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Workshops on Using Principles of Pond Dynamics
to Optimize Fertilization Efficiency
Pond Dynamics Research 2 (10PDR2)/Activity/Bangladesh, Cambodia, Laos, Thailand, and Vietnam
Asian Institute of Technology, Thailand
Michigan State University
John Grover, International Center for Living Aquatic Resources Management, Nepal
Douangchitch Litdamlong, Regional Development Coordination for Livestock & Fisheries in Southern Laos
Pham Anh Tuan, Research Institute for Aquaculture #1, Vietnam
Hav Viseth, Aquaculture Office, Department of Fisheries, Cambodia
The primary objective of the proposed workshops is to transfer existing scientific knowledge, generated through the PD/A CRSP, on how to improve the predictability of pond management and productivity through an understanding of pond dynamics. By teaching host country university, government, and aquaculture extension personnel how to practically apply ecological principles to improve pond fertilization efficiencies, this knowledge can then be transferred to the farmers who will benefit the most. Specifically, the objectives are to teach through demonstrations, presentations, and informal discussions the following topics:
1) Managing factors which control primary and secondary productivities in fertilized ponds;
2) Ecological benefits and limitations of organic and inorganic fertilizers as related to pond dynamics;
3) Pond characteristics that affect fertilization decisions;
4) Methods for determining fertilization requirements; and
5) How to use the algal bioassay test kit for identifying pond- and time-specific fertilization requirements.
It is well established that the rate of fish production raised on natural foods is directly related to the rate of net algal production (McConnell et al., 1977; Almazan and Boyd, 1978; Liang et al., 1981). This relationship is quite logical, since algal productivity is the energetic foundation for secondary production and detritus formation, and all three are basic and valuable food sources for omnivorous and detritivorous fish (Schroeder et al., 1990). The issue then becomes, how to most efficiently stimulate algal productivity and natural food production in the pond? Over and under fertilizations are wasteful, economically inefficient, and usually lead to lower and more unpredictable fish yields. Efficient fertilization means giving the pond algal community what it needs to grow at that timenothing more and nothing less.
Factors which generally limit algal productivity in ponds are the availabilities of soluble phosphorus (P), soluble inorganic nitrogen (N), inorganic carbon (C; particularly in rain-fed ponds), and light. If there is an ample supply of P, N, and C, then the algal community will continue to grow until light availability becomes limiting due to self-shading (and/or inorganic turbidity). If one or more of these nutrients are in short supply relative to the needs of the algal community, then algal productivity is said to be limited by that nutrient(s).
These conditions of nutrient and light limitation are time- and pond-specific, particularly in fertilized ponds where N, P, and sometimes C are added in large quantities to stimulate algal growth, and light can be limiting due to sediment resuspension from rain/wind storms or fish activity. What might be appropriate for one pond may be inefficient for the pond next to it. This is particularly true with P, since the age of the pond and the pond's history of prior fertilizations will affect how much of P fertilizer gets adsorbed by the pond's sediments and how much remains available for algal uptakeeven during the course of a grow-out period (Knud-Hansen, 1992). In another example, changes from N limitation to C limitation were observed in ponds with low carbonate alkalinities and fertilized with urea (Knud-Hansen et al., 1991). These variable ecological factors, among others (e.g., pond depth, wind exposure, bank stabilization, etc.), make generalized fertilization recipes inefficient, both with respect to stimulating algal growth and to farm economics.
The culture pond can become a more efficient and predictable production system if the farmer, or the
advising the farmer, understands dynamic aspects of pond ecology, including dissolved oxygen dynamics, thermal stratification, primary production and decomposition, and the role of inorganic turbidity. Decisions on where to place the ponds, types of source water, pond depth and surface area, and managing pond sediments are all affected by pond dynamic considerations (Knud-Hansen, 1998). In particular, understanding pond ecology promotes knowledgeable choices of appropriate fertilizers to both optimize fertilization efficiency and minimize unwanted environmental impacts (Knud-Hansen and Pautong, 1993; Knud-Hansen et al., 1993; Shevgoor et al., 1994).
Understanding pond ecology helps the farmer manage ponds, but it does not necessarily identify the nutritional requirements of each pond's algal community. Since fish productivity is directly linked to algal productivity, growing more fish food means growing bigger fish. A simple way to identify what the algal community needs to satisfy its nutrient limitation(s) is with an algal bioassay.
Algal bioassays have been used for decades by limnologists to identify nutrient limitation for lake management, i.e., what not to put in the lake to make it eutrophic (Middlebrooks et al., 1976). The algal bioassay is a simple responsive test where pond or lake water is fertilized (or spiked) with specific algal nutrients, particularly N and P. If the indigenous algal community grows in response to a single nutrient addition, then that nutrient is said to be limiting. If there already is an excess supply of that nutrient in the water, then adding more will not result in an algal growth response. Sometimes both N and P can be limiting when the availabilities of both nutrients are low. In other cases, fertilizing with one nutrient can promote the limitation of another (Knud-Hansen et al., 1991). Pond fertilization fixed-input recipes are designed to avoid this, but variabilities between ponds limit the utility of recipes, and explain why ponds fertilized identically will give an unpredictable range of fish yields.
To account for the effects of these ecological variabilities, the algal bioassay method has been specifically adapted for determining pond fertilization requirements on a pond- and time-specific basisi.e., to identify what to put in the pond to turn it green (Knud-Hansen, 1998). The algal bioassay method eliminates the inefficiencies of a single recipe because it determines the fertilization needs based on the individual chemical and biological conditions of each pond at that time. For example, if algal growth in a particular pond is limited by N availability, then fertilizing with P is wasteful, regardless of what a fertilization recipe says. The algal bioassay method identifies primary limitation (i.e., the single nutrient which is in least supply to that pond's algal community's requirements), secondary limitation (e.g., when P is only slightly limiting so that the fertilization with P will then make N limitingin this case P would be fertilized at full rate for that week, while N only at half the rate), co-limitation (e.g., both N and P are limiting, and both are fertilized at full rates), and light limitation (e.g., due to high algal biomass and/or inorganic turbidity, in which case neither N or P or C would be added at that time, since there is insufficient light availability for the algae to utilize the added nutrients).
The algal bioassay method for pond fertilization has been tested under controlled and field conditions, and it has proven superior in terms of nutrient fertilization efficiencies and farm economics to standard fertilization recipes and fertilization requirements determined by computer modeling (Knud-Hansen et al., 1996; Knud-Hansen et al., accepted for publication). The proven benefits of the algal bioassay method are both economic and environmental. Fertilization requirements are fine-tuned on a pond-by-pond basis, so algal productivity is maximized with the minimal amounts of nutrients added. Fish yields are more consistent and predictable, and there is no excess accumulation of N and P in the pond water, so environmental effects upon discharge are minimized. Furthermore, it eliminates the risk of ammonia toxicity since over-fertilization with N is impossible. Lastly, aquaculture extension officers are empowered with the knowledge, confidence, and simple means to improve the economic and environmental sustainability of semi-intensive, pond aquaculture production systems. It does not matter whether the fish culture is monoculture or polyculture, just as long as the culture species utilize natural foods.
Knud-Hansen has developed a portable algal bioassay kit (described below) that requires no water chemistry, no electricity, no computers, and even literacy to use. By teaching people within the university, government extension, and NGO host country aquaculture community the principles of pond dynamics and how to use the algal bioassay test kit, this expertise can then be transferred to the farmers whose lives can be improved through more sustainable fertilization practices.
Quantified Anticipated Benefits
There should be a total of about 90 aquaculture university professors, students, government extension workers, fisheries staff and others in five Southeast Asian countries who will have a working knowledge of how to apply principles of pond dynamics for improving the yields and sustainabilities of semi-intensive aquaculture. The primary economic beneficiaries of the proposed workshops will be aquaculture farmers, who will be able to improve fertilization efficiencies to produce higher yields while minimizing fertilization inputs through the guidance of workshop participants.
In order to transfer this knowledge, workshops will be given on pond dynamics and the application of the algal bioassay test kit for determining pond-specific fertilization requirements. Part of the workshop will be informal lectures to discuss principles of pond ecology which have a direct relationship towards efficient pond management.
The workshops will each have about 15-20 participants, and will be given at locations where the PD/A
CRSP and/or the Asian Institute of Technology (AIT) aquaculture program have established formal connections:
1) AIT, Bangkok, Thailand, to university aquaculture students and government extension officers;
2) Bangladesh Agricultural University, Dhaka, Bangladesh, to university students and government fisheries staff;
3) Cambodia Department of Fisheries, Phnom Penh, Cambodia, to office staff, university teachers, fisheries station staff, and possibly NGO staff;
4) Regional Development Coordination for Livestock and Fisheries, Savannakhet, Laos, to provincial fisheries staff; and
5) Research Institute for Aquaculture, Bac Ninh, Vietnam, to researchers, university teachers, and extension workers.
The primary source material will the PD/A CRSP publication Pond Fertilization: Ecological Approach and Practical Applications (Knud-Hansen, 1998). Since this can be downloaded from the PD/A CRSP website, access to the book is universal. Discussions will not necessarily be at the same technical level as the book, but will still focus on such topics as managing factors which control primary and secondary productivities (e.g., concepts of nutrient limitation), ecological benefits and limitations of organic and inorganic fertilizers as related to pond dynamics, pond characteristics that affect fertilization decisions (e.g., pond location, depth, use of structures such as hapas and cages), and the advantages and disadvantages of current methods for determining fertilization requirements.
Where applicable, demonstrations will be used to illustrate ecological principles. For example a portable fluorometer (which measures both chlorophyll a and turbidity) and dissolved oxygen meter (which also measures temperature) will be used to demonstrate diel changes and differences between ponds. These data will then be analyzed during the workshop to illustrate ecological principles of productivity, decomposition, thermal stratification/destratification, and others that can influence fertilization strategies. Each participant will leave with a greater understanding of how a pond works ecologically, how to use that knowledge to improve predictable fish yields with reduced economic/environmental costs, and how to recognize and prevent pond conditions that will hinder fish production.
The source book also describes in detail the algal bioassay method for determining pond fertilization requirements. Algal bioassay test kits will be provided for each workshop participant. They will gain experience with its application with field demonstrations using ponds fertilized under different loading rates to promote limitations of P, N, C, and light. The test kits will remain in the host country.
The algal bioassay test is very simple to conduct. Pond water is added to nine clear plastic bottles and each spiked with either N, P, C, N+P, N+C, P+C, N+P+C, and de-ionized water (the 9th is the initial). The nutrient spikes can be made from local fertilizers. The eight bottles are incubated in the specially designed kit box either in the pond or on land under indirect sunlight for 2-3 days to allow pond algae to respond to specific nutrient enrichments. After incubation, a measured sample from each flask is filtered, and filter colors are compared visually. If colors are not distinguishable, then there is likely light limitation. There are only 21 possible filter color combinations. A chart is provided to determine from the specific filter-color combination for that test how that pond should be fertilized for that week. The portable test kit provides the incubation container, filtering apparatus (hand filter using a 50 mL plastic syringe and a Millipore Swinnex filter holderfilters can also be punched out of paper coffee filters), charts, and all other necessary materials that are either made of "unbreakable" plastic or are locally available. Continued use of the test kit will not result in any reliance on foreign materials/supplies.
The Regional Plan for Southeast Asia strongly encourages strengthening current linkages with AIT and the PD/A CRSP to neighboring countries. These workshops to be conducted in Bangladesh, Cambodia, Laos, and Vietnam will facilitate that goal. Knud-Hansen, who will be giving the workshops, has had associations with the PD/A CRSP since 1985, and with AIT since 1988. He will continue to work and collaborate with PD/A CRSP and AIT researchers through this proposal as well. These workshops also provide a forum for extending scientific knowledge gained from years of PD/A CRSP research beyond the borders of PD/A CRSP host countries. These workshops will help solidify the informational and research networks necessary to best achieve the goals of the PD/A CRSP. Information dissemination and regional integration are the two main benefits of these workshops.
The five proposed 4-day workshops will take place between January and May 2002, which has already been found acceptable to the participating institutions. The exact timing of each workshop will be coordinated to coincide with Knud-Hansen's two trips to AIT to conduct the zeolite technology experiments described in the work plan for 10ATR5. Attempts will be made to schedule two workshops during the first trip and the other three workshops during the second trip. All travel to Bangladesh, Cambodia, Laos, and Vietnam will originate from Bangkok, Thailand. Final report will be submitted no later than 31 July 2002.
Almazan, G., and C.E. Boyd, 1978. Plankton production and tilapia yield in ponds. Aquaculture, 15:7577.
Knud-Hansen, C.F., 1992. Pond history as a source of error in fish culture experiments: a quantitative assessment using covariate analysis. Aquaculture, 105:2136.
Knud-Hansen, C.F., 1998. Pond Fertilization: Ecological Approach and Practical Application. Pond Dynamics/ Aquaculture Collaborative Research Support Program, Oregon State University, Corvallis, 125 pp.
Knud-Hansen, C.F. and A. Pautong, 1993. On the role of urea in pond fertilization. Aquaculture, 114:273283.
Knud-Hansen, C.F., T.R. Batterson, and C.D. McNabb, 1993. The role of chicken manure in the production of Nile tilapia (Oreochromis niloticus). Aquaculture and Fisheries Management, 24:483493.
Knud-Hansen, C.F., K. Hopkins, and H. Guttman. A comparative analysis of the fixed-input, computer modeling, and algal assay approaches for identifying pond fertilization requirements. Aquaculture. (accepted)
Knud-Hansen, C.F., T.R. Batterson, H. Guttman, C. K. Lin, and P. Edwards, 1996. Field testing least intensive aquaculture techniques on small-scale farms in Thailand. Pond Dynamics/Aquaculture Collaborative Research Support Program, Oregon State University, Corvallis.
Knud-Hansen, C.F., C.D. McNabb, T.R. Batterson, I.S. Harahat, K. Sumatadinata, and H.M. Eidman, 1991. Nitrogen input, primary productivity and fish yield in freshwater ponds in Indonesia. Aquaculture, 94:4963.
Liang, Y., J.M. Melack, and J. Wang, 1981. Primary production and fish yields in Chinese ponds and lakes. Transactions of the American Fisheries Society, 110:346350.
McConnell, W.J., S. Lewis, and J.E. Olson. 1977. Gross photosynthesis as an estimator of potential fish production. Transactions of the American Fisheries Society, 106:417423.
Middlebrooks, E.J., D.H. Falkenborg, and T.E. Maloney (Editors), 1976. Biostimulation and nutrient assessment. Ann Arbor Science, Ann Arbor, Michigan.
Schroeder, G.L., G. Wohlfarth, A. Alkon, A. Halevy and H. Krueger, 1990. The dominance of algal-based food webs in fish ponds receiving chemical fertilizers plus organic manures. Aquaculture, 86:21229.
Shevgoor, L., C.F. Knud-Hansen, and P.E. Edwards, 1994. An assessment of the role of buffalo manure as a fish pond input Part 3: Limiting factors. Aquaculture, 126:107118.
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