The Integration of Mulberry Cultivation, Sericulture and Fish Farming
Hu Bao-tong and Yang Hua-zhu
Regional Lead Centre in China
Asian-Pacific Regional Research and Training Centre for Integrated Fish Farming, Wuxi, China
NETWORK OF AQUACULTURE CENTRES IN ASIA
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The close integration in mulberry cultivation, sericulture and fish farming is one of the models of integrated fish farming to fully exploit the production potentials of the ecosystem. This type of integration is known in China as “mulberry dike-fish pond” in the Pearl River delta and “mulberry plot-fish-pond” in the Taihu basin. The development of the integration of mulberry cultivation, silkworm rearing and fish farming has promoted the development of silk reeling and other processing industries. It is a more complete, scientifically based man-made ecosystem.
Pond mud or humus is the main nutrient source for mulberry cultivation. After fish harvest in winter each year, the pond mud is removed to form the “base soil” (base manure) of mulberry plants. The soil added is in a solid and dry form known as adding “Tani” in Kwantong Province, and “Baini” in Zhejiang Province. During summer and autumn, liquid humus known as “Nihua” or “Hsiaoni” are applied 2–3 times in smaller quantity. At the end of each year, the base soil of the mulberry plants has increased by 5–6 cm thick. According to the estimation of the farmers from Shunde County, the fertilization efficiency of 100 tons of “liquid humus” is equivalent to that of 50 kg of chemical fertilizers. The amount of pond mud that are added on the base of the mulberry plants at the end of the year is estimated to be approximately equivalent to the application of 15 kg of urea. The pond mud which are applied on the base of the mulberry plants not only acts as a source of fertilizer but also resists drought and prevents the growth of weeds aside from having a longer effective time of fertilization; especially during high temperature in summer and drought, addition of pond humus has increased significantly the production of mulberry leaves.
Due to the variation in climatical and other natural conditions, integrated fish farms in the Pearl River delta produce 2,400–2,500 kg of mulberry leaves per mu sufficient to rear 8 cycles of silkworm whilst 1000–1500 kg of mulberry leaves per mu are produced in the Taihu basin rearing 4–5 cycles of silkworms.
Fifty kg of mulberry leaves can produce 4 kg of silkworm cocoons. In Pearl River delta, production of cocoons from the one mu of mulberry field is between 160 and 200 kg. In Taihu basin, the production is 80–120 kg/mu. For every 50 kg of cocoons, an average of 3.5 kg of raw silk can be obtained. The average production of raw silk per mu of mulberry plants in Pearl River delta is 11.2–14 kg, while in Taihu basin, the production is 5.6– 8.4 kg. After processing, the silk are exported and will not be recycled back to the system. Other organic waste or subsidiary products such as pupae, worm dregs and the waste silk extraction from boiled cocoons again enter the process of recycling.
According to survey, 50 kg of mulberry leaves can produce 4 kg of cocoons with 15 kg (in Taihu basin) or 25 kg (in Pearl River delta) of worm dregs which are comprised of the feces and sloughs of silkworm as well as mulberry residues. These worm dregs can be used to fertilize fish ponds or as feedstuff of fish. Usually 4 kg of worm dregs produce 0.5 kg of fish. Each mu of mulberry plants yields 300–450 kg of worm dregs in Taihu basin and 1,200–1,250 kg in Pearl River delta. By just feeding the pond fish with worm dregs alone, each mu of mulberry can produce 37.5–56.2 kg of fresh fish in Taihu basin and 150–156.25 kg in Pearl River delta. The production of cocoons from per mu of mulberry also varies with locality. However, the amount of waste water obtained after extraction of silk from the cocoons is about 2,500 kg per mu irrespective of locality. Using the experience of fish farms and their production output in Wuxi as basis, generally, 100 kg of waste water from silk extraction of cocoons can raise 0.5 kg of fish. Hence, just waste water alone can produce 12.5 kg of fresh fish.
The convertion rate of pupae to fish is 1.5–2.0:1. Using 2 as the convertion ratio, 50 kg of cocoons can yield 40 kg of pupae. Thus one mu of mulberry after raising cocoons can yield 64–96 kg of pupae in Taihu basin and 128–140 kg in Pearl River delta. If all the pupae are solely used as fish feeds, each mu of mulberry can yield 32–48 kg of fresh fish in Taihu basin and 64–70 kg in Pearl River delta. (Table 1)
Thus, each mu of mulberry can provide the basic requirements of feeds and fertilizers to yield 82–116.75 kg of fish in the Taihu basin and 226.5– 238.75 kg in the Pearl River delta. Of course, parts of the feedstuff that are given to the fish in the pond may not be eaten but deposited on the pond bottom and together with the pond mud are recycle to manure the mulberry plants.
Apparently, the area for mulberry cultivation and fish farming must be in harmonious proportion to ensure sufficient supply of fertilizers and feeds for fish. According to the experience of farmers from Pearl River delta, each mu of mulberry plants can yield worm dregs, pupae and waste water to provide feeds and fertilizers sufficient for 1 mu of fish ponds. Hence, the ratio of areas of dike and water surface is 1:1. However, if there are other additional source of feeds or fertilizers, then the ratio of water surface and dikes can be reduced to 6:4 or 7:3. However, in actual practice, the ratio of water area to dike surface area is more complicated and generally, governed by traditional practice. The Dongson Commune of Wuxian County in Suchow, for example, still retains a traditional type “Mulberry plot-fish pond”. A 6-mu (0.4 ha) fish pond with 3.6 mu (0.24 ha) water area and 2.4 mu (0.16 ha) dike surface area. The water/ dike ratio is 6:4. Some of the farmers are still using 6 mu as the basic unit for their calculations of production output and its value. In relatively aged “mulberry plot-fish ponds”, the dikes near the pond gate tend to collapse due to weathering by heavy rain and heat; each side of the dike tend to become loss steep as a result of erosion. If such ponds are not regularly repaired, the area for mulberry cultivation will certainly be reduced each year.
1. one mu = 666.7 m2 or one hectare = 15 mu
“Mulberry plot fish ponds comprises two semi-closed manmade ecological systems, one of which, as described earlier, is formed by the integration of mulberry cultivation, silkworm rearing and fish farming into a terrestial-aquatic ecosystem known as the larger ecological system. Within this large system, exists a semi-closed aquatic ecosystem formed by the fish pond. Mulberry forms the base of the larger ecosystem while fish pond constitutes the subject component. The fish pond provides the basic requirements for mulberry cultivation and pond mud for dike maintenance. The pond itself is the base for inputs of feedstuff and fertilizers. Sufficient supply of feedstuff and fertilizers can sustain a higher fish biomass and hence a larger quantity of fish excrement as well as a thicker layer of pond mud, serving as an excellent base manure for growth. The mulberry leaves are the main but indirect source of nutrients for fish production. Hence, analyzing the system as a whole, maintaining a well developed growth base of the integrated farming system, i.e. mulberry cultivation, is the fundamental step to ensure efficient energy recycling in a “mulberry plot-fish pond”.
Mulberry cultivation, silkworm rearing and fish farming complement each other in the man-made ecosystem. However, irrespective of whether in Pearl River delta or Taihu basin, such ecosystem is rather incomplete. Most of them have not incorporated silk reeling industry. If silk reeling factory is established within the “mulberry plot-fish pond” ecosystem and pupae, worm dregs and waste water from the factory can be adequately and effectively channelled into the ponds, thus enabling a more complete, recycling of organic waste. The establishment of the factory reduces transportation cost and instead increase the rate of economic returns. This is the real type of “mulberry plot-fish pond” integrated fish farming model.
The actual yield from a 6 mu “mulberry plot-fish pond” belonging to Jinwan Brigade is shown in Table 2. The actual produce from the farm was 107.7 kg of cocoons, valued at 330 yuan; worm dregs as fertilizers for producing woffia which produced 20,400 summer fingerlings (5 cm carps) valued at 57.12 yuan (28 yuan/10,000 fingerlings). The total value of both products were 387.12 yuan.
The cost of producing 1217.5 kg of food fish is shown in Table 3. Among the feedstuff and fertilizers, 282 man-days have been spent to collect 70,500 kg of aquatic plants from Taihu lake for feeding the fish, in addition, 150 kg of rape-seed cake, 2,000 kg of pig and sheep manure, 500 kg of nightsol have to be bought. Apparently, there is no close coordination between mulberry cultivation, silkworm rearing and fish farming. The only close integration is the use of pond humus/mud - the base manure for mulberry cultivation. As it is the production cost per kilogram of fish is 1.216 yuan.
2. one yuan = 50.5 US cents.
If Jinwan Production Brigade is able to freely utilize the mulberry residues and worm dregs and waste water to raise food fishes by constructing a silk reeling factory, then 107.7 kg of cocoons will yield 14 kg of raw silk and the side products of 86.15 kg of pupae, 4308 kg of waste water and 850 kg of worm dregs can be used to produce 170.8 kg of fish. This supplies 14% of the feeds and fertilizers inputs. Besides the scrappy silk obtained from silk reeling after further processing can be used for making blankets, cushins and pillows. The scrappy silk together with silkworm moulds and sericin make up 7% of the total cocoon weight.
From the economic stand point, the production of raw silk compared with the sale of cocoons alone will increase income by about 29.4%. Thus the establishment of a mulberry cultivation-silkworm rearing-silk reeling-fish farming integrated farming system not only enable a closer integration of the recycling of matter within the “mulberry plot-fish pond” ecosystem, but also creating a more compact and complete energy flow whereby the dikes of the pond are used for mulberry cultivation; the mulberry leaves for silkworm culture; cocoons for silk reeling and its by-products consisting of worm dregs, pupae and organic waste water for fish farming. From socio-economic view point, it is essential to economize on fish farming expenditure (based on the production cost per kilogram of fish according to Table 3 and total fish yield in Table 4, a saving of 207.75 yuan can be obtained) so as to increase the income from mulberry cultivation and silkworm rearing, creating new production industry and increase employment opportunity.
At present, some of the newly-established production bases maintain dike-water surface ratio at 1:1 and depth 3.5 m but decrease to 2.5 m during fast growth summer season, leaving 1.5 m of slope between the surface of the water and that of dike which is about 0.1 mu in every mu of water surface, hence permitting cultivation of green fodders. In actual fact, the average water depth is about 1.5 meter before June, therefore, leaving about 1/5 of the slope of dike in the first half of the year and 1/10 in the second half. Base on the production rate of 5,000 kg of green fodder per mu, the slope can produce 750 kg of English rye grass and other fodder crops. If convertion rate of fodder crop is 30:1, then, about 25 kg of grass carp and 15 kg of silver and bighead carps can be harvested (faces produced by a 0.5 kg grass carp can fertilize the water allowing an additional cropping of 0.3 kg of silver and bighead carps). The total production is 40 kg, and with additional fertilizers from mulberry residue and worm dregs etc, “the mulberry plot-fish pond” in Taihu basin can produce 122–156.75 kg of fish while that in Pearl River delta produce 266–278.75 kg. Vegetable and other fast-growing crops are also being cultivated on the dikes of fish ponds in Taihu basin or Pearl River delta. About 3,000 kg of vegetable were produced in each mu of dike surface in the Pearl River delta. Thus it is not difficult to achieve fish production at a level of 150–200 kg/mu in Taihu basin and 250–300 kg/mu in Pearl River delta in such “mulberry plot-fish pond” model. If fish production is to be raised, e.g. 50 kg or higher per mu using the above model, then then there is a necessity to increase energy input. If more fish are reared, more excrement are produced; with increase in feedstuff and fertilization, more pond mud will be accumulated, thus not only a higher fish yield will be obtained, there is also increased provision of pond mud for mulberry cultivation.
More energy input not only increase fish yield, but also increase the production potentials of the “mulberry plot-fish pond” ecosystem. Thus in the “mulberry plot-fish pond” system, pond is the most important component, the control of its production processes regulate other land-based production activities and hence increase the production efficiency of the “mulberry plot-fish pond” ecosystem.
Based on the results of the survey, a hypothetical model is suggested for the stocking of a “mulberry plot-fish pond” with an expected yield of 200 kg/mu. (Table 5).
Acknowledgements are due to Mr. Min Kuan-hong for the translation of the paper into English and to the NACA international staff for the various assistance rendered.
Table 1. The basis of integration of mulberry cultivation-sericulture and fish farming model in Taihu basin and Pearl River delta.
|ITEMS||JINWAN PROD. UCTION BRIGADE||TAIHU BASIN||PEARL RIVER DELTA|
|waste water from silk extraction|
|total fish produced|
*. Figures from Jinwan Production Brigade are absolute data obtained from the Brigade that of Taihu basin and Pearl River delta is based on the survey statistics.
**. Figures in parenthesis denotes equivalence of fish yield.
***. Average annual production or silk from Jinwan Production Brigade is 13%; rest based on national average of 7%.
Table 2. Yield from a 6-mu mulberry plot-fish pond at Jinwan Production Brigade.
|ITEM||YIELD (KG)||AVERAGE YIELD PER MU (KG)||REMARKS|
|mulberry leaves||2100||8750||used for feeding silkworm only.|
|cocoon||107.7||44.9||4 rearing cycles of silkworm.|
|worm dregs||850||354||for the yield of 2550 kg of wolffia which produces 1.5 cm - 20400 grass carp fingerlings.|
|fish yield||2171.5||338||net yield from 3.6 mu water area.|
Table 3. Feeds, fertilizers & production cost of a 6-mu mulberry plot-fish pond (3.6 mu water area) at Jinwan Production Brigade.
|disease treatment (medication)||10|
|labour cost in both stocking & harvesting, etc.||30||15 man-days at 2 yuan/ per man-day|
(1) Based on the price of Wuxian Country for different size and species.
(2) Aquatic weeds from Taihu Lake need 282 man-day at 2 yuan per man-day.
(3) Production cost 1.216 yuan/kg.
Table 4. Calculated fish production converted from waste of mulberry and sericulture from a 2.4-mu dikes at Jinwan fish ponds.
|CONVERTION RATE||FISH PRODUCTION (KG)||REMARKS|
|pupae||26.15||1.5–2||43.10||based on 2 as convertion rate|
|waste water from silk extraction||4308||200||21.5||(1)|
(1) The waste water which constains sericin and parts of silkworm sloughs are used as feeds and fertilizers.
(2) At fish price of 1.216 yuan/kg a saving about 207.75 yuan was obtained. Fish production from worm dregs, pupae and waste water constitute 14% of total pond production.
Table 5. Stocking of fingerlings of a “mulberry plot-fish pond” with expected yield of 200 kg/mu in the Taihu Lake basin.
|FISH SPECIES||STOCKING||WEIGHT (KG)||SURVIVAL RATE||WEIGHT3 INCREMENT||HARVEST||NET PRODUCTION|
|SIZE (IND/KG)||NO. OF FINGERLINGS||SIZE|
|NO. OF FISH|
|3. Weight increment =||Production|
|intial stocking wt|