| AFRICAN REGIONAL AQUACULTURE CENTRE PORT HARCOURT, NIGERIA | ARAC/TECH.REP./81/1 |
- Report of Consultant on Soil and Water Management,
V.P. Singh
 | NIGERIAN INSTITUTE FOR OCEANOGRAPHY AND MARINE RESEARCH CENTRE REGIONAL AFRICAIN D'AQUACULTURE |
 | UNITED NATIONS DEVELOPMENT PROGRAMME PROGRAMME DES NATIONS UNIES POUR LE DEVELOPPEMENT PROGRAMA DE LAS NACIONES UNIDAS PARA EL DESARROLLO |
 | FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS ORGANISATION DES NATIONS UNIES POUR L'ALIMENTATION ET L'AGRICULTURE ORGANIZACION DE LAS NACIONES UNIDAS PARA LA AGRICULTURA Y LA ALIMENTACION |
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The African Regional Aquaculture Centre (ARAC), Port Harcourt, Nigeria where the training of fisheries personnel from participating countries is conducted, presently uses the existing pond facilities of the Brackishwater Aquaculture Station, Nigerian Institute for Oceanography and Marine Research (NIOMR) at Buguma, and the Freshwater Fish Farm of the Imo State Government at Okigwi. In addition to this, three 1-ha ponds are now being constructed and developed at Buguma. The construction of ponds at Aluu, which has been selected to be the site for freshwater facilities, according to recent information, is scheduled to begin within two weeks. The contracts for this have already been awarded to three contractors. Once the construction of ponds at Aluu is complete, ARAC will move its freshwater research and training operations to this site from that at Okigwi.
At Buguma, besides the construction of three 1-ha new ponds, the dikes of other ponds which were constructed in the 1960s have also recently been renovated. The existing information and some preliminary investigations show that these ponds are largely built on acid sulphate soils with patches of peat material. The newly built fish ponds are more acidic than the older ones, where the old ponds have better pond bottom and substrate. The results reported herein are only partial because some of the work, such as soil analysis, is not yet completed. A supplementary report will be prepared at a later date when the results of the analyses are available.
During the period 6 October to 8 December 1981, a consultancy was carried out at the African Regional Aquaculture Centre, Buguma and Aluu, in collaboration with the Nigerian Institute for Oceanography and Marine Research, Port Harcourt, Nigeria, under the following terms of reference:
To formulate and implement a research programme for the improvement of acid sulphate soils for aquaculture.
To study soil conditions in the site selected for the regional centre's fish farms at Aluu and Buguma and recommend measures needed, if any, for their improvement.
To participate in the instruction programme at the Centre, with special reference to fish farm soils and their treatment.
Mr. M. A. Afinowi, Senior Research Officer, NIOMR/Centre Manager, ARAC, Port Harcourt, Nigeria, designated Mr. M. Amago as counterpart to the consultant. The counterpart became available from 10 November 1981.
3.1 Research
The entire research programme was basically aimed on studying the physico-chemical properties of soils at Aluu and Buguma and developing some remedial measures to improve the productivity of acid sulphate soils. To attain this, based on the nature of the studies conducted, the locations involved, and the type of fish ponds (brackish or fresh water), a detailed research proposal, including the methods of analyses, was prepared in close consultation with the Chief Technical Advisor, and the programme was divided into the following four studies (for details please see Annex A):
Study 1 - Physico-chemical characteristics of ponds soils and water at Buguma.
Study 2 - Reclamation and management of acid sulphate soils for fish ponds at Buguma.
Study 3 - Physico-chemical characteristics of soils selected for ponds construction at Aluu, and
Study 4 - Development of remedial measures to improve the productivity of fish ponds, and determine the fertilizer requirement of acid sulphate pond soils at Buguma.
For Buguma area, the studies included physico-chemical characteristics of pond soils, reclamation and management of acid sulphate soils and development of other remedial measures including the fertilizer requirements of pond soils. For Aluu area, presently only one study on physico-chemical properties of soils selected for the construction of fish ponds was prepared because the ponds were yet to be constructed. In addition, it was clear from the topographical map that the construction of ponds in this area may require a large amount of earthwork/movement which may seriously affect the pond bottom properties. Therefore, it was thought proper that once the fish ponds construction is completed and the basic physico-chemical properties of the resultant pond soils known, a research proposal on the productivity including fertilizer requirements, etc. should be developed and implemented at a later date.
The research programme implemented and the progress of the work during the period of assignment of the consultant, is discussed in the following sections.
3.1.1 Study 1 - Physico-chemical characteristics of pond soils and water at Buguma
For the characterization of physico-chemical properties of pond soils at Buguma, profile soil samples up to a depth of 1 m from three newly constructed ponds and from two locations outside the area, and one composite representative sample from the surface layer (0–20 cm) of each of the old ponds (Fig. 1), were collected on 13 October 1981, air dried, prepared and packed for analysis. In situ profile descriptions, soil pH measurements, and rough estimates of soil texture were also made. But, other necessary soil analysis could not be done because of lack of analytical facilities at ARAC and also because of the inaccessibility or unavailability of these facilities in the institutions in the country, namely, University of Science and Technology, Port Harcourt, International Institute of Tropical Agriculture, Ibadan, and National Root Crops Research Institute, Umudike, Umuahia, Imo State.
Preliminary investigations revealed that the soils of new ponds, both inside and outside, were acidic in reaction where the pH of dry soil (1:1 soil:water) ranged from as low as 2.8 to a maximum of 3.7. The pH of the soil was below 4 throughout, down to 1 m depth. After drying, a thin milky white layer of aluminium sulphate and a dark red layer of iron hydroxide and salt crystals were apparent on water surface. In some cases, the wet soil pH was about 5.5 and 6.0 but when treated with hydrogen peroxide it decreased to 3.2 after about 15 minutes. The soils had a low bulk density owing to the high amount of fibrous roots of mixed mangrove vegetation and other partly decomposed organic matter contained. The surface soils also had a coarse texture but deeper layers contained appreciable amounts of clay. These ponds also had a high amount of organic matter in the surface layer, somewhere in the range of 20–30 percent (rough estimate) in some places, but it was mostly either undecomposed or only partly decomposed. The dikes of these ponds were dry which, both on the top surface and slopes clearly showed the presence of pale yellow coloured mottles of jarosite, a potentially dangerous material leading to acid water during rains.
The investigation of older ponds showed that except for a few, the ponds had a better bottom with a thin layer of 1–3 cm of silt deposited over time with irrigation water. The dry pH of these soils was high, in the range of 5.0 and 5.5. Underneath, these soils also contained large quantities of fine fibrous roots and soil had a dark black colour. Water samples collected from ponds also had fine fibrous suspended roots. The pH of the wet soil was about 7.5 and the smell of hydrogen sulphide was apparent. The newly renovated dikes had a low pH (generally below 4.5) and the jarosite mottles were apparent. There was no sign of algal growth in these ponds. The majority of the ponds were leaking excessively because of crab holes in the dikes. There was also upwelling of water in few ponds owing to the highly porous pond bottom. Water control and management in general was not adequate.
3.1.2 Study 2 - Reclamation and management of acid sulphate soils for fish ponds at Buguma
Knowing the history of pond soils at Buguma, and by doing some preliminary investigations, a research project on the reclamation of acid sulphate soils began on 10 November 1981. Some of the ponds were not available for this work because they were being used for other investigations. Originally it was planned that this study should be conducted in newly constructed, as well as in old ponds for comparison, but due to the unavailability of new ponds as they were not yet fully developed and levelled, the study was started in two small (200 m2) old ponds only. These ponds had a dry soil pH of 4.8 to 5.2. They were initially drained and the leaks on the sides closed to dry them so that the acids from the pond bottom could be removed in the subsequent flushings. The pond bottom was also levelled, which needed a large amount of earthwork. Frequent and regular rains, and upwelling of perched water during high tide, made the drying operation very difficult. Subsequently, when the rains stopped, the draining, drying and flushing operations were carried out as scheduled, but still complete drying was not possible. After each draining, the left over fingerlings were scooped out of ponds to remove the unwanted fishes. In the third sequence of reclamation process on 24 November 1981, the pond was fairly dry. All throughout, a low lift pump was used to fill and drain the pond. After five sequences of reclamation process, on 1 December 1981, finely ground lime at the rate of 1 t/ha, i.e. 600 kg/ha on the pond bottom and 400 kg/ha on the dike surface was broadcast. At this time there was already some sign of algal growth in the reclaimed pond. On 5 December 1981 chicken manure, obtained from a nearby poultry farm, was applied at the rate of 2 t/ha and the pond was filled to depth of 10 cm. At this time, the pH of the pond soil improved to about 7.5 and 8.0 and there was a good indication of benthic growth. A detailed schedule of activities was prepared and thoroughly discussed with the persons concerned (Annex B). Before the consultant left Port Harcourt, it was apparent that the reclamation process was successful and that this pond may yield good fish harvest.
3.1.3 Study 3 - Physico-chemical characteristics of soils selected for pond construction at Aluu
The fish pond area was first delineated on the topographic map and by using the soil survey tools, the pond area and the boundaries were established on the ground. This also helped in pegging the pond area for construction purposes. On the basis of the relative elevation of the area, it was divided into three categories, namely, higher land which is to be cut or scraped; lower land which is to be filled; and intermittent area. The soil sampling points were identified and marked. About 22 sampling points of 1 m2 were dug to about 2 m depth with a spade, and the bulk profile soil samples from 0–20, 20–50, 50–100, 100–150 and 150–200 cm layers were collected. They were air-dried and prepared for soil analysis. The in situ profile description was also made.
Again, due to the unavailability of analytical facilities, the soil samples could not be analysed in Nigeria. The profile description revealed that all the higher land had large amount of lateritic material at some depth, generally at about 140 cm and below. In some places, lateritic materials were also found on the soil surface. Intermediate areas had shallow water table and also some laterite in 1 m depth. Lower areas, which are on an old creek, contain large quantities of partly decomposed organic matter and had low bulk density. On the basis of weight or volume, the organic matter in these areas seems to be more than 30 percent. These areas also have shallow water table, which was in some places within 40 cm depth. At 50 cm depth, they contained whitish sandy clay soil, which was loose when wet and very hard when dry. In fact, during high tide they seemed like quicksand.
3.1.4 Study 4 - Development of remedial measures to improve the productivity of fish ponds, and determine the fertilizer requirement of acid sulphate pond soils at Buguma
Bulk soil samples from the newly constructed ponds were collected, air-dried and prepared to fill an aquarium. Other operations, such as application of the treatments and monitoring of water analysis, will be carried out by the ARAC staff and the counterpart from NIOMR following the research proposal.
3.2 Training
The consultant actively participated in the training programme of ARAC by delivering 14 hours lectures/practicals on the following topics:
Soil quality considerations for site selection
Nitrogen and phosphorus fertilizers management in fish ponds
Acid sulphate soils, their reclamation and management for brackish water fish ponds.
In addition, lecture notes on soil quality considerations for site selections, the management of acid sulphate soils and water quantity and quality considerations in site selection, were also prepared and provided to the trainees.
Although there were quite a few problems (such as unavailability and inaccessibility to the analytical facilities, lack of transport services, unavailability of ponds and other inputs like chicken manure and lime, which used to be bought in Lagos, and lack of manpower) encountered during the consultancy, they were easily solved with little extra efforts except for the soil analysis. A source for inputs, i.e. poultry manure, lime and fertilizers, was found in a nearby area, where these were available relatively easily. In fact, poultry manure in large quantities was available free of cost.
The basic investigation of ponds at Buguma led to the conclusion that the majority of the ponds are affected by acid sulphate soil conditions. A proper reclamation and proper fertilization and water management is needed to improve the production of these ponds. For this, it is recommended that if the results of the ongoing research prove positive, the research proposal prepared during the consultancy should be extended to all the ponds. Soil analysis and interpretation of the results would provide some more in-depth knowledge for fertilizer management.
Profile examination and description of soils at Aluu reveal that scraping and filling during the ponds construction would affect the soil fertility and productivity considerably. After the ponds are constructed, analysis of basic soil physico-chemical properties and a research programme for the management of these soils is highly recommended.
The analysis of soil samples collected from Buguma and Aluu which is felt to of vital importance, should be carried out as soon as possible and the results may be sent to the consultant for interpretation. Is is hoped that a strong communication link between the consultant and the staff at Port Harcourt who are continuing the work can be maintained. This will provide timely suggestions and feedback on the progress of work and modifications, if any needed.
If a basic soil and water analytical laboratory (not too sophisticated) could be established at Aluu, Port Harcourt, this would solve the problem of analysis. This would also help in regular monitoring of soil and water quality, and reduce the costs involved considerably. The methods of analyses have already been prepared and are available at ARAC.
The author gratefully acknowledges Mr. M.A. Afinowi, Senior Research Officer, Mr. I. Marioghae, Research Officer, Mr. M. Amago, Research Officer and all staff of NIOMR for their assistance and cooperation during the implementation of this programme.
Studies on fish pond soils: A research proposal
Introduction
This proposal covers two sites: one at Buguma which is a brackish water area and the other at Aluu a fresh water area. The fish ponds at Buguma site are largely built on acid sulphate soils with patches of peat material. This site has some older ponds which were constructed in the 1960's, but there are also two large recently constructed fish ponds which are not yet fully developed. The preliminary investigations show that the new fish ponds are more acidic than the older ones and the old ponds have better pond bottom and substrate.
The other area is at Aluu where fish ponds are yet to be constructed and the resultant ponds will be totally under fresh water influence.
This research proposal is basically aimed at studying the physico-chemical properties of soils of both the sites and developing some remedial measures to improve the productivity of acid sulphate soils for fish production at Buguma.
Based on the nature of the studies to be conducted, the locations involved, and the type of fish ponds (brackish water and fresh water) these areas have, the research proposal is divided into four studies.
For Buguma area, the studies include physico-chemical characteristics of pond soils, reclamation and management of acid sulphate soils for fish ponds and to develop other remedial measures including the fertilizer requirements of pond soils for brackish water fish ponds. For Aluu area, presently only one study on physico-chemical properties of soils selected for the construction of fish ponds is prepared because the ponds are yet to be constructed. In addition, it is clear from the topographic map that the construction of ponds in this area may require large amount of earthwork/movement which may seriously affect the pond bottom properties. Therefore, it is thought proper that once the fish ponds are constructed and the basic physico-chemical properties of the resultant individual ponds soils known, a research proposal on the pond productivity including fertilizer requirements, etc., similar to that for Buguma should be developed and implemented, if felt necessary, at a later date.
This research proposal is prepared in close consultation with the Chief Technical Adviser and it was always considered that the studies do not require very sophisticated facilities. It is estimated that all the studies listed herein should normally be completed in a period of 6 to 9 months if the necessary facilities and other resources are available on time.
Study 1
Objectives: To study the physico-chemical properties of pond soils and water at Buguma.
Materials needed:
The details of the equipment, reagents, glassware and other needed facilities are included in the methods of analysis.
3. Procedure
3.1 Collection, preparation and preservation of soil and water samples
Ideally soil samples from each pond should be collected from three to five location points, depending on the size of the pond, to a depth of about 1 m at 20 cm layer intervals. The samples could be collected by using a sampling tube, soil auger or spade, if possible. But, for the older and established ponds under production, soil samples from only top (10–20 cm) layer and different locations can provide adequate information on the physico-chemical characteristics of that pond.
The soil bulk of about one kg from each layer and location be separately placed in a properly marked plastic bag. The pH of the soil, if it is wet, should be measured immediately and noted. Alternatively, samples of the same profile layer from various locations within a pond could be mixed thoroughly and a representative composite sample of one kg taken. The samples of two ponds or more should never be mixed. Rough estimates of soil colour, texture, etc., should also be made in the field for further use.
The soil samples, thus collected should be air-dried in plastic or paper trays by spreading the soil thinly on trays and keeping them in shade. Once the samples are dried, they should be pulverized by using a wooden mallet and passed through a 2 mm sieve.
For the analysis of organic matter and total Na sub-samples of about 10 g should be ground to pass the soil completely through 0.5 mm sieve. About 200 g of 2 mm and 10 g of 0.5 mm sample should be placed separately in smaller plastic bags and used in the analysis.
Each plastic bag should be labelled chronologically and its identification and description noted in a notebook for ready reference.
Likewise representative water samples from various points in the pond be collected and placed in bottles and marked properly. The water samples should be analysed within 4–8 h of collection. If it is not possible to analyse them within the said period, then they should be preserved with 0.05 percent mercuric chloride solution by adding 1 ml of this solution to every 100 ml of water sample collected. Further, the samples treated this way should be placed in a refrigerator and analysed as soon as possible. If the analysis could not be performed within 72 hours after collection, the samples should be discarded and new samples collected.
The samples thus collected and prepared should be analysed for various physico-chemical properties listed below. The details of the methods of analyses are given at the end of this proposal.
3.2 Methods of analysis
3.2.1 Soil analysis
3.2.2 Water analysis
Study 2
1. Objective: Improving the productivity of acid sulphate soils used for brackish water fish ponds.
2. Materials needed
3. Procedure
There will be two treatments involved in this study which will be tested in two locations i.e. newly constructed and old fish ponds. The treatments to be tested will include the following:
control; no reclamation, only the application of fertilizers;
complete reclamation, which is a package of treatments that include drying, tilling, flushing and leaching of pond bottom; leaching or washing or flushing of pond dikes and application of lime, chicken manure and inorganic fertilizers.
The reclamation of the ponds involves a planned sequence of filling, draining and drying of ponds, cultivation by tooth harrow or a spade and finally of broadcasting a small amount of lime without incorporating this in the pond soil. In the same period, the top of the dikes should also be leached by making a series of long, narrow paddies by small levees along their edges, and pumping or carrying sea or brackish water into these.
A pH meter or a roll or strips of pH indicator paper should be available. A tooth harrow or small space is also needed for cultivating the pond bottom. About one ton of powdered agricultural lime per hectare is also required.
The whole work can be completed in about two months or less. All work should preferably be done in the dry season. Treatment of the dikes and pond bottom should proceed at the same time.
3.1 Treatment of the pond bottom
In the early part of the dry season, the pond has to be prepared for removal of acid. This is done by drying the pond thoroughly. Small drains should be dug to let all remaining patches of standing water run dry. After about one week's drying the pond bottom should be tilled in two directions. It may be again cultivated after thorough drying so that the surface soil layer is broken into small pieces, but not into a powder. If there is no rain the total drying period will probably take about two weeks.
Now the acid in the dry layer is ready to be removed. Brackish or salt water is brought in to fill the pond. The pH of the water is measured immediately after filling and every few hours thereafter. The pH is expected to drop rapidly from that of sea water (7–9) to lower than 4, often about 3.
At the first opportunity after the pH has become constant, the pond should be drained; the drainage water should go to the drainage canal and not to any other pond. The pond is refilled and pH checked again. The water should be drained as soon as possible after it has a constant pH. The refilling and draining process should be continued as long as the constant pH remains below 5. This may take from less than a week (4–6 refills) to about 2 weeks. When the water remains at a higher pH, the pond bottom is drained and thoroughly dried again as described above.
After thorough drying, the pond bottom is cultivated and again refilled as described above. This time, the pH probably will not drop as low as in the first series of filling and draining.
When the pH remains above 5 in the water brought into the dry pond, the pond is drained and 500 kg agricultural lime per ha is broadcast well over the bottom. The lime should not be incorporated into the soil. The pond is ready to start normal operations, if the dikes have been treated.
3.2 Treatment of dikes
At the same time the acids are removed from the pond bottom, the acids in and on the dikes should also be removed. Because the dikes are normally dry, the acid can be washed without first drying as needed for the pond bottom.
Normally on bigger dikes, small levees should be constructed on the top of the dikes and along the sides, and the surface between them should be levelled carefully. If the dike material is very loose and erodible, for example owing to high organic matter content, a small ditch can be dug along the centre of the level dike crest. This would have somewhat broader levees. Or if the dikes are very small they could simply be washed by using a low pressure pump. Specifications for the dikes to be constructed in acid sulphate areas should include levelling of the dike tops and construction of levees or ditching to avoid delay in reclamation.
After this, seawater or brackish water should be pumped or brought up into the levelled paddies on top of the dikes, enough to keep them flooded to more than 10 cm depth. Acid water will soon seep out towards the pond or the canal. Pumping of brackish water (not acid drainage water) should be continued as necessary to keep all the tops of dikes flooded.
When the pond bottom is ready to be dried again, the top of the dikes should be allowed to dry out. When the pond bottom has thoroughly dried and has been cultivated, the top of the dikes should be flooded again during the next series of filling and draining the pond. When the pH of the water in the pond remains 5 or above, the standing water on the top of the dikes should be removed.
After completing this work on dikes between two ponds, both levees are removed and the soil material brought towards the centre. On dikes along a canal, only the levee along the side of the canal should be removed and the material brought towards the other levee.
Then one kg agricultural lime per 10 m is broadcast on the slopes of the dikes along each pond, and one kg per 20 m on the dike tops. Now the pond is ready to start normal operations.
3.3 Pond preparation, growing of fish food and stocking
The water intake and drainage gate of each pond should be repaired and screened to prevent the entry of wild fish and escape of stocked fish.
After the pond reclamation procedure is completed, chicken manure at 2 t/ha should be broadcast in the reclaimed and unreclaimed ponds and two days after, the ponds flooded with water to a depth of 5 cm. After about a week algal growth on the pond bottom may be noticed as blue green or green thin patches. If this is not noticed, the ponds may have to be inoculated with algae collected from outside.
If there is algal growth, nitrogen at 10 kg/ha and phosphate at 20 kg/ha in the form of urea (about 44 kg/ha) and super phosphate (100 kg/ha) should be uniformly broadcast in the pond water. This could also be applied by dissolving the fertilizer in water and spreading it in the pond water. Alternatively, the fertilizer mixture could be placed in a basket or in a jute bag, which should be firmly placed on a platform or hung and semi-submerged in water near the water intake gate during flooding of the pond. The fertilizer will be dissolved in water and will be uniformly distributed throughout the pond. The depth of pond water can be increased by 3–5 cm every flooding (i.e. 3–5 days) and brought to a desired level of 30–40 cm for bottom feeding fishes and deeper for column feeders. The application of fertilizer should be repeated every two weeks using the same rate and methods of application as mentioned above throughout the culture period; but it should be stopped two weeks before the harvesting. To avoid algal loss after fertilizing and stocking, the pond water should not be drained. However, the water loss through seepage and percolation and evaporation should be replenished when needed.
After the application of first fertilizer dose, when a thick mat of algae or good plankton growth is noticed, the pond is ready for stocking. Stocking of fish, however, should be done with older and heavier fingerlings of known initial weight than usually practised in a normal fish pond.
3.4 Prevention of fish kills during rains
Although much acid has been removed from the dikes during reclamation, there may still be a danger of acid water seeping from the dikes into the pond during heavy rains. As soon as heavy rains start, the pH of the pond water along the dikes should be monitored. Monitoring should be continued for several hours. If the pH drops below 5, agricultural lime should be broadcast immediately into the pond water along the dikes. About 1 kg of lime should be used per 10 m in each pond along each dike. This is about 1 bag (50 kg) of lime for the four sides of a 1-ha pond.
3.5 Water quality measurements
Water quality in terms of pH, alkalinity, ammonia and nitrate nitrogen and phosphate concentrations, salinity, water temperature and dissolved oxygen should be measured every two weeks, by using the methods described at the end of this proposal.
3.6 Primary productivity measurement
The primary productivity of the ponds could be measured by using a D.O. meter and measuring the dissolved oxygen on a 24 hour cycle. Or some measurements could also be made by using light and dark bottles and incubation.
Alternatively, benthic productivity can be estimated by using a PVC core of 30 cm in diameter and 50 cm in length. By pushing this core into the soil to about 10 cm depth at several locations in the pond the soil core including the benthic algae can easily be removed from the pond. The soil core should be removed from the PVC tube and the algae on the soil surface carefully scrapped using a steel spatula. The soil particles, if any, attached to algae should be carefully separated from the sample. This could also be done by centrifuging the sample at low speed. The algal sample obtained this way should be weighed to obtain the fresh weight, oven dried and reweighed to get the dry weight of the algae. The weight of the algae should be expressed in grams per unit area of pond soil sampled. Furthermore, the algal samples could be furnaced at high temperature (generally 500°C) and the ash-free dry weight can be calculated.
For the measurement of plankton in the water column, a representative water sample of known volume from the ponds should be collected and filtered using a fine filter paper (Wahtman 60) and weighed including the filter paper. The dry weight of the filter paper should have already been taken. The filter paper plus the plankton sample should be ovendried to evaporate the water and dry weight should be noted. By subtracting the weight of filter paper from the dry weight of filter paper plus the plankton, the dry weight of plankton per unit volume of water sampled can be calculated and expressed in weight/litre. The primary productivity can also be estimated by using a secchi disc.
3.7 Fish harvesting
The stocked fish should be harvested by completely draining the pond and all fishes collected. They should be weighed and the weight of fingerlings at the time of stocking should be subtracted to determine the weight gain of fish in the culture period. This weight could be divided by the number of days in a culture period to obtain the daily weight gain.
Study 3
Objective: To study the physico-chemical properties of soils selected for pond construction at Aluu.
Materials needed: Same as for Study 1.
Procedure
3.1 Sample collection and preparation
Based on the relative elevation of the area selected for the construction of fish ponds and also about 50 m border outside the delineated area the entire site should be delineated into three categories:
The depth of cut and fill should also be roughly known from the topographic map because as shown in the master plan, the entire area will be levelled and all the ponds will be at the same elevation. Ideally once the area has been delineated and the depth of cut and fill known, the sample collection points should be marked on the map in a linear manner of about 50 m intervals in the area to be cut and about 100 m in the area to be filled, along the total length and also the width of the area.
The depth of the soil profile to be sampled will vary according to the three categories discussed above i.e. deepest in the area of cut (2 m or more) and shallower in the area of fill (50 cm or less). The sampling depth in the intermediate area will be about 1 m. Perhaps there is no need for sample collection in the area which is to be filled because the quality of soil which is used as fill will be known by studying the profile depth properties of the area of cut.
Soil profile samples from these location points should be collected to the depths specified above at 20 cm depth intervals, using soil auger or spade if possible.
Due to the inadequacy of topographic map and also due to the lack of knowledge of cut and fill of the area, it is suggested that the entire area (pond area plus the border) should be marked with sampling points at 100 m linear intervals along the total length and the width of the area. Based on the general elevation of the area it is justifiable to roughly divide the site into higher, lower and intermediate areas. The depth of sampling be maintained as deepest (2 cm or more) for the higher area, shallowest (1 m or less) for the lower area and about 1.5 m in the intermediate area (see attached map, Fig. 1).
The profile soil samples for the location points thus marked, should be collected to the depths specified above at 20 cm depth intervals by soil auger or spade.
The soil volume of about 1 kg from each layer of profile should be placed in plastic bags and each bag properly marked. After this, the drying and preparation of the samples should be done, following the methods described in Study 1.
The prepared soil samples should be analysed for the following properties by using the methods of soil analysis discussed at the end of this proposal.
Study 4
1. Objective: To develop remedial measures to improve the productivity of pond soils and to determine the fertilizer requirements of acid sulphate soils for fish ponds at Buguma.
This study is to be conducted in two phases, under controlled conditions in plastic tanks or glass aquaria and later to be followed in ponds.
2. Materials needed
3. Procedure
Bulk soil samples from an identified acid sulphate area should be collected air-dried and pulverized. The sample should be thoroughly mixed and homogenized and a representative sample analysed. Each experimental unit should be filled with 40 kg of this soil material and about 15 1 brackish water should be gently poured in each unit to bring the soil and water to an equilibrium. One week after, the excess water from all the units should be syphoned or leached and collected in glass containers and analysed to know how much acidity and other elements are removed by leaching or flushing. The same process should be repeated for one more week.
After this, the following treatments should be applied to determine the effectiveness of fertilizers on physico-chemical properties, primary productivity and the fertilizer requirement of the fish ponds built on acid sulphate soils.
3.1 Treatments
The rates of application of lime and chicken manure at 2 t/ha; nitrogen at 60 kg/ha in the form of urea; phosphate at 120 kg/ha in the form of superphosphate; and potash at 30 kg/ha in the form of muriate of potash. Since phosphorus is known to be deficient in these soils, another separate study should be made where the levels of phosphate could be varied as 0, 45, 60, 90, 120 and 150 kg/ha. Lime and chicken manure, at 2 t/ha and nitrogen at 60 kg/ha should be applied in all treatments as blanket applications.
For both the studies, all organic fertilizers and lime should be applied after second flushing and the inorganic fertilizers divided into 6 equal quantities and each quantity applied weekly either by broadcasting on the water surface or by dissolving it in water and sprinkling it on the water surface.
In both the studies each treatment should be replicated 3-4 times and the experimental units kept under a clear roof, even made of white plastic.
After the application of organic fertilizer, brackish water should be gently admitted to each unit to a depth of 5 cm. One week after admitting the water the first dose of inorganic fertilizers should be applied and water depth gradually increased to 15 cm. Every week thereafter the application should be repeated till the last dose is applied.
Beginning one day after the application of first dose of organic fertilizers, pH, ammonia, nitrate and phosphate concentrations and if possible aluminium and iron in the overlying water, should be monitored weekly. Samples from all the units should be taken on the same day. About 200 ml of water sample is enough for these analyses, and the water collected for analysis should be replaced by adding new brackish water.
For the measurements of plankton growth a known volume of water from each unit, beginning the first week after inorganic fertilizer application, should be collected and filtered. The residue on the filter paper should be dried and weighed. If the weight of the filter paper is subtracted from the weight of the paper plus plankton, a rough estimate of relative growth of plankton per unit volume of water can be made.
Frequent dissolved oxygen measurements would also reflect the relative primary productivity, if the measurements are done with care and the values computed and analysed properly.
About three weeks after the first inorganic fertilizer application and every two weeks thereafter some benthic algae from a unit area of about 100 cm2 could be carefully scraped by a steel spatula, oven-dried and weighed to know the dry weight of the algae. Alternatively this could also be furnaced to determine the ash-free dry weight. These measurements which are to be done every two weeks, will provide a crude estimate of total primary productivity.
Comparison of the values of physico-chemical properties and benthic and plankton growth among treatments would reflect the effectiveness of the fertilizers and will also provide the estimate of the quantities of fertilizers needed. From this, the promising treatments could be selected and tested under pond conditions.
Schedule of activities at Buguma
| 8 December 1981 | Application of fertilizers; urea (46-0-0) and superphosphate (0-20-0), there is 435 g of urea and 2 000 g or 2 kg of superphosphate. The fertilizers could be broadcast, if possible, or could be dissolved in water and applied in solution. |
| 15 December 1981 | Water sampling for the measurements of pH, NH3, NO3, PO4, salinity, D.O. and temperature. If algal growth is not satisfactory please repeat the fertilizer application as above. No increase in water depth. If algal growth is satisfactory do not apply the fertilizers and repeat the fertilizer application the week after stocking. |
| 22 December 1981 | Stock the fish at the rate of 100 fingerlings in each pond i.e. one fish/2 m2 of land surface area. The fingerlings should be heavier and healthier in the range of 15–25 g each. If stocking is done, increase the water depth to a desired level. If fertilizers were not applied on 15 December then they should be applied now. |
| 30 December 1981 | Measurement of primary productivity and water analysis. |
| 5 January 1982 | Fertilizer application as stated above. |
| 12 January 1982 | Water analysis. |
| 19 January 1982 | Fertilizer application as above. |
| 26 January 1982 | Measurement of primary productivity. Also, water analysis. |
| 2 February 1982 | Fertilizer applications as above. |
| 9 February 1982 | Water analysis. |
| 16 February 1982 | Fertilizer application. |
| 23 February 1982 | Water analysis. |
| 2 March 1982 | Measurement of primary productivity and fertilizer application. |
| 9 March 1982 | Water analysis. |
| 16 March 1982 | Fertilizer application. |
| 23 March 1982 | Water analysis. |
| 30 March 1982 | Measurement of primary productivity and fertilizer application. |
| 6 April 1982 | Water analysis. |
| 20 April 1982 | Harvesting of fish. |
Note:
Fertilizer applications are to be made every two weeks using the same rate as used initially and in pond B, only.
Water analysis includes pH, NH3, NO3, PO4 salinity, D.O. temperature and if possible alkalinity. This should also be done every two weeks but beginning one week after first application of fertilizer and should be done for both ponds.
Measurement of primary productivity should be done every month beginning one month after the first fertilizer application and should be done for both ponds.
Except the fertilizer application which is to be done only in pond B, all other operations should be done in both ponds.
Make any adjustment in operations as felt necessary.
Total number of fertilizer applications will be 8 times, water analysis 9 times and primary productivity 4 times in the whole culture period from 8 December 1981 to 20 April 1982.
There should be a strict control of water. Water should not be allowed to come in and go out freely, as observed in other ponds, because it leads to plankton and nutrient losses. Water should be replenished when needed to compensate for losses only to maintain a desired depth.
