BOTTOM SOIL QUALITY IN PONDS FOR CULTURE OF CATFISH,
FRESHWATER PRAWN, AND CARP IN THAILAND
Except where reference is made to the work of others, the work described in this
dissertation is my own or was done in collaboration with my advisory committee.
This dissertation does not include proprietary or classified information.
John W. Odom
Associate Professor
Agronomy and Soils
Chhorn Lim
Affiliate Professor
Fisheries and Allied Aquacultures
Claude E. Boyd, Chair
Professor
Fisheries and Allied Aquacultures
Yolanda J. Brady
Associate Professor
Fisheries and Allied Aquacultures
Stephen L. McFarland
Acting Dean
Graduate School
Idsariya Wudtisin
Certificate of Approval:
BOTTOM SOIL QUALITY IN PONDS FOR CULTURE OF CATFISH,
FRESHWATER PRAWN, AND CARP IN THAILAND
Idsariya Wudtisin
A Dissertation
Submitted to
the Graduate Faculty of
Auburn University
in Partial Fulfillment of the
Requirements for the
Degree of
Doctor of Philosophy
Auburn, Alabama
May 11, 2006
iii
BOTTOM SOIL QUALITY IN PONDS FOR CULTURE OF CATFISH,
FRESHWATER PRAWN, AND CARP IN THAILAND
Idsariya Wudtisin
Permission is granted to Auburn University to make copies of this dissertation at its
discretion, upon the request of individuals or institutions at their expense.
The author reserves all publication rights.
Signature of the Author
Date of Graduation
iv
VITA
Idsariya Wudtisin, daughter of Prawim Wudtisin and Wongduan Wudtisin, was
born in Rayong, Thailand, on April 13, 1977. She has two sisters, Wararat and Masalin
wudtisin. She earned a bachelor degree in Thailand (B.S. in Environmental Health, from
Burapha University in 1998). Then she earned a master?s degree in Environmental
Science with a distinct award from the graduate school of Kasetsart University in
Thailand in 2001 and completed the Ph.D. from Department of Fisheries and Allied
Aquacultures, Auburn University in May, 2006.
v
DISSERTATION ABSTRACT
BOTTOM SOIL QUALITY IN PONDS FOR CULTURE OF CATFISH,
FRESHWATER PRAWN, AND CARP IN THAILAND
Idsariya Wudtisin
Doctor of Philosophy, May 11, 2006
(M.S., Kasetsart University, 2001)
(B.S., Burapha University, 1998)
100 Typed Pages
Directed by Claude E. Boyd
Bottom soil samples were collected from 42 catfish (Clarias hybrid) ponds, 40
freshwater prawn (Macrobrachium rosenbergii) ponds, and 18 carp (Puntius spp.) ponds
in Thailand. The ponds ranged from 1 to 30 years in age. Regression analysis revealed
that pond age was not a major factor influencing the physical and chemical composition
of pond soils. Sediment depth, S horizon thickness, and bulk density of S horizon were
greater for carp ponds than for catfish and prawn ponds. This resulted because sediment
was removed from catfish and prawn ponds more frequently than from carp ponds. Total
carbon, organic carbon, and total nitrogen concentrations were higher in carp ponds than
vi
prawn and catfish ponds. However, few ponds had sediment organic carbon
concentrations above 3%, and carbon:nitrogen ratios did not differ among the three
cultured species.
Total phosphorus and other soil phosphorus fractions increased in the order prawn
ponds, carp ponds, and catfish ponds. Soil sulfur concentrations also increased in the
same order. There were no differences in major or minor nutrients in bottom soils that
would influence aquacultural production. Although there were significant correlations
between various soil quality variables, no single variable or group of a few variables
would be useful in estimating soil quality.
Best management practices recommended for improving pond bottom quality
were drying of bottom between crops, liming, tilling, and periodic sediment removal.
Best management practices for preventing high total suspended solids concentrations in
pond effluents also were recommended.
vii
ACKNOWLEDGEMENT
The author would like to thank all the people who supported her during her
program. She thanks Mr. Prawim Wudtisin, Director General for Department of Marine
and Coastal Resources Department, who encouraged her to study in the United States.
Thanks to Dr. Claude E. Boyd, who give her an opportunity to do and conduct her
research. Dr. John W. Odom, Dr. Chhorn Lim and Dr. Yolanda J. Brady, who assisted
her during her study. Besides, the author would like to thanks Mr. Puan Pengseng for his
assistance about laboratory works, and thanks to Dr. Tarworn Thunjai for his advice
about her dissertation format.
The author also would like to thank the CRSP for financial support under the
Pond Dynamics/Aquaculture Collaborative Research Support Program (PD/A CRSP)
funded by the United States Agency for International Development. Very special thanks
to Miss Wararat Wudtisin, her lovely sister, who always take care of her and give her all
supports to living strong overseas.
viii
Style manual or journal used: Journal of the World Aquaculture Society
Computer software used: Microsoft Word 2000, Microsoft Excel 2000, SigmaStat 2.03,
and SigmaPlot 8.0.
ix
TABLE OF CONTENTS
LIST OF TABLES???????????????????..????..?..?x
LIST OF FIGURES?????????????????????.????...xi
INTRODUCTION?????????.?.?????????..??..??.?...1
LITERATURE REVIEW???????????...??.???????..??.3
Bottom soil-water interface????????????..???????..5
Pond soil development and Pond soil profiles?????????..???.7
Soil pH??????????????????...?????????9
Soil organic matter???????????????????...???.10
Nitrogen in Aquaculture Ponds??????????????....?.??12
Phosphorus in Aquaculture Ponds????????????..?..???13
Best management practice (BMPs)????????????.????..16
MATERIALS AND METHODS???????????????...?...???19
Soil and water samples??????????????????.???.19
Soil analyses?????????????????????.????.21
Water analyses????????????????????????..24
RESULTS?????????????????.?????...??????.25
DISCUSSION??????????????????????.??.??.?46
REFFERENCES???????????????????????..?..?...83
x
LIST OF TABLES
1. Number, areas, and depths of catfish, carp, and freshwater prawn culture pond
used in this study???????????????????????????..57
2. Distribution of ponds by age??????????????????????58
3. Physical characteristics, carbon, nitrogen, phosphorus, sulfur, and exchangeable
cation data for bottom soil samples from 42 catfish ponds in Thailand?????.?...59
4. Physical characteristics, carbon, nitrogen, phosphorus, sulfur, and exchangeable
cation data for bottom soil samples from 40 freshwater prawn ponds in Thailand??..?..60
5. Physical characteristics, carbon, nitrogen, phosphorus, sulfur, and exchangeable
cation data for bottom soil samples from 18 carp ponds in Thailand????..???..61
6 Major cations and minor elements in bottom soil samples from 42 catfish ponds
in Thailand??????????????????????????????.62
7. Major cations and minor elements in bottom soil samples from 40 freshwater prawn
ponds in Thailand??????????????.?????????????..63
8. Major cations and minor elements in bottom soil samples from 18 carp ponds in
Thailand?????????...????????????.?????????.64
9. Correlation coefficient (r) matrix for bottom soil variables from 100 ponds used
for culture of catfish, freshwater prawn, and carp in Thailand?????...????...65
10. Correlation coefficients (r) for relationships between pond age (X) and bottom
soil quality variables (Y) in 42 catfish ponds, 40 freshwater prawn ponds, and
18 carp ponds in Thailand????????????????????...??.?..66
11. Concentrations of water quality variables in 42 catfish ponds in Thailand???.?68
12. Concentrations of water quality variables in 40 freshwater prawn ponds in
Thailand?????????????????????????????.??69
13. Concentrations of water quality variables in 18 carp ponds in Thailand?????70
14. Lime requirement for aquaculture pond bottom soils based on soil pH?...?...??71
xi
LIST OF FIGURES
1. Map of Thailand showing location of sampling areas????..?????...?72
2. Histograms showing average concentrations of soil quality variables measure
in bottom soils from catfish, freshwater prawn, and carp ponds in Thailand. Bars
in each histogram represented by the same letter are not different (P > 0.05).
Data on concentrations of some variables in Tilapia pond soil in Thailand
(Thanjai, 2002) are provided for visual but not statistic????...???.???..73
3. Relationship between soil organic carbon concentration and soil total carbon
concentration in samples from ponds for production of catfish, freshwater prawn,
and carp in Thailand?????????.???????...????.????78
4. Relationship between soil total carbon concentration and soil total nitrogen
concentration in samples from ponds for production of catfish, freshwater prawn,
and carp in Thailand??????????...????????.??????.79
5. Histogram showing average concentrations of water quality variables in ponds
for culture of catfish, freshwater prawn, and carp in Thailand. Bars in each
histogram indicated by the same letter did not differ (P > 0.05)????...?.?....80
6. Relationship between magnesium concentration and calcium concentration in
water samples from ponds for catfish, freshwater prawn, and carp production in
Thailand????????????????????????????..?82
1
INTRODUCTION
Marine shrimp farmers generally believe that bottom soil quality in ponds
deteriorates over time because of sediment accumulation, declining pH, and increasing
organic matter concentration. Pond bottom soil management has received much attention
in marine shrimp culture (Boyd 1995; Limsuwan and Chanratchakool 2004), but much
less effort has been devoted to the condition and management of freshwater pond
bottoms. Discussions with practical aquaculturists indicate a general belief that bottom
soils have less importance in fish culture than in marine shrimp culture because shrimp
spend much time on the bottom while fish stay in the water column.
Studies of freshwater fish culture in the United States revealed that sediment
accumulated and organic matter and nutrient concentrations increased over time in
research ponds for sunfish Lepomis spp. and channel catfish Ictalurus punctatus (Munsiri
et al. 1995), commercial channel catfish production ponds (Tucker 1985; Steeby et al.
2004; Silapajarn et al. 2004), and bait minnow Notemigonus crysoleucas, Carassius
auratus, and Pinephales promelas ponds (Tepe and Boyd 2002). Although no soil
management practices had been applied to ponds in those studies, the main problem with
pond bottoms was the accumulation of soft sediment in the deeper areas after about 20
years of use.
A recent study of freshwater ponds for tilapia Oreochromis spp. in Thailand
demonstrated that the composition of bottom soil differed little between ponds less than 5
2
years old and those over 20 years old (Thunjai et al. 2004). The correlation coefficient
between pond age and soil organic carbon concentration was only 0.36. Liming materials
had been applied liberally to these ponds and sediment had been removed from some of
them. This study suggested that ponds for semi-intensive production of tilapia could be
used for at least 25 to 40 years with relatively little bottom soil management intervention.
One objective of the present study was to evaluate pond bottom soil management
techniques and pond bottom soil quality in ponds used for production of hybrid catfish
Clarias, carp Puntius spp. and freshwater prawn Macrobrachium rosenbergii in
Thailand. The other objective was to recommend better practices for pond bottom soil
management for use in Thailand.
3
LITERATURE REVIEW
Aquaculture has developed rapidly in South East Asia. To achieve efficient
production of fish, crustaceans, and other aquatic organisms, many natural resources have
been used. Feed, lime, manure and fertilizer play an important role to provide greater
yields; however, poor management of those materials can have negative effects on water
quality and the condition of pond bottom sediment (Munsiri et al. 1995).
A wide variety of organic materials have been used as pond manures.
Manures, fertilizers, and feeds applied to ponds to enhance production only can be
partially converted to animal biomass (Boyd and Tucker 1998). Large inputs of
manure into ponds can result in the accumulation of organic matter in sediment
(Munsiri 1995).
The most commonly aquacultural species in Thailand are hybrid catfish (Clarias
macrocephalus x Clarias gariepinus), Nile tilapia (Oreochromis niloticus), freshwater
prawn (Macrobrachium rosenbergii) and carp (Pantius spp.). Areerat (1987) stated that
the culture of Clarias in Thailand began in the late 1950s, and originally in the Bangkok
area. Clarias culture gave a higher annual income than other forms of agriculture. The
number of Clarias farms increased every year and people who lived nearby started to
complain about the bad smell of polluted water in catfish ponds. Finally, the
municipality forced the farm owners to move away from the Bangkok area (Sidthimunka,
1971). Most of the farms are now found in the central part of Thailand. The polluted
4
water was the result of using large amounts of pig, duck, cow and poultry excreta for
maintaining the productivity of natural food of Clarias and other species. The use of organic,
aquaculture waste products is common in Asian aquaculture.
Hickling (1962) gave the following list of organic materials used in pond
fertilization: livestock dung, leaves, grass and weeds; wastes from distilleries, tanneries,
dairies, and sugar refineries; cottonseed meal; and dry hay. Many other agricultural
wastes and by-products can be similarly useful (Boyd and Tucker 1998).
Zoccarato et al. (1995) conducted a 4-month trail in Northern Italy to evaluate the
possibility of recycling pig manure through carp production in ponds. There were three
treatments each for common carp and grass carp. The initial mean weights of fish were
450 g and 440 g, respectively. Pond were fertilized with pig manure supplied with feed;
or both as a percentage of fish biomass as follow: (A) 3% manure; (B) 1.5% manure and
1.5 % feed; (C) 3% feed. The final mean weight of fish were 570, 1,050 and 1,670 g for
common carp and 630, 1,330 and 1,480 g for grass carp in treatments A, B and C,
respectively. In Israel, ponds stocked with common carp, tilapia hybrids, silver carp and
grass carp received dry chicken manure as the only nutritional input at three different
rates. The standard rate was 50 kg dry matter/ha/day, increasing by 25 kg/ha/day every 2
weeks up to 175 kg/ha/day. The other two rates were half, and twice the standard. The
total yield and common carp growth rate and yield increased with manuring rate (Milsten
et al. 1991). The two studies summarized above clearly illustrate that manures can
increase fish production dramatically.
Studies supported by The Pond Dynamic/Aquaculture Collaborative Research
Support Program (PD/A CRSP) of the United States Agency for International
5
Development (USAID) have reported that there is a significantly higher level of fish
yield in ponds fertilized with chicken manure than in ponds fertilized with inorganic
fertilizer alone (Diana et al. 1990). The ranges of manure application were usually
from 50 to 100 kg dry weight/day, but rates as high as 200 kg/day have been used
(Boyd 1995).
Organic acids that leak from manures impart color to water. Manure particles
suspended in water become mixed with suspended clay particles, and bacterial activity
favors flocculation of clay particles (Irwin 1945). The decomposition of organic
matter from manure mineralizes nutrients, but large amounts of dissolved oxygen
are consumed by aquatic organisms to decompose organic matter. Dissolved
oxygen depletion often is a serious water quality problem in heavily manured ponds
(Boyd and Tucker 1998).
Boyd and Tucker (1998) provided a list of the problems that can result from using
manure as follows: difficulties in handling and storage of the manure, large quantities are
necessary to enhance production, high oxygen demand, large residues of sludge in pond
bottoms, discoloration of water by humic substances, manures have a high heavy metal
content, possibility of antibiotics in certain animal manures, possible off-flavor in fish,
potential of disease transfer to humans, and nonacceptance of products from
manure-based systems by some consumers.
Bottom soil-water interface
Reactions occurring at the bottom soil-water interface have a major influence on
dissolved oxygen concentration. Oxygen diffusion to the pond bottom is slow and often
6
at an insufficient rate to maintain aerobic conditions (Boyd and Tucker 1998). Wind and
mechanical aeration produce water currents and mix the water column to oxygenate the
bottom soil layers (Ritvo et al. 2004).
Boyd and Tucker (1998) stated that dissolved oxygen concentration in pond waters
depend on five major processes: air-water gas transfer, sediment oxygen uptake, animal
respiration, plankton respiration, and photosynthesis. The last two factors are considered
the major factors affecting the concentration of dissolved oxygen. Photosynthesis is the
largest source of oxygen while plankton respiration is the largest sink of oxygen. When
oxygen depletion occurs, other terminal electron acceptors are used to mediate the
decomposition of organic matter. This process leads to the production of reduced and
potentially toxic compounds such as reduced iron and manganese, nitrite, and hydrogen
sulfide and reduced organic compounds (Avnimelech and Ritvo 2003). The development
of anaerobic conditions clearly has adverse affects on water quality and fish production.
Boyd and Tucker (1998) revealed that in the absence of molecular oxygen, many
common heterotrophic bacteria could use nitrate or other oxidized forms of nitrogen
instead of oxygen as electron acceptor in respiration. They are the denitrifying bacteria.
Nitrate-based fertilizer can be used to supply nitrate for denitrification and sustain an
oxidized soil layer. However nitrate fertilizers are expensive and not used by fish
farmers in Thailand.
Ritvo et al. (2004) conducted an experiment to measure the effects of common
carp bioturbation on fish pond bottom soil. The results showed that bioturbation
generated by fish can improve bottom soil quality by increasing oxygen supply to a
greater depth in aquaculture pond bottoms, decreasing the concentration of toxic reduced
7
compounds, and sustaining a more efficient food web by recycling nutrients from organic
matter.
Pond soil development and Pond soil profiles
Sediment, mud, or soils are materials composing the bottoms of streams, lakes,
and ponds. These terms, often used interchangeably, describe the bottom material in
ponds (Boyd 1995). The original pond bottom is made of terrestrial soil, and when the
pond is filled with water the bottom becomes wet. At this point, the bottom soil is a
mixture of solid material and water that is often called mud. Solids settle from the water
and cover the pond bottom with loose mineral and organic material known as sediment.
During construction, the surface soil is scraped from the area to be the pond
bottom and used as earth fill for embankments. The newly finished pond bottom usually
is subsoil low in concentrations of organic matter and nutrients. Pond bottoms are often
high in clay content and low in pH in tropical and subtropical areas with highly leached
soils.
Once a pond is filled with water, the transformation of the pond bottom into a
pond soil begins. Erosion from the watershed brings inorganic matter and suspended soil
particles. Wave action, water currents from mechanical aeration, and rainfall erode
embankments and shallow edges to suspend soil particles that then settle in deep areas of
the pond. Fertilizers, manures, and feeds cause phytoplankton blooms that increase the
concentration of suspended organic particles (Boyd et al 2002). The sediment layer may
be several to many centimeters thick in older ponds. The four most important features of
soil to aquacultural production are texture, organic matter content, pH, and nutrient
8
concentrations (Boyd 1995).
In contrast to terrestrial soil, pond soils develop distinct profiles within a few
years, while terrestrial soils take many years to develop a soil profile (Boyd 1995).
The major factors influencing pond soil development appear to be sedimentation,
organic matter input, and wetting and drying processes between crops (Thunjai
2002).
Pond soils develop profiles with characteristic horizons that can be identified
easily in pond bottom cores where waters are deeper than 75 cm and especially in older ponds
(Munsiri 1995). The pond soil profiles include the flocculent layer called the F horizon
that is recently settled material laying on the bottom above the soil-water interface.
Immediately below the F horizon is the soil-water interface and the top of the first
sediment layer. The entire first layer is called the S horizon. The uppermost part of the S
horizon is called S
o
horizon. It is a thin, oxidized (aerobic) surface sublayer has a low
bulk density (<0.3 g/cm
3
), and it is mixed by water currents and biological agents. The
deeper, reduced sublayer beneath the S
o
horizon is called the S
r
horizon. It is a thicker,
anaerobic and not as well mixed as the S
o
sublayer. Below the S horizon is the M
horizon. This layer is not mixed and denser than the S horizon. The transition from the
M horizon to the original pond bottom (P horizon) is named the T horizon. (Munsiri
et al. 1995). The original pond bottom beneath the sediment is the P horizon.
Thunjai (2002) reported that total sediment depth in tilapia ponds in Samutprakarn
Province,Thailand ranged from 2.7 to 59.3 cm, the S horizon averaged 7.22 cm in depth
and ranged between 1.1 to 39.8 cm. Bulk density values were 0.08 to 0.35 g/cm
3
.
Averaged bulk density was 0.23 g/cm
3
.
9
+
Soil pH
Soil pH is a measure of the activity of hydrogen in the soil solution. The pH is the
negative logarithm of the hydrogen ion activity (H
+
) and may be expressed by the
following equation:
pH = -log (H
+
)
Soils are referred to as being acidic, neutral, or alkaline (basic), depending on their pH
values on a scale from 0 to 14. A pH of 7 is neutral; less than 7 is acidic; greater than 7
is alkaline (MaCauley et al. 2003).
Before biological activity adds to or removes carbon dioxide from water, the
initial pH of pond waters in equilibrium with atmospheric carbon dioxide is a function of
the total alkalinity of the water. Low alkalinity waters are acidic, moderate alkalinity
water are near neutral, and high alkalinity waters are basic. The activities of plants,
animals and bacteria cause the pH to cycle diurnally. High pH (>9) is normally found
in the afternoon in aquaculture ponds when conditions favor rapid photosynthesis and
removal of carbon dioxide (Boyd and Tucker 1998).
The pH has both direct and indirect effects on other environment variables.
For example, the proportion of total ammonia nitrogen (NH
4
+ NH
3
) existing in the
toxic, un-ionized form (NH
3
) increases as the pH increases. In water with low total
alkalinity, pH is low resulting in a shortage of inorganic phosphorus and carbon
dioxide for plant growth (Boyd and Tucker 1998). However, in water of low
alkalinity, rapid photosynthesis sometimes causes a dangerously high pH. Ponds
10
often are treated with liming materials to increase alkalinity.
Thunjai (2002) reported that tilapia ponds in Changrai and Samutprakarn,
Thailand had average soil pH of 7.43 and 7.50, respectively. The soil pH were between
6.63 and 9.40 in Changrai and 6.62 and 7.90 in Samutprakarn.
Banerjea (1967) suggested that the best pH range for pond soils is 6.5 to 7.5 while
5.5 to 8.5 is the acceptable pH range. Boyd (1988) also pointed out that optimum pH for
good health and high growth rate of freshwater animals is between 6.5-9.0.
Soil Organic Matter
Jim?nez-Montealegre et al. (2002) stated that soil organic matter (SOM) is a
heterogeneous mixture. It is composed of products that result from microbial and
chemical transformations of organic remains. The increase or decrease of organic matter
in the sediments varies between the rate of in situ production and allochtonous input of
organic material that settles to the bottom before being mineralized, and the rate of
organic matter mineralization in the sediment. The size, shape, and density of particles
and water density and viscosity were used to determine the rate of sedimentation of
particulate matter (J?rgensen 1989). Small particles such as clay and finely divided
organic matter settle very slowly, while sand and silt settles rapidly.
Boyd et al. (2002) stated that soil organic matter is about 45 to 50% carbon, so a
rough approximation of organic matter may be obtained by multiplying soil organic carbon
by two. Soil organic carbon concentrations rapidly increased to 2 or 3% in the S and M
horizons, but they remain low in soil from greater depth in pond bottoms (Munsiri et al.
1995).
11
The concentrations of organic matter in aquaculture pond soils range from less than
1% in highly leached mineral soils in extensive ponds to over 20% in ponds constructed on
organic soils (Boyd 1995). In terms of their relationship to aquaculture, Boyd et al. (2002)
provided the following classification of pond soil organic matter concentration:
Organic carbon (%) Comment
>15 Organic soil
3.1 to 15 Mineral soil, high organic matter content
1.0 to 3.0 Mineral soil, moderate organic matter
content, best range for aquaculture
<1 Mineral soil, low organic matter content
Comparing fertilized ponds and unfertilized ponds, fertilized ponds had higher
nutrient concentrations and larger organic carbon influxes than unfertilized ponds
(Thunjai 2002). Channel catfish ponds with feeding have larger nutrient and organic
carbon influxes than do fertilized sportfish ponds (Boyd 1995). When organic matter and
nutrient loading of ponds is discontinued, the nutrients dissolved in the water columns
decline quickly and limit the growth of phytoplankton (Diana et al. 1990).
According to Thunjai (2002), for 17 tilapia ponds in Changrai,Thailand,
organic carbon averaged 2.22 %. The organic carbon was between 1.08 and 3.08 %.
Boyd et al. (1994) reported the average organic carbon concentrations in 358 freshwater
ponds from Honduras, Rwanda, Bhutan, and the United States and 346 brackish
water ponds from Thailand, Ecuador, Philippines, and Venezuela. The averages
12
+
were remarkably similar, 1.78% and 1.79%, respectively. However, some samples
from freshwater ponds contained up to 8% organic carbon, and some samples from
intensive brackish water shrimp ponds contained more than 10% organic
carbon.
Banerjea (1967) concluded that the acceptable range of organic carbon for
aquaculture ponds is 0.5 to 2.5 %. The best range is 1.5 to 2.5 %. According to
Boyd (1995), when soil pH is below 7 and organic carbon concentrations are above
2.5% (around 5% organic matter) within the S horizon, natural productivity that
supports fish growth decreases in ponds.
Nitrogen in Aquaculture Ponds.
Hargreaves (1998) stated that fertilizer and formulated feed are an important
source of nitrogen to ponds. An excess of nitrogenous inputs can lead to the deterioration
of water quality. Nitrogenous compounds such as nitrite and ammonia are potentially
harmful to aquatic species. Fish excreta and sediment flux from mineralization of
organic matter and diffusion of reduced sediment are usually important sources of
ammonia in the ponds. Phytoplankton uptake and nitrification are considered the
principle sinks of ammonia. Boyd and Tucker (1998) stated that application of
nitrogen to fertilize ponds usually is in the form of urea, which rapidly hydrolyzes
to ammonia, salts of ammonium and nitrate, or organic nitrogen in manure. Ammonia
(NH
3
) and ammonium (NH
4
) normally exist in the water in a temperature and
pH dependent equilibrium. ammonium (NH
4
) normally exist in the water in a
temperature and pH dependent
+
13
-
+
NH
4
+ OH = NH
3
+ H
2
O
As the pH increases, the proportion of NH
3
increases (Boyd and Tucker 1998).
Denitrification is an important pathway of nitrogen removal from ponds.
It occurs in anaerobic sediment, although the rate of this process is relatively low because
nitrification and denitrification are coupled in sediment and sediment nitrification is
limited by oxygen penetration into sediment (Hargreaves 1998).
Phosphorus in Aquaculture Ponds
Boyd and Tucker (1998) pointed out that phosphorus is a key nutrient
limiting aquatic productivity for most natural waters. Compared to natural waters,
aquaculture pond waters are often enriched with phosphorus, and the discharge of
ponds may pollute receiving water with phosphorus compounds and lead to
excessive plant growth. Pond sediment interacts with the water column affecting
the phosphorus cycle in natural waters (Reddy et al. 1999). This interaction is also
a major factor in pond aquaculture (Boyd and Musig 1981; Boyd 1995).
Boyd and Tucker (1998) stated that plants assimilate phosphorus as
orthophosphate ions, which may be considered as ionization products of orthophosphoric
acid. (H
3
PO
4
):
H
3
PO
4
=
H
+
+ H
2
PO
4
pK
a,1
= 2.1
H
2
PO
4
=
H
+
+ HPO
4
pK
a,2
= 7.2
HPO
4
=
H
+
+ PO
4
pK
a,3
= 12.3
2- 3-
2-
-
-
14
Boyd and Tucker (1998) also revealed that at a normal environmental pH range in
aquaculture ponds of 7 to 9, most of the orthophosphate exists as a mixture of H
2
PO
4
and
HPO
4
, that can be considered equally available to plankton. Phytoplankton cells and the
particulate matter or detritus of algal origin are the largest phosphorus fraction in
aquaculture pond waters.
Pond soil can be considered a source or a sink for phosphorus, and aerobic soils
are particularly important as a phosphorus sink (Boyd and Musig 1981). Phosphorus
normally reacts with aluminum and calcium in sediments to form complexes with
relatively low solubilities under aerobic conditions. The vital key that affects the
solubilities of calcium and aluminum bound phosphates is pH. Aluminum normally
reacts with phosphorus under acidic condition while calcium phosphates form in
alkaline soil. Iron phosphates in sediment become highly soluble at low pH and low
redox potential (Eh) (Rowan 2001; Boyd and Tucker 1998).
At high pH values, phosphorus is adsorbed to calcite and precipitated as
hydroxyapatile. When pH is decreasing, calcium phosphates increase in solubility
(Golterman 1995).
The solubility of gibbsite (aluminum hydroxide) is regulated by pH. It is a
common aluminum compound in soil (Adams 1971) and dissolves as follows:
Al(OH)
3
= Al
3+
+ 3OH
-
Thus, a decreasing pH favors solubility of gibbsite (and other aluminum
oxides and hydroxides in soil). Aluminum ions from the dissociation of gibbsite or
-
2-
15
other aluminum compounds reacts with phosphorus to form insoluble aluminum
phosphate:
Al
3+
+ H
2
PO
-
4
= AlPO
4
+ 2H
+
Boyd and Tucker (1998) summarized literature showing that mud removed
phosphorus from water in the form of iron, aluminum, and calcium phosphate compounds
with limited solubilities. Solubility of aluminum and iron phosphates increases with
decreasing pH while the solubility of calcium phosphate compounds decrease with
increasing pH. Formation of iron phosphates depends on the amount of oxygen in mud.
Under aerobic conditions, much of the phosphorus is basically combined with amorphous
ferric (Fe
3+
) oxyhydroxide gels or as phosphorus coprecipitated in coating of ferric oxide
surrounding silt or clay particle. Under anaerobic conditions, ferric iron is normally
reduced to soluble ferrous (Fe
2+
) iron and the associated phosphorus is soluble.
Bohn et al. (2001) revealed that the calcium phosphate series ranges from the least
soluble Ca
5
(OH, F)( PO
4
)
3
(apatite) through Ca
4
H(PO
4
)
3
(octocalcium phosphate) and
CaHPO
4
to the most soluble form Ca(HPO
4
)
2 .
Shrestha and Lin (1996) pointed out that the amount of phosphorus loss to
sediment is usually different among aquatic culture systems. Boyd (1985) demonstrated
that 55 % of phosphorus in feed applied to channel catfish ponds was adsorbed by bottom
soil. In earthen raceways for channel catfish culture, 44 to 46 % added phosphorus was
adsorbed by sediment (Worsham 1975). In eel pond culture, sediment removed 40 to
50 % of added phosphorus (Chiba 1986).
16
Dobbins and Boyd (1967) suggested that the application of phosphorus in
fertilized ponds should be based on phosphorus concentration in bottom soil and other
bottom soil characteristics. According to Masuda and Boyd (1994), total phosphorus
concentrations in clayey bottom soils of ponds at Auburn, Alabama, were greater in deep
water than shallow water areas. The highest phosphorus concentration was in the 5 to 10
cm soil layer. However, phosphorus accumulated above its original concentration to
depths between 20 to 40 cm. The average depth to which phosphorus concentration had
increased above its original level in bottom soils of ponds at Auburn University was 36.8
cm (Masuda and Boyd 1994).
Thunjai (2002) reported high phosphorus concentrations in bottom soil of tilapia
ponds at Samutprakarn, Thailand. The extractable phosphorus concentration ranged from 78
to 944 ppm with an average of 217 ppm. The water extractable phosphorus concentration
ranged between 5 to 31 ppm. The average was 9 ppm. He concluded the high
concentrations resulted from applying phosphorus fertilizer to ponds over several years.
Best management practices (BMPs)
BMP isBMPs are the most economically feasible and technically practical methods of
reducing environment impacts. For example, BMPs provide means to prevent overfeeding of
fish to avoid excessive nutrient loading in ponds, and to minimizing the environment impact
from effluent released from ponds to receiving water (Boyd et al. 2003).
Thunjai (2002) pointed out that high soil organic matter, loss of the oxidized layer
and accumulation of soft sediment, are the major concerns for bottom soil management in
aquaculture.
17
Aquaculture pond bottom soils receive large amounts of nutrients and organic
matter from erosion, uneaten feed and fertilizer. It is generally thought that nutrients and
organic matter tend to accumulate in the bottom soils as pond age increases (Boyd 1992).
High nutrient concentrations are not undesirable in pond soil, but large amounts of
organic matter can have adverse effects (Boyd 1995). Thus, BMPs are needed for
preventing excessive accumulation of organic matter in pond soils.
According to pond studies by Boyd and Teichert-Coddington (1994), when the
ponds were completely dried, the decomposition rate of organic matter in pond soil
increased. Boyd (1995) suggested that air penetrates into the cracks in the dried pond
bottom enhancing oxygenation and improving the decomposition of organic matter.
Oxygen supports microbial decomposition of organic matter and chemical oxidation of
reduced substances.
Seo and Boyd (2001) reported that drying and tilling ponds at Auburn,
Alabama could decrease the concentration of phosphorus and nitrogen in pond water
during the next crop.
Liming pond bottoms is one of the methods to improve bottom soils for
aquaculture. According to Thunjai (2002), liming material should be applied after
each crop to maintain soil pH in the range of 7 to 8. He suggested that agricultural
limestone should be applied according to soil pH or total alkalinity of water in old
ponds.
Pond draining and the discharge of effluents through ditches to streams can
cause erosion and suspension of soil particles (Schwartz and Boyd 1994). Thus, ponds
should be drained slowly to lessen water velocities and reduce the potential for
18
erosion. Ditches should be constructed to avoid excessive water velocity and above
water areas protected from erosion by grass cover or other means.
19
MATERIALS AND METHODS
The ponds for this study were selected in Supanburi Province in central Thailand
(Fig. 1) with the assistance of the Thailand Department of Fisheries. There were 42
ponds for culture of hybrid catfish Clarias macrocephalus ? C. gariepinus, 40 ponds for
culture of freshwater prawn, and 18 ponds for culture of carp. The fish and prawn farms
were visited in February 2002, and information on pond features, culture methodology
and production data, and bottom soil management were obtained by interviewing the
owners. Water and soil samples also were collected. Additional information on
production practices were requested from biologists in the Department of Fisheries or
obtained from publications on practical aquaculture in Thailand (Brohmanonda and
Sahavacharin 1985; Areerat 1987).
Soil and water samples
Bottom soil samples were taken with 5-cm diameter, clear plastic, core liner tubes
(Wildlife Supply Company, Buffalo, New York, USA). Workers waded into ponds and
inserted the tubes into the bottoms by hand at five places in the deep end of each pond
where water was 1 to 1.5 m in depth. Tubes were hammered with a wooden mallet to
force them into the original pond bottom soil or P horizon (Munsiri et al. 1995). Tubes
were beneath the water, and a plastic cap was put on the upper end so that they could be
20
withdrawn from the bottom with soil cores intact and undisturbed by water movement.
Caps were placed on the bottom ends of tubes before they were lifted from the water to
prevent soil cores from slipping out. Tubes were maintained in a vertical position to
avoid disturbing the surface of the core.
Water was siphoned from the tubes by aid of flexible, 0.75-cm diameter latex
tubing leaving only 1 to 2 cm of water above the core surfaces. The thickness of the S
horizon and total sediment thickness (S and M horizons) was measured with a ruler
(Munsiri et al. 1995).
Soil cores were pressed upward in the core liner tubes using a core removal tool
(Wildlife Supply Company). A core segment ring made from a piece of core liner tube
(Munsiri et al. 1995) was placed on top of the core liner tube containing the soil core.
The part of the soil core comprising the S horizon was pressed into the core segment ring.
The S horizon was separated by inserting a thin, 10-cm wide spatula between the bottom
of the core segment ring containing the S horizon and the core liner tube containing the
rest of the core. The S horizon from one core in each pond was placed in a tared soil
moisture canister. The S horizons from the other four cores from each pond were
combined in a single plastic container to make a composite sample from each pond. The
samples were held in an insulated ice chest for 6 to 12 h until they were transferred to
drying ovens.
Water samples were dipped from the surface of each pond. These samples were
stored in tightly-sealed, 1,000-mL plastic bottles.
21
Soil analyses
Soil samples in tared canisters were dried to constant weight at 102
o
C, and the dry
bulk density was calculated (Blake and Hartge 1986) in grams per cubic centimeter.
Composite soil samples were dried at 60
o
C for 72 h in a mechanical convection oven.
The dry soil samples and water samples were shipped to Auburn University for further
analyses.
Dry samples were pulverized with a mechanical soil crusher (Custom Laboratory
Equipment, Inc., Orange City, Florida, USA) to pass a 40-mesh (0.425-mm) sieve and
stored in plastic containers.
Soil pH was measured with a glass electrode inserted into a 1:1 mixture of dry,
pulverized soil and distilled water (Thunjai et al. 2001). The concentration of total
carbon was measured with a Leco Model EC 12 induction furnace carbon analyzer (Leco,
St. Joseph, Michigan, USA). Organic carbon was measured by the Walkley-Black
sulfuric acid (H
2
SO
4
)-potassium dichromate (K
2
Cr
2
O
7
) oxidation procedure (Nelson and
Sommers 1982). Total nitrogen concentrations were determined with a Leco Carbon-
Hydrogen-Nitrogen Analyzer CHN 600 by the Auburn University Soil Testing
Laboratory.
Total phosphorus was measured by the dry ash method (Tavares and Boyd 2003).
In this procedure, 1.00 g of dry soil was placed in a 10-mL high-form crucible, covered
with a pyrex watch glass, and ashed at 450
o
C for 4 h or until the ash was a grayish-white
color. After cooling, the ash was treated with 10 mL of 1 N nitric acid (HNO
3
). The
crucible was placed on a hotplate and heated until the nitric acid evaporated. Next, 10
mL of 1 N hydrochloric acid (HCl) was added to the ash, and the temperature was
22
increased until the hydrochloric acid boiled. The acid and residue were transferred to
a 100-mL volumetric flask and made to volume with distilled water. The sample was
filtered through an acid-washed, Number 40 Whatman filter paper. The filtrate was
analyzed for phosphorus by the vanadomolybdate method (Olsen and Sommers 1982).
Water-soluble phosphorus was measured by shaking 2-g soil samples with 100 mL of
distilled water for 24 h, removing the soil by filtration through a Whatman Number 40
filter paper, and measuring phosphorus concentrations in the extracts by the ascorbic acid
method (Boyd and Tucker 1992). Dilute-acid soluble phosphorus was extracted from
1.0-g soil samples with a solution of 0.05 N hydrochloric acid and 0.025 N sulfuric acid.
Extracts were filtered through Whatman Number 40 filter paper, and dilute-acid
extractable phosphorus was measured with a Jarrel-Ash ICAP 9000 Plasma
Spectrophotometer by the Auburn University Soil Testing Laboratory. Phosphorus also
was extracted from soil samples by the Lancaster (Mississippi) method for calcareous
soils (Hue and Evans 1986). The extractant was made by adding 90 mL glacial acetic
acid (CH
3
COOH), 6.5 g of malonic acid [CH
2
(CO
2
H)
2
], 120 g of malic acid
[CH
2
CHOH(CO
2
H
2
)
2
], and 1.38 g of ammonium fluoride (NH
4
F) to 750 mL of
deionized water. The solution was mixed well to dissolve reagents, and 3.0 g of
aluminum chloride (AlCl
3
) were added and the solution mixed again. The pH was
adjusted to 4.0 with ammonium hydroxide (NH
4
OH), and the solution was diluted to
1,000 mL with deionized water. Extraction consisted of placing 5-g soil in 20 mL of
extracting solution and shaking at 180 oscillations/min for 5 min. The extracts were
passed through a Whatman Number 40 filter paper. Phosphorus in filtrates was measured
by the vanadomolybdate method (Olsen and Sommers 1982).
23
Soil sulfur was measured by the method of Bardsley and Lancaster (1960).
A 2.5-g soil sample was mixed with 0.5 g of sodium bicarbonate (NaHCO
3
) in a crucible,
and 0.5 g of sodium bicarbonate was spread over the surface of the sample. The crucible
and its contents were placed in a muffle furnace for 3 h. After cooling, the contents of
the crucible were transferred to a 50-mL Erlenmeyer flask. A 25-mL volume of
extracting solution containing 4.6 g of monosodium phosphate (NaH
2
PO
4
?H
2
O) dissolved
in 2 N acetic acid was added, and the flask was agitated for 30 min at 150
oscillations/min. Following filtration through a Whatman Number 40 filter paper, the
solution was analyzed for sulfate-sulfur by the barium chloride method. The sulfur
concentration in the soil was calculated.
Major cations and minor elements were extracted from soil samples with a
solution of 0.05 N hydrochloric acid and 0.025 N sulfuric acid (Hue and Evans 1986).
Ionic concentrations in extracts were measured with a Jarrel-Ash ICAP 9000 Plasma
Spectrophotometer by the Auburn University Soil Testing Laboratory.
The cation exchange capacity (CEC) was determined by saturating exchange sites
with potassium by shaking soil samples in a 1 N potassium chloride (KCl) solution.
After washing the soils free of excess potassium chloride solution, the potassium was
exchanged with ammonium by shaking samples in a neutral, 1 N ammonium chloride
(NH
4
Cl) solution. Potassium displaced by ammonium was measured in the ammonium
chloride solution using an Atomic absorption Spectrophotometer. The amount of
potassium displaced in milliequivalents per 100 g of soil was equal to the cation
exchange capacity (CEC) of the soil sample.
24
Major cations, calcium, magnesium, sodium and potassium, and minor elements,
aluminum, iron, manganese, zinc, copper, boron, cadmium, chromium, and lead,
were extracted from soil samples with dilute, double acid solution (0.05 N hydrochloric
acid + 0.025 N sulfuric acid as described by Hue and Evans 1986). Concentrations of
elements in extracts were determined by ICAP.
Exchangeable acidity was measured from the pH change in a solution containing
20 g soil and 40 mL buffer. The buffer was made by dissolving 10 g p-nitrophenol, 7.5 g
boric acid (H
3
BO
4
), 37 g potassium chloride (KCl), and 5.25 g potassium hydroxide
(KOH) in distilled water, adjusting the pH to 8.00 ? 0.01, and diluting to 1,000 mL (Hue
and Evans 1986). A pH change of 0.10 units in 40 mL of this buffer equals 0.08 mEq of
exchangeable acidity.
Particle-size analysis was conducted by a simplified hydrometer method
described by Weber (1977). The sample was suspended in a 0.5% solution of
hexametaphosphate [(NaPO
3
)
6
] in a 1-L sedimentation cylinder and hydrometer readings
were made after 40 sec to allow estimation of percentage clay plus silt and after 2 hr to
permit estimation of percentage clay. Silt was estimated as clay plus silt minus clay and
sand was calculated as 100% minus percentage clay and silt.
Water analyses
Water samples were analyzed for total alkalinity (acidimetry), total hardness
(titration with ethylenediaminetetraacetic acid), chloride (mercuric nitrate-
diphenylcarbazone method), sulfate (barium chloride turbidimetry), and major cations
(ICAP) following protocol described by Clesceri et al. (1998).
25
RESULTS
Study area
The study area was situated within the Central Plain of Thailand. The terrain was
mostly flat, and the land form resulted from low alluvial terraces of both old and recent
alluvium (Khaewreenrom 1990). Soils can be classified as inseptsols, and they can vary
from very sandy to heavy clays. The soils also can vary greatly in pH with some areas
having extremely acidic soils and others with neutral to slightly alkaline soils. Annual
rainfall is about 1,400 mm. There is a distinct wet season from June to September with
relatively little rainfall during the rest of the year. Average annual air temperature within
the Central Plain is 28 to 30
o
C. The hottest weather corresponds to the later part of the
dry season and the rainy season.
The Central Plain is primarily an agricultural region with rice production being
the major crop. There are many canals that serve as a source of irrigation water. These
canals also are the water source for aquaculture ponds in the Central Plain.
Ponds
The ponds were made by constructing earthen embankments around the area in
which water was impounded. Carp and freshwater prawn ponds tended to have
26
larger water surface areas than catfish ponds, but catfish ponds tended to be deeper than
other ponds (Table 1). The inside slopes of embankments of some catfish ponds were
lined with stone to minimize erosion. Water for filling ponds was either pumped from
canals into ponds using ?long-tailed? pumps (Yoo and Boyd 1993) or gates with dam
boards (monks) were installed to allow water from canals to enter ponds. Ponds were
emptied using pumps or gates.
Ponds varied in age from 1 year to 30 years (Table 2), but few ponds were more
than 15 years old. Over 60% of ponds were 10 years or less in age.
Production methods
The description of production methodology will be given separately for each of
the three species. The description will begin at the end of harvest, and pond preparation
for the next crop will be the first activity described.
Catfish
Following draining and harvest, most farmers treat the wet pond bottom with lime
(burned limestone) at about 600 to 800 kg/ha. This treatment apparently is intended
mainly to temporarily raise the soil pH and effect disinfection. However, it also has a
more lasting effect by neutralizing soil acidity and increasing the total alkalinity and total
hardness of pond waters (Boyd and Tucker 1998). Bottoms usually are allowed to dry
from 10 to 14 days, and at about 2-year intervals, sediment is removed manually by
aid of shovels from the deep ends of ponds. This sediment usually is placed on
the embankments. After dry-out, burned lime was spread over bottoms at 800 to 1,600
27
kg/ha. The pond was then filled to a depth of 50 to 80 cm with water and fish were
stocked. The water level gradually was increased to the full-pond depth of 1.5 to 2.5 m
as fish grew.
Stocking rates ranged from 30 /m
2
with large fingerlings to about 300 /m
2
with
small fingerlings. Fertilizer was not used in ponds, but chicken slaughterhouse wastes
were minced and applied to ponds daily at roughly 10% of estimated fish body weight.
However, feeding with slaughterhouse waste was based largely on each farmer?s
judgment, and records of typical annual inputs to ponds were not available. Some
farmers also applied pelleted feed twice daily. The feed contained 35% crude protein,
and daily feed inputs for fingerlings, juvenile, and adult fish probably were about 8 to
10%, 4 to 6%, and 1 to 2%, respectively. Again, farmers did not keep good records, and
estimates of typical annual inputs could not be made.
Water quality deteriorates rapidly in catfish ponds because of the large inputs of
waste and feed. Waters had visibly high concentrations of suspended organic matter and
often were black in color. Mechanical aeration was not used to increase dissolved
oxygen concentrations, but these catfish are air-breathers and can tolerate low dissolved
oxygen concentrations quite well. Water exchange was used to improve water quality.
Typically, farmers added about 20% of pond volume every 3 days to flush low quality
water from ponds.
Catfish were harvested after 4 to 6 months when they have reached 150 to 300 g
in size. The ponds were drained, and the fish captured by scoop nets. Typical production
was 60,000 to 80,000 kg/ha/year.
28
Freshwater prawn
After draining for final harvest, accumulated sediment was removed from the
deeper areas of the pond by aid of a tractor. The bottoms were dried for about 2 weeks.
This procedure kills disease organisms, wild fish, and other organisms that can persist in
ponds between crops. Where pond bottoms could not be dried, rotenone was applied to
bottoms to kill wild fish and other organisms. Pond soils were limed at 60 to 625 kg /ha.
Following refilling with water, ponds were stocked with prawns at 25 to 75 /m
2
.
Fertilizers were not used, and prawns were provided a commercial, pelleted feed
containing 40 to 45% crude protein. Daily feed inputs declined from about 8 to 10% of
body weight for recently stocked prawn to about 2% of body weight for adult prawn.
Daily feed input reached 50 to 70 kg /ha.
Water quality is a critical factor in freshwater prawn culture. When dense blooms
of phytoplankton develop in ponds, dissolved oxygen concentration often declines.
Farmers exchanged water to flush out excess nutrients and plankton, but mechanical
aeration was not used to enhance dissolved oxygen concentrations. The normal water
exchange program was given as follows:
? During the first 2 months of culture, water exchange was not necessary, but water
was applied weekly to gradually fill ponds completely.
? During the remainder of the grow-out period, water was exchanged 2 to 4 times
per month by removing one-third of the pond water and replacing it with water
from the supply canal.
29
? Emergency water exchange was applied anytime that deteriorating water quality
was considered harmful to prawns.
Water exchange also was thought to improve prawn growth by aiding the molting
process.
Most prawn farmers applied microbial inocula to ponds. This treatment was
thought to improve microbial degradation of waste from feed. In addition, farmers
dragged a chain over the pond bottom two or three times during the period when
water was discharged for water exchange. This procedure was considered useful in
suspending organic particles so that they could be flushed from ponds. However,
farmers indicated that the chain dragging procedure was not appropriate where large
amounts of waste had accumulated on the bottom. In these cases, a small hand-
operated suction device (dredge) was used to remove accumulated wastes and soft
sediment.
Prawns grow at variable rates, but after 6 months of culture marketable-sized
prawn usually can be found in ponds. Seines with 4- to 5-cm mesh openings were
used to partially harvest prawns at intervals. The seine was stretched across the
width of the pond and pulled the entire length of the pond. Most small prawns
passed through the mesh openings, but any small prawns caught in the seine were
returned to the pond. After 11 to 12 months of culture, ponds were drained
completely to complete the harvest of prawns. Normal production usually was
1,800 to 3,000 kg/ha/year (crop).
30
Carp
There were two systems of carp culture. One system involved production of carp
in relatively small ponds. These ponds were drained each year for harvest. Sediment
was removed when considered necessary and usually at 3- to 5-year intervals. Bottoms
were dried for 2 or 3 weeks and ponds refilled. Data on stocking rate could not be
obtained. Chicken house wastes were applied to these ponds, but the farmers could not
provide an estimate of the amount used. Pelleted feed containing 25% crude protein also
was applied to ponds at 1 to 2% of body weight one time per day. Mechanical aeration
was not applied, and farmers only used water exchange when water quality deteriorated
to dangerous levels in ponds. Fish were harvested by draining ponds. Production usually
was about 3,000 to 4,000 kg/ha/year.
The other carp production system was integrated with chicken farming. The chicken
houses were constructed over relatively large (2 to 5 ha) carp ponds, and waste feed and feces
from chicken cages fell into the pond. Other inputs of fertilizers and feeds were not made to
ponds. Mechanical aeration was not applied, and water exchange was only applied in water
quality emergencies. Fish were harvested by seining, and 4,000 to 6,000 kg/ha typically were
removed per year. After 3 to 5 years, ponds may be completely drained to permit sediment
removal.
Bottom soils
The means, standard deviations, and ranges for soil variables were presented by
culture species for sediment physical characteristics, pH, carbon fractions, nitrogen,
phosphorus fractions, sulfur, and cation exchange capacity and exchangeable acidity
31
(Tables 3, 4, and 5). Tables 6, 7, and 8 contain information on major cations,
calcium, magnesium, potassium, and sodium, and minor elements, aluminum, iron,
manganese, zinc, copper, and boron concentrations. The variables were compared
among culture species, including tilapia ponds in Thailand (Thunjai et al. 2004), in
Fig. 2.
Sediment physical characteristics
Sediment depth was highly variable among ponds for all three culture species
(Tables 3, 4, and 5). Much of this variation likely was related to the length of time that
had passed since sediment was removed from individual ponds. Mean sediment depth
ranged from 11.9 cm in freshwater prawn ponds to 33.4 cm in carp ponds. Sediment
depth was significantly greater (P < 0.05) in carp ponds than in ponds for prawn and
catfish (Fig. 2). This difference was related to less frequent removal of sediment from
carp ponds. Total sediment thickness in tilapia ponds was 16 cm (Fig. 2), and more
similar to catfish and prawn ponds than carp ponds.
The thickness of the S horizon also varied greatly among ponds for all species
(Tables 3, 4, and 5). Mean S horizon thickness was greater in carp ponds than in catfish
and prawn ponds (P < 0.05). Tilapia ponds had an average S horizon thickness of 7 cm
(Fig. 2) ? similar to catfish and prawn ponds.
Dry bulk density was greater (P < 0.05) in sediment of carp ponds than in that of
catfish and prawn ponds. Tilapia ponds had an average dry bulk density of 0.23 g /cm
3
(Fig. 2). Thus, average bulk density of the S horizon ranged from 0.17 to 0.28 g /cm
3
in
ponds for the culture of four, freshwater species in Thailand. Munsiri et al. (1995)
32
defined the S horizon as the upper, well-mixed layer of sediment with a dry bulk density
of 0.3 g /cm
3
or less. Results of this study and the findings for tilapia ponds in Thailand
support the bulk density limit in the definition of the S horizon suggested by Munsiri et
al. (1995). The S horizon is the layer that is most active in exchange of substances
between sediment and water, and it is thought to have a large influence on pond water
quality (Boyd 1995).
The particle size distribution in bottom soils differed greatly among ponds (Tables
3, 4, and 5). Sand concentrations were low averaging between 0.21 and 13.72%. Catfish
and carp ponds were similar in sand concentration and had more sand (P < 0.05) than
prawn ponds. Average silt concentrations were between 53.2% and 63.6%, and prawn
ponds had a greater percentage of silt than catfish or carp ponds. Average clay
concentrations were from 33.1 to 38.3%, and catfish ponds had a greater percentage of
clay than carp ponds. In general, pond soils contained more than 30% clay and 50% silt.
The differences in percentages of sand, silt, and clay probably were related to original
characteristics of pond bottom soil rather than the influence of aquaculture. In spite of
the differences among ponds in percentages of sand, silt, and clay, soil texture based on
average particle size was silty clay loam for the three groups of ponds, and most
ponds actually had soils of this texture. However, a few ponds used for catfish
culture had sandy loam soils and several ponds for all species had silt loam soils.
The texture classes found in the ponds are suitable for pond aquaculture (Boyd 1995).
Thunjai et al. (2004) did not determine the particle-size distribution of tilapia pond
soils in Thailand.
33
pH
Soil pH ranged from 3.81 in a carp pond to 7.82 in a catfish pond (Tables 3, 4,
and 5). However, average pH did not differ (P > 0.05) among the three types of ponds
(Fig. 2). Moderate amounts of liming materials had been applied annually to the ponds,
but most ponds still had slightly acidic soils with pH values between 6 and 6.8. In tilapia
culture, liming rates usually were 3 or 4 times greater than those used in the ponds for
this study. Soil pH in tilapia ponds averaged 7.5 and only one pond out of 35 ponds in
the study by Thunjai et al. (2004) had a pH below 7.
The optimum pH range for aquaculture pond soils is 7.5 to 8.0, for microbial
activity is most rapid in this pH range (Boyd and Pipoppinyo 1994). Microbial
decomposition of organic matter recycles nutrients and prevents accumulation of large
amounts of organic matter in pond bottoms.
Carbon
Concentrations of total carbon ranged from 0.38 to 7.08% (Tables 3, 4, and 5).
The average total carbon concentration of 3.02% in carp ponds was more than two-
fold greater (P < 0.05) than those of catfish and prawn ponds ? 1.46 and 1.38%,
respectively. Tilapia ponds were similar to carp ponds with respect to total carbon
concentration (Fig. 2).
Organic carbon concentration ranged from 0.26 to 5.07%, but few samples had
more than 3%. Carp ponds had a higher average organic carbon concentration (P < 0.05)
than catfish or prawn ponds (Fig. 2). Tilapia ponds had an average organic carbon
concentration of 1.90% - similar to carp ponds. Results of organic carbon analyses for
34
many ponds in Thailand confirm the statement by Boyd (1995) that aquaculture pond
soils seldom contain more then 3% organic carbon.
The optimum range of organic carbon in pond soils is 1 to 3% (Banerjea 1967).
Lower concentrations are unfavorable for growth of benthic organisms that are important
food for young of many species, and higher concentrations favor anaerobic conditions at
the soil water interface.
The organic carbon method by sulfuric-acid-potassium dichromate oxidation does
not oxidize all of the organic matter in a soil sample (Nelson and Sommers 1982). The
induction furnace method used for total carbon oxidizes essentially all organic carbon,
and it decomposes soil carbonate to release and measure inorganic carbon. Soils in this
study were usually slightly acidic or neutral in reaction and not thought to contain
appreciable carbonate. Thus, the difference between total carbon and organic carbon
likely consisted primarily of organic matter resistant to oxidation by acidic, potassium
dichromate solution and heat. Total carbon analysis requires an expensive, complex
instrument while organic carbon can be measured with relatively simple laboratory
apparatus or with a portable kit (Queiroz and Boyd 1998). Soil organic carbon also is of
more concern to aquaculturists because it is the more labile form that decomposes rather
quickly and can lead to low redox potential in the pond bottom (Boyd 1995). Soil
organic matter contains about 50 to 58% carbon, and factors of 1.724 to 2.0 have been
used to convert organic carbon concentrations to organic matter concentrations (Nelson
and Sommers 1982).
There was a strong relationship between organic carbon and total carbon for soils
from ponds for all three species. The coefficients of determination (R
2
) for regressions
35
were 0.935 for catfish, 0.748 for carp, and 0.744 for prawn. The regression line for data
from all samples (Fig. 3) has R
2
= 0.851.
Nitrogen, phosphorus, and sulfur
Total nitrogen concentration ranged from less than 0.05 to more than 0.5%
(Tables 3, 4, and 5). Carp pond soils had an average total nitrogen concentration of
0.28% that was greater (P < 0.05) than averages for catfish ponds (0.18%) and prawn
ponds (0.l4%). Carbon:nitrogen ratio did not differ (P > 0.05) for the three groups of
ponds and the average for all ponds combined was 9.3. Assuming that pond soil
organic matter is about 52% carbon, it would contain roughly 5% nitrogen.
Terrestrial soil organic matter also contains about 5% nitrogen (Brady 1990). The
carbon: nitrogen ratio, however, was quite variable among samples (Fig. 4), but the
R
2
value for the regression was 0.757 and verifies that there is a close relationship
between soil carbon and soil nitrogen in aquaculture pond soils. Of coarse, this
relationship has long been recognized in terrestrial soils (Brady 1990).Tilapia ponds
in Thailand had an average total nitrogen concentration of 0.19% and a
carbon:nitrogen ratio of 11 (Thunjai et al. 2004). The ideal carbon:nitrogen ratio for
aquaculture ponds is thought to be 8 to 12 (Boyd 1995).
Total phosphorus concentration averaged 1,567, 1,085, and 334 ppm in catfish,
carp, and prawn pond soils, respectively (Tables 3, 4, and 5), and each type of pond
differed from the others (Fig. 2). The input of feed and animal by-products to ponds to
promote fish production increased in the same order as did total phosphorus
concentrations. Averages for dilute-acid extractable and water-soluble phosphorus did
36
not differ between carp and prawn ponds, but catfish ponds had much higher
concentration than the other two classes of ponds. The Lancaster extraction method
extracted an average of about 200 ppm phosphorus from soils of catfish and carp ponds.
This concentration was greater (P < 0.05) than that of 76 ppm extracted by this solution
from prawn pond soils. There was a positive relationship between total phosphorus
concentration and phosphorus extracted by the three solutions as follows: water-
extractable phosphorus, R
2
= 0.201; dilute-acid extractable phosphorus, R
2
= 0.417;
Lancaster solution-extractable, R
2
= 0.436. However, total phosphorus would not be a
good predictor of any of the three fractions because of the relatively low R
2
values.
Thunjai et al. (2004) did not measure total phosphorus or determine the amount of
phosphorus extracted by the Lancaster method for tilapia pond soils. However,
concentrations of water and dilute-acid extractable phosphorus averaged 9 and 217 ppm,
respectively, for tilapia pond soils. According to Banerjea (1967), increasing phosphorus
concentrations in pond soils favor a greater potential for fish production. Nevertheless, if
pond soils become saturated with phosphorus, they will no longer remove phosphorus
from pond water. High concentration of phosphorus in water form dense phytoplankton
blooms and low dissolved oxygen concentrations will occur frequently (Banerjea 1967;
Boyd 1995).
Ponds of the three types of aquaculture differed in average sulfur concentration.
Individual values for all ponds ranged from 73 to 7,197 ppm, and averages were 837,
1,590, and 2,874 ppm for prawn, carp, and catfish pond soils, respectively (Tables 3, 4,
and 5). The increase in sulfur concentration is in order of increasing input of organic
matter in feed and other organic material to the ponds for the three species. Thus, the soil
37
sulfur probably was primarily in organic form. The study of tilapia pond soils was
conducted in Samutprakarn area where soils often contain deposits of iron pyrite
(FeS
2
) (Thunjai et al. 2004). Sulfur concentrations reached 3.03%, and the average
was 1.18%. Sulfur concentrations above 0.75% are indicative of acid-sulfate soils
(Soil Survey Staff 1994). Such soils tend to be highly acidic (Dent 1986), and
heavy applications of liming materials are necessary to counteract acidity from
pyrite oxidation.
Cation exchange capacity and exchangeable acidity
The CEC of the soils did not differ among the three types of pond culture
(Fig. 2). The averages for CEC were near 30 mEq/100 g. The lowest CEC was
11.92 mEq/100 g and the greatest value was 43.8 mEq/100 g (Tables 3, 4, and 5).
These CEC values are similar to those for tilapia ponds in Thailand (mean = 35 and
range = 12.1 to 42.6 mEq/100 g) (Thunjai et al. 2004). These are rather high CEC
values, and a moderate to high CEC is desirable in pond soils. It is associated with
adequate concentrations of major cations to assure that pond waters contain enough
cations to promote good osmoregulatory function in the culture species (Boyd
1995).
The exchangeable acidity was low (0 to 6.0 mEq/100 g) as expected from the
near neutral pH of the samples. This was the result of frequent applications of
liming materials to the pond bottoms. Exchangeable acidity usually was less than 1
mEq/100 g in soils from tilapia ponds (Thunjai et al. 2004).
38
Major cations
Individual calcium concentrations ranged from 1,216 to 7,832 ppm. The averages
were nearly 5,000 ppm for catfish and carp ponds and about 4,000 ppm for prawn ponds
(Tables 6, 7, and 8). Catfish ponds had greater concentrations of soil calcium than prawn
ponds, but they did not differ in calcium concentration from carp ponds (Fig. 2).
Magnesium concentrations were roughly one-tenth of calcium concentrations and ranged
from 94 to 938 ppm. The averages for the three bottom soil groups ranged from 438 to
498 ppm, but did not differ (P > 0.05). There was no correlation (P > 0.05) between soil
calcium and soil magnesium for the samples. Potassium concentrations were between 27
and 479 ppm for individual samples with averages between 144 and 205 ppm. Carp
ponds had greater soil potassium concentrations than the other ponds. This likely
resulted from potassium entering ponds from the chicken houses or from chicken manure
applied to ponds. Sodium concentrations averaged between 28 and 700 ppm for the three
classes of fish culture. Averages were between 136 and 183 ppm, and they did not differ
among the types of pond culture.
Means for all samples were as follows: calcium, 4,866 ppm; magnesium, 465
ppm; potassium, 169 ppm; sodium, 161 ppm. These values correspond to the following
concentrations in milliequivalents per 100 g soil: calcium, 24.28; magnesium, 3.83;
potassium, 0.43; sodium, 0.7. The total concentration of major ions is equal to 29.24
mEq/100g. The average CEC for all samples was 30.39 mEq /100 g. Thus, the
measured CEC agreed quite closely with the concentration of exchangeable cations in
the soil.
39
The exchangeable cations were extracted with dilute acid. Thus, if soils had
contained appreciable calcium carbonate, the acid would have dissolved the calcium
carbonate and the concentration of major ions would have exceeded the CEC. Thus, the
difference in total carbon concentration and the organic carbon concentration found in
this study does not represent inorganic carbon in carbonate. The difference, as mentioned
above, resulted from a lower percentage recovery of organic carbon by the Walkley-
Black method as compared to the induction furnace method.
Thunjai et al. (2004) did not report concentrations of major cations for samples of
bottom soils from tilapia ponds in Thailand. Boyd et al. (1994) developed concentration
categories for major cations in pond soils based on data from 358 ponds mostly in the
United States. When ranked according to these concentration categories, the averages
(all ponds) for samples in this study were high for calcium, very high for magnesium,
potassium, and sodium. However, no guidelines for optimum concentrations of major
cations in soils of fish and prawn ponds could be found in the literature.
Minor elements
Aluminum concentrations ranged from 0.6 to 226 ppm (Tables 6, 7, and 8), but
averages (83 to 104 ppm) for the three kinds of pond culture did not differ (P > 0.05)
(Fig. 2). Iron and manganese concentrations were as variable as those of aluminum
(Tables 6, 7, and 8). Average iron concentrations of 91 and 96 ppm in prawn and catfish
pond soil, respectively, were lower (P < 0.05) than the average of 202 ppm for carp pond
soil. The average manganese concentration of 55 ppm in catfish pond soil was lower
(P < 0.05) than average values of 86 and 90 ppm in prawn and carp pond soils,
40
respectively. Zinc and copper concentrations were much lower than those for aluminum,
iron, and manganese as usually is the case in soil samples (Brady 1990). The greatest
zinc concentration was 32 ppm while the highest copper value was 6.9 ppm. The average
zinc was higher (P < 0.05) in soils of carp ponds than in those of the other two types of
aquaculture. Copper concentrations also were greater in carp pond soils. Boron
concentrations ranged between 1.0 and 6.8 ppm. Average concentrations of boron did
not differ among ponds for different species (P > 0.05). Nickel was measurable in pond
soils and ranged from 0.5 to 4.1 ppm and average nickel concentrations did not differ
(P > 0.05) among the three kinds of aquaculture. The ICAP procedure also analyzed
samples for cobalt, cadmium, chromium, and lead. However, all samples contained less
than detectable concentrations (< 0.1 ppm) of these four elements.
Thunjai et al. (2004) did not provide data on minor element concentrations in soils
from tilapia ponds in Thailand. Boyd et al. (1994) reported concentration categories for
soil chemical variables based on analyses of 358 samples from freshwater aquaculture
ponds mostly in the United States. By comparison with these categories the averages for
minor elements in pond soils from Thailand were medium in aluminum, medium (prawn
and catfish ponds) or high (carp ponds) in iron, high in manganese, very high in zinc,
medium or high in copper, and very high in boron. In general, minor elements tended to
be higher in the carp pond soils than in soils from catfish and prawn ponds. The reason
for this tendency is not known. However, animal manures are typically high in
concentrations of minor elements (Boyd and Tucker 1998). Thus, the application of
chicken house wastes to carp ponds was possibly the reason for the tendency for higher
concentrations of minor elements in soils of carp ponds than in other ponds. As with
41
major cations, optimum soil concentrations of minor elements are not known (Boyd et al.
1994).
Correlation among soil variables
A correlation matrix for soil physical and chemical variables is provided (Table
9). Because of the large sample size (n = 100), a number of the correlation coefficients
were significant. However, most did not account for a large proportion of the variation
between two variables. The largest correlation coefficients were as follows: total
sediment depth versus S horizon depth (r = 0.785); silt versus sand (r = 0.932); pH
versus exchangeable acidity (r = 0.840); organic carbon versus total carbon (r = 0.955);
total carbon versus total nitrogen (r = 0.870); organic carbon versus total nitrogen
(r = 0.811). None of the correlations listed above are surprising; however, it was
interesting that so many of the variables were not correlated. This suggests that there is
no single soil quality variable or a few soil quality variables that can be measured and
used to estimate overall soil quality.
Soil pH and organic carbon are the two most commonly measured soil quality
variables in commercial aquaculture. The two variables are thought to be important
indicators of the potential of ponds to produce fish or shrimp (Banerjea 1967; Boyd
1995). However, neither of these two variables were useful as general predictors of soil
chemical and physical characteristics.
Influence of pond age
Regression analyses between pond age (X) and all individual soil quality
variables (Y) were conducted to ascertain if pond soil variables changed in relation to
42
pond age. There were few significant correlations between pond age and any of the
variables (Table 10). Earlier studies (Tucker 1985; Thunjai et al. 2004) found that pond
age and total and organic carbon in pond soils were correlated, but the relationship did
not account for much of the variation in organic carbon concentration. Munsiri et al.
(1995) and Tepe and Boyd (2002) found that several soil quality variables increased in
pond soils over time. A study of shrimp farm bottom soils in Madagascar also revealed
that total phosphorus concentrations increased as ponds aged (Boyd et al. 2006).
Studies showing an increase in pond soil quality variables over time were
conducted in ponds where sediment was not routinely removed or never removed.
Sediment was removed at intervals from ponds in the present study. Thus, the lack of
correlation between pond age and sediment quality in freshwater aquaculture ponds in
Thailand probably is related to the practice of sediment removal.
Water quality
Water quality analyses (Tables 11, 12, and 13; Fig. 5) were restricted to pH
that could be measured on site, and major ions, total alkalinity, and total hardness that
do not change appreciably during sample storage in sealed bottles (Boyd and Tucker
1998).
The pH was seldom below 7, but one catfish pond had a pH of 5.45. Average
pH for the three groups of ponds ranged from 7.60 to 7.86, but there were no differences
among the groups. A pH of 7 to 8.5 is considered excellent for pond fish culture (Boyd
and Tucker 1998). Thus, most ponds had acceptable pH.
43
Total alkalinity and total hardness concentrations exhibited wide ranges of 0.48 to
235.7 mg/L and 47.0 to 805.8 mg/L, respectively. However, concentrations for most
ponds were above 50 mg/L and below 300 mg/L. The lowest concentration of average
total alkalinity (79.0 mg/L) in freshwater prawn ponds differed (P < 0.05) from those of
catfish (117.1 mg/L) and carp (104.4 mg/L) ponds. Total hardness did not differ among
the different classes of ponds, and total hardness and total alkalinity were not correlated.
Nevertheless, total hardness was consistently greater in concentration than total
alkalinity. This is a common phenomenon in aquaculture ponds. When liming materials,
burnt lime, hydrated lime, or agricultural limestone, are added to water they react with
carbon dioxide to increase the bicarbonate concentration (alkalinity) and calcium and
magnesium concentration (hardness). However, native acidity from bottom soils and
hydrogen ions from decomposition and nitrification react with alkalinity and lessen its
concentration, but the calcium and magnesium ions remain to increase total hardness
(Boyd and Tucker 1998).
Ponds for food fish production should have total alkalinity concentrations of
50 to 200 mg/L (Boyd and Tucker 1998). Most ponds in this study had acceptable
concentrations of alkalinity. Total hardness concentrations also should exceed 50
mg/L, but concentrations above 200 mg/L are acceptable (Boyd and Tucker 1998).
Concentrations of major anions and cations varied widely among individual
ponds. Chloride concentrations were as low about 2 mg/L and as high as 400 mg/L, but
averages for the three kinds of aquaculture were between 22.8 and 54.6 mg/L, and they
did not differ (P > 0.05). Sulfate concentrations ranged from about 3 mg/L to over 200
mg/L, but averages were 53.6 to 65.9 mg/L and did not differ.
44
Calcium concentrations were mostly above 20 mg/L, and averages exceeded 30
mg/L, while magnesium concentrations normally were above 5 mg/L with averages of
11.6 to 15.0 mg/L. Catfish ponds had a higher average calcium concentration than carp
or prawn ponds. Magnesium concentration did not differ among the three ponds of
aquaculture. The ratio of calcium to magnesium averaged 3.42:1. There was a
significant relationship between calcium and magnesium concentrations (Fig. 6) in the
pond waters.
Potassium and sodium concentrations also varied greatly among ponds. Averages
were between 5.5 and 9.6 mg /L for potassium and 33.2 and 63.0 mg/L for sodium.
Potassium concentrations were greatest in carp ponds (P < 0.05), but sodium
concentrations did not differ (P > 0.05) among the three culture types. The average
sodium and potassium concentrations for all ponds was 55.5 mg/L and 6.9 mg/L,
respectively, for a sodium:potassium ratio of 8.04:1.
Soil pH was not correlated (P > 0.05) with any of the measured water quality
variables. In unlimed ponds, there is a positive correlation between soil pH and
total hardness, total alkalinity, calcium, and magnesium in pond water (Boyd 1974).
However, ponds in this study had been routinely treated with liming materials.
Liming increased soil pH and the concentration of alkalinity, hardness, calcium,
and magnesium in the water obscuring the natural relationships among these
variables.
Soil calcium and magnesium were not correlated with water calcium and
magnesium. Again, liming would have obscured a relationship if it had existed in the
original pond soils. There was a correlation between soil potassium and water potassium
45
(R
2
= 0.228), but the correlation was likely partially obscured by additions of potassium
in feeds and agricultural wastes. The relationship between soil sodium and water sodium
had an R
2
= 0.648.
It was not possible to measure variables such as nitrogen and phosphorus
fractions, dissolved organic matter, dissolved oxygen, and soil redox potential to regress
them against soil quality variables. It is likely that some of these variables would have
been correlated with soil quality.
46
DISCUSSION
The results reported above suggest that pond age is not an important factor
determining the quality of catfish, freshwater prawn, and carp pond bottom soils in
Thailand. This finding is in agreement with that of an earlier study of tilapia pond
bottom soils in Thailand (Thunjai et al. 2004).
There were some differences in pond bottom soil quality among ponds for the
culture of the three species of this study and tilapia. Carp ponds had a greater total
sediment depth and thickness of the S horizon than ponds for other species. This
probably was related to the longer period between sediment removal from carp ponds
than other ponds.
Carp, catfish, and prawn ponds had lower soil pH than tilapia ponds because
tilapia ponds were treated with greater amounts of liming material.
Carp ponds and tilapia ponds had greater concentrations of total and organic
carbon than catfish and prawn ponds. Catfish ponds receive the largest inputs of organic
matter and prawn ponds the lowest inputs. However, sediment removal is done more
frequently in these two types of aquaculture than in the other two kinds. Nitrogen
concentration tended to increase in response to increasing carbon concentrations, and
carbon to nitrogen ratios were similar among ponds for the different culture species.
Total phosphorus and the different soil phosphorus fractions increased in the
order prawn ponds, carp ponds, and catfish ponds. Phosphorus inputs to the ponds
47
increased in the same order, and phosphorus is rapidly removed from pond water and
bound in sediment (Boyd 1995). Sediment removal did not obscure this relationship even
though large amounts of phosphorus were likely removed in sediment. The practice of
removing sediment is likely beneficial in preventing saturation of sediment near the
sediment-water interface with phosphorus.
Sulfur concentrations increased in the same order as total phosphorus
concentrations. The soils of the Central Plain usually do not contain pyritic sulfur
(Khaewreenrom 1990), and the sulfur in soils of this study probably was primarily
organic sulfur. Tilapia ponds are much higher in sulfur concentration and contained
pyritic sulfur.
The ponds of this study and tilapia ponds had moderately high and similar CEC.
This is a native characteristic of the soils and not related to pond aquaculture.
The differences in major cations and minor elements are not thought to be
significant in aquaculture. However, some of the differences, and especially differences
in minor elements, may be related to aquaculture inputs.
The pond soils generally had favorable quality for use in aquaculture. However,
ponds had been subjected to soil management to include liming, dry-out between crops,
and sediment removal.
There is considerable concern about the possible negative environmental impacts
of pond aquaculture (Goldburg and Triplett 1997; Clay 1997, 2004). With respect to
pond soils, erosion of earthwork, draining for harvest, and sediment removal can increase
inputs of suspended soils to nearby streams or other water bodies.
48
Best management practices for pond soils
Based on evaluation of pond features, production practices, and physical and
chemical characteristics of bottom soil, a list of best management practices for possible
use in freshwater pond aquaculture in Thailand have been developed. These practices
should maintain pond bottom soil quality within a suitable range for aquaculture and
avoid negative, off-site environmental impacts.
Practice 1. After ponds are drained for harvest, bottoms should be dried for 2 to 3 weeks
before refilling with water.
Accumulation of fresh, labile organic matter in pond bottoms can lead to high
rates of microbial respiration. Sediment usually is anaerobic below a depth of a few
centimeters in ponds for extensive production. In intensive ponds, only the upper few
millimeters of sediment are aerobic (Munsiri et al. 1995), and if organic matter inputs are
especially great, microbial respiration can result in dissolved oxygen depletion at the
sediment-water interface. This phenomenon is undesirable because potentially toxic
compounds from anaerobic metabolism of bacteria, e.g., nitrite, ferrous iron, hydrogen
sulfide, and organic fermentation products, can enter the water.
The concentration of labile organic matter increases during an aquaculture crop
usually reaching a maximum near harvest time. When ponds are drained, some of the
labile organic matter is suspended by outflowing water and removed from ponds (Ayub,
et al. 1993), but much remains. Drying of the pond bottom allows air to enter into pore
spaces and cracks to accelerate aerobic microbial activity and oxidize reduced
49
compounds (Wurtz 1960; Boyd 1995). This is beneficial in reducing the amount of labile
organic matter that will be present at the beginning of the next crop. It also oxidizes
inorganic compounds so that they can be used again as sources of oxygen by anaerobic
bacteria with the anaerobic zone of sediment. The labile organic fraction and reduced
inorganic compounds can be mostly oxidized within 2 or 3 weeks. The refractory
organic matter usually does not decompose fast enough to cause anaerobic conditions at
the sediment-water interface (Boyd 1995).
Freshwater fish and prawn farmers in Thailand practiced bottom dry-out between
crops when ponds were drained for harvest. The reported dry-out period of 2 to 3 weeks
is probably adequate in ponds without deep sediment. Drying for longer periods usually
is not beneficial because soils become so dry that bacterial activity is retarded for lack of
moisture (Boyd and Teichert-Coddington 1994). Deep sediment will take several months
to dry.
Practice 2. The bottoms of empty ponds should be tilled to a depth of 10 to 15 cm with
a disk harrow to improve soil aeration.
Tilling greatly increases the exposure of pond soil to the air to accelerate drying
and oxidation. Tilling is especially important in soils with a clay content over 20 or 30%.
Although such soils often crack into columnar blocks upon drying (Pettry and Switzer
1993), air cannot enter into the blocks (Boyd 1995). Tilling pulverizes these blocks of
soil to allow the wet soil from inside the blocks to dry and oxidize. Farmers interviewed
in this study did not till pond bottoms between crops. Many of the ponds had a clay
content above 20%, and tilling of pond bottoms would likely be beneficial in freshwater
50
aquaculture in Thailand.
Practice 3. Pond bottom soils should be treated with liming materials to increase soil pH
to between 7.5 and 8.
Acidic bottom soils are associated with low total alkalinity in pond waters (Boyd
and Tucker 1998). Aquaculture ponds with low alkalinity waters do not have a large
reserve of carbon dioxide but they have high concentrations of nitrogen and phosphorus.
Phytoplankton blooms that develop in ponds with low alkalinity water cause an
excessively high pH by depleting the free carbon dioxide supply. Moreover, acidic
conditions in bottom soils limit the growth of benthic organisms important as natural
food for culture species. Bacteria also are limited by low pH, and organic matter may
accumulate in pond bottoms and nutrient recycling will be slow.
Pillai and Boyd (1985) presented a lime requirement method for determining
the liming rate for aquaculture ponds. However, if this method cannot be used, the
lime requirement could be based on soil pH. Ponds with soil pH of 7.5 or above
would not need lime. A liming rate of 500 kg /ha would likely be adequate for pH
values between 7.0 and 7.4, and the liming rate could be increased incrementally as
soil pH declines (Table 14). Where producers do not have a means of measuring soil
pH, an initial liming rate of 2,000 kg /ha could be used, and afterwards, 500 kg /ha
could be applied annually.
Ponds for catfish, freshwater prawns, and carp would benefit from greater
applications of liming materials for soil pH was below 7 in many of them. However,
tilapia ponds in Thailand are heavily limed, and in some cases, applications could be
51
reduced (Thunjai et al. 2004).
Practice 4. Sediment should be removed from ponds before it becomes deep enough to
interfere with pond management procedures.
Part of the sediment in ponds has its origin in suspended solids in incoming water
that settle to the pond bottom. Erosion of pond embankments and shallow areas by
waves and water currents suspends soil particles that tend to settle in deep areas. Organic
matter from plankton, uneaten fish feed, and feces also become sediment (Boyd 1995).
Sediment is comprised mainly of mineral soil particles, but organic matter deposits onto
the sediment as a flocculent layer and is gradually mixed into the sediment mass (Munsiri
et al. 1995).
Deep sediment has several undesirable effects in ponds (Boyd 1995; Steeby et al.
2001). Feed pellets may sink into it and not be eaten by the culture animals. Feed pellets
decompose rapidly and may cause localized zones of especially low redox potential. Soft
sediment fills nets and seines during harvest making it difficult to pull them. A large
volume of mud in nets or seines can injure aquatic animals and also make them difficult
to remove. When ponds are dried between crops, areas with deep sediment will not dry
out.
Sediment removal is practiced by fish and freshwater prawn farmers in Thailand.
Nevertheless, some ponds, and especially carp ponds, had deep sediment. More attention
to sediment removal would be beneficial in some ponds.
Some farmers interviewed in this study dragged chains over pond bottoms or used
suction devices to remove soft sediment during crops. Previous studies showed little
52
benefit of such practices (Beveridge et al. 1994; Gomes 2003), and disturbance of
anaerobic sediment might release harmful amounts of metabolites into the water.
Microbial products also are applied to ponds to improve the quality of soft sediment.
A recent review (Boyd and Silapajarn 2005) did not find documentation of soil and water
quality benefits following applications of microbial products. Therefore, sediment
removal appears to be the most effective way of dealing with soft sediment in aquaculture
ponds.
Practice 5. Use sedimentation basins to remove suspended soil particles from incoming
water.
In some cases, the water supply for ponds was highly turbid with suspended soil
particles from erosion on watersheds. Because these particles will settle in ponds, it is
beneficial to install a sedimentation basin to remove coarse suspended particles before
they enter ponds. A settling time of 1 or 2 h can be beneficial, but for best results,
a settling time of 4 h or more should be provided (Boyd 1995).
Practice 6. Install vegetation, stone, or other cover on pond embankments to reduce the
potential for erosion.
Erosion of pond embankments can be a major source of settleable solids in ponds.
Soil particles may be suspended by waves and currents in ponds and by rain falling on
bare soil of embankments. Installation of cover to avoid erosion reduces the sediment
load to ponds and protects the embankments.
53
Practice 7. Use proper side slopes and compaction when constructing new ponds or
renovating old ones.
This practice will reduce the tendency of earthwork to erode and reduce the
internal sediment load in ponds. It also reduces maintenance costs for repairing
embankments.
Recommended side slopes for embankments made of clay, clayey sand, clayey
gravel, sandy clay, silty sand, or silty gravel are 3:1 (horizontal:vertical) on the wet side
and 2:1 on the dry side. Slopes of 3:1 should be provided on both sides of an
embankment made of silty clay or clayey silt. Where well-graded soil has been
compacted properly, the side slopes may be 1:1 or 2:1 on both sides (Yoo and Boyd
1993). Even with proper side slopes, vegetative cover or rock must be provided to avoid
erosion.
Practice 8. In ponds with mechanical aeration, install aerators to prevent water currents
from eroding insides of embankments. Install rip-rap (stone) on bottom in front of
aerators to prevent scouring of the pond bottom. If bottoms of heavily aerated ponds are
tilled between crops, compact bottoms with heavy roller before refilling.
Mechanical aerators induced strong water currents in ponds. If the aerators are
placed too close to embankments, currents flowing parallel to embankments may cause
erosion. However, if water currents are directed at embankments even greater erosion
may occur. There also is a tendency for increased erosion of the pond bottom in front of
aerators. Tilling of pond bottoms loosens the soil making it more susceptible to erosion
by water currents generated by aerators.
54
Mechanical aerators were not used by farmers interviewed in this study.
However, mechanical aeration is a very effective practice that improves water quality and
allows greater production. In the future, freshwater aquaculturists in Thailand will
probably use aeration. It is commonly used by marine shrimp farmers in Thailand.
Practice 9. Do not leave ponds empty longer than necessary during rainy weather to
prevent erosion of soil from shallow area with deposition of soil in deeper areas.
Practice 10. Do not allow livestock to walk on pond embankments or wade in shallow
water edges.
Livestock can make paths by walking along the same route each day. These paths
often are sites of erosion that can develop into small gullies.
Practice 11. Avoid operating equipment that will cause ruts and other inundations in
pond bottoms.
Ruts or other depressions in pond bottoms often fill with soft sediment. They also
create areas that cannot be drained and dried completely.
Best management practices for preventing off-site impacts
Aquaculture in ponds can cause negative, off-site environmental effects. For
example, effluents contain suspended solids, nutrients, and organic matter and they can
cause turbidity, sedimentation, and eutrophication in receiving water bodies (Goldburg
55
and Triplett 1997). Sediment removed from ponds may be discarded in piles on vacant
land (Boyd et al. 1994). This practice can result in destruction of vegetation and other
terrestrial ecological nuisances. Moreover, erosion of sediment piles can cause turbidity
and sedimentation in nearby water bodies. Best management practices also can be used
to avoid off-site environmental impacts. Some soil-related practices that would be useful
in Thailand are listed below:
Practice 12. Design and construct discharge canals to minimize bottom scouring and
erosion of side slopes. This should include installation of grass cover and stone
reinforcement of erosion prone areas in canals.
Rather complex engineering practices are necessary to minimize erosion in
earthen canals (Yoo and Boyd 1993). However, the basic principle is to make the
channel cross section large enough to prevent excessive water velocity and make the
channel side slopes gentle enough to prevent erosion.
Practice 13. Do not use water jets to wash pond bottoms by hydraulic pressure as is
sometimes done by marine shrimp farmers in Thailand.
The practice of washing pond bottoms is a method of sediment removal.
However, the material suspended by water pressure is discharged into canals.
The effluent from pond cleaning can cause turbidity, excessive oxygen demand
and sedimentation in canals. This will lessen the quality of water for other
water users.
56
Practice 14. Pass pond effluents through a settling basin to remove coarse suspended
solids before final discharge into natural waters.
Settling basins have already been discussed above.
Practice 15. Dispose of sediment removed from pond bottoms or settling basins in
a responsible manner.
Preferably, the sediment should be placed back over the areas on pond bottoms
and embankments from which it originated. Pond sediment has a high nutrient content,
so it could be spread over and incorporated into agricultural soil. Pond sediment also can
be used as earthfill. If it is spread over the land, grass cover should be established to
prevent erosion.
The quality of bottom soils in ponds for the three types of aquaculture was
generally good. However, it could be improved and external environmental impacts
prevented through the use of BMPs. This would help improve the sustainability of
catfish, freshwater prawn, and carp farming in Thailand.
57
Table 1. Number, areas, and depths of catfish, carp, and freshwater prawn culture pond
used in this study.
Catfish Prawn Carp
Number of ponds 42 40 18
Pond area (m
2
)
400-6,400 2,400-40,000 600-48,000
Average area (m
2
) 1,904 8,480 16,096
Pond depth (m) 1.5-2.0 1.0-1.5 1.0-2.0
Average depth (m) 1.65 1.37 1.44
58
Table 2. Distribution of ponds by age.
Pond age (yr) Catfish (n=42) Prawn (n=40) Carp (n=18)
1-5 24 12 4
6-10 6 6 10
11-15 4 12 2
16-20 4 7 2
>20 4 3 0
59
Table 3. Physical characteristics, carbon, nitrogen, phosphorus, sulfur, and exchangeable
cation data for bottom soil samples from 42 catfish ponds in Thailand.
Variables Mean + SD
1 ?
Minimum Maximum
Sediment depth (cm) 19.9 + 18.5 0 60.9
S-horizon thickness (cm) 8.9 + 8.7 1 32
Dry bulk density (g/cm
3
) 0.17 + 0.10 0.02 0.42
Particle size distribution:
Clay (%) 38.3 + 4.3 25.7 47.7
Silt (%) 53.7 + 17.6 0 74.6
Sand (%) 9.02 + 17.47 0 72.51
pH (standard units) 6.63 + 0.75 4.64 7.82
Total carbon (%) 1.46 + 0.8 0.38 3.46
Organic carbon (%) 1.20 + 0.66 0.26 2.85
Total nitrogen (%) 0.18 + 0.11 0.03 0.54
Sulfur (ppm) 1591 + 1433 125 7197
Total carbon/total nitrogen 8.1 + 3.2 3.54 17.65
Exchange acidity (mEq/ 100 g) 1.7 +0.8 0 4.1
Cation exchange capacity (mEq/ 100 g) 29.3 + 6.5 11.9 36.5
Dilute acid - extractable phousphorus (ppm) 190 + 320 0.98 1769
Water - extractable phousphorus (ppm) 22.4 + 24.3 0.13 131
Lancaster -extraction phosphorus (ppm) 200 + 172 6.93 709
Total phosphorus (ppm) 1566 + 1197 28.6 5948
SD
1 ?
= Standard deviation
60
Table 4. Physical characteristics, carbon, nitrogen, phosphorus, sulfur, and
exchangeable cation data for bottom soil samples from 40 freshwater prawn ponds in
Thailand.
Variables Mean + SD
1 ?
Minimum Maximum
Sediment depth (cm) 11.9 + 9.7 0 47
S-horizon thickness (cm) 4.2 + 2.8 1 10.4
Dry bulk density (g/ cm
3
) 0.18 + 0.06 0.06 0.32
Particle size distribution (%)
Clay 36.2 + 5.4 10.8 42.9
Silt (%) 63.6 + 5.4 57.1 89.2
Sand (%) 0.2 + 1.3 0 7.5
pH (standard units) 6.71 + 0.81 4.33 7.51
Total carbon (%) 1.38+ 0.43 0.64 2.55
Organic carbon(%) 1.07+ 0.36 0.45 1.81
Total nitrogen (%) 0.14 + 0.04 0.06 0.22
Sulfur (ppm) 837 + 951 73.1 5194
Total carbon/total nitrogen 9.9 + 1.8 6.22 16.09
Exchange acidity (mEq/ 100 g) 1.7 + 0.8 0.3 3.4
Cation exchange capacity (mEq/ 100 g) 31.4 + 4.8 20.8 43.8
Dilute acid - extractable phousphorus (ppm) 5 + 4 0.5 15.9
Water - extractable phousphorus (ppm) 5.7+ 6.9 0.1 32.3
Lancaster -extraction phosphorus (ppm) 75.6+ 52.3 18.7 316.8
Total phosphorus (ppm) 344 + 179 43.3 769
SD
1 ?
= Standard deviation
61
Table 5. Physical characteristics, carbon, nitrogen, phosphorus, sulfur, and
exchangeable cation data for bottom soil samples from 18 carp ponds in Thailand.
Variables Mean + SD
1 ?
Minimum Maximum
Sediment depth (cm) 33.4 + 16.6 0 63.6
S-horizon thickness (cm) 17.1 + 11.0 0 42
Dry bulk density (g/ cm
3
) 0.28 + 0.07 0.12 0.4
Particle size distribution :
Clay (%) 33.1 + 7.8 21 41.7
Silt (%) 53.2 + 20.1 1.7 69.2
Sand (%) 13.7 + 18.4 0 56.6
pH (standard units) 6.48 + 0.87 3.81 7.25
Total carbon (%) 3.02 + 1.5 1.14 7.08
Organic carbon(%) 2.08 + 1.06 1.02 5.07
Total nitrogen (%) 0.28 + 0.12 0.11 0.62
Sulfur (ppm) 2873.7 + 1801.46 342.6 6199.8
Total carbon/total nitrogen 10.8 + 2.0 5.46 15.22
Exchange acidity (mEq/ 100 g) 2 + 1.3 0.6 6
Cation exchange capacity (mEq/ 100 g) 31.1 + 6.9 17.7 41.3
Dilute acid - extractable phousphorus (ppm) 34.5 + 86 1 369.5
Water - extractable phousphorus (ppm) 9.1 + 7.5 0.1 23.1
Lancaster -extraction phosphorus (ppm) 206.8 + 155.9 29.3 557.8
Total phosphorus (ppm) 1085. + 624 159 2683
SD
1 ?
= Standard deviation
62
Table 6. Major cations and minor elements in bottom soil samples from 42 catfish
ponds in Thailand.
Variables Mean + SD
1 ?
Minimum Maximum
Calcium (ppm) 5189 + 1682 1649 7833
Potassium (ppm) 143 + 68 27 373
Magnesium (ppm) 438 +211 95 939
Sodium (ppm) 183 +146 28 701
Aluminium (ppm) 83 + 69 1 226
Iron (ppm) 97 + 137 <0.5 686
Manganese (ppm) 55 + 49 8 253
Zinc (ppm) 7.29 + 6.63 <0.5 32.12
Copper (ppm) 1.51 + 1.05 <0.5 3.79
Boron (ppm) 1.87 + 0.93 1.19 6.83
Nickel (ppm) 1.75 + 1.07 <0.5 4.05
SD
1 ?
= Standard deviation
63
Table 7. Major cations and minor elements in bottom soil samples from 40 freshwater
prawn ponds in Thailand.
Variables Mean + SD
1 ?
Minimum Maximum
Calcium (ppm) 4081 + 1320 1216 6361
Potassium (ppm) 148 + 40 53 226
Magnesium (ppm) 457 + 158 211 853
Sodium (ppm) 168 + 127 52 619
Aluminium (ppm) 104 + 49 1 191
Iron (ppm) 91 + 84 >0.5 320
Manganese (ppm) 86 + 56 12 225
Zinc (ppm) 6.6 + 3.38 0.55 12.56
Copper (ppm) 1.87 + 1.44 >0.5 5.53
Boron (ppm) 1.79 + 1.01 1.05 6.74
Nickel (ppm) 2.06 + 0.84 >0.5 4.03
SD
1 ?
= Standard deviation
64
Table 8. Major cations and minor elements in bottom soil samples from 18 carp
ponds in Thailand.
Variables Mean + SD
1 ?
Minimum Maximum
Calcium (ppm) 4881 + 1389 2348 7434
Potassium (ppm) 204 + 90 80 479
Magnesium (ppm) 498 + 195.16 104 734
Sodium (ppm) 136 + 76 4 252
Aluminium (ppm) 102 + 65 1 198
Iron (ppm) 203 + 203 <0.5 766
Manganese (ppm) 90 + 68 14.1 260
Zinc (ppm) 11.1 +5.9 1.4 24
Copper (ppm) 2.57 + 2.06 0.53 6.88
Boron (ppm) 1.85 + 0.42 1.3 3.22
Nickel (ppm) 2 + 1 <0.5 4.1
SD
1 ?
= Standard deviation
T
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.
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S
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to
ta
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d
i
m
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t
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H
D
=
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h
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r
i
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o
n
th
ic
k
n
e
s
s
; BD
=
d
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b
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d
e
n
s
it
y
;
T
C
=
t
o
ta
l
c
a
r
b
o
n
;
O
C
=
o
r
g
a
n
ic
c
a
r
b
o
n
; T
N
=
t
o
ta
l
n
i
tr
o
g
e
n
;
c
/
n
=
c
a
r
b
o
n
/n
itr
o
g
e
n
; T
P
=
t
o
ta
l
p
h
o
s
p
h
o
r
u
s
;
WE
P
=
w
a
t
e
r
e
x
tr
a
c
ta
b
l
e
p
h
o
s
p
h
o
r
u
s
; D
EP
=
d
i
lu
te
a
c
id
e
x
tr
a
c
ta
b
l
e
p
h
o
s
p
h
o
r
u
s
;
LE
P
=
La
n
c
a
s
te
r
s
o
lu
ti
o
n
e
x
tr
a
c
ta
b
l
e
P
; C
EC =
c
a
t
io
n
e
x
c
h
an
g
e
c
ap
a
c
i
t
y
,
E
A
= e
x
c
h
an
g
e
ab
l
e
ac
i
d
i
t
y
66
Table 10. Correlation on coefficients (r) for relationships between pond age (X) and bottom soil
quality variables (Y) in 42 catfish ponds, 40 freshwater prawn ponds, 18 carp ponds in Thailand.
Variables Catfish
1 ?
Prawn
2 ?
Carp
3 ?
Sediment depth (cm) 0.338 0.032 0.298
S-horizon thickness (cm) 0.349 0.105 0.167
Dry bulk density (g/cm
3
) 0.474 0.071 0.173
pH (standard units) 0.114 0.513 0.265
Total carbon (%) 0.173 0.0774 0.100
Organic carbon (%) 0.205 0.0547 0.032
Total nitrogen (%) 0.164 0.134 0.232
Sulfur (ppm) 0.300 0.035 0.071
Total carbon/total nitrogen 0.315 0.122 0.322
Particle size distribution:
Clay (%) 0.122 0.077 0.212
Silt (%) 0.297 0.055 0.603
Sand (%) 0.286 0.335 0.579
Total phosphorus (ppm) 0.063 0.205 0.158
Lancaster extractable Phosphorus (ppm) 0.170 0.045 0.100
Water - extractable phosphorus (ppm) 0.276 0.032 0.277
Dilute acid - extractable phosphorus (ppm) 0.285 0.084 0.032
Exchange acidity (mEq/ 100 g) 0.032 0.465 0.063
Cation exchange capacity (mEq/ 100 g) 0.454 0.118 0.089
Calcium (ppm) 0.158 0.187 0.063
Potassium (ppm) 0.438 0.158 0.184
67
Table 10 Continued.
Variables Catfish
1 ?
Prawn
2 ?
Carp
3 ?
Magnesium (ppm) 0.438 0.239 0.148
Sodium (ppm) 0.251 0.148 0.055
Aluminium (ppm) 0.158 0.063 0.243
Iron (ppm) 0.032 0.063 0.032
Manganese (ppm) 0.032 0.468 0.152
Zinc (ppm) 0.055 0.182 0.014
Copper (ppm) 0.118 0.205 0.277
Boron (ppm) 0.202 0.077 0.326
Nickel (ppm) 0.126 0.307 0.214
1 ?
Correlation on coefficients (r) greater than or equal to 0.304 and 0.393 are significant
levels of 5% and 1%, respectively.
2 ?
Correlation on coefficients (r) greater than or equal to 0.312 and 0.466 are significant
levels of 5% and 1%, respectively.
3 ?
Correlation on coefficients (r) greater than or equal to 0.468 and 0.590 are significant
levels of 5% and 1%, respectively.
68
Table 11. Concentrations of water quality variables in 42 catfish ponds in Thailand.
Variables Mean + SD
1 ?
Minimum Maximum
pH 7.6 + 0.62 5.45 8.45
Total alkalinity (mg/L as CaCO
3
) 117 + 58 0.5 236
Total hardness (mg/L as CaCO
3
) 184 + 123 71 806
Chloride (mg/L) 43 + 72 3 403
Sulfate (mg/L) 65.9 + 62.6 3.4 236
Calcium (mg/L) 55 + 45 17 279
Potassium (mg/L) 7.1 + 7.8 2.3 40.7
Magnesium (mg/L) 15.0 +13.7 4.0 82.8
Sodium (mg/L) 63 + 72 7 328
SD
1 ?
= Standard deviation
69
Table 12. Concentrations of water quality variables in 40 freshwater prawn ponds in
Thailand.
Variables Mean + SD
1 ?
Minimum Maximum
pH 7.86 + 0.41 6.9 8.3
Total alkalinity (mg/L as CaCO
3
) 79 + 23 28 162
Total hardness (mg/L as CaCO
3
) 137 + 54 62 266
Chloride (mg/L) 58 + 86 2 364
Sulfate (mg/L) 55 + 41 4.9 172
Calcium (mg/L) 39 + 16 6.6 79
Potassium (mg/L) 5.5 + 2.3 2.6 13.3
Magnesium (mg/L) 11.6 + 8.2 2.2 41.4
Sodium (mg/L) 57.7 + 56.1 3.8 265.8
SD
1 ?
= Standard deviation
70
Table 13. Concentrations of water quality variables in 18 carp ponds in Thailand.
Variables Mean + SD
1 ?
Minimum Maximum
pH 7.76+ 0.47 7 8.4
Total alkalinity (mg/L as CaCO
3
) 104 + 40 43 185
Total hardness (mg/L as CaCO
3
) 159 + 89 47 450
Chloride (mg/L) 23 + 42 2 193
Sulfate (mg/L) 53.6 + 40.5 10.3 170.6
Calcium (mg/L) 34.5 + 16.1 8.3 72.6
Potassium (mg/L) 9.6 + 4.9 2.3 19.3
Magnesium (mg/L) 12.2 + 5 5.3 22.8
Sodium (mg/L) 33.2 + 10.1 14.6 50.6
SD
1 ?
= Standard deviation
71
Table 14. Lime requirement for aquaculture pond bottom soil based on soil pH.
Soil pH Lime requirement (kg/ha)
7.5 or above 0
7.4 to 7.0 500
6.9 to 6.5 1,000
6.4 to 6.0 1,500
5.9 to 5.5 2,000
5.5 or less 3,000
1
Based on agricultural limestone with neutralizing value of 100%.
72
Sample areas
Figure 1. Map of Thailand showing location of sampling areas.
Source : http://www.thailand-community.de/th-map.htm Nov 1, 2005
73
Total sediment depth(cm)
a
a
b
0
5
10
15
20
25
30
35
40
catfish
prawn
carp
tilapia
Dry bulk density(g/cm
3
)
a
a
b
0
0.05
0.1
0.15
0.2
0.25
0.3
catfish
prawn
carp
tilapia
pH
a
a
a
0
1
2
3
4
5
6
7
8
catfish
prawn
carp
tilapia
Total carbon (%)
a
a
b
0
0.5
1
1.5
2
2.5
3
3.5
catfish
prawn
carp
tilapia
Organic carbon (%)
a
a
b
0
0.5
1
1.5
2
2.5
catfish
prawn
carp
tilapia
Figure 2. Histograms showing average concentrations of soil quality variables measure in
bottom soils from catfish, freshwater prawn, and carp ponds in Thailand. Bars in each
histogram represented by the same letter are not different (P > 0.05). Data on concentrations of
some variables in Tilapia pond soil in Thailand (Thanjai, 2002) are provided for visual but not
statistic.
S horizon thickness (cm)
a
a
b
0
2
4
6
8
10
12
14
16
18
catfish
prawn
carp
tilapia
74
Exchangable acidity (mEq/100g)
0
0.5
1
1.5
2
2.5
catfish
prawn
carp
tilapia
C:N ratio (%)
a
b
b
0
2
4
6
8
10
12
catfish
prawn
carp
tilapia
Water extractable phosphorus (ppm)
a
b
b
0
5
10
15
20
25
catfish
prawn
carp
tilapia
Cation exchange capacity(mEq/100g)
a
a
a
0
5
10
15
20
25
30
35
catfish
prawn
carp
Sulfur (ppm)
0
500
1000
1500
2000
2500
3000
3500
catfish
prawn
carp
Figure 2. Continued.
Total nitrogen (%)
a
a
b
0
0.05
0.1
0.15
0.2
0.25
0.3
catfish
prawn
carp
tilapia
a
a
a
a b
a b
75
Dilute acid extractable phosphorus
(ppm)
a
b
b
0
50
100
150
200
250
s
catfish
prawn
carp
tilapia
Total phosphorus (ppm)
0
200
400
600
800
1000
1200
1400
1600
1800
catfish
prawn
carp
Lancaster extractable phosphorus
(ppm)
a
b
a
0
50
100
150
200
250
catfish
prawn
carp
Soil calcium (ppm)
0
1000
2000
3000
4000
5000
6000
catfish
praw n
carp
Figure 2. Continued.
Clay (%)
0
5
10
15
20
25
30
35
40
45
catfish
prawn
carp
Silt (%)
a
b
a
0
10
20
30
40
50
60
70
catfish
prawn
carp
a a
a b
a a
b b
a b
a b
76
Sand (%)
a
b
a
0
2
4
6
8
10
12
14
16
catfish
prawn
carp
Soil potassium (ppm)
a
a
b
0
50
100
150
200
250
catfish
prawn
carp
Soil magnesium (ppm)
a
a
a
400
410
420
430
440
450
460
470
480
490
500
510
catfish
prawn
carp
Soil sodium (ppm)
a
a
a
0
20
40
60
80
100
120
140
160
180
200
catfish
prawn
carp
soil aluminium (ppm)
a
a
a
0
20
40
60
80
100
120
catfish
prawn
carp
Soil Copper (ppm)
0
0.5
1
1.5
2
2.5
3
catfish
prawn
carp
Fig. 2 Continued.
b b
a a
77
Soil Manganese (ppm)
b
a
a
0
10
20
30
40
50
60
70
80
90
100
catfish
prawn
carp
Soil Nickel (ppm)
a
a
a
0
0.5
1
1.5
2
2.5
catfish
prawn
carp
Figure 2. Continued.
Soil Boron (ppm)
a
a
a
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
catfish
prawn
carp
Soil Iron (ppm)
a
a
b
0
50
100
150
200
250
catfish
prawn
carp
Soil Zinc (ppm)
a
a
b
0
2
4
6
8
10
12
catfish
prawn
carp
78
y = 1.3008x + 0.0093
R
2
= 0.8507
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
0.00 1.00 2.00 3.00 4.00 5.00 6.00
Organic carbon (%)
Tota
l
c
a
t
bon (%)
Figure 3. Relationship between soil organic carbon concentration and soil total carbon
concentration in samples from ponds for production of catfish, freshwater prawn, and
carp in Thailand
79
y = 0.0872x + 0.0283
R
2
= 0.7569
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0.00 2.00 4.00 6.00 8.00
Total carbon (%)
Tota
l
ni
troge
n
(%)
Figure 4. Relationship between soil total carbon concentration and soil total nitrogen
concentration in samples from ponds for production of catfish, freshwater prawn, and
carp in Thailand.
80
Total hardness (mg/l as CaCO
3
)
a
a
a
0
50
100
150
200
250
300
catfish
prawn
carp
tilapia
Chloride (mg/L)
a
a
a
0
10
20
30
40
50
60
70
catfish
prawn
carp
Figure 5. Histogram showing average concentrations of water quality variables in ponds for
culture of catfish, freshwater prawn, and carp in Thailand. Bars in each histogram indicated by
the same letter did not differ (P > 0.05).
Water pH
a
a
a
0
1
2
3
4
5
6
7
8
9
catfish
prawn
carp
Total alkalinity (mg/l as CaCO
3
)
a
b
a
0
50
100
150
200
250
catfish
prawn
carp
tilapia
Sulfate (mg/L)
a
a
a
0
10
20
30
40
50
60
70
catfish
prawn
carp
Water calcium (mg/L)
a
b
b
0
10
20
30
40
50
60
catfish
prawn
carp
81
Figure 5. Continued.
Water Potassium (mg/L)
a
a
b
0
2
4
6
8
10
12
catfish
prawn
carp
Water Magnesium (mg/L)
a
a
a
0
2
4
6
8
10
12
14
16
catfish
prawn
carp
Water Sodium (mg/L)
a
a
a
0
10
20
30
40
50
60
70
catfish
prawn
carp
82
y = 0.2862x + 0.2616
R
2
= 0.7806
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
0.0 50.0 100.0 150.0 200.0 250.0 300.0
Calcium
M
a
gne
s
i
um
Figure 6. Relationship between magnesium concentration and calcium concentration in
water samples from ponds for catfish, freshwater prawn, and carp production in Thailand.
83
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