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Fertilization, soil and water qualitymanagement in small-scale ponds:

Fertilization requirements and soil properties

S. Adhikari

Central Institute of Freshwater Aquaculture, Kausalyaganga, Bhubaneswar 751002, India, Emailsadhikari66@indiatimes.com

Since most of the potential areas forinland aquaculture have already beenexplored in India, additional productioncan only be achieved throughsuccessful manipulation of availableresources that influence theproductivity of various aquaculturesystems. One of the main ways this isachieved is through maintenance ofadequate levels of nutrients in thepond environment. Pond managementin fish culture is mainly concerned withfertilization requirements andstrategies; and with good managementof pond soil and water quality.

Fertilization requirements offish ponds

The natural productivity of a fishculture system depends largely on theavailability of natural food organismsand on favorable environmentalconditions for the fish.

Phytoplankton, the floatingmicroscopic plants that give water itsgreen color, are the first step in thefood chain of fish ponds. Otherorganisms also feed on them andmultiply, increasing the availability ofnatural food for fish stocked in thepond. In addition to carbon dioxide(C02), water and sunlight forcarbohydrate synthesis, phytoplanktonneed mineral elements includingnitrogen, phosphorus, potassium,calcium, sulfur, iron, manganese,copper and zinc for their growth andnutrition. To promote phytoplanktongrowth and maintain the optimumnatural productivity of ponds, thewater must contain adequate amountsof these nutrients. Managing the pondsoil and water effectively can therefore

help provide an adequate amount ofnatural food for stocked fishes,promoting the healthy growth of fryand fingerlings.

Pond soil plays an important role inregulating the concentration ofnutrients in the pond water. Knowledgeof the nature and properties of pondsoil can help a farmer to developefficient management practices that willboost production. The most importantchemical properties of bottom soilinfluencing the nutrient managementpractices of ponds are as follows:

Properties of pond soils

Soil reaction (pH)

The pH of soil is one of the mostimportant factors for maintaining pondproductivity since it controls most ofthe chemical reactions in the pondenvironment. Near neutral to slightlyalkaline soil pH (7 and a little above) isconsidered to be ideal for fishproduction. If the pH is too low(strongly acidic) this can reduce theavailability of key nutrients in the waterand lower pond fertility.

Organic carbon content

Organic carbon acts as a source ofenergy for bacteria and other microbesthat release nutrients through variousbiochemical processes. Pond soils withless than 0.5% organic carbon areconsidered unproductive while those inthe range of 0.5-1.5% and 1.5-2.5% tohave medium and high productivityrespectively. Organic carbon content ofmore than 2.5% may not be suitable forfish production, since it may lead to an

excessive bloom of microbes andoxygen depletion in the water.

Carbon to nitrogen ratio

The carbon to nitrogen (C:N) ratio ofsoil influences the activity of soilmicrobes to a great extent. This in turnaffects the rate of release of nutrientsfrom decomposing organic matter. Therate of breakdown (mineralization) isvery fast, moderately fast and slow atC:N in the range of less than 10, 10-20and more than 20 respectively. Ingeneral, soil C:N ratios between 10-15are considered favorable foraquaculture and a ratio of 20:1 ornarrower gives good results.

General nutrient status

Nitrogen, phosphorus and potassiumare the major nutrients required byphytoplankton. Inorganic fertilizers canbe applied to provide these nutrients.The appropriate dosage depends onthe amount of individual nutrientspresent in the pond soil in an availableform. Generally, relatively smallamounts of potassium are needed infish ponds. However, newlyconstructed ponds or those situated onpoor soils may need potassiumapplication. The single most criticalnutrient for the maintenance of pondproductivity is the availablephosphorus content of pond soil andwater. Pond soils with 30 ppm, 30-60ppm, 60-120 ppm and more than 120ppm available phosphate (P2O5) areconsidered to have poor, average, goodand high productivity respectively.Ponds with less than 250 ppm availablesoil nitrogen are considered to have

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low productivity while concentrationsin the range 250-500 ppm and above500 ppm are considered to be mediumand highly productive respectively.

Fertilization schedule ofnursery ponds

Nursery ponds

The natural productivity of nurseries isoften unsatisfactory due to adeficiency of one or more of thenutrient elements in soil and water,which may be caused by otherenvironmental conditions. Correctionof deficiencies by application ofmanures or fertilizers containing thesenutrients in suitable form and inoptimal amount is necessary toaccelerate biological production andenhance productivity. Accordingly,small shallow ponds are preferred fornurseries for easy management andmanipulation of environmentalconditions.

Use of organic manures

Both organic manures and chemicalfertilizers are widely used for improvingthe productivity of nurseries. Cowdung is the most widely used organicmanure in many areas and is typicallyapplied at a rate of 5,000-15,000 kg/hain one installment well in advance ofstocking with spawn, preferably atleast a fortnight prior. The amount isreduced to 5,000 kg/ha when mohua oilcake is used as a fish toxicant inshallow nursery ponds. Sometimes, tohasten the process of decomposition ofadded manures, nurseries are limed(CaCO3) at a rate of 250-350 kg /ha afterthe application of manure. Sometimesspaced manuring with cow dung at arate of 10,000kg/ha 15 days prior tostocking followed by subsequentapplication of 5,000 kg/ha seven daysafter stocking has been practiced forsustainable production of zooplanktonin nurseries. When more than one cropis raised, nurseries may be manuredwith cow dung at 5,500 kg/haimmediately after the removal of thefirst crop. Besides the cow dung, acombination of mustard oil cake, cowdung and poultry manure in the ratio of6:3:1 at 1,100 ppm have beensuccessfully used for the culture ofzooplankton for carp spawn.

Inorganic fertilizers

Inorganic fertilizers containing a fixedpercentage of individual nutrientelements or a combination of more thanone element are also able to enhancethe productivity of nurseries. A ratio ofnitrogen : phosphorus ration (N:P) of4:1 is considered most effective forincreased production in nurseries.Weekly application of nitrogen :phosphorus: potassium mixture (N:P:K)in the ratio of 8:4:2 ppm is suitable forincreased production of fish foodorganisms. Use of N:P:K in the ratio of18:8:4 at 500 kg/ha after liming at 200kg/ha is quite effective in enhancingthe production of slightly acidic andunproductive soils used for nurseries.

Nitrogenous fertilizers containingdifferent forms of nitrogen (amide,ammonium-cum-nitrate and ammonium)are suitable for management ofnurseries. These three forms offertilizers (e.g. urea, calcium ammoniumnitrate and ammonium sulfate) areeffective for slightly acidic to neutral,moderately acidic and alkaline soilsrespectively and a rate of 80 kgnitrogen/ha is most suitable for rearingof rohu spawn in nurseries.

Combining organic andinorganic fertilization

The combined use of both organic andinorganic fertilizers is another strategyfor increased production of either fishfood organisms or fry. The combinationof mustard oil cake and 6:8:4 :N:P:Kinorganic fertilizer on equivalentnutrient basis (at 12 kg nitrogen/ha) issuitable as compared to either organicto inorganic for nutrient management ofnurseries. However, on an equivalentnutrient basis (N:P:K) organic manure(cow dung) is the most suitablefertilization strategy for management ofcarp nurseries compared to eitherinorganic fertilizer or combined use oforganic and inorganic fertilizer.

Fertilization of rearing andstocking ponds

Acidic pond soils reduce microbialactivity and the availability of nutrientsin pond water and may renderfertilization ineffective. Therefore, theapplication of lime is the first step ofmanagement for all stages of fish

culture. Liming raises the soil pH to adesirable level (near neutral) andestablishes a strong buffer system inthe aquatic environment, improving theeffectiveness of fertilization.

Liming stimulates the microbialdecomposition of organic matter,supplies calcium to the pond, increasesnitrate content in the pond andmaintains sanitation in the pondenvironment. Generally, groundlimestone is extensively used andspread over the dry bed or broadcastover the water surface in a single doseat least 15-20 days before stocking. Onthe basis of soil pH, the followingdosages of lime are usually applied toponds. Besides initial application, somecompensatory applications of lime inthe range of 100-200 kg/ha may also bemade in the stocking pond from time totime to neutralize the acidity developedthrough application of acid-forminginorganic fertilizers and organicmanures and also when fishes arediseased or distressed.

In India, organic manures are morecommonly used than inorganicfertilizers. A variety of agriculturalwastes, including cow dung, poultrydroppings, pig manures and biogasslurry etc. can be used as organicmanures. In rearing ponds, applicationof raw cow dung or biogas slurry isobserved to give better results.Depending on the organic carboncontent of pond soil in the rearingpond, application of raw cow dung orbiogas slurry in the range of 3-7 or 5.5-12 t/ha respectively and addition of 2.5-5 t/ha/year of cow dung or 10-30 t/ha/year biogas slurry or 5-15 t/ha/yearpoultry droppings respectively instocking ponds give good results. Inrearing ponds, usually 50% of the totalrequirement is given 15-20 days prior tostocking of fry and the remaining intwo equal monthly splits during rearingperiod. In stocking ponds, on the otherhand, 20% of the total requirement isapplied initially and the rest is given inequal monthly split. But if the pondsare treated with mohua oil cake toeradicate unwanted fishes, the initialapplication of the organic manure canbe dispensed with in both the culturesystem.

The efficiency of nitrogen fertilizersin enhancing the productivity of pondsdepends largely on their forms. Thecommonly used nitrogen fertilizers are

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Growth enhancement of carp andprawn through dietary sodium chloride

urea, ammonium sulfate and calciumammonium nitrate. Among these, ureais suitable for slightly acidic to neutralsoil, ammonium sulfate for alkaline soiland calcium ammonium nitrate foracidic soil. Depending on the availablenitrogen content of the pond soil,application of 50-70 kg nitrogen/ha (i.e.108-152 kg urea/ha; 200-280 kg calciumammonium nitrate/ha; 250-3 50 kgammonium sulfate (ha) in rearing pondsand 75-150 kg/ha/year (i.e. 163-326 kgurea /ha/year; 300-600 kg calciumammonium nitrate /ha/year; 375-750 kgammonium sulfate/ha/year) in stockingponds give good results. The fertilizershould be applied in equal monthlysplits alternately with organic manurewith a gap of about a fortnight.

Single Super Phosphate (SSP) ismost commonly used as a phosphatefertilizer in fish ponds. Depending onthe available phosphate content ofpond soil, application of 25-50 kgphosphate (P2O5) /ha (i.e. 156-312 kgSSP/ha) and 40-75 kg P205/ha/year (i.e.250-468 kg SSP/ha) in rearing andstocking ponds, respectively give goodresults. To get better utilizationefficiency, phosphorus fertilizersshould be applied in weekly intervalsand the first installment should begiven seven days after initial organicmanuring.

Muriate of potash (potassiumchloride, KCl) and sulfate of potash(potassium sulfate, K2S04) arecommonly used as potassium fertilizers

intestine and hepatopancreas of thetreated fish as well as prawn (Table 2).The type of diet is known to influencethe activity of digestive enzymes15).Increased digestive enzyme activitycoupled with higher nutrientdigestibility might have beenresponsible for better utilization ofnutrients from salt incorporated diets.

Our results suggest that dietaryinclusion of salt can be beneficial.

References

1. De Silva, S.S. and Aderson. T.A. 1995. Fish Nutritionin Aquaculture. Chapman & Hall. London. 319 p.

2. Matty. A.J. 1988. Growth promotion. In: M.M.Joseph (ed.) The First Indian Fisheries ForumProceedings. Asian Fisheries Society, IndianBranch. Mangalore, India. p 13-15.

3. Veerina, S.S., Nandeesha. M.C., Rao, K.G. and DeSilva, S.S. 1993. Status and technology of Indianmajor carp farming in Andhra Pradesh, India. AsianFisheries Society. Indian Branch, Mangalore. 30 pp.

4. Yakupitiage, A. 1993. On-farm feed preparation andfeeding strategies for carps and tilapias. In: M.B. New.A.G.J. Tacon and I. Csavas (eds.) Farm-madeAquafeeds. Proceedings of the FAO/AADCPRegional expert consultation on farm-madeAquafeeds. FAO-RAPA/AADCP. Bangkok.Thailand. p. 87-100.

5. Ogino. C. and. Kaniizono, M 1975. Mineralrequirements in fish. I. Effects of dietary salt mixturelevel on growth, Mortality and body compositionin rainbow trout and carp. Bull. Jap. Soc. Sci. Fish.41: 429-434.

6. Murray, M.W. and Andrews, J.W. 1979. Channelcatfish: the absence of an effect of dietary salt ongrowth. Prog. Fish Cult. 41:155-156.

7. Gatlin. D.M. Mackenzie. D.S. Craig. S.R. and NeillW.H. 1992. Effects of dietary sodium chloride on reddrum juveniles in waters of various salinities. Prog.Fish Cult. 54: 220-227.

8. Varghese, T.J., Devaraj, K.V. Shantharam. B. andShettv. H.P.C. 1976. Growth response of commoncarp. Cyprinus carpio var. Communis to protein richpelleted feed. Proceedings of the Symposium onDevelopment and Utilisation of Indian FisheryResources. Colombo (Sii Lanka). FAQ RegionalOffice for Asia and the Far East, Bangkok, Thailand.408 pp.

9. Duncan, D.B. 1955. Multiple range and multiple F-tests. Biometrics 11: 1-42.

10. Arai, S., Nose. T. and Kawatsu H. 1974. Effect ofminerals supplemented to the fish mealdict on growthof eel Anguilla japonica. Tansuika SuisanKenkvusho Kenkvu Hokoku 24: 95-100.

11. Holsapple, D.R. 1990. The effect of dietary sodiumchloride on red drum (Sciaenops oceliatus) in freshand brackish water. Master’s Thesis. Texas A and MUniversity, College Station.

12. MacLeod. M.G. 1978, Relationship between dietarysodium chloride, food intake and food conversionin the rainbow trout. J. Fish Biol. 13: 73-79.

13. Salman. N.A. and Eddy. F.B. 1988. Effect of dietarysodium chloride on growth, food intake andconversion efficiency in rainbow trout, Salinogairdneri (Richardson). Aquaculture 70:131-144.

14. Tacon, A.G.J., Knox, D. and Cowey, C. B. 1984. Effectof different dietary levels of salt mixtures on growthand body composition in carp. Bull. Jap. Soc. Sci.Fish. 50: 12 17-1222

15. Bazaz, M.M. and Keshavanath. P. 1993. Effect offeeding different levels of sardine oil on growth,muscle composition and digestive enzyme activitiesof mahseer, Tor khudree. Aquaculture 115: 111-119.

in fish ponds. Application of 10-20 kgK20/ha (i.e. 16-32 kg KCl/ha or 20-40 kgK2S04/ha) and 25-40 kg K20/ha/year(i.e. 41-66 kg KCl/ha or 52-83 kg K2S04/ha/year) in rearing and stocking ponds,respectively give good results. Thefertilizer should be applied in equalmonthly splits.

Application of manure and fertilizershould be suspended if thick green orblue green blooms of algae develop inthe pond in order to avoid depletion ofoxygen.

Careful use of organic manures andchemical fertilizers in combination is asound strategy. Occasionaldevelopment of un-hygenic conditionsin the pond may be avoided by usingpre-decomposed organic manure. Useof excessive amounts of raw organicmanure can result in excessive bloomsof microbes during aerobic breakdownof large amount of raw organic manure,and may also caused oxygen depletion.

An understanding of chemical andbiological conditions of pond soil andwater through regular monitoringsystems and adoption of efficient andcareful management practices will leadto enhanced production of fish foodorganisms and thereby increase thegrowth and survival of fish.

Shrimp pond maintenance. Photo: U Win Latt