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A study on the relative efficiency of organic manures and the effect of salinity on its mineralisation in brackishwater fish farm soil
Aquaculture, 5 (1975) 359-366 o Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
A STUDY ON THE RELATIVE EFFICIENCY OF ORGANIC MANURES AND THE EFFECT OF SALINITY ON ITS MINERALISATION IN BRACKISHWATER FISH FARM SOIL
S.R. GHOSH Estuarine Fisheries Research Barrackpore (India)
Unit of Central inland
Fisheries
Research
Institute,
(Received August 12th, 1974; revised November 19th, 1974)
ABSTRACT Ghosh, S.R., 1975. A study on the relative efficiency of organic manures and the effect of salinity on its mineralisation in brackishwater fish farm soil. Aquaculture, 5: 359-366. The influence of salinity on the mineralisation of organic nitrogen in the form of mustard oil cake, poultry manure and cow-dung in brackishwater pond soils was studied under laboratory conditions. The concentration of mineralised nitrogen for mustard oil cake and poultry manure showed a marked increase during 7 to 30 days after which it decreased gradually and in 90 days assumed practically the same value as that of the control over the salinity range of 0-40’/,, . The mineralised nitrogen of cow-dung treatment’was lower than that of the control,till 30 days,after which it increased gradually. The loss of nitrogen is minimum in the higher salinity range for all three types of manure used. Mustard oil cake is a better manure for ‘brackishwater soil than poultry droppings and cow-dung. INTRODUCTION
In an experiment to study the optimum salinity for the growth of fish food organisms Bose (1960) observed that salinity ranging between.5 and 17°/oo was most favourable in brackishwater ponds. Schuster ($952) reported that a higher salinity between 15 and 45 o/oo was most favourable for their growth. Therefore, the enhancement of the growth of these organisms by the provision of optimum salinity is very important for fish culture in brackishwater fish ponds. The present study was undertaken to investigate the effect of salinity on the mineralisation of organic nitrogen added in the form of organic manures and their relative efficiency in brackishwater fish culture. iGhosh (quoted in Mandal, 1962) observed that loss of nitrogen could be minimised by the addition of inorganic fertilisers in combination with potassium chloride. It was therefore intended to note in this study whether sodium chloride would also have the same effect as potassium chloride on the mineralised nitrogen in brackishwater fish farms.
360
MATERIALS
AND METHODS
The soils for this study were collected from Kakdwip Brackishwater Fish Farm located in the estuarine areas of West Bengal. The soil samples from the pond bottom were collected by an Ekman’s Dredge and were subsequently oven dried. The relevant data on the physical and chemical characteristics of the soil are presented in Table I. This soil is composed of silty-clay, low in nitrogen, phosphorous and organic carbon, and alkaline in reaction. Portions (10.0 g) of the oven-dried soil samples were transferred to test tubes of 2 cm X 30 cm size. The contents of each tube were then soaked with 50 ml of sodium chloride solution of different concentrations (0 to 40%,, at intervals of lOo/oo ) which stood 10 cm above the soil. The tubes were kept in a dark corner of the laboratory and the loss of water by evaporation was made up by adding distilled water periodically. 6 weeks after this soaking procedure, manure was added on an equivalent nitrogen basis at the rate of 15 mg per tube. Three types of manure were used, namely, cow-dung, poultry droppings and mustard oil cake, with estimated nitrogen content values of 0.9%, 3.7% and 4.5% respectively. For each type of manure, one set was kept as control without any treatment. Total mineralised nitrogen for each set was determined by estimating NH4 -N, NO3 and NOz -N in both soil and water under pretreatment conditions and subsequently at periodic intervals of 7, 15, 30,45,60 and 90 days. For soil analysis, methods recommended by the International Bureau of Soil Science (Piper, 1950) were followed and water analysis was done by methods adopted by the American Public Health Association, (1965). The mineralised nitrogen values calculated for both native soil and soil immersed in different salinity media are presented graphically in Figs l-5.
TABLE I Physical and chemical characteristics Sand Silt Clay Organic carbon Salinity Free CaCO, Cation exchange capacity Total exchangeable cations Carbonate Bicarbonate Total nitrogen Available nitrogen Available phosphorus
of the soil used
8% 35% 55% 0.34% 1.00%. 3.46% 13.47 meq/lOO g 49.58 meq% 0.05 meq% 2.00 meq% 0.069% 18.5 mg/lOO g 4.0 mg/lOO g
361
RESULTS
AND DISCUSSION
The efficiency of cattle manure is stated to be only 50% of that of inorganic nitrogenous fertilizeqwhile that of the easily decomposable organic manures like oil cake,is reported to be on par with that of inorganic fertilizers (Gokhale, 1956). This observation was substantiated by Mandal and Pain (1965) in their study with inorganic fertilizers and organic manures. They observed that the easily decomposable mustard oil cake, when applied. continuously over a protracted period of 15 years, resulted in early mineralisation of nitrogen; however cow-dung, a resistive type of manure under the same conditions, became mineralised relatively later, as was apparent in the increase in total and available nitrogen and organic carbon in cow-dung treated plots at the end of 15 years. From the results of this same experiment, it was also found that the amount of available nitrogen as a percentage of the total nitrogeqwas higher in the mustard oil cake treated plots than the cow-dung treated plots. Similarly, in this present experiment,mustard oil cake was observed to be more efficacious as an organic manure than poultry droppings and cow-dung in brackishwater media as far as the mineralisation was concerned, as can be seen from the higher values of mineralised nitrogen shown in Table II. The second best manure was poultry droppings, the utility of which as a manure had earlier been indicated by Ray and David (1969), though not in brackishwater media. Ray and David, however, did not make any comparative study regarding the relative efficiency of mustard oil cake. TABLE II The average mineralised nitrogen values (in mg) over a period of 90 days of experimentation in media of different salinity Treatments
Control Mustard oil cake Poultry manure Cowdung
Average
Salinity media (o/00) 0
10
20
30
40
7.07 46.02 16.62 6.84
10.40 54.83 42.58 12.99
11.57 60.14 49.12 13.80
12.77 63.55 54.53 15.54
14.19 81.09 68.41 21.34
11.20 61.12 46.25 14.10
The concentration of mineralised nitrogen for soils treated with mustard oil cake and poultry droppings showed a marked increase during the first 7 to 30 days after which it decreased gradually and at 90 days, assumed practically the same value as that of the controls for the salinity range O--Z@‘/,, (Pigs 1--3),while for the salinity range 30-40°/oo (Figs 4 and 5) it still showed a higher value. The mineralised nitrogen in the soil treated with cow-dung, unlike the soil treated by the other two organic manures, showed a lower
362
value than the control, till 30 days after manure treatment. This is possibly due to the smaller fraction of easily decomposable nitrogen of cow-dung utilised by the soil microbes. After 30 days this mineralised nitrogen value gradually increased indicating the amount present in excess of the biological demand ef these microbes (Figs 1-5). PearsaIl (1950) reported that soils in the reducing state (i.e. under waterlogged conditions) liberate larger amounts of exchangeable cations, particularly iron, manganese and aluminium. At higher salinities most of the exchangeable cations are partially satisfied by sodium ions (Allison et al., 1953). It is observed in the present study that the mineralised nitrogen of different organic manures increased with the rise of salinity. This may be explained by the alkaline soil reaction caused by the exchangeable cations,which are partially satisfied by sodium ions,favouring decomposition of organic manures in the soil during the formation of ammonia appearing in the exchange complex. Pillay et al. (1962), in an ecological study of bheris, concluded that higher salinity ranges are conducive to greater production of benthic algae. A statistical test was applied in this study to determine the significance between treatments and salinities; the results are shown in the analysis of vari‘ante table (Table III). It is observed that there is a differential effect among salinity and there is a highly significant variation of treatment effect. Mandal (1962) observed that more nitrogen was found in the soil complex
120
-
110 lOO-
--.--._-
Control 90
-
__.-.-.-\ ‘\
80 70
-
-._.-.-._
Mot Poultry
‘\
manure _.
Cowdung
._
._
.. _
‘\
/
‘\ 60-
‘\
/’
\ 50-
‘\
/
\ !
40
\
!
I
0
i 10
20
30
40
50
60
70
00
ooya
Fig.1. Mineralisation
of organic nitrogen in trace salinity.
90
363
100
c
10
0
__.--.-
Control
20
30
40
50
60
70
00
90
Days
Fig.2.
Mineralisation
of organic
nitrogen
in 1Ool,,0 salinity.
120 I 110 -
/.-+\ .I.-.
100
;
‘I.
/’
go-
--.--.-
Control Mot
‘.
‘...
Pod-y
\
/
_._.-.manure
Cow duna
\
-..-..-..
\
_..---__
.--__. I
0
IO
20
30
40
50
60
70
60
Days
Fig.3.
Mineralisation
of organic
nitrogen
in 2O0/0o salinity.
90
364
1
0
10
20
30
50
40
60
70
00
90
Days
Fig.4. Mineralisation of organic nitrogen in 30’/,,, salinity. 130 --.--.--
Control
120
-.-.-.-. 110
Poultry
manure _.._..
-.._
100
90
60
70
6C 5C
40
30
2c
10
10
20
I 30
!
I 40
50
60
70
60
Days
Fig.5. Mineralisation of organic nitrogen in 40”/,, salinity.
90
365
TABLE III Analysis of variance. *P = 0.01: significant; **P = 0.01: highly significant Source of variation
Salinity Treatment Error Total
Degrees of freedom
4 3 12 19
Sum of squares
11320.53 63 770.55 5 078.05 80 169.13
Mean square
2 830.13 21256.85 423.17
Variance ratio (F)
6.68* 50.23**
Total value at 5%
1%
3.26 3.49
5.41 5.95
the higher salinity treatment and that the nitrification rate was also lower as a result of minimal nitrogen loss in the higher salinity treatment. It can be seen in this present investigation that at 90 days after treatment the percentage loss of mineralised nitrogen is inversely proportional to the salinity in all the organic treatments (Table IV).
in
TABLE
IV
Effect of salinity on loss of nitrogen from soil treated with mustard oil cake, poultry manure and cow-dung Salinity (%, )
Trace 10 20 30 40
Total nitrogen per 100 g of soil (in mg) Percentage
After 90 days
At start
Soil : Added:
69 mg 150 mg
Total:
219 219 219 219 219
mg mg mg mg mg
of nitrogen loss
Mustard oil cake
Poultry manure
Cow-dung
Mustard oil cake
Poultry manure
Cow-dung
30.19 31.31 128.31 141.12 181.68
105.62 177.31 182.70 196.48 198.00
57.01 168.23 173.22 184.25 190.00
86.30 85.84 41.55 35.61 17.34
51.59 19.17 16.43 10.50 9.58
73.51 23.28 21.00 15.98 13.28
From the findings presented in this paper,it can be concluded that for alkaline silty-clay brackishwater soil with low organic matter and available nitrogen, mustard oil cake is a better manure than poultry droppings or cow-dung. With regard to the farm manures - cow-dung and poultry droppings - poultry manure is far better than cow-dung. ACKNOWLEDGEMENTS
The author is grateful to Dr V.G. Jhingran, Director, Central Inland Fisheries Research Institute for his kind permission to publish the paper, to
Dr V. Gopalakrishnan, Officer-in-Charge, Estuarine Division and to Shri A.N. Ghosh, Officer-in-Charge of the Estuarine Unit at Kakdwip for their encouragement during the course of thestudy. REFERENCES Allison, F.E., Kefauver, M. and Roller, E.M., 1953. Ammonium fixation in soils. Proc. Soil Sci. Sot. Am., 17: 107-110 American Public Health Association, 1965. Standard Methods for the Examination of Water and Waste Water. Am. Publ. Health Assoc., New York, 12thEdn, 769 pp. Bose, B.B., 1960. An experimental study of the optimum salinity for the growth of the benthic blue green alga Oscillator-a splendia Grevile of brackish water ponds. Proc. Nat. Inst. Sci. India, 26 (1): 19-21 Gokhale, N.G., 1956. Nitrogenous fertilisers of tea. J. Ind. Sot. Soil Sci., 4: 205-214 Mandal, L.N., 1962. Effect of salinity on the transformation of nitrogen in the brackish water fish farm soil. J. Ind. Sot. Soil Sci., lO(4): 255-262 Mandal, L.N. and Pain, A.K., 1965. Effect of continuous application of organic manures and ammonium sulphate in mulberry field on some soil properties. J. Ind. Sot. Soil Sci., 13 (1): 37-42 Pearsall, W.H., 1950. The investigation of wet soils and its agricultural implication. Emp. J. Exp. Agric., 13: 289-298 Pillay, T.V.R., Vijayaraghawan, M.R. and Thakurta, SC., 1962. An ecological study of benthic flora in brackish-water bheris. Proc. Nat. Inst. Sci. India, 28( 5): 416-431 Piper, C.S., 1950. Soil and Plant Analysis. Univ. Adelaide, Adelaide, 368 pp. Ray, P. and David, A., 1969. Poultry manure as potential plankton producer. Labdev, J. Sci. Technol., 7(3): 229-231 Schuster, W.H., 1952. Fish Culture in Brackishwater Ponds of Java. Spec. Publ. IndoPacific Fish Count. 1, 50 pp.
A STUDY ON THE RELATIVE EFFICIENCY OF ORGANIC MANURES AND THE EFFECT OF SALINITY ON ITS MINERALISATION IN BRACKISHWATER FISH FARM SOIL
S.R. GHOSH Estuarine Fisheries Research Barrackpore (India)
Unit of Central inland
Fisheries
Research
Institute,
(Received August 12th, 1974; revised November 19th, 1974)
ABSTRACT Ghosh, S.R., 1975. A study on the relative efficiency of organic manures and the effect of salinity on its mineralisation in brackishwater fish farm soil. Aquaculture, 5: 359-366. The influence of salinity on the mineralisation of organic nitrogen in the form of mustard oil cake, poultry manure and cow-dung in brackishwater pond soils was studied under laboratory conditions. The concentration of mineralised nitrogen for mustard oil cake and poultry manure showed a marked increase during 7 to 30 days after which it decreased gradually and in 90 days assumed practically the same value as that of the control over the salinity range of 0-40’/,, . The mineralised nitrogen of cow-dung treatment’was lower than that of the control,till 30 days,after which it increased gradually. The loss of nitrogen is minimum in the higher salinity range for all three types of manure used. Mustard oil cake is a better manure for ‘brackishwater soil than poultry droppings and cow-dung. INTRODUCTION
In an experiment to study the optimum salinity for the growth of fish food organisms Bose (1960) observed that salinity ranging between.5 and 17°/oo was most favourable in brackishwater ponds. Schuster ($952) reported that a higher salinity between 15 and 45 o/oo was most favourable for their growth. Therefore, the enhancement of the growth of these organisms by the provision of optimum salinity is very important for fish culture in brackishwater fish ponds. The present study was undertaken to investigate the effect of salinity on the mineralisation of organic nitrogen added in the form of organic manures and their relative efficiency in brackishwater fish culture. iGhosh (quoted in Mandal, 1962) observed that loss of nitrogen could be minimised by the addition of inorganic fertilisers in combination with potassium chloride. It was therefore intended to note in this study whether sodium chloride would also have the same effect as potassium chloride on the mineralised nitrogen in brackishwater fish farms.
360
MATERIALS
AND METHODS
The soils for this study were collected from Kakdwip Brackishwater Fish Farm located in the estuarine areas of West Bengal. The soil samples from the pond bottom were collected by an Ekman’s Dredge and were subsequently oven dried. The relevant data on the physical and chemical characteristics of the soil are presented in Table I. This soil is composed of silty-clay, low in nitrogen, phosphorous and organic carbon, and alkaline in reaction. Portions (10.0 g) of the oven-dried soil samples were transferred to test tubes of 2 cm X 30 cm size. The contents of each tube were then soaked with 50 ml of sodium chloride solution of different concentrations (0 to 40%,, at intervals of lOo/oo ) which stood 10 cm above the soil. The tubes were kept in a dark corner of the laboratory and the loss of water by evaporation was made up by adding distilled water periodically. 6 weeks after this soaking procedure, manure was added on an equivalent nitrogen basis at the rate of 15 mg per tube. Three types of manure were used, namely, cow-dung, poultry droppings and mustard oil cake, with estimated nitrogen content values of 0.9%, 3.7% and 4.5% respectively. For each type of manure, one set was kept as control without any treatment. Total mineralised nitrogen for each set was determined by estimating NH4 -N, NO3 and NOz -N in both soil and water under pretreatment conditions and subsequently at periodic intervals of 7, 15, 30,45,60 and 90 days. For soil analysis, methods recommended by the International Bureau of Soil Science (Piper, 1950) were followed and water analysis was done by methods adopted by the American Public Health Association, (1965). The mineralised nitrogen values calculated for both native soil and soil immersed in different salinity media are presented graphically in Figs l-5.
TABLE I Physical and chemical characteristics Sand Silt Clay Organic carbon Salinity Free CaCO, Cation exchange capacity Total exchangeable cations Carbonate Bicarbonate Total nitrogen Available nitrogen Available phosphorus
of the soil used
8% 35% 55% 0.34% 1.00%. 3.46% 13.47 meq/lOO g 49.58 meq% 0.05 meq% 2.00 meq% 0.069% 18.5 mg/lOO g 4.0 mg/lOO g
361
RESULTS
AND DISCUSSION
The efficiency of cattle manure is stated to be only 50% of that of inorganic nitrogenous fertilizeqwhile that of the easily decomposable organic manures like oil cake,is reported to be on par with that of inorganic fertilizers (Gokhale, 1956). This observation was substantiated by Mandal and Pain (1965) in their study with inorganic fertilizers and organic manures. They observed that the easily decomposable mustard oil cake, when applied. continuously over a protracted period of 15 years, resulted in early mineralisation of nitrogen; however cow-dung, a resistive type of manure under the same conditions, became mineralised relatively later, as was apparent in the increase in total and available nitrogen and organic carbon in cow-dung treated plots at the end of 15 years. From the results of this same experiment, it was also found that the amount of available nitrogen as a percentage of the total nitrogeqwas higher in the mustard oil cake treated plots than the cow-dung treated plots. Similarly, in this present experiment,mustard oil cake was observed to be more efficacious as an organic manure than poultry droppings and cow-dung in brackishwater media as far as the mineralisation was concerned, as can be seen from the higher values of mineralised nitrogen shown in Table II. The second best manure was poultry droppings, the utility of which as a manure had earlier been indicated by Ray and David (1969), though not in brackishwater media. Ray and David, however, did not make any comparative study regarding the relative efficiency of mustard oil cake. TABLE II The average mineralised nitrogen values (in mg) over a period of 90 days of experimentation in media of different salinity Treatments
Control Mustard oil cake Poultry manure Cowdung
Average
Salinity media (o/00) 0
10
20
30
40
7.07 46.02 16.62 6.84
10.40 54.83 42.58 12.99
11.57 60.14 49.12 13.80
12.77 63.55 54.53 15.54
14.19 81.09 68.41 21.34
11.20 61.12 46.25 14.10
The concentration of mineralised nitrogen for soils treated with mustard oil cake and poultry droppings showed a marked increase during the first 7 to 30 days after which it decreased gradually and at 90 days, assumed practically the same value as that of the controls for the salinity range O--Z@‘/,, (Pigs 1--3),while for the salinity range 30-40°/oo (Figs 4 and 5) it still showed a higher value. The mineralised nitrogen in the soil treated with cow-dung, unlike the soil treated by the other two organic manures, showed a lower
362
value than the control, till 30 days after manure treatment. This is possibly due to the smaller fraction of easily decomposable nitrogen of cow-dung utilised by the soil microbes. After 30 days this mineralised nitrogen value gradually increased indicating the amount present in excess of the biological demand ef these microbes (Figs 1-5). PearsaIl (1950) reported that soils in the reducing state (i.e. under waterlogged conditions) liberate larger amounts of exchangeable cations, particularly iron, manganese and aluminium. At higher salinities most of the exchangeable cations are partially satisfied by sodium ions (Allison et al., 1953). It is observed in the present study that the mineralised nitrogen of different organic manures increased with the rise of salinity. This may be explained by the alkaline soil reaction caused by the exchangeable cations,which are partially satisfied by sodium ions,favouring decomposition of organic manures in the soil during the formation of ammonia appearing in the exchange complex. Pillay et al. (1962), in an ecological study of bheris, concluded that higher salinity ranges are conducive to greater production of benthic algae. A statistical test was applied in this study to determine the significance between treatments and salinities; the results are shown in the analysis of vari‘ante table (Table III). It is observed that there is a differential effect among salinity and there is a highly significant variation of treatment effect. Mandal (1962) observed that more nitrogen was found in the soil complex
120
-
110 lOO-
--.--._-
Control 90
-
__.-.-.-\ ‘\
80 70
-
-._.-.-._
Mot Poultry
‘\
manure _.
Cowdung
._
._
.. _
‘\
/
‘\ 60-
‘\
/’
\ 50-
‘\
/
\ !
40
\
!
I
0
i 10
20
30
40
50
60
70
00
ooya
Fig.1. Mineralisation
of organic nitrogen in trace salinity.
90
363
100
c
10
0
__.--.-
Control
20
30
40
50
60
70
00
90
Days
Fig.2.
Mineralisation
of organic
nitrogen
in 1Ool,,0 salinity.
120 I 110 -
/.-+\ .I.-.
100
;
‘I.
/’
go-
--.--.-
Control Mot
‘.
‘...
Pod-y
\
/
_._.-.manure
Cow duna
\
-..-..-..
\
_..---__
.--__. I
0
IO
20
30
40
50
60
70
60
Days
Fig.3.
Mineralisation
of organic
nitrogen
in 2O0/0o salinity.
90
364
1
0
10
20
30
50
40
60
70
00
90
Days
Fig.4. Mineralisation of organic nitrogen in 30’/,,, salinity. 130 --.--.--
Control
120
-.-.-.-. 110
Poultry
manure _.._..
-.._
100
90
60
70
6C 5C
40
30
2c
10
10
20
I 30
!
I 40
50
60
70
60
Days
Fig.5. Mineralisation of organic nitrogen in 40”/,, salinity.
90
365
TABLE III Analysis of variance. *P = 0.01: significant; **P = 0.01: highly significant Source of variation
Salinity Treatment Error Total
Degrees of freedom
4 3 12 19
Sum of squares
11320.53 63 770.55 5 078.05 80 169.13
Mean square
2 830.13 21256.85 423.17
Variance ratio (F)
6.68* 50.23**
Total value at 5%
1%
3.26 3.49
5.41 5.95
the higher salinity treatment and that the nitrification rate was also lower as a result of minimal nitrogen loss in the higher salinity treatment. It can be seen in this present investigation that at 90 days after treatment the percentage loss of mineralised nitrogen is inversely proportional to the salinity in all the organic treatments (Table IV).
in
TABLE
IV
Effect of salinity on loss of nitrogen from soil treated with mustard oil cake, poultry manure and cow-dung Salinity (%, )
Trace 10 20 30 40
Total nitrogen per 100 g of soil (in mg) Percentage
After 90 days
At start
Soil : Added:
69 mg 150 mg
Total:
219 219 219 219 219
mg mg mg mg mg
of nitrogen loss
Mustard oil cake
Poultry manure
Cow-dung
Mustard oil cake
Poultry manure
Cow-dung
30.19 31.31 128.31 141.12 181.68
105.62 177.31 182.70 196.48 198.00
57.01 168.23 173.22 184.25 190.00
86.30 85.84 41.55 35.61 17.34
51.59 19.17 16.43 10.50 9.58
73.51 23.28 21.00 15.98 13.28
From the findings presented in this paper,it can be concluded that for alkaline silty-clay brackishwater soil with low organic matter and available nitrogen, mustard oil cake is a better manure than poultry droppings or cow-dung. With regard to the farm manures - cow-dung and poultry droppings - poultry manure is far better than cow-dung. ACKNOWLEDGEMENTS
The author is grateful to Dr V.G. Jhingran, Director, Central Inland Fisheries Research Institute for his kind permission to publish the paper, to
Dr V. Gopalakrishnan, Officer-in-Charge, Estuarine Division and to Shri A.N. Ghosh, Officer-in-Charge of the Estuarine Unit at Kakdwip for their encouragement during the course of thestudy. REFERENCES Allison, F.E., Kefauver, M. and Roller, E.M., 1953. Ammonium fixation in soils. Proc. Soil Sci. Sot. Am., 17: 107-110 American Public Health Association, 1965. Standard Methods for the Examination of Water and Waste Water. Am. Publ. Health Assoc., New York, 12thEdn, 769 pp. Bose, B.B., 1960. An experimental study of the optimum salinity for the growth of the benthic blue green alga Oscillator-a splendia Grevile of brackish water ponds. Proc. Nat. Inst. Sci. India, 26 (1): 19-21 Gokhale, N.G., 1956. Nitrogenous fertilisers of tea. J. Ind. Sot. Soil Sci., 4: 205-214 Mandal, L.N., 1962. Effect of salinity on the transformation of nitrogen in the brackish water fish farm soil. J. Ind. Sot. Soil Sci., lO(4): 255-262 Mandal, L.N. and Pain, A.K., 1965. Effect of continuous application of organic manures and ammonium sulphate in mulberry field on some soil properties. J. Ind. Sot. Soil Sci., 13 (1): 37-42 Pearsall, W.H., 1950. The investigation of wet soils and its agricultural implication. Emp. J. Exp. Agric., 13: 289-298 Pillay, T.V.R., Vijayaraghawan, M.R. and Thakurta, SC., 1962. An ecological study of benthic flora in brackish-water bheris. Proc. Nat. Inst. Sci. India, 28( 5): 416-431 Piper, C.S., 1950. Soil and Plant Analysis. Univ. Adelaide, Adelaide, 368 pp. Ray, P. and David, A., 1969. Poultry manure as potential plankton producer. Labdev, J. Sci. Technol., 7(3): 229-231 Schuster, W.H., 1952. Fish Culture in Brackishwater Ponds of Java. Spec. Publ. IndoPacific Fish Count. 1, 50 pp.