by
PAWEL WOLNY
Experimental Pond Station, Inland Fisheries Institute
Zabieniec, Poland
FERTILIZATION OF WARM-WATER FISH PONDS IN EUROPE
Abstract
The first part of the paper outlines the main problems of fertilization of fish ponds under European climatic and economic conditions. The change in opinions, from the theory of nitrogenless fertilization which was believed in during the period between world wars, to the modern approach that recommends inter alia nitrogenous fertilizers, is reviewed. The characteristics of Norway saltpetre, ammonium sulphate and liquid ammonia, which are the three commonly used fertilizers in pond culture, are given. Information concerning experiments conducted with urea and acidic ammonium carbonate is also presented. The second part of the paper reviews the use of the more important organic fertilizers.
LA FERTILISATION DES ETANGS DE PISCICULTURE A TEMPERATURE ELEVEE EN EUROPE
Résumé
Dans une première partie, la communication décrit les principaux problèmes que pose la fertilisation des étangs de pisciculture dans les conditions climatiques et économiques régnant en Europe. L'auteur examine les raisons pour lesquelles la théorie de la fumure sans azote, qui avait cours entre les deux guerres mondiales, a fait place à la théorie moderne qui recommande d'utiliser, entre autres, des engrais d'azotés. Il indique les caractéristiques du salpêtre de Norvège, du sulfate d'ammonium et de l'ammoniac liquide qui sont les trois engrais communément employés en pisciculture. Il présente également des renseignements concernant les expériences menées avec de l'urée et du carbonate acide d'ammonium. Dans une deuxième partie, la communication passe en revue l'utilisation des principaux types d'engrais organiques.
FERTILIZACION DE LOS ESTANQUES PISCICOLAS DE AGUAS TEMPLADAS EN EUROPA
Extracto
La primera parte del estudio expone los principales problemas de la fertilización de estanques piscícolas en las condiciones climáticas y económicas europeas. Se examina el cambio observado de opiniones que van desde la teoría de la fertilización sin nitrógeno, en la que se creyó durante el período comprendido de las dos guerras mundiales, al moderno método que recomienda inter alia fertilizantes nitrogenados. Se indican las características del nitrato potásico noruego, el sulfato amónico y el amoníaco líquido, que son los tres fertilizantes empleados generalmente en el cultivo en los estanques. Se ofrece también información sobre los experimentos realizados con urea y carbonato amónico ácido. En la segunda parte del estudio se examina el empleo de los fertilizantes orgánicos más importantes.
What fertilizers should be used to raise the fertility of ponds by creating better conditions for the development of natural fish food, thus reducing the volume of fodder consumed by carp (Cyprinus carpio L.)? Further, how can the oxygen conditions be improved in waters which are prone to violent deterioration when the fish are fed intensively (Szpet and Feldman 1959)? These basic questions, if answered, would open further prospects for a marked increase of fish production in warm-water ponds in Europe.
An additional problem concerns the quantitative and qualitative variation in the invertebrate fauna in ponds, as this falls to the minimum in August, just the month with the best thermal conditions for carp growth, for the carp is a warmth loving species. This bears on the deterioration of the optimum ratio of natural to artificial food (Gurzẹda,1965).
Furthermore, the aims and practical aspects of pond fertilization in Europe must reckon with both the climatic conditions and the economic conditions in individual countries.
The extent to which the European climate limits primary production is exemplified by two figures. The first is the average daily insolation, expressed in percent of the maximum possible insolation; according to Liebmann and Keitz (1965) this is 39 percent for the Experimental Pond Station at Wielenbach (Germany, Federal Republic). The second applies to the number of days during the year, with mean water temperature above 20°C; according to Stegman (1960) and Backiel (1964) this determines the level of fish productivity in ponds. At the Experimental Pond Station at Zabieniec near Warsaw, in the centre of the physical map of Europe, the period of time with water temperature above 20°C, averages no more than sixty days in the year.
The production of carp for the table in Europe is governed on the one hand by the climatic factor, and on the other by the generally higher quality standards set for the market compared with other countries outside Europe. The rearing of carp weighing between 0.5 and 2 kg requires at least two years under European climatic conditions. This involves splitting the carp production cycle into two years, setting out from fingerlings weighing between 25 and 100 g the first season, followed by about a six-month growthless winter period, then the required individual weight is attained by fish during the following season.
The oxygen demand of fry, nearly double that of two-year old carp (Priwolnjew, 1957; 1958) restricts the use of organic manures in fry ponds.
We come now to the question of whether the chemical composition of European inland waters includes the biogenic constituents essential for photosynthesis in sufficient amounts to ensure full utilization of the solar energy.
The relatively scarce, rather superficial studies on the chemical composition of inland waters give only a general idea as to which biogenic constituents seem to limit photosynthesis in aquatic plants.
Mackareth ((1956), relying upon fairly ample analytical material, came to the conclusion that calcium, sodium and manganese do not restrict phytoplankton production. Rodhe (1948), reported that the optimal concentration of potassium in the case of Scenedesmus quadricauda is 1 mg per litre.
According to Lund (1956), mass-scale phytoplankton development is quite often encountered in lakes even at a potassium level within the limits of 0.04 to 0.4 mg K, but not as often as when it is within the limits of 0.4 to 2 mg/l.
Winberg (1953) and Braginski (1955; 1958; 1961) established that in many ponds on Byelorussian fish farms, in which the waters contained up to 4 mg/l/K, potassium was not a factor limiting the fish crop, and furthermore, the fishing effects remained unchanged whether potassium was administered by itself or together with phosphorus and nitrogen.
Stangenberg - Oporowska (1961) ascertained on the basis of ample material that the potassium level in Polish ponds keeps within 2 to 6 mg/l in most cases, and shows an upward trend from spring to autumn. As not much potassium is contained in phytoplankton (0.5 to 1 percent of the dry weight), there is very little likelihood of this constituent being in short supply.
In Germany and a number of neighbouring countries, phosphorus-potassium fertilization of ponds used to be employed in the inter-war period (Mortimer, 1954). In post-war times pond fertilization with potassium was generally abandoned except for peat ponds, which are as a rule scantily provided with this constituent. The level of phosphorus and nitrogen in European inland waters is however, unlike potassium, in short supply to a greater or lesser degree, and limits phytoplankton development.
The results of the present research on the influence of nitrogen on fish crops in ponds contradict those obtained by a number of German investigators after the first world war (Demoll, 1925; Wunder, 1949).
The ratio P:N seems to be an agent limiting the efficacy of nitrogenous fertilization of ponds. From among the few investigations on the subject in Europe mention should be made of the results obtained by Kuzmiczewa (1965).
Using Norway saltpetre at the rate of 1 mg/l/N in one group of ponds, 5 mg/l in another and 0.1 mg/l P in both cases, she obtained P:N ratios of 1 : 4 and 1 : 44 respectively. The extent to which the ratio of phosphorus to nitrogen can affect primary, secondary and final production is illustrated by the results given below.
Primary production in the two groups of ponds was 1.47 mg/l O2 and 3.3 mg/l O2 respectively. Not withstanding the differences in phytoplankton biomass, she obtained the same quantity of zooplankton in both groups, 4.4 mg/l in each case. She established no correlation between nitrogen concentration in the water and fish production (10.1 kg fish per pond and 13.8 kg/pond). Thus the phosphorus deficit clearly had an adverse effect on the full utilization of five times as great nitrogen concentration. The results obtained by Kuzmiczewa favour, therefore, the acceptance of P : N = 1 : 4, as determined by Swingle and Smith (1938), to be the optimum ratio.
The determination of the optimum P : N ratio is, however, a most difficult proposition in pond practice since both the bicarbonate level in the water and the acidity level in the bottom sediments are subject to constant variation during the vegetative season, which may affect the variation in P : N ratio. It would be reasonable to suppose that the ratio of phosphorus to nitrogen could be kept wider apart in well mineralized waters, and even more so in cases where the pond bottom is alkaline.
An inverse physico-chemical situation should be expected in ponds having soft water and in the presence of acidified bottom sediments. In such cases, the P : N ratio should be rather narrowed. Possibly that is the reason why Winberg and Ljachnowicz (1965) suggest the possibility of variation of the optimum P : N ratio within fairly broad limits, from 1 : 4 to 1 : 8.
The results of investigations conducted in the “Nivka” experimental ponds near Kiev (Feldman and Suchowij, 1961) also suggest that 1 : 4 P : N ratio is most favourable.
Lack of appreciation of the significant róle played by the phosphorus-nitrogen ratio in pond fertilization was probably among the reasons underlying the promotion of the theory of nitrogenless fertilization of ponds (Demoll, 1925), based mainly on the research at Wielenbach where the waters are exceptionally rich in mineral nitrogen (Liebmann and Keitz, 1965).
It seems that better effects of pond fertilization could be expected if broader investigations into the span of the P : N ratio variation were launched in ponds built on different substrata, that is on sandy, loamy and clay soils, and especially on peat soils because upon these are built large numbers of ponds in many European countries.
Müller (1957; 1961a; 1961b) found no effect of liming on pond fish growth, and Swingle (1947) recorded even a decline in fish growth when lime was administered to pond water showing an alkaline reaction. According to Winberg and Ljachnowicz (1965), liming is unnecessary and even harmful in very alkaline water, above 3 mV/l, because under such conditions, phosphorus is bound into the insoluble calcium phosphate which is deposited on the bottom.
However, liming seems not to be a factor limiting fish growth because in waters of medium mineralization (those with an alkalinity of 2 mV/l which corresponds to 56 mg/l CaO or 560 kg per ha) even with 1,000 kg fish per ha, only about 1.25 percent CaO, or 12.5 kg, is found in the fish, and this amounts to a mere two percent of the total amount of this constituent in the water. Thus it seems that a lime deficiency only occurs in isolated cases, in ponds with exceptionally poorly mineralized water.
On the other hand, the value of adding lime seems to be indisputable for ponds with acid water and bottom sediments.
If we take it that the most general purpose of liming is to increase the alkalinity of the water, in other words to raise the bicarbonate content, then this can only be achieved in the presence of free carbon dioxide by the following reaction:
CaCO3 + CO2 + H2O = Ca (HCO3)2
The alkalinity of the water cannot be raised by the addition of CaCO31 unless carbon dioxide is liberated in the course of decay of organic matter. The increase in alkalinity of the water proceeds much faster when slaked lime is used in the presence of dissolved carbon dioxide.
If slaked lime is administered above the carbon dioxide surplus capacity, this may instead of increasing the alkalinity produce its decline due to the deposition of calcium carbonate, which is insoluble, in the following reaction:
Ca(OH)2 + Ca(HCO3)2 = CaCO3 + 2H2O
Therefore, alkalinity depends above all on the amount of free CO2 in water. Carbon dioxide in water is derived from organic matter decay processes. For this reason, the liming of ponds poor in organic sediments or organically unmanured produces no effect.
The role of liming in phosphate and nitrogenous fertilization consists in neutralizing the acid reaction of the bottom sediments. Neutralization of sediments weakens the phosphorus ion bond, thereby facilitating the passage of ions into the water. The acid reaction of the environment holds back the micro-biological processes of ammonification, nitrification and the fixation of free nitrogen. Thus liming produces accelerated circulation of nitrogen and its faster action.
Liming speeds up the decomposition of organic matter and thereby the exuding of CO2 from the bottom sediments. Moreover, it stimulates the development of microflora, an important food item for invertebrate larvae.
One of the chief objectives in liming ponds is to reinforce the buffer system of the water. This system consisting of CO2 - HCO3 - CaCO3, and designed to prevent fluctuations in the pH of the water beyond the lethal limits for fish, is still relatively little known. Further research is required in particular into the role of carbon dioxide, which is, according to Maucha (1958), also an agent limiting phytoplankton development.
When the pH of the water is high due to the assimilation processes of plants in ponds fertilized with ammonia-derived nitrogen, a marked concentration of NH4 ions, strongly toxic for fish, may take place. Such situations are especially dangerous for the postembryonic stages of carp.
1 i.e. not above 15 ppm in CaCO3 (This solubility of CaCO3 in water at 20°C)
1.7.1 Type of nitrogenous fertilizer
Scheuring and Leopoldseder (1934) have shown that ammonium fertilizers are more toxic than nitrates. For young carp over 7 cm long the lethal concentration of ammonium sulphate (death within six hours) was 0.03 percent at pH 7.47, but of sodium nitrate it was 2 percent at pH 7.58.
1.7.2 Species and size of fish
The toxic action of fertilizers on carp depends not only on fish size but also on type of scale cover (Wolny, 1964). The fast growing mirror carp, between the time of hatching and growing to 5 cm in body length, is found to be more sensitive to nitrogenous fertilizers than is the slow growing scaleless carp. If percentage mortality be taken as the criterion of toxicity, the most toxic treatment appears to be ammonia liquor applied at the rate of 15 kg/ha N every three days, next ammonium sulphate and least toxic urea. Carp fry above 5 cm long are found to be resistent to a concentration of 2 mg/l N of the above named fertilizers. Therefore, in addition to the proper choice of fertilizers for ponds stocked with carp at different ages, no less important is the method of administering fertilizers, to exclude the possibility of fish running into a lethal concentration zone. The same largely applies to nursery ponds, especially fry ponds stocked with fish a few days old which are exceptionally sensitive to any environmental changes. Swingle and Smith (1938) and Smith and Swingle (1938) offset the toxic action of ammonium sulphate by extra fertilization with basic slag, in place of superphosphate which acidifies the environment.
1.7.3 Physico-chemical properties of water
Soft water with a weak buffer action stimulates the toxicity of ammonia (Schäperclaus, 1961). A rise in temperature has an equally stimulating effect. At Zabieniec experiments showed that a concentration of 50 mg NH4OH per litre was lethal for young carp individuals weighing 50 g after 30 minutes when the water temperature was 17°C, but in the event of a temperature rise to 23°C, death took place within 13 minutes.
1.8.1 Stock density
The maximum increment in carp per unit area takes place, according to the curve of Nordquist (1928), at an optimum stock density for a given pond type. Optimum stock abundance stimulates carp to feed on the bottom (Gurzẹda, 1965). Should the stock density become unduly low or high, the proportion of bottom fauna in carp food diminishes in favour of zooplankton. There is therefore a clear correlation between stock abundance, fish crop, and the ratio of bottom fauna to zooplankton in carp food. The most intense penetration of the pond bottom takes place at optimum fish abundance. The constant stirring of bottom sediments by fish seeking chironomid larvae accelerates the mineralization of organic matter and the circulation of nutrient salts.
It seems that the determination of the fertilizer requirements under conditions of optimum stock density at which the maximum growth of fish is reached, may provide more unbiassed criteria for estimating the action of fertilizers on primary and secondary production. In the latest investigations by Winberg and Lyakhnovich (1965), Kuzhmicheva (1965) and others, the secondary production is understood first and foremost as animal plankton. However at optimum stock density the plankton is of much less importance than bottom fauna since the latter is the main food of carp (Gurzẹda, 1965).
1.8.2 Agrotechnical measures
Agrotechnical operations on the bottom of the pond are designed to remove vascular plants and to neutralize the sour silt. The clearing of rooted flowering plants, mosses and Characeae from the bottom determines the efficacy of pond fertilization.
1.8.3 Periodical drainage
Periodical drainage of the pond bottom as borne out by the investigations conducted by Danielewski (1965), results in the mineralization of organic compounds. During the winter drainage period, the mineral nitrogen content in bottom sediments made up of phytoplankton increased by 142.2 kg/ha, as against a decrease of this constituent by 18.5 kg in ponds filled throughout the winter.
1.8.4 Technique of fertilizer administration
Doses of nitrogenous fertilizers administered at seven to ten day intervals are recommended by nearly all writers (Wróbel, 1962; Danielewski and Włodek, 1962; Wolny, 1964; Janeĉek, 1963; Winberg and Ljachnowicz, 1965). The number and concentration of nitrogen doses depends on the pond category. Fry ponds at Zabieniec are fertilized at three day intervals, and the nitrogen concentration varies between 1 and 1.5 mg per litre. The last dose is given a week before the pond is fished.
Fingerling ponds are fertilized once a week up to the end of August. Fertilization of yearling and commercial ponds begins fourteen days before stocking and ends in mid-August. Nitrogen concentration is kept within the limits of 1 to 2 mg/l. Phosphorus fertilizers are administered every two weeks or even once a month.
The conditions for autochthonous synthesis of organic matter, which takes place in aquatic plants, chiefly phytoplankton are improved through mineral fertilization (Winberg and Ljachnowicz, 1965).
The effect of sole administration of mineral phosphorus fertilizers on fish growth was investigated between 1913 and 1949 in the Experimental Pond Station at Wielenbach (Germany, Federal Republic). Superphosphate was administered at a rate of 25 to 30 kg/ha P2O5 in two doses, the first applied to the bottom before the spring filling of the ponds, and the second, in water, usually in May. The increased crop, on an average over a number of years, was 72 kg/ha (Demoll, 1925; Probst, 1950). Thus, 0.4 kg P2O5 or 2.3 kg superphosphate, went into 1 kg increment of carp weight.
The high efficiency of phosphorus fertilization is limited, however, to a specified level. As demonstrated by Schäperclaus (1961), a further two or threefold increase of superphosphate, to the level of 75 kg/ha P2O5, would produce a violent increase in superphosphate consumption to 12 to 15 kg per 1 kg increment of fish weight.
The disproportion between the effect in regard to fish weight increment and the increased superphosphate doses shows that it is not only phosphorus that limits the increase in fish production under conditions of exclusive phosphoric fertilization.
Neither does exclusive nitrogen fertilization, as borne out by the experiments of Winberg (1958) give satisfactory results. In his experiments nitrogen consumption was as high as 7 to 12 kg 35 percent Norway saltpetre per 1 kg of fish weight increment. Under the same conditions but with the addition of superphosphate, seven times as great utilization of Norway saltpetre was obtained.
The theory of nitrogenless fertilization advanced by Demoll (1925), as well as the practical indications consequent upon it, have been subject to a profound evolution resulting from limnological researches especially during the past fifteen years.
Several types of ammonium fertilizers in combination with phosphates have already found wider uses, and the development of other types is at the stage of experiment and research carried on mainly by fisheries institutes in a number of countries.
It seems that the fertilizer selection method for various pond types, as well as the method of determining optimum doses in experimental ponds, could be successfully supplemented, in view of the inadequate number of ponds available, by the use of tiny plots made of plastic foil and mounted on a portable scaffold (Janeĉek, 1963). This plot method may advance the solution of the problem of choice of fertilizers suitable for different soils and climatic conditions.
Wider uses in pond practice have up to the present provided information about the following fertilizers.
2.2.1 Norway saltpetre
Norway saltpetre, NH4NO3 contains 20 percent pure nitrogen in the ammonium form and 15 percent nitrogen in the nitrate form. The microbiological investigations by Rodina (1958) have contributed, among other things, to the widespread use of this fertilizer, mainly in the Soviet Union. They showed that phytoplankton, chiefly blue-green algae, developed quickly under the action of the fertilizer. The development of denitrification bacteria is slowed down under the favourable conditions thus created. Since aquatic plants in general assimilate nitrogen more readily in the ammonium form Norway saltpetre has physiologically weak acidic properties.
The experiments conducted by Winberg (1958) in the “Shemetevo” Breeding Centre in Byelorussia revealed a three- to fourfold increase of carp production in ponds fertilized with nitrogenous-phosphate fertilizers. To obtain 1 kg increment in fish, 1.47 kg 35 percent Norway saltpetre and 2 kg 16 percent superphosphate were utilized. In a region further to the south, Feldman, Prosianyj and Suchowij (1961) obtained between 79 and 290 kg/ha gain in weight, using exclusively nitrogenous-phosphate fertilizers at the rate of 0.65 to 2.33 kg superphosphate and 0.41 to 1.67 kg Norway saltpetre per 1 kg weight increment in carp.
Particularly high fertilizer doses were employed by Mamontowa (1961) for ponds in the vicinity of Moscow. Using 730 kg/ha superphosphate and 1,350 kg/ha Norway saltpetre, she secured a three to three-and-half-fold increase in natural growth, and in individual cases the gain in weight came to as much as 799 kg/ha.
At these maximum doses, 1.64 kg superphosphate and 3 kg Norway saltpetre went into 1 kg carp growth.
It seems, however, that at such a high nitrogen concentration oxygen deficiencies, dangerous to fish, may occur at night under conditions of intense phytoplankton blooms.
In the experiments of Ljachnowicz (1963), the superphosphate dose was 400 kg/ha and that of Norway saltpetre 800 kg/ha. The fertilizers were administered to the water in small lots throughout the growth season. The weight increment of fish came to 400 kg/ha. The mean consumption of fertilizers per 1 kg carp growth was 0.67 kg N and 0.25 kg P2O5.
The cost of fertilizers per 1 kg of fish weight increment was one-third that of the fodder that would be required to produce the same gain in weight.
The annual demand for Norway saltpetre and superphosphate and the effects of fertilization obtained in various regions of the Soviet Union are given by Winberg and Ljachnowicz (1965). The estimated annual fertilizer demands ranged from 350–450 kg/ha saltpetre and 300–400 kg/ha superphosphate in north Europe and Siberia, to 700–1,000 kg/ha saltpetre and 600–800 kg/ha superphosphate in south Europe. The carp yields with fertilization ranged from 200–300 kg/ha (compared with 70–80 kg/ha from unfertilized waters) in north Europe and Siberia, to 600–700 kg/ha (compared with 220–250 kg/ha unfertilized) in south Europe.
2.2.2 Ammonium sulphate
Ammonium sulphate, (NH4)2SO4, containing 20 percent nitrogen is one of the most widely used fertilizers in the U.S.S.R., Poland, Rumania, Yugoslavia, Germany (eastern), Czechoslovakia and elsewhere.
Ponds fertilized with ammonium sulphate promptly give rise to phytoplankton blooms. The stimulating effect of this fertilizer on bottom fauna was ascertained by Zuntz (1919) and on the extended development of zooplankton over the season by Schäperclaus (1966). Bank (1959) demonstrated that fish grow better in ponds fertilized with ammonium sulphate.
It follows from the investigations on ammonium sulphate, ammonia liquor and urea, conducted by Wróbel (1962) in Golysz and Landek experimental fish farms (southern Poland) situated on loamy soils, that individual fertilizers act differently on the chemical composition of water. The primary production of phytoplankton was doubled at 50 kg/ha N and showed more than a threefold increase at 70 to 85 kg/ha N. Ammonium sulphate produced the least variation in the primary production of phytoplankton. In control ponds, the oxygen output could not meet the demand.
The ammonium nitrogen concentration delivered in the form of ammonium sulphate or ammonia liquor, about 1 mg N-NH4/l, used to drop to the level prior to fertilization in no more than four to five days. If after applying the fertilizers cloudy weather set in with a drop in temperature, almost invariably nitrites used to appear and the nitrate content would increase. Since in the third year of the experiment, Wróbel recorded a clear decline in fish growth increments, he considered that ammonium sulphate should not be used as fertilizer because most likely a deposition of sulphates takes place.
In the experimental ponds at Zabieniec, which are on sandy soil, a well-marked decline in young carp production was observed even after a year in ponds fertilized with ammonium sulphate at the rate of 15 kg N/ha every three days. Two-year old carp grew 17 percent less on ammonium sulphate than they did on ammonia liquor.
Janeĉek (1963) recorded in the experimental ponds of the Fisheries Institute at Vodniany a 7 percent lower carp increment in plastic-foil plots fertilized with ammonia liquor than in those fertilized with Norway saltpetre.
It is possible that the considerably higher calcium content in Israelian pond waters (Hepher, 1962), compared with waters on the European continent, more effectively eliminates the adverse after-effects of ammonium sulphate on the fish crop.
2.2.3 Ammonia liquor
Ammonia liquor, NH4OH, containing 20 percent nitrogen, has been in use in some European countries just a few years. The nitrogen contained in ammonia liquor rapidly and strongly stimulates the development of phytoplankton, green algae in particular (Massalski, unpubl.). Ammonia liquor used by Wróbel (1962) in his experiments at the rate of 150 l/ha had only a slight effect on the pH, raising it from 7 to 7.6. The relatively better result of fertilization of the ponds at Zabieniec with ammonia liquor during the cool summer of 1965 was probably related to the reduced toxicity of NH4 ions at lower temperature. However, in the absence of systematic observations over many years on ammonia liquor fertilization under European climatic conditions, it is impossible to draw as far-reaching conclusions as in the case of the nearly forty-year long investigations on superphosphate (Mortimer, 1954).
Ammonia liquor as fertilizer finds an ever wider application on fish farms. An interesting experiment with ammonia liquor used for fertilizing peaty ponds was made by Mints and Khairulina (1965). About a dozen tons of peat were soaked in ammonia liquor containing 0.9 percent ammonia nitrogen (NH3) and 15 kg of superphosphate was added per ton of peat. The peat thus treated was transferred in part to the bottom of a pond and after flooding it, another six doses of the treated peat were distributed on the water. Altogether 12.7 tons peat per ha were administered throughout the season. In terms of nitrogen, ammonia liquor consumption was 40.9 kg per ha. The control ponds received 210 kg/ha N in the form of Norway saltpetre.
An examination of the biological activity of the peat pond bottom showed 0.95 mg CO2/100 g peat. After administering the treated peat, the biological activity rose to 2.4 mg CO2/100 g. Moreover, the amount of phosphates, nitrates and ammonia in the water increased threefold.
The increased biological activity of the peaty pond bottom was obtained through the bonding of humic acids with ammonia into soluble ammonium compounds. These compounds are reported to stimulate the growth of plants and improve the soil structure. Moreover, ammonia liquor sets in motion the activation of the nitrogen contained in peat.
Since the market price of ammonia liquor is half that of ammonium sulphate, the question arises whether this form of ammonia nitrogen, notwithstanding its toxic action on carp hatchlings and the restricted possibilities of using it in soft waters showing weak buffer action, has any prospects for wide use in practice. The above-mentioned adverse characters are offset by a rapid and high primary production which is by no means unimportant in the European climate marked by a relatively short season of carp growth and only a small number of days over the year with temperature around 25°C.
The action of acidic ammonium carbonate and urea on the pond environment has been the subject matter of experiments carried on now for several years. These fertilizers are bicomponent, as apart from nitrogen they contain carbon dioxide which, like nitrogen, when at minimum value, limits phytoplankton development (Maucha, 1958).
2.2.4 Acidic ammonium carbonate
Acidic ammonium carbonate (NH4HCO3) contains 16 percent nitrogen and 50 percent carbon dioxide. Unlike ammonium sulphate, this salt is not physiologically sour as fertilizer since both its constituents (N and CO2) can be readily assimilated by aquatic plants. Experiments with acidic ammonium carbonate carried on in the period 1963–1965 at Zabieniec revealed a number of favourable properties of this compound which had not hitherto been used as pond fertilizer.
The investigations by Danielewski (unpubl.) revealed a number of changes favourable for fish in the chemical composition of water. The alkalinity of water and carbonate hardness increased under the action of acidic ammonium carbonate. The reinforcement of the buffer system of water under the action of carbon dioxide held in check the biological decalcification of water, which occurred in the most acute form when using ammonia liquor as fertilizer. The relatively small variation of oxygen and pH value of water was, no doubt, linked with the improved buffer system.
Investigations into the species composition of phytoplankton (Massalski, unpubl.) showed that almost a mono-culture of green algae (Protococcales 92 percent of the total cell abundance) developed, whilst simultaneously the number of diatoms decreased to one-quarter. This result corresponds with the investigations by Lund (1965) who ascertained a mass development of diatoms in soft waters. Acidic ammonium carbonate proved to be, therefore, a quick-action fertilizer, which is of major importance for carp fry production under the system of Dubisch which involves a double transfer of fish from the spawning pool, first to a fry pond and then to a fingerling pond, so the ponds are only in use for short periods of one to three months. Ichthyological research revealed (Wolny, 1965) that NH4 action from acidic carbonate was harmless even for hatchlings a few days old.
A doubled natural increment in carp fry was obtained with the action of acidic ammonium carbonate in 1964. The extra natural growth was 234 kg per ha, which means that 1.17 kg carp was gained per 1 kg N, compared with 0.99 kg per 1 kg N contained in ammonium sulphate. The beneficial effect of ammonium carbonate on oxygen conditions was also manifest in ponds in which fry were intensely fed on sorghum. The oxygen level at 1,098 kg fry per ha was even slightly higher there than in unfertilized ponds with a considerably lower fish production (692 kg/ha).
Microbiological investigations of the near-bottom water layer in ponds fertilized with ammonium carbonate in which the carp fry were supplied with fodder, showed that the abundance of bacteria per milli-litre water was smaller than in similar ponds fertilized with ammonium sulphate, and producing less fish (Zolnierkiewicz, unpubl.). Possibly green algae (Protococcales) in decomposing autolytically (Winberg and Ljachnowics, 1965) failed to produce a medium for an appreciable number of bacteria. The results of chemical analysis which showed a higher mineral phosphorus level in pond water fertilized with ammonium carbonate, pointed to a decomposition of green algae without the agency of bacteria, and to the liberation of mineral phosphorus through autolysis.
Further investigations should answer the question whether acidic ammonium carbonate is as good for fertilizing ponds designed for older, two to three-year old carp as it is for fry ponds.
2.2.5 Urea
Urea, (NH2)2 CO, containing 45 to 46 percent pure nitrogen represents a highly concentrated fertilizer with nitrogen in the amide form. The ammonification of urea in water proceeds along bacterial and enzymatic lines. Under the action of the urease it is hydrolyzed to ammonia and carbon dioxide. Since aquatic plants assimilate both ammonia and carbon dioxide, urea can be considered a physiologically neutral fertilizer; it is a bicomponent fertilizer, and contains 78 kg carbon dioxide per 100 kg fertilizer. It still remains open for research to determine at what concentration urea as a chemical compound begins to be toxic for various age groups of fish and invertebrates.
The usefulness of urea for pond fertilization has not yet been sufficiently studied. Wróbel (1962) considers it to be a slow-action fertilizer because in his investigations phytoplankton first appeared in the latter part of the growth season. Since a marked increase in zooplankton occurred in the first part of the season, he suggests the use of a mixture composed of the fast ammonia liquor and the slow urea.
The experiments made at Zabieniec between 1963 and 1965 confirmed the slow action of urea on phytoplankton development. Investigations into the species composition of phytoplankton (Massalski, unpublished) showed that urea held back the development of diatoms. The toxic action of urea on carp hatchlings at 15 kg/ha N resulted in the effect of fertilization being 20 percent lower than that in control ponds (Wolny, 1964). But in the following years, while maintaining the same conditions of the experiment, an ever better fish increment was obtained, fish productions in 1964 and 1965 being more than 24 and 38 percent respectively over those in control ponds. Economic considerations are also encouraging to continued research on urea as it is a cheaper nitrogenous fertilizer than, say, ammonium sulphate, and in addition, it contains carbon dioxide which also stimulates phytoplankton development.
Organic fertilizing is instrumental in direct enrichment of the pond with allochthonic substances as a ready food for zooplankton and bottom fauna, and as an indirect source of nutrient salts and carbon dioxide. The scale on which it is possible to step up fish production chiefly through manuring is well exemplified by Trebon, one of the largest fish farms in Czechoslovakia (Dejdar, 1956). Here, fish production between 1927 and 1935 increased from 310 to 1,060 tons per year, whilst fodder consumption was reduced. On the other hand, the consumption of barnyard, pig and poultry manure, as well as compost, increased from 1,425 to 5,600 tons. Superphosphate fertilization also increased from 38 to 925 tons, and liming from 290 to 1,797 tons.
Among the forms of manure used most frequently in European countries are the following:
Mowczan (1948) managed to obtain a gain in fish growth of from 50 to 205 percent in barnyard-manured, as against unmanured ponds. He recommended repeated administration of this manure or compost, which should be placed in small heaps along the pond dyke. Depending on the quality of manure or compost, the amount required per individual carp increment varies between 18 and 70 parts of the fertilizing agent.
Havlena (1956) using between 1.8 and 10.0 tons per ha of pig manure obtained an extra growth of fish of between 31 and 417 kg/ha, i.e. by 9 to 167 percent. The calculated average individual growth came to 2.5 to 3 kg carp per 100 kg manure. The optimum dose of pig manure is 5 tons per ha (Bena, 1957; Stedronsky and Pekar, 1958; Vaclavik, 1957; et al.).
Woynarovich (1956a; 1956b; 1956c; 1957) designed an original device, a “manure cannon” for uniform distribution of pig manure over the pond surface. Manure should be oxidized on the pond surface as quickly as possible because once it has settled down at the bottom under almost oxygen-less conditions, the decay of organic matter proceeds at a much slower pace. A manure dose of four to five tons per ha under conditions of intense photosynthesis produces no oxygen deficiency.
Munich city sewage effluents, mechanically purified and diluted with pure water in the proportion of 1:3 or 1:5 served as an organic manure for ponds (Demoll, 1924). The annual growth increment in carp varied between 400 and 600 kg/ha.
Sewage effluents of Berlin, biologically purified by the filtration field method when brought into ponds at Schönerlinde, produced a natural growth of carp at the rate of 800 to 900 kg/ha (Schäperclaus, 1961).
Town sewage effluents of Kielce (central Poland) purified by the activated sludge process and introduced into ponds without being diluted made an excellent medium for phytoplankton which was composed chiefly of Scenedesmus and Chlorella algae. The natural fish growth under these conditions came to as much as 1,300 kg/ha (Wolny, 1962). The natural food of carp consisted mainly of Chironomidae (55 percent), and Crustacea (30 percent).
The method of utilizing wastes from the foodstuff industry in fish ponds was developed by a group of Czechoslovak investigators, namely for
dairy wastes (Pytlik and Svec, 1954)
sugar-mill wastes (Pytlik, Votava and Benes, 1954)
slaughter-house wastes (Pytlik and Dusek, 1956; Pytlik, 1957)
starch-mill wastes (Pytlik, et al., 1957)
Unprocessed sewage and wastes deposited in ponds are treated with a lime dose of about 5 tons/ha. The fish crop from this type of effluent averages 500 to 600 kg/ha.
Cerny (1961) reported that he obtained an increment of 748 kg in natural growth of carp in a pond fed with starch water from one of the mills in Austria. The high rate of survival recorded was evidence that both physical and chemical agencies formed a favourable set-up in the above pond.
The method of duck breeding in carp ponds developed by Probst (1934), has been widely used on fish farms in several European countries during the past twelve years or so. Duck breeding in ponds has developed in particular in Germany (Eastern), where carp and duck production are almost on the same level (Menzel, 1965), and also in Czechoslovakia where domestic-duck breeding in carp ponds comes to several million individuals yearly. The presence of flocks of ducks in ponds brings about essential changes in both phyto and zoocenoses. In a pond with a flock of duck of about 200 individuals per ha, Ceratium hirudinella and Dinobryon divergens were predominant in phytoplankton (Sosnowska, 1956), whereas in a pond fertilized with superphosphate, the blue algae Anabaena spiroides and Microcystis aeruginosa predominated. Diatoms predominated in the control ponds.
The optimum abundance of a flock of duck per ha varies within fairly broad limits depending on the character of the environment. Carp growth in ponds with ducks may increase two to fivefold, up to 500 kg/ha, under favourable conditions (Frček, 1957; Janeček, 1958).
This is an atypical form of organic manuring of ponds, which cannot be judged easily in terms of fish growth but can only be surmised from indirect indices, either biological, for example by weight increase of chironomid larvae (Wójcik-Migala, 1965) or a greater biomass and individual size of invertebrate fauna consumed by carp (Gurzẹda, 1965), or from abiotic indices, such as a violent decline in oxygen to the minimum required by carp (Szpet and Feldman, 1959). Oxygen requirements may thus limit the fertilization of the water by these means.
In the light of the facts presented here the question should be raised as to what place pond fertilization holds in the economic model of pond fish production.
To sum up the above considerations, one may say that pond fertilization holds a key position along the road to the development of a system of multi-stage intensification of pond productivity. On the one hand, mineral fertilization improves oxygen conditions in the water, and on the other, it helps to reduce fodder consumption per carp production unit, as it improves the ratio of natural to artificial feed.
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