Embankment fish culture, along with bamboo and mulberry culture, has been practiced in the Yangtze River delta and Pearl River delta areas of central and south China for centuries. Originally, the delta was just a waterlogged area. Farmers dug and moved soil, piling it into huge rectangular or round shapes and utilized these raised embankments for planting crops. The excavated areas became deeper, making them ideal for fish culture. Where embankments are wide enough, mulberry, bamboo, etc., can be grown (see Figures 1 and 2). The mud is scraped from the bottom of the pond and applied as fertilizer to the embankment 2-5 times annually at a rate of 750-1 125 kg/ha/year.
In this system, which is more common in form of large-scale farming systems, the mulberry leaves are used as feed for silkworms. The sericulture provides a large variety of feeds and fertilizers for fish farming. On the other hand, the technology requires high labour input.
It has been determined that 36 700 kg/ha of mulberry leaves can be produced which can yield 2 700 kg of cocoons and 18 400-18 750 kg of silkworm excreta and silkworm sloughs (molted skins). The silkworm excreta can both serve as feed and fertilizer for fish. The cocoons contain 80 percent pupae by weight. The feed conversion ratio of pupae to fish is 2:1 such that 2 kg of pupae can produce 1 kg of fish. All the feeds and manure from silkworm farming can support a good fish yield; see Figure 3 for the cycling process of the silkworm wastes. The suggested fish stocking in mulberry plot-fishpond is listed in Table 1.
Table 1. Stocking for mulberry plot-fishpond
The produce from bamboo farming is mainly bamboo shoots. Zhangchai Township, Fusan, Guangdong province, has long been processing canned bamboo shoots. It is estimated that 25-30 percent of the wastes and by-products could be used for fish farming. Wastes and by-products from a 1 ha harvest of bamboo shoots can produce about 500 kg of fish.
A modest estimate from the farmers of Zhangchai Township shows that bamboo production per hectare ranges from 22.5 to 26.3 t/year. But when shoot production is over, the farmers harvest the old bamboo poles, totaling 52.5 to 67.5 t/ha/year. These can be used as firewood, construction materials for livestock pens or support materials for climbing plants (see Figure 4).
The mud from the bottom of the pond provides a very large amount of compound fertilizer for the bamboo plot. In shoot production, 6 000 kg/ha of pond mud containing 168 kg N, 109 kg P and 150 kg K are needed, but one-fourth of the supplied amount of pond mud is more than sufficient to supply the needed nutrients. Therefore, the total amount of nutrients supplied by the mud cannot be fully absorbed by the plants. The farmers in Zhangchai Township realize that the shoot production is 20-30 percent higher in the pond plot than in hilly areas, probably because of good ventilation in between plants and adequate water and fertilizer supply. Mud application moreover impedes the growth of wild plants and improves the soil quality. Bamboo plot-fishpond stocking rates are illustrated in Figure 5. Figure 6 shows the farming calendar in fish-sericulture-bamboo production.
Issues for further consideration
The mulberry-fish system has declined with industrialization in many areas of southern China because of opportunity costs of land and labour. The bamboo-fish system is dependent upon a processing industry in the vicinity. In most cases, the bamboo shoots are not the major crop.
Both mulberry and bamboo systems are unusual, compared to many potential embankment crops, in that they are perennial crops. The considerable amounts of mud that need to be removed from the pond for dike crop fertilization require considerable amounts of labour.
In the last ten years the practice is losing its popularity due to economic changes manifested by increased cost of labour, shifts in market demand, changes in food preferences and availability of other livelihood opportunities.
The mulberry-fish system requires high labour inputs. A silk processing factory should be in the vicinity.
For bamboo shoot production, there should be adequate market demand, processing facilities in the area, high rainfall and a year-round humid climate.
Required nutrient inputs need to be verified depending on soil quality and plant requirements. It is unclear if additional fertilizer amounts are given to the dike crops, aside from the pond mud.