIFT = acronym for "Genetically Improved Farmed Tilapia". See Eknath, A. E. 1992. Final Report: Genetic Improvement of Farmed Tilapias. International Center for Living Aquatic Resources Management, Philippines.) (Oreochromis niloticus L.) and the aquatic fern Azolla (Azolla microphylla) were cultured in lowland irrigated ricefields. Azolla was cultivated as monocrop and incorporated as basal organic fertilizer before rice transplanting. Azolla provided half of the nitrogen fertilizer requirement of the rice while the other half came from chemical fertilizer. Azolla mat developed to serve as weed suppressant and in situ feed for Nile tilapia and ducks. Nine-month old mallard duck (Anas platyrynchos) at density of 400 birds/ha (367 ready-to-lay ducks and 33 drakes) were integrated in the farming system. The birds were pastured during the fallow period after rice transplanting. A duck house made of cheap local materials was built over the fish pond refuge where ducks were confined when they were not foraging. Some of the results of the research are discussed.

Mean productions in t/ha/year of rice, Nile tilapia and mallard duck from the different production systems are summarized in Table 2. Treatment effects were highly significant for rice and fish yields but not for the total mallard duck eggs production.

Table 2: Mean yields of rice grain, Nile tilapia (Oreochromis niloticus) and mallard duck (Anas platyrynchos) eggs in different rice-based cropping systems.

Highest rice yields were obtained in the cropping systems RFAD-(duck-Azolla)-RFAD and RAD-(duck-Azolla)-RAD. These were followed by systems RFA-(fallow-Azolla)-RFA and RFD-duck-RFD. The rice yields from the cropping systems RA-(fallow-Azolla)-RA had higher yield compared with the conventional rice cropping system (RF+HM-fallow-RF+HM) but not with conventional rice-fish culture (RF+HM). No significant differences were observed in the rice yields from the cropping systems RA-(fallow-Azolla)-RA, RD-duck-RD and conventional rice-fish culture. The Rice-falllow-Rice cropping system had a yield not significant with RD-fallow-RD and the two conventional systems. The RF-fallow-RF system had the lowest yield among the different cropping systems. Generally, the results showed that the two-way and three-way combinations of Azolla, duck and fish gave higher rice yields compared to the conventional rice monoculture or rice-fish culture systems.

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Nile tilapia yield was highest in the production system RFAD followed by RFD and RFA. The lowest yields were obtained from the production systems RF and RF+HM. The results indicated that systems with more feed available for Nile tilapia such as Azolla and spilled duck feed gave higher fish yields. Moreover, the manuring effect of duck manure increased plankton production.

Egg production did not differ significantly in the various cropping systems with ducks. Duck pasture was not observed to contribute to significant variations in egg production in the different treatments. Most of the eggs produced during the entire egg laying period belonged to medium and large sizes. Generally, the overall egg laying percentage was over 60 % which is well above the country's national average of 35 % for ducks under the traditional management (Alejar and Aragones, 1989). The egg laying percentage of mallard duck was highly variable, attributed to the sensitivity of the birds to changes in weather conditions and feeding from pasture to confinement. Feed given to the ducks during pasture was greatly reduced (30 % and zero level) to economize on feed costs. Natural food such as aquatic plants, snails, fallen rice grains, shrimps and other on-farm resources served as feed of ducks during pasture in ricefields. Furthermore, the occasional moulting of the birds in selected plots greatly affected egg production. Eggs produced were processed to "balut" and salted eggs. Using a draft-type egg incubator, the "balut" percentage of success or per cent fertility after incubation period of 17-19 days was about 70 % while infertile eggs and dead embryo were about 18 % and 11 %, respectively. The egg salting percentage of success was about 94 %.

The herding of ducks not only economized on feed costs but was also very effective in controlling the herbivorous golden apple snails (GAS). Figure 2 presents the effect of mallard duck on golden apple snail density in ricefield before and after pasture during the rice fallow period in three cropping seasons. The pasture of 400 mallard ducks per ha in 30-48 days during the fallow period before rice transplanting controlled the GAS to density levels not potentially detrimental to the young rice plants. It was observed that GAS abundance was markedly decreased to 85 %, 91 % and 79 % after DP in the first, second and third croppings, respectively. This corresponded to reduced density of 1-2 snails/m2 after DP from an initial density of 8-17 snails/m2 before DP in the first and second croppings. In the third cropping, there were 30 snails/m2 before DP and 6 snails/m2 after DP. It was observed further that densities of GAS decreased considerably after duck pastures in succeeding fallow periods from the first two cropping seasons. Hence, there was a need to re-inoculate the field with GAS before duck pasture for the next cropping season for experimental purposes. Ducks were observed to be size selective i.e. snails with shell height <4 cm were significantly controlled. According to Oya et al. (1986), young snails<1.5-1.6 cm shell height are too small to feed on rice seedlings but 2 cm and greater can potentially damage young rice plants depending on their density (Basilio, 1989).

As expected, duck pasture before rice transplanting seemed to effect better control of the snails than pasturing the ducks after rice transplanting for a period of 14-19 days.

Figure 2: Effect of mallard duck (Anas platyrynchos) pasture (DP) during the fallow period for a period of 30-48 days in ricefield on the mean golden apple snail density (Pomacea canaliculata Lamarck) of all sizes in three cropping seasons in the Philippines. (Note: The P values below the cropping seasons refer to Probability levels of comparison between snail densities before and after DP.) Reducing the density of GAS before rice transplanting is more beneficial to newly transplanted rice which is very vulnerable to snail damage.

The effect of Nile tilapia in controlling GAS abundance after 83-fish culture days with rice was not clear but there were indications that observed densities of small snails with shell height 2-2.9 cm decreased in the presence of Nile tilapia. It might be possible that newly hatched snails that fell on the surface of the water were consumed by tilapia which have the capacity to crush up soft-shelled mollusks.

Azolla was observed as a good feed and an effective biological attractant for the golden apple snails. Snails grouping at the Azolla mat can be an advantage to the farmers who practice hand-picking to control the snails. The use of Azolla as food attractant for the snails may be better than other plant leaves such as taro (Calocasia esculenta), papaya (Carica papaya) and ipil-ipil (Leucaena spp.). Azolla has other uses such as fresh fodder for duck and fish besides being an organic fertilizer for the rice.

The study demonstrated that higher productions can be achieved in cropping systems with integration of Nile tilapia, Azolla and mallard duck compared to the conventional systems such as rice monoculture, rice-fish culture and rice-duck farming. The assessment of the profitability of the new production system is a meaningful undertaking and ultimately a determining factor for the adoption of the new technology by farmers.

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We thank Dr. Roger Pullin of ICLARM for reviewing the manuscript. We also extend our deepest appreciation to the Food and Agriculture Organization, Rome, Italy; the Catholic University of Louvain, Belgium and the Freshwater Aquaculture Center, Central Luzon State University, Philippines for supporting the research project.

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