II/E-4
PROBLEMS IN CARP POND FERTILIZATION

by

NIKOLA FIJAN
Veterinary Faculty, University of Zagreb
Zagreb, Yugoslavia

Abstract

Fertilization experiments were run on the carp ponds of a total area of more than 300 ha, for four years. Different doses of calcium and different doses and frequencies of phosphorus or phosphorus plus nitrogen fertilizers did not increase yield in the majority of cases. Experiments indicated that even a negative influence of fertilization on yield could exist. When the results of experiments were applied on a country-wide scale, the use of fertilizers on fish farms was lowered by about 48 percent without any negative effect on yield and feed coefficient. Chemical analyses of inflow water and water in ponds showed high concentrations of phosphorus and nitrogen and a sufficient concentration of calcium. As inflow water influenced positively the balance of elements in ponds, fertilization under such conditions seemed to be unnecessary. Supplementary feeding with cereals in densely stocked ponds is considered to be another factor which enriched the ponds with phosphorus and nitrogen. It was presumed that the analyses of factors influencing the balance of nutritive elements in ponds would give an indication whether fertilizers should be used or not.

PROBLEMES DE FERTILISATION DES ETANGS DE CARPICULTURE

Résumé

Des expériences de fertilisation ont été menées pendant quatre ans dans des étangs à carpe couvrant une superficie totale de plus de 300 hectares. Différentes doses de calcium et différentes doses de phosphore ou d'engrais phosphorés et azotés déversées à des intervalles variables n'ont entraîné, dans la plupart des cas, aucune augmentation de la production. Il semblerait même que la fertilisation puisse avoir une influence négative sur le rendement. A la suite de ces expériences, l'utilisation d'engrais dans les établissements piscicoles de l'ensemble du pays a été diminuée d'environ 48% sans que l'on constate d'effets négatifs sur la production et sur le coefficient de conversion alimentaire. L'analyse chimique des eaux d'alimentation et de l'eau des étangs a révélé de fortes teneurs en phosphore et en azote et une concentration suffisante de calcium. Etant donné l'enrichissement des étangs dû aux eaux d'alimentation, il est apparu que la fertilisation était inutile dans ces conditions. L'auteur estime que le déversement d'aliments d'appoint à base de céréales dans des étangs fortement peuplés contribue également à élever la teneur des eaux en phosphore et en azote. L'analyse des facteurs influant sur l'équilibre des éléments nutritifs des étangs devrait vraisemblablement donner une indication quant à la nécessité d'employer des engrais.

PROBLEMAS DE LA FERTILIZACION DE LOS ESTANQUES DE CARPAS

Extracto

Se llevaron a cabo experimentos de fertilización en los estanques dedicados a la cría de la carpa con una extensión total de más de 300 ha durante cuatro años. Diferentes dosis de calcio y diferentes dosis y frecuencias de aplicación de fertilizantes fosforados, o fosforados y nitrogenados, no hicieron aumentar el rendimiento en la mayoría de los casos. Los experimentos indicaron que incluso podría existir una influencia negativa de la fertilización sobre el rendimiento. Cuando se aplicaron los resultados de los experimentos al plano nacional, el empleo de fertilizantes en las granjas piscícolas disminuyó en casi el 48 por ciento sin ningún efecto negativo en el coeficiente de rendimiento y de alimentación. Los análisis químicos de las aguas afluentes y de las aguas de los estanques mostraron altas concentraciones de fósforo y de nitrógeno y una concentración suficiente de calcio. Como las aguas afluentes hicieron variar positivamente el equilibrio de los elementos en los estanques, la fertilización en tales condiciones pareció ser innecesaria. La alimentación suplementaria con cereales en estanques densamente poblados se considera otro factor que hizo aumentar el fósforo y el nitrógeno en los estanques. Se supone que el análisis de los factores que influyen en el equilibrio de los elementos nutrientes en los estanques podría dar una indicación acerca de si se deben utilizar fertilizantes o no.

1 FERTILIZATION EXPERIMENTS

1.1 Moderate and heavy fertilization with nitrogen, phosphorus and calcium

Bojčić et al. (1960; 1961) showed that higher stocking density, intensive feeding and fertilization resulted in the significant increase of carp (Cyprinus carpio) yield in fattening ponds in Yugoslavia. The higher rates of stocking and intensive feeding were adopted in fish farms all over the country and a considerable increase of the average yield was thus obtained.

The question arose whether it is possible to get even higher yields by improving the methods of fertilization. As experimental ponds were not available, experiments were conducted under field conditions in fattening ponds on three fish farms from 1961 to 1963. The results of experiments in ll ponds on three fish farms were summarized by Fijan et al. (1964) after three years. Surprisingly, different doses of phosphorus (37.5 to 135.8 kg/ha P₂O₅), phosphorus + nitrogen in doses and frequencies as on fish farms in Israel (Livojević, 1961), and different doses of calcium had not increased the yields. Three of four unfertilized ponds gave higher yields than fertilized ponds stocked at the same rate. In one unfertilized pond the yield was 10.7 percent lower than that of the fertilized pond of the same group.

Two ponds (one in the Našice fish farm and the other in the Končanica fish farm) were not fertilized for two years. This did not decrease the yields compared with average yields during three previous years or yields in fertilized ponds of the same group. (Tables I and II). On the contrary, the unfertilized pond in Končanica gave the best yield compared with 22 other ponds on the farm which had been all fertilized with phosphorus or calcium + phosphorus.

Table I

Yields in an unfertilized pond (Group I) and four fertilized ponds (Group II) in Končanica

* the pond was fertilized before the experiment

Table II

Yields in unfertilized ponds (Group I) and fertilized ponds (Group II) in Našice

* the ponds were fertilized before experiment

Organic fertilizers - pig manure and grass - were used in experiments during 1961. It was concluded that they did not have a clear influence on the yield. On the other hand, pig manure was not available in sufficient quantities to be widely applied and the costs for manual labour in zonal green fertilization with grass (method described by Martўsev, 1958), were too high.

Routine analyses of plankton and bottom fauna did not show differences between the ponds in the experiment. Chemical analyses of the water also did not show any differences (Asaj et al., 1962; Asaj and Fijan, 1966).

1.2 Experiments with phosphorus only

Influenced by the fact that the majority of workers considered phosphorus fertilization of greatest importance, and by Hickling's (1962) statement, that “it is unlikely that a case exists where phosphates would not be beneficial”, we continued the experiments with superphosphate only in 1964. It was planned to experiment on the same three fish farms as during 1961–63, but unfortunately the rates of stocking were not the same among the groups of ponds on two fish farms. The results obtained did not, therefore, allow us to draw any definite conclusion, but we gained the impression that in Poljana the yield was higher in the fertilized pond and in Našice the yield was higher in the unfertilized pond. So we took into consideration only the results in Končanica where the experiments were set up under comparable conditions.

The ponds in Končanica are more than fifty years old and on an average about 1.5 m deep. The bottom is non-porous and covered with mud of neutral or slightly alkaline reaction. Twelve ponds varying in size from 9 to 48 ha (total area 282 ha) were divided into three groups of two ponds and two groups of three ponds. As is shown in Table III, during the preceding four years the ponds in each group had similar stocking rates and yields. In group V the ponds were partially covered by emergent vegetation and all other ponds were free of it. All of the ponds had been fertilized with lime and superphosphate for many years.

In spring 1964 the rates of stocking were not the same in all groups because of the differences in fertility among the groups and because of the demand for fish of different sizes. The groups differed also in average weight of carp fry and rate of stocking of additional fish (tench, pike perch, catfish). But within the groups the average weight of carp fry and amount of additional fish stocked were the same (see Table III).

Table III

Fertilization experiments on Končanica Fish Farm in 1964

In group I superphosphate was added in nine doses at fortnightly intervals. In other groups the fertilizer was added in one dose at the end of May. Lime or other calcium fertilizers were not used at all.

Fish were fed with maize and lower quality wheat and the daily amount of feed was regulated according to the feeding practice on the fish farms in Yugoslavia. The total amount of feed given per ha did not differ significantly in the ponds within the same group. The emptying of the ponds took place late in autumn when there was no growth of carp.

In the first three experimental groups the net yield of carp, the total net yield and the feed coefficient were better in the unfertilized ponds. The average values for two fertilized in group IV were somewhat lower than the values in the unfertilized pond. In group V better results were achieved in the fertilized pond.

Considerable differences in real density, i.e. number of carp fished out per ha, were found in the ponds of the same group. This is not unusual and could sometimes happen in the experimental ponds as well. In our opinion such marked differences as in some groups of our experiment could not be corrected adequately, but to prove the impression that the yields were better in unfertilized ponds a rough correction was made. In each group the number of carp fished out was equalized in all ponds to the density found in the pond with the lowest losses. The mean weight of carp fished out was calculated for every pond, and based on this the gain in weight was estimated. As it is known that carp grown under the same conditions but at higher densities will have lower mean weight, and as the fertilized ponds had higher losses than unfertilized ones, this correction of net yields was more favourable for the fertilized ponds. Table IV shows that even after this rough correction of yields there was no visible positive influence of phosphorus fertilization in our experiment.

Table IV

Differences in net yield and corrected net yield between fertilized and unfertilized ponds (fertilized = 100%) in Končanica in 1964

1.3 Application of the results of experiments

As the experiments were conducted on fish farms the results achieved were immediately applied. The yearly reports on the experiments also contributed to the diminished use of fertilizers on the fish farms.

According to Basioli (1965) the use of fertilizers per unit area of fish ponds in Croatia in 1964 was 46 percent lower than in 1961. The yield and the use of supplementary food remained at the same level. The statistical data for fish farms in Yugoslavia showed that the use of fertilizers for production of one kg of fish decreased from 1.75 kg in 1961 to 0.71 kg in 1964 (Pažur, personal communication). The average yield and the food conversion did not change significantly.

The analysis of the data given by Basioli (1962; 1965) on the use of different fertilizers showed that the average dose of phosphorus fertilizers decreased from 346 kg/ha in 1961 to about 247 kg/ha in 1964. Nitrogen fertilizers (112 kg/ha in 1961) were not in use any more. The use of the calcium fertilizers decreased from 1,105 kg/ha in 1961 to 596 kg/ha in 1964. It has to be noted that lime used for disinfection and for treatment during outbreaks of branchiomycosis and summer oxygen deficiency was considered as calcium fertilization. A further drop in use of fertilizers is expected in 1965.

2 FACTORS COUNTERACTING THE POSITIVE EFFECTS OF FERTILIZATION

2.1 Water

The quality of water supply of the ponds could have an influence on the effect of fertilization. A good example of this was given by Hepher (1962). In the experimental station Sdeh-Nahum in Israel fertilization increased the yields by 74 percent and at the experimental station Dor sometimes even by 732 percent. These differences were attributed to the differences in inflow water quality. Wróbel (1963) found that the need for fertilization with calcium depended on the amount of this element in the water supply. When there was 40 mg/l or more calcium in the inflow water, there was no need for liming. Müller (1958) stated that the yields were not increased when lime was added to ponds sufficiently rich in calcium. The ponds in our experiments were supplied water rich in phosphorus, calcium and nitrogen (Asaj and Fijan, 1962; 1966). The concentration of phosphorus in inflow water of Končanica, Poljana and Našice varied between 1.4 and 4 mg/l. This means that the experimental ponds received from the inflow water yearly an amount of phosphorus that is equal to the doses of about 225 to 642 kg/ha of superphosphate. This could explain the inability of phosphorus fertilizers to increase the yields.

The inflow water on all three farms contained more than 40 mg/l of calcium. Our experiments showed in accordance with data given by Müller (1958) and Wróbel (1963), that there was no need for liming under such conditions. Hepher (1958) found that excess lime precipitated phosphates, and Hickling (1962) that excess limestone slightly decreased the fish crop in ponds fertilized with phosphate.

Water could influence the balance of elements in ponds. According to Wróbel, a water supply rich in calcium could increase the calcium deposited on the bottom. On the other hand water poor in calcium would take it from the bottom.

When we compared data on the concentration of calcium in the inflow water and in the waters of our experimental ponds before emptying, we found a decrease of about 10 to 15 mg/l. This calcium remained in the pond mud or was used by fish directly or indirectly. About 50 to 70 percent of phosphorus, and an even higher percentage of nitrogen compounds entering with the water also remained in the pond. This indicated that the inflowing water acted as a fertilizing agent bringing nutrients into the ponds. Although literature indicates that many waters are not so rich in mineral nutrients as our waters, the fertilizing effect of the inflow water, and its effect in the pond should always be taken into account.

The fact that in all experimental ponds the phosphorus level in the water was rather high could be explained by the assumption of Hepher (1958) that in older fish ponds the adsorption of phosphate by the mud will decrease as the result of the accumulation of organic matter on the bottom, and partial saturation of the adsorption complex by regular fertilization with phosphate. Hickling (1962) supposed also that in long-established ponds which had developed mud rich in organic matter, the fixation of phosphate would be lower. In view of this, we are of the view that phosphorus and organic fertilization is unnecessary in old ponds like the ones used in our experiments.

2.2 Stocking rate and supplementary feeding

The main characteristics of intensive fish culture are high stocking rates and supplementary feeding. When the higher stocking rates and intensive feeding were adopted in carp fish farms in Yugoslavia the average yield increased. These measures could also influence the effect of fish pond fertilization. The general belief exists that the benefits of fertilization will be even greater when the carp are intensively fed.

Although the fertilization effect of supplementary feeding is generally recognized, only Gieraltowski (1961) calculated the amount of faeces and urine excreted by carp in an intensively managed pond. He found that a crop of 1,000 kg/ha of carp would produce about 11,000 kg/ha of excreta during the growing season in Poland. According to data published by the National Academy of Sciences, U.S.A. (Anon, 1958) maize contains 85–88.5 percent of dry matter. Our preliminary investigations showed that carp from our fish ponds contained about 31 percent of dry matter. From these data we calculated that about 2,350 kg/ha of organic matter or its components and salts would remain yearly in a pond with a yield of 1,500 kg/ha and feed coefficient of 2.2.

The influence of feeding on the balance of elements is of even greater importance. Schäperclaus (1961) calculated that about 10 kg/ha P₂O₅ would be taken out from a pond with a yield of 500 kg/ha. But about 8 kg/ha P₂O₅ was brought into the pond by the feeding with barley. Schäperclaus used for this calculation data from Geng et al. who found that the maximum P₂O₅ content of living carp could be 2 percent. Our analysis showed the phosphorus content of a carp from the fertilized pond to be about 0.4 percent, i.e. about 0.92 percent of P₂O₅. Our carp is the mirror carp variety with only few scales and, as it is fleshy and fat, its skeleton forms a smaller part of the body than of some other varieties of carp. This could explain the relatively low content of phosphorus in our carp. As maize contains about 0.3 percent and carp about 0.4 percent of phosphorus, we assume that about 3.9 kg of phosphorus, i.e. 8.9 kg/ha P₂O₅ will remain yearly in a pond with the yield of 1,500 kg/ha and feed coefficient of 2.2. This calculation shows that under conditions of our experiments positive influence of feeding on phosphorus balance in ponds existed. The higher the yield and the feed coefficient, the more positive is the balance of phosphorus in the pond. Generally speaking, the balance of phosphorus in the pond can be influenced by (a) the stocking rate, which is the determinant factor for the size of yield and feed coefficient, (b) the kind and amount of the supplementary food, as well as (c) species of fish, their size and condition.

Such positive or negative influence of the above-mentioned factors must also be expected for the balance of other elements in the pond. We calculated the differences in the balance of nitrogen that could exist in a pond if the yields varied between 500 and 2,500 kg/ha and conversion rates of maize varied from 0.5 to 2.5. For these calculations we used the finding of Livojević (1964) that our carp contained about 14 percent of protein. The content of maize was taken as 9.3 percent for these calculations (i.e. the mean value of two sets of data mentioned in Anon., 1958). At the yield of 500 kg/ha and a feed conversion of one, the balance would be negative for 3.76 kg/ha. The same feed conversion at the yield of 1,000 kg/ha would make the balance negative for 7.52 kg/ha. At the yields of 2,000 and 2,500 kg/ha and at the feed coefficient of 2 or 2.5 the balance would be positive for 14.7 or 29.6 kg and positive for 18.4 or 37.3 kg/ha of nitrogen. In intensive carp culture feeding with maize will benefit the nitrogen balance in pond. Of course other feeds, other compositions of fish, or species of fish raised, could influence the nitrogen balance differently. The inflow water and nitrogen exchange with air also would influence this balance.

Higher yields and higher individual weights of fish in the majority of unfertilized ponds in our experiments indicated the possibility of a negative influence of fertilization with superphosphate. Such an indication is very exceptional and could only be compared to findings of Wróbel (1965), who stated that polytrophic levels in the pond caused by intensive feeding, could deteriorate the oxygen conditions sufficiently to provoke heavy mortalities. In our experiments, in 1964 we noted a higher mortality in fertilized ponds, but we did not find any marked differences in oxygen content from periodical routine analyses, or the symptons of oxygen deficiency or mass mortality. However, influence on the oxygen conditions seems to be the only explanation for the higher losses and presumed negative effect of fertilization on yields.

3 CONCLUSIONS

The fertilization of long-established and well cultivated carp ponds seems to be unnecessary when they are supplied with water rich in calcium, phosphorus and nitrogen, and the fish are intensively fed with cereals. Under such conditions fertilization could even depress the yield.

The amount and the chemical composition of inflow water, supplementary feeds and fish crop could all have different influences on the balance of nutritive elements in the pond. The analyses of these factors could give an indication whether a pond requires fertilization.

4 REFERENCES

Asaj, A. et N. Fijan, 1966 Zapažanja pri umjetnom gnojenju ribnjaka. Vet.Arh., 36(1–2):41–8

Asaj, A. et al., 1962 Neki podaci o količini dušika, fosfora i kalcija u vodi različito gnojenih ribnjaka. Vet.Arh., 32(3–4):83–91

Basioli, J., 1962 Slatkovodno ribarstvo NR Hrvatske u 1961 godini. Ribarst.Jugosl., 17(2):46–52

Basioli, J., 1965 Slatkovodno ribarstvo SR Hrvatske u 1964 godini. Ribarst.Jugosl., 20(3):59–63

Bojčić, C.et al., 1960 Pokusu u svrhu povećanja prinosa u šaranskim ribnjacima pomoću gustog nasada na ribnjačarstvu Poljana 1959 godine. Ribarst.Jugosl., 15(1):1–7

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Gieraltowski, M., 1961 W sprawie nawozenia stawów. Gospod.rybna, 13(5):28–32

Hepher, B., 1958 On the dynamics of phosphorus added to fish ponds in Israel. Limnol. Oceanogr., 3(1):84–100

Hepher, B., 1962 Ten years of research in fish ponds fertilization in Israel. 1. The effect of fertilization on fish yields. Bamidgeh, 14(2):29–38

Hickling, C.F., 1962 Fish Culture. London, Faber and Faber, 295 p.

Livojević, Z., 1961 Slatkovodno ribarstvo Izraela. Ribarst.Jugosl., 16(6):146–54

Livojević, Z., 1964 Nove metode uzgoja šarana i postizanje visokih prinosa u ribnjacima. Zagreb, Unpubl.Diss. 171 p.

Martyshev, F.G., 1958 Prudovoe rybovodstvo. Moskva, Sovetskaia Nauka, 584 p.

Müller, W., 1958 Teichdüngungsversuche mit Kalk, Phosphat und ihrer Kombination in Königswarta (Lausitz). Z.Fisch., 7(7/8):583–9

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Wróbel, S., 1963 Chemische Untersuchungen von Fischteichen in der Woiwodschaft Kielce. Acta hydrobiol., Kraków, 5(2–3):215–27

Wróbel, S., 1965 Causes and consequences of pond eutrophication. Acta hydrobiol., Kraków, 7(1):27–52

Anon., 1958 Nutrient requirements of domestic animals. 4. Nutrient requirements of beef cattle. Publs.natn.Res.Coun.,Wash., (579):32 p.