by
M.I. VAN DER LINGEN
Henderson Research Station
Mazoe, Rhodesia
FERTILIZATION IN WARM-WATER POND FISH CULTURE IN AFRICA
Abstract
Experience in the use and effects of fertilizers in Africa is summarized and the views of workers on the value of different fertilizing methods and their role in fish culture examined. Organic fertilizers appear to be widely used but in some areas much use has been made of inorganic compounds, mainly phosphates with lime as a “conditioner”. The need for critical work on the biology and chemistry of fertilized water is stressed as is the importance of a background knowledge of waters and water chemistry in order to understand the role of fertilizers. There appears to be conflicting evidence on the value of inorganic fertilizers but it has an important role particularly in Tilapia culture and where costs of foodstuffs are high.
L'UTILISATION D'ENGRAIS DANS LA PISCICULTURE EN ETANG A TEMPERATURE ELEVEE EN AFRIQUE
Résumé
Cette communication résume les expériences menées en Afrique sur l'utilisation et l'effet des engrais et passe en revue les opinions des chercheurs sur la valeur des différentes méthodes de fertilisation et leur rôle dans la pisciculture. L'emploi des engrais organiques paraît être largement répandu mais, dans certaines régions, il a été fait un grand usage de composés inorganiques, notamment de phosphates associés à de la chaux servant d' “amendement”. L'auteur insiste sur la nécessité d'entreprendre des travaux critiques sur la biologie et la chimie des eaux fertilisées et souligne que le rôle des engrais ne sauraient être compris sans une connaissance générale des eaux et de la chimie des eaux. Il semble y avoir des témoignages divergents quant à la valeur des engrais inorganiques mais ces éléments jouent un rôle important, notamment dans l'élevage des Tilapia et là où les produits alimentaires coûtent cher.
FERTILIZACION DE LOS ESTANQUES DE AGUA TEMPLADA EN AFRICA
Extracto
Se hace un resumen de los resultados del empleo y efecto de los fertilizantes en Africa y se examinan las opiniones de los investigadores sobre el valor de los diferentes métodos de fertilización y su función en la piscicultura. Los fertilizantes orgánicos se utilizan ampliamente, pero en algunas zonas se ha recurrido también a los compuestos inorgánicos principalmente fosfatos con cal como “acondicionador”. Se hace resaltar la necesidad de un trabajo crítico sobre la biología y química de las aguas fertilizadas, así como la importancia de un conocimiento básico de las mismas y de la química acuática, con el fin de comprender la función de los fertilizantes. Parecen ser contradictorias las pruebas sobre el valor de los fertilizantes inorgánicos, pero éstos tienen un papel importante, particularmente en el cultivo de Tilapia y en los casos en que los costos de los productos destinados a la alimentación son elevados.
Natural fresh-water fisheries have long been important in Africa, but the cultivation of fish in ponds is a recent innovation. Tilapia species, which are the most commonly used pond fish in Africa, were apparently first tried in ponds in Kenya, in the nineteen twenties (Copley, 1952), although carp (Cyprinus carpio) had been tried in South Africa in 1859 and in Madagascar in 1914 (Bard, 1962). Fish culture was also started before the second world war in the then Belgian Congo, but it was not until after this war that fish culture was seriously investigated in Africa.
This review deals with methods of pond fertilization suggested in reports and publications in tropical and south Africa and Madagascar; though very few investigations have been made on a statistical and scientific basis. Little critical work has been carried out on the effects of fertilizers on the biological cycle of ponds in Africa. Much reliance has been placed on work in Europe, America and the Far East. The careful studies recently carried out at the Malacca Tropical Fish Culture Research Institute should help to stimulate the much needed critical scientific work in Africa.
In Africa much basic and background knowledge is required before fertilizers can be used to best advantage. Studies by Van Someren and Whitehead (1959) in Kenya have provided some basis for understanding the biology of Tilapia in unfed and unfertilized ponds; Le Roux (1955) in South Africa carried out tank experiments to follow chemical and biological changes following fertilization with poultry manure, and Depasse (1956) has considered water quality. Hey (1952) and observations at Fisheries Research Centre Rhodesia (unpublished) stress the role of soils and pond mud. In Africa there are great differences between one area and another; conflicting results in various reports may in many cases be traced to differences in soil and water types, and definite results on fertilizer use under varying conditions are not yet available.
The economic and social environment for most African fish culture suggests use of small domestic ponds of one to two acres, so feeding utilizing cheap wastes, and the use of organic manure, have been stressed, rather than fertilizer use. The value of inorganic fertilizers is appreciated, but these are generally too highly priced for general use in most parts of Africa. However this situation may change (Bard, 1962), and Mortimer (1962) points out clearly the monetary advantage to be obtained when foodstuffs are even moderately expensive and fertilizers are obtainable; taking natural production as unity, the profit index is two with artificial food, 7.5 with fertilizer.
Capart and Kufferath (1957) point out that algae are generally more efficient primary producers than higher plants and that energetically it is more efficient to produce food in the pond through chemical elements added or by bacterial transformation of organic material; they propose a scheme of investigations to relate potential production, as calculated by biochemical means, to the real production, and so help to answer the question how best to obtain maximum yield at minimum cost.
It is clear from the published work that the importance of critical work and the role of fertilizers are appreciated, but very little of the basic investigations have yet been made in Africa, and fertilizers are not yet widely used.
The existing information on the use of different types of fertilizers in the various parts of Africa is briefly reviewed below.
South African workers find the use of lime valuable. Hey (1952) gives recommendations based on European fish culture for soils of differing pH and types and points out that the application of mineral fertilizers may have little or no effect in waters deficient in calcium as judged by their alkaline reserve. He cautions against the sudden change of soil pH which may render the pond bottom sterile until the existing organisms are replaced by forms preferring alkaline medium. The incorporation of superphosphates of lime in organic manure is recommended and following American workers ground limestone is used in inorganic mixtures. Van Schoor (1959) has confirmed in the same area that lime as Ca Co3 has a negative effect on plankton production as shown by American workers, and he studied the effect of nitrogenous fertilizers with a neutral effect such as limestone and ammonium nitrate. His results are somewhat inconclusive since the experimental ponds leaked badly, but in general a rise in alkaline reserve was found.
Lombard (1959) in a useful practical handbook on fish farming in the Transvaal recommends the use of agricultural lime at a rate of 900 kg per hectare (800 lb per acre), spread on the dry pond bottom and ploughed in lightly. He also mentions the use of quick-lime as a disinfectant at rates of 450 kg/ha (400 lb per acre) but this practice does not seem to be widespread.
Maar (1956) in Rhodesia recommends between 360–1,120 kg/ha (300–1,000 lb per acre) as a suitable application prior to the use of fertilizers. Mortimer (1961) suggests 1,675 kg/ha (1,500 lb) spread on the water at monthly intervals for ponds with soft water.
The use of lime is also recommended in early work in Uganda by Simpson (1955) as an improvement for acid water and (1956) in order to reduce turbidity of water on clay soils. No quantities are mentioned. Lime is used in routine practice in carp culture in Nigeria, Anon (1957).
Bonemeal treated with sulphuric acid would provide calcium and phosphates and de Bont (1950) mentions that in combination with maize sweeping (500 kg per hectare) gave excellent results as judged by turbidity and plankton response. Other Belgian workers agree as to the value of this. Huet (1957) mentions the value of lime since many waters in the Congo are poor in calcium, but points out that cost is a negative factor. Gruber (1960) suggests the use of wood ash at rates of some 3,000 kg/ha which would have a decided effect on alkalinity.
Charpy (1956) presents evidence showing the unimportant role of water chemistry and points out that the productivity of water with a high lime content is not very different from that of water with low lime content. He also mentions that liming gave disappointing results.
In Madagascar, Kiener (1956; 1957) obtained excellent results following the use of phosphate fertilizer containing 45 percent Ca O; he also suggests that liming at drainage will be useful for improving the muddy bottom of ponds.
According to FAO/UN (1961) quoted by Bard (1962), excess mud on the pond bottom is useless if not positively dangerous and that the mineralization of the mud by the application of lime permits an increase in the nitrate and phosphate content. As has been shown, the value of liming may be through a variety of interactions, lessening turbidity, releasing materials and increasing the calcium content. High applications do not seem to be required after initial dosage, but moderate quantities may well serve in the capacity of conditioner. The many sided effects are pointed out by Lombard (1959) who discusses the effects and uses of lime. In general the continuous use of lime on soils rendered neutral is probably at best unnecessary and at worst detrimental. Moderate quantities as a hygienic measure on muddy bottoms and where organic manure has been used is in most cases beneficial.
There are numerous reports on the use of various inorganic fertilizers, mainly phosphatic and nitrogenous, but none on critical experiments to determine optimum levels and the exact chemical consequences. Frequency of application is discussed but here again most conclusions seem to be very much rule of thumb. De Bont (1956) in an annual report quotes work by Maes which discusses the background to inorganic fertilizing. He mentions that phosphate applied may be lost by precipitation as calcium phosphate or iron phosphate in waters rich in calcium and iron. How does one determine whether phosphates, for instance, form a limiting factor, asks Maes and suggests in answer that a determination of dissolved salts' variation with time, in relation to plankton concentration is the best method, those elements decreasing markedly at plankton increases being the most likely limiting factors. Maes makes a good case for the use of inorganic fertilizers, because of their high concentration of nutrient salts, in combination with organic manures which ensure a sufficiency of carbon dioxide.
In South Africa Hey (1952) suggested similar recommendations as American workers. Although inorganic manures are more costly he suggests that the labour involved in the preparation of organic manures renders them less attractive. Combinations of nitrogen, phosphorus and potash in a 1:2:1 mixture gave good results in the Cape Province when made up as follows:
18 kg ammonium sulphate or 27 kg sodium nitrate,
27 kg superphosphate of lime,
2.3 kg muriate of potash, and
7 kg ground limestone.
This was applied at 224 kg/ha as an initial dose and thereafter at approximately monthly intervals to maintain a green brown colour and transparency of less than 30 cm.
van Schoor (1959 and in litt.) carried out some interesting work on inorganic fertilizer in glass jars and small ponds, basing his doses originally on American work. This author discusses the value of urea, calcium ammonium nitrate, ammonium nitrate and ammonium sulphate with the addition of agricultural lime. He finds no benefit from the addition of potash which he feels is of value only as a trace element. In slightly acid to neutral waters he has developed a satisfactory mixture which is applied weekly during the warmer months only (due to the temperate climate at the Cape of Good Hope). This is 5 kg urea, 14 kg 19 percent superphosphate and 86.5 kg fowl manure per week per hectare. He suggests that in alkaline water 11.2 kg/ha of ammonium sulphate replaces urea.
Lombard (1960) states that in the Transvaal as much as four times the natural yield is obtained using lime and phosphatic fertilizers and that the production by this method is comparable with production in which fish are artificially fed. He used annual applications of 185 kg/ha of 19 percent superphosphate or 225 kg per hectare of basic slag which contains trace elements. Basic slag is usually more effective in acid water, although this seems to be the most effective phosphatic fertilizer in an experimental fish farm in Nigeria where the water is generally alkaline (Anon, 1963). Lombard (in litt.) mentions that in the first year in Tilapia mossambica ponds agricultural lime and superphosphate increased the yield 4.4 times with a maximum of 600 kg per ha at a stocking rate of 42,000 fish per ha (17,500 per acre). In carp ponds the yield was increased 3.5 times to 264 kg per ha. This author mentions that one disadvantage of fertilizers is their stimulating effect on weeds in farm ponds.
In Natal using Tilapia melanopleura Crass (in litt.) applied 330 kg/ha 19 percent superphosphate and obtained over a five month period increases of 240 kg/ha of fish, over natural production.
Maar (1956) makes recommendations for the fertilization of dams or farm ponds - small to large water storage reservoirs - in Rhodesia but points out that quantities required will vary with locality. He recommends N:P:K at 8:8:4 at approximately 220 kg/ha as an initial application and thereafter as required, (similar to Hey's recommendations). In soft waters sodium nitrate is to be used and in hard waters ammonium sulphate, in making this mixture. One to five applications per year may be required. In older dams superphosphate only is required. This author mentions that fertilizer should only be applied in shallow water less than five m (many of these ponds are deeper than this and stratify in summer for limited periods) and in weed free waters.
Application of 19 percent superphosphate in experimental ponds in Rhodesia consistently gave total production of 1,700 kg/ha and net productions of 1,100 kg/ha using mixed tilapia stocking. Nitrogen tended to show a depressing effect on yields of carp in artificially fed ponds at the Fisheries Research Centre in Rhodesia.
In the 1950s Sklower (1951) while admitting the lack of experiments on fertilizer use in N. Rhodesia suggested the use of single superphosphate at rates of 150 kg/ha for a quick reaction or of rock phosphate, usually only necessary after the first year of operation.
Mortimer (in litt.) has some interesting observations on the method of application in relation to persistence of dissolved phosphorus. Using granular double superphosphate (30 percent) spread on the surface, fertilizer in floating perforated cannisters and in solution he found that while all showed a decrease in time the drop is remarkably less rapid in the water which received the solution and that the concentration after four weeks was considerably higher than with the other methods. Floating cannisters gave better results than conventional application by spreading. Unpublished results in Rhodesia where phosphate fertilizer was applied in hanging sacks in the water showed a greater response in plankton production, support this finding. Mortimer (1962) used applications of 55 kg/ha of double granular phosphate per month and obtained encouraging results in softer waters.
In Uganda Simpson (1956) mentions that the addition of ammonium sulphate causes light but transitory blooms of phytoplankton. Previously (1953) the addition of phosphate and sulphates was recommended for increasing yield from ponds. Wurtz in his report on fish culture (FAO/UN, 1961) recommends the addition of phosphate after liming, particularly in carp culture. However, the Chief Fisheries Officer of Uganda reports (in litt.) that Pruginin working in Uganda on carp 1962–65 found no positive results on carp yield and growth due to phosphate and nitrogen fertilization.
De Bont (1952) mentions the use of phosphates as fertilizer and suggests that only small quantities should be used at a time to avoid excessive plankton blooms. In some industrial fish cultures near Elizabethville, phosphate fertilizers were used in addition to organic manure. Huet (1957) in his valuable survey of ten years of fish culture in the previous Belgian Congo suggests that applications of 150–200 kg/ha of phosphate fertilizer can be very valuable.
Kiener working in Madagascar finds the addition of 2,000 kg/ha of a compound containing 25 percent P2O5 useful in association with organic manure (1956; 1957).
Nigerian fish culture in ponds is stated to be still in the investigational stage (Niven in litt.), but nevertheless some results are available from this area. Carp appears to be the fish of most importance and on an experimental farm on the Jos plateau (Anon., 1963) 36 kg/ha of basic slag is applied at monthly intervals as a standard procedure. At normal stocking rates of 500 fish/ha phosphate alone at 1.15 tons/ha gave no advantage. At 1,000 fish/ha some advantage was found while again at 1,500 fish/ha there appeared to be no advantage.
The most noticeable effects would appear to be in soft water ponds and in the absence of feeding. Clearly there is much to be done in assessing rates and methods of application under different conditions.
The use of organic manures and the combination of animal rearing with fish culture is widespread. Cautions against excessive use and the limitations of organic manures are voiced by a number of workers.
Hey (1952) in the Cape Province of South Africa recommends the use of 2 tons of horse or cattle manure per ha (1 ton per acre) or 500–1,000 kg per ha of poultry manure. Compost if used should have a carbon to nitrogen ratio of 10:1 and the addition of 68 kg of sodium nitrate per ha of compost is recommended. This and other organic manures should be dug into the soil before filling, having been spread evenly on the pond bottom, or if applied while the pond is full, should be placed in heaps around the perimeter to avoid excessive de-oxygenation. Van Schoor also mentions the use of fowl manure (1959 and in litt.).
Lombard (1959) recommends 4 to 14 tons of manure or compost per acre in addition to inorganic phosphate fertilizer, but cautions that this should be spread over the whole season and not applied in bulk to avoid oxygen deficiency.
In Natal Crass (in litt.) states that ducks at a rate of 1,200 per ha were the most effective means of fertilizing ponds and that fowl manure was twice as expensive as phosphate in order to achieve a comparable result.
Belgian workers achieved high production using waste grain, cereals and other industrial by-products; de Bont (1950) used as much as 10 tons/ha of mill sweepings. In a subsequent paper he mentions (1952) that 5,000–9,000 kg/ha of fish were obtained with the use of mill sweepings which would serve partly as food and partly as fertilizer. With manures alone he had productions from 1,000–2,000 kg/ha. This author suggests digging cotton seed, ground nut seed and sunflower seed cake into the pond bottom after an application of 1.5 tons/ha. Farmyard manure at 3 tons/ha may be necessary only every two years. The use of composted water weeds, particularly Characeae which may be dug in when the pond is dry or scattered on the water, is also stated to be efficacious. As a precaution, when organic manure is applied in quantity a good inflow of well oxygenated water is necessary. Gruber (1960) recommends animal manures and composts at 3,000 kg/ha before filling and subsequent applications which should not exceed 10,000 kg/ha/annum. Recommendations at a meeting on fish culture in the previous Belgian Congo were 3,000 kg/ha of compost and farmyard manure after each draining.
Charpy (1956) mentions that little benefit seems to be had from the use of industrial by-products as organic manures rather than as food, but in the same paper quotes production of 9,000 kg/ha in tilapia ponds at an agricultural station in the previous French Congo resulting from the combined rearing of pigs and fish.
In Cameroon the use of the Coypu (Myocastor coypus) for weed control is reported to have also the effect of providing useful food and manure for the fish as has been found elsewhere (Bard, 1965).
In Madagascar Kiener (1957) recommends addition of nitrogen, potash and bonemeal to a compost of grass which is applied when mature at 3,000 kg/ha.
In Nigeria grass from the banks and pond walls is composted and applied in ponds. To what extent these heaps serve as nurseries for fish food are eaten, or are acting as fertilizers, is not clear. However, in most cases the combination of grass compost and phosphate provides excellent results and increases the volume of plankton.
In Rhodesia (van der Lingen, 1960) the use of pig manure gave net productions of up to 2,000 kg/ha, while ducks when kept on or near ponds at rates of 1,000 ducks per ha were able to ensure up to 4,000 kg/ha. In Northern Rhodesia (1958) also ducks have been used with good results.
Lombard (1959) in the Transvaal advocates green manure in tilapia nursery ponds which are sown sparsely with an appropriate crop and filled a week before stocking without ploughing in the plants. If beans or other vegetables are grown the crop is harvested and the stalks left as a fertilizer. Gruber (1960) suggests that Lagarosiphon may be used in flooded ponds or rice grown and inundated at a height of 20–30 cm, this crop being especially valuable for Tilapia melanopleura. In these cases the effect is mainly a direct one as the green crop is eaten by the fish. This author also suggests the use of the dry pond bottom for a crop which is alternated with fish, but states that in the Central African territories this is not common. In Cameroon (Anon, 1957) maize is used as an alternating crop in a rotational system, but it is felt that the practice of green manuring and cropping does not give as high a yield as intensive feeding.
The drying of ponds is implied or specifically recommended in many areas in Africa. This is usually associated with the amelioration of the bottom by liming, organic or other fertilizing and the removal of excess silt. Recommendations in the previous Belgian Congo were that a pond should be dried for 18 days and during this period compost applied to the bottom. Huet (1957) points out that the advantages are well-known and suggests either simply drying out to allow mineralization or a combination with a cropping practice. He recommends that the optimum period be determined. There is apparently no need to keep ponds dry for as long as in European practice but the weight of opinion seems to suggest that some benefit at least is obtainable. It is noticeable that production may drop in ponds under continual culture (Depasse, 1956), and there may well be much in favour of a closer study of drying and cropping particularly in areas of poor soil and water fertility. This author attributes the drop in yield to the absence of a long dry period.
While there is already a large body of work on fertilizers it is clear that more detailed information is required. The fertilization practices are likely to require modifications in tropical and sub-tropical waters but much use can be, and has been, made of experiences elsewhere in the world. There are many different approaches and different economical and social environments in which fish culture is pursued. In many parts of Africa fish culture is being successfully carried out in water bodies not designed primarily for fish production, and these pose special problems of their own vis-a-vis fertilization. The effects of fertilizers on all biological phases culminating in fish production need further investigation and it is hoped that in the next few years more critical studies will be made in this field.
The author's grateful thanks are due to colleagues for their generosity in supplying details of work being carried out. In addition to those mentioned in the text must be included Mrs. Rosemary Hutchinson, Natal Parks, Game and Fish Preservation Board, Republic of South Africa, the Centre Technique Forestier Tropical, Section de Madagascar, the Director of Fisheries, Tanzania, and the Chief Fisheries Officers of the Nigerian Federal Fisheries Service, Kenya, and Ghana.
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