Surface aquaponics is different from hydroponics and more different from land cultivation. By this method 140 terrestrial plant species and 59 varieties including cereal and oil crops, vegetables and floristic plants, which belong to 83 genera of 46 families, were successfully cultivated on floating-beds in different types of natural waters in Zhejiang Province, China during the period of 1990-1995. Planting terrestrial higher plants on floating-beds could combine with aquaculture. Under the premise of 25% coverage rate of terrestrial higher plants and without grass carp stocked, the fish yield and its production value could increase by 20% and 30%, respectively. It indicated that both rice and fish could get bumper harvest. The rice yield reached 7.92 t/ha and the fish 5,638 kg/ha. The economic return was $ 3,769 per ha of fishponds.

Keywords: 
Surface aquaponics, Aquaculture, eutrophication, Physico-chemical factors
 

INTRODUCTION

Surface aquaponics is different from hydroponics and more different from land cultivation. Surface aquaponics have been developed since 1989 (Song et al 1991, Song et al 1996). The researches are based on the fact that the potential crisis of food shortage has been existing in China, and the average arable land is decreasing as the population grows, and with scanty spare arable land, the fully utilization of ample surface of inland waters may be of immense value. By this method 140 terrestrial plant species and 59 varieties including cereal and oil crops, vegetables and floristic plants, which belong to 83 genera of 46 families, were successfully cultivated on floating-beds in different types of natural waters in Zhejiang Province, China during the period of 1990-1995. The list of plants is shown in Table 1 in Song et al. paper (unpublished). The accumulated trial area has reached to more than 10 ha. The results showed that the survival rate of 90% of the trial plants was 90% and the growth of 57.7% plants were similar to, or even better than that in land cultivation (Table 2 & 3 in Song et al. unpublished). Rice Oryza sativa L. gained higher yield, and the floristic crops of canna Canna generalis Bailey, iris Iris tectorum L., and umbrella sedge Cyperus alternifolius L. gained greater biomass. The average unit rice yield reached 8.7 t/ha in 3.82 ha in one growing season, and the highest average 10.07 t/ha as a case. The experiments show that surface aquaponics can be combined with aquaculture and environmental protection. 

China has a long history of pond fish culture. In 1996 the area of pond culture reached 1.96 million ha with the fish production of 8.11 million tons (Chinese Agricultural Almanac 1997). It enriched the market of aquatic products in China. However, fertilization often causes eutrophication in fishponds. It not only deteriorates the water quality of fishponds resulting in prevalent fish diseases, and even fish mortality in large amounts, but also accelerates the eutrophication process of rivers or lakes because of water exchange between fishponds and the natural waters surrounding fishponds. Such kind of production model can not be sustainable.

Song proposed to combine surface aquaponics with aquaculture for the purpose of setting up an agriculture-aquaculture ecological economic system in 1991, which will not affect the present fish production and will not cause adverse effects on aquatic environment (CNRRI Annual report 1993). In 1991 the experiment proved it was feasible. In 1993-94 an experiment was conducted in a fishpond to study the effects of surface aquaponics with different coverage of floating beds with terrestrial higher plants on the improvement of water quality and fish yields. The results indicated that surface aquaponics greatly improved water quality. When the coverage rate of terrestrial higher plants was less than 25%, and without grass carp stocked, it positively increased both fish production and its output value. Both fish and rice gained bumper harvest (Diagram 1).
 
 

MATERIALS AND METHODS

The area of test fishpond was 0.603 ha with an average water depth of 1.5 m. The contents of KN and TP were 2.15 mg/l and 0.26 mg/l, respectively. The test fishpond was divided by bamboo screens covered with plastic sheets into 4 test areas with different coverage of floating beds (15%, 25%, 40% and blank). Late rice cultivar Xiushui 11 was planted in three test areas. Three fish species (crucian carp Carassius auratus, common carp Cyprinus carpio and silver carp Hypophthalmichthys molitrix) were stocked into four test areas with the same density before rice planting. The experiment was carried out from Dec 1993 to Nov 1994. Crucian carp, common carp and silver carp were stocked on 22 Dec 1993, 18 Feb 1994 and 2nd April 1994, respectively. The density is shown in Table 1.
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During the rearing period pig manure was applied by 10 t/ha and pallet feed by 4.95 t/ha. No aerator and agricultural chemicals were applied. Rice plants were transplanted on to floating beds (20 cm x 15 cm) with 3-4 plants each hill. Top dressing was applied on the first and the 7th day after transplanting. That fertilizer was specially formulated for rice on floating beds with equivalent to 90kg pure nitrogen per ha.

Physico-chemical factors were monitored including KN, TP, pH, Conductivity, Temperature, Turbidity, Dissolved Oxygen, CODcr, BOD5, and SS (Suspended Solid). Samples were collected from 40 cm below the water surface. KN, TP, CODcr and BOD5 were measured by Kjeldahl Nitrogen Fixed Method, Stannous Chloride Reduction Method, Dichromate Method, and Dilution Inoculating Method, respectively. The rest were measured by using a Water Quality Apparatus (Horiba u-10, made in Japan). Rice sampling was examined as usual before harvesting, and fish was weighed after harvest

RESULTS AND DISCUSSION

Good harvest of rice gained from all three different coverage of floating beds. The biomass and rice grains were more than 15 tons and 7.5 tons/ha, respectively (see Table 2). The less the coverage, the higher the rice harvest. It is due to more nutrients (nitrogen and phosphorus) which can be absorbed by plants in less coverage. The rice biomass was shown in photos (Rice, ryegrass, flower cultivation on the surface of a fishpond). 

The test showed that the appearance of water body was apparently improved and purified. Nine of ten physico-chemical parameters got improved in certain extent except negative impact on dissolved oxygen (See Table 3). 

Table 3 Impact of different coverage on water quality

Among ten parameters, KN, TP, COD_cr, BOD₅ and SS were greatly improved (See Table 4). The purification effects of these five main parameters were apparent. The more coverage, the better the purification effects. It is due to absorption and adsorption of the root system of rice plants to remove the surplus nutrients of nitrogen and phosphorus so that over population of blue-green algae was inhibited, and the content of organic matter reduced, and the quality of water improved. However, from fish farming point of view, it is better to keep BOD₅ between 20-35 mg/l, especially for plankton feeders. 

The stocking of fry and fingerlings depended on the fish target of gross production 4.5 t/ha. Results indicated that all the test areas achieved the fish target. The unit fish output and the unit production value from 25% coverage were the highest as 5.64 t/ha and 31172.2 yuan per ha (about $3,800/ha), respectively (See Table 5).

The results indicated that the general mortality reduced, but the mortality of silver carp was higher because DO was between 1.54-1.17 mg/l. The normal growth of crucian carp, common carp and silver carp needs 2 mg/l, 4 mg/l and 5.5 mg/l DO and the anoxia, 1 mg/l, 1.5 mg/l and 1.75 mg/l, respectively (Boyd, 1998).

CONCLUSION

This experiment shows that agriculture-aquaculture system under the 25% coverage of floating beds with terrestrial higher plants will not only increase fish yields and output value, but also will get bumper harvest of rice, vegetables or flowers in an improved aquatic ecology. This agriculture-aquaculture ecological economic system can recycle part of aquaculture effluent, improve the water quality, and alleviate pressure to eutrophication during interchange between the pond water and surrounding natural waters, and secure sustainable development of aquaculture without serious prevalent fish diseases. So this model is a benign ecosystem as well as a good economic system. It can be extended to pond culture, lake fish culture and reservoir culture for further promotion of the development of aquaculture in China. Thus, the small-sized and medium-sized lakes can be fully utilized for aquaculture and cultivation of terrestrial higher plant on its surface, not fear that pen culture or cage culture will jeopardize aquatic ecology and cause eutrophication of lakes.

Acknowledgments

The authors would like to thank the Chairpersons of this Internet Conference on Nutrient Flow Analysis for their comments and suggestions. Also the author would like to express our gratitude for their support of the organizers of the Internet Conference and the financial support from AEON Foundation, Japan. The above researchers were the research projects of the National Natural Science Foundation No. 39270442 and the Honda Foundation Donor No. 93-II-041. 

REFERENCES

Annual Report of CNRRI, 1993.

Boyd Claude E., Water Quality for pond aquaculture, 1998.

Chinese Agricultural Almanac, 1997.

Song Xiangfu, Ying Huodong, Zhu ming et al. 1991. Study on rice cultivation on floating-beds in natural waters. Scientia Agricultura Sinica, 1991,24 (4): 8-13

Song Xiangfu, Wu Weiming, Ying Huodong et al. 1996. Studies on the ecological adaptability of growing rice with floating bed on the natural waters. Chinese J. Rice Science., 1996, 10 (4): 227-234