Aquaculture Pond Fertilization PDF

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Sodium is a macronutrient for culminating in fish and other aquaculture species. some species, and diatoms need a relatively large sil- This task is accomplished by applying either chem- icon amount. The common micronutrients are iron, ical fertilizer or organic matter such as animal dung manganese, zinc, copper, and molybdenum—some and other agricultural wastes. Chemical fertilizers plants also require one or more other elements such dissolve in pond water increasing nutrient concen- as chloride, boron, and cobalt. trations and stimulating phytoplankton growth. Or- Carbon dioxide enters water from the atmosphere ganic matter is decomposed by saprophytic microor- and from microbial organic matter decomposition. ganisms with mineralization of inorganic nutrients Hydrogen and oxygen are available from water. for use by phytoplankton. Organic matter also may The major nitrogen source is organic nitrogen min- be a direct organic nutrient source for invertebrate eralization to ammonia nitrogen during microbial fish food organisms, and some fish species feed di- organic matter decomposition. Other nutrients are rectly on manure particles. Pond treatment with or- derived from mineral dissolution. Sources of these ganic matter actually represents combined fertiliza- nutrients may be runoff entering ponds following tion and feeding. contact with minerals in catchment soils, spring or In this chapter, only inorganic nutrients resulting well water contacting minerals in aquifer forma- from chemical fertilizer and organic matter applica- tions, and mineral dissolution in pond bottom soil. tions to ponds will be considered. These nutrients Seawater and estuarine water used in coastal ponds participate in complex biogeochemical cycles, and have high major cation concentrations. effective pond fertilization programs must consider According to Liebig’s Law of the Minimum how these cycles influence fertilizer nutrient avail- (Odum 1975), plant growth is limited by the nu- ability to phytoplankton. trient present in shortest supply relative to its need by phytoplankton. Phytoplankton and other aquatic plants are limited most commonly by inadequate 1.2 PLANT NUTRIENTS phosphorus and nitrogen, but in waters of either low Green plants require numerous inorganic nutrients in or high alkalinity, a carbon dioxide shortage may relatively large amounts (macronutrients) or in fairly limit plant growth (Boyd 1972). In seawater, it is Aquaculture Pond Fertilization: Impacts of Nutrient Input on Production, First Edition. Edited by Charles C. Mischke.  C 2012 John Wiley & Sons, Inc. Published 2012 by John Wiley & Sons, Inc. 3 4 General Fertilization Concepts suspected that low iron and manganese concentra- tions may also limit phytoplankton growth (Nadis Phosphorus concentration in plants Luxury 1998). consumption Liebig’s Law does not imply that a single nutrient controls phytoplankton growth. To illustrate, sup- pose, phosphorus is the most limiting nutrient in a Growth pond to which a phosphorus fertilizer application s nt pla is made. After fertilizer application, phytoplankton h t ow in abundance will increase in response to the greater Gr P phosphorus concentration until some other nutri- ent becomes limiting. Remaining added phosphorus will not elicit a growth response until more second limiting nutrient is applied. Adding more second Phosphorus concentration in water limiting nutrient could lead to a third nutrient be- coming limiting (Polisini et al. 1970). Thus, Liebig’s Figure 1.2. Luxury consumption of Law applies to multiple limiting nutrients (Fig. 1.1). phosphorus by phytoplankton. Plant response to nutrients also may be con- founded by luxury consumption (Gerloff and Skoog 1954, 1957). In luxury consumption, plants absorb can be limiting to phytoplankton growth at low con- more nutrient than necessary for maximum growth. centrations, but be toxic to phytoplankton at higher The excess nutrient is stored in plant cells for later concentrations (Boyd and Tucker 1998). In fact, cop- use, or in the case of phytoplankton cells, the nu- per sulfate is probably the most common algicide trient may be passed on to succeeding generations in use today. Most nutrients can be toxic at high when cells divide. The luxury consumption concept concentration, but in ponds, nutrient concentrations is illustrated in Figure 1.2. seldom reach toxic levels. Liebig’s Law was expanded by Shelford’s Law of Factors other than nutrients also can limit phy- Tolerance (Odum 1975). This law states there may toplankton growth. Some examples are inadequate be either too little or too much nutrient or other en- light because of cloudy weather or excessive pond vironmental factors as illustrated in Figure 1.3 for turbidity, low temperature, and low pH. light. In the case of nutrients, some such as copper Water analyses may be used to measure nutri- ent concentrations, but it is difficult to determine which nutrients limit phytoplankton growth. In lake Phosphorus + nitrogen + sulfur Death Insufficient Optimum Excessive Death Phosphorus + nitrogen Phosphorus Growth Growth Light intensity Nutrient concentration Figure 1.3. Illustration of Shelford’s Law of Figure 1.1. Multiple limiting nutrients and Tolerance using effect of light on phytoplankton growth. phytoplankton growth.  Nutrient Cycling 5 eutrophication studies, water samples were filtered ever, several factors influence the fate of nitrogen and to remove phytoplankton, aliquots were placed in phosphorus added to ponds in fertilizers, and adding flasks, nutrients were added singly and in various nitrogen and phosphorus in fertilizers according to combinations to flasks, flasks were inoculated with the Redfield ratio does not assure the same ratio of a planktonic algal species, and after a few days, the the two nutrients in pond water. algal abundance was more in the flasks compared with algal abundance in a flask to which no nutrients 1.2.1 Phosphorus were added (Miller et al. 1974; Golterman 1975). Because of its complexity, this procedure is seldom Forms in Water suitable for determining nutrient requirements for There are several phosphorus forms in water; the individual ponds, but it could be used in a study most common are: (1) soluble inorganic phospho- to assess nutrient limitations in ponds across a re- rus, (2) soluble organic phosphorus, (3) phospho- gion. Results of such a study would reveal the likely rus in particulate organic matter (living plankton limiting nutrients for ponds in the region. or detritus), and (4) phosphorus adsorbed on sus- Experience with pond fertilization in many pended mineral particles. Soluble inorganic phos- countries suggests nitrogen and phosphorus are the phorus is an ionization product of orthophosphoric only two nutrients normally needed in fertilizers for acid (H3 PO4 ): freshwater ponds (Mortimer 1954; Hepher 1962; Hickling 1962; Boyd and Tucker 1998). These two H3 PO4 = H+ + H2 PO4 − K = 10−2.13 nutrients also are most commonly used in fertilizing − + H2 PO4 = H + HPO4 2− K = 10−7.21 ponds filled with brackish water or seawater. However, micronutrients are sometimes included HPO4 2− = H+ + PO4 3− K = 10−12.36 in fertilizers for shrimp ponds. Moreover, because they think diatoms are a superior natural food for Pond water pH is usually between 6 and 9, and the shrimp, farmers in Central and South America often most common soluble inorganic phosphorus forms apply silicate fertilizer such as calcium silicate to are H2 PO4 − and HPO4 −. These two ion proportions shrimp ponds. are equal at pH 7.21—at lower pH, H2 PO4 − is dom- There is a widespread idea, phosphorus is not as inant and at higher pH, HPO4 − is more abundant. important in brackish water and seawater ponds as All soluble phosphorus in water is not in inorganic in freshwater ponds. This has led to frequent use form; some associated with soluble organic com- of wide N:P ratios in fertilizers for shrimp ponds pounds. The most common way of estimating plant- in Central and South America. However, a recent available phosphorus in water is to measure solu- review (Elser et al. 2007), suggested nitrogen and ble reactive phosphorus (SRP) concentration (Eaton phosphorus limitation of freshwater, marine, and ter- et al. 2005). This test measures all soluble inorganic restrial ecosystems are similar. phosphorus, but it also measures some soluble or- Another common idea about nutrient ratios in fer- ganic phosphorus. Soluble organic phosphorus is not tilizer originates in the observation of the average available to phytoplankton until it is mineralized to molecular ratio of carbon, nitrogen, and phospho- phosphate by microbial activity. rus in marine phytoplankton of 106:16:1 (weight ra- The other common phosphorus measurement is tio = 41:7.2:1)—the Redfield ratio (Redfield 1934). for total phosphorus. For practical purposes, the Brzezinski (1985) suggested including silicon in the SRP concentration subtracted from total phosphorus Redfield ratio—the molecular ratio C:Si:N:P for ma- concentration is a particulate phosphorus concentra- rine phytoplankton is 106:15:16:1 (weight ratio = tion estimate. This is not entirely true, because SRP 41:13.6:7.2:1). The Redfield ratio suggests phyto- determination does not include all soluble organic plankton need nitrogen and phosphorus in roughly a phosphorus (Eaton et al. 2005). 7:1 ratio, and it is often recommended that pond fer- More detailed analyses required to precisely de- tilizers for freshwater and saline water ponds should termine soluble organic phosphorus and to sepa- contain nitrogen and phosphorus in this ratio. How- rate particulate organic phosphorus from particulate 6 General Fertilization Concepts inorganic phosphorus are seldom done with regards to pond fertilization. 20 AIPO4.2H2O Forms in Pond Soil Phosphorus occurs in soils in a variety of iron, alu- 10 minum, and calcium phosphate compounds (Brady 2002). Representative iron and aluminum phos- phates and their dissolution equations are shown as follows: Phosphorus (µg/L) 0 + AlPO4 · 2H2 O + 2H = Al 3+ + H2 PO4 2− 5 6 7 + 2H2 O K = 10−2.5 + 10 FePO4 · 2H2 O + 2H = Fe 3+ + H2 PO4 2− Ca5(PO4)3OH −6.85 + 2H2 O K = 10 Iron and aluminum oxides in soil also can adsorb 5 phosphorus as follows: Al(OH)3 + H2 PO4 − = Al(OH)2 H2 PO4 + OH− FeOOH + H2 PO4 − = Fe(OH)2 PO4 + OH− 0 7 8 9 Iron and aluminum phosphate compound solubil- pH ity increases with decreasing pH as illustrated in Figure 1.4 for AlPO4 ·2H2 O. Nevertheless, even at a Figure 1.4. Concentration of phosphorus at pH 5, phosphorus solubility from this compound at equilibrium between waters of different pH equilibrium is only 0.017 mg/L. and aluminum phosphate (AlPO4 ·2H2 O) and Highly leached, acidic soils usually contain calcium phosphate [Ca5 (PO4 )3 OH]. large amounts of iron and aluminum oxides and hydroxides (Lal and Sanchez 1992). Two examples of such minerals and their dissolution equations are Example 1.1. Concentration of phosphate in as follows: equilibrium with Al(OH)3 : Al(OH)3 + 3H+ = Al3+ + 3H2 O K = 109 Highly soluble monocalcium phosphate, Ca(H2 PO4 ) is dissolved in water of pH 6 to Fe(OH)3 + 3H+ = Fe3+ + 3H2 O K = 10−3.54 give a solution 1 mg/L in phosphorus. A few grams Iron and aluminum oxides and hydroxides sol- solid phase Al(OH)3 are added to the flask. The ubility increase with decreasing pH. Phosphate phosphorus concentration remaining in the water at added to acidic soils will precipitate quickly and equilibrium will be calculated. be fixed as highly insoluble iron and aluminum Solution phosphate—especially as aluminum phosphate, be- cause Al(OH)3 is more than five orders of magnitude The Al(OH)3 will dissolve as follows: more soluble than Fe(OH)3 at the same pH (Boyd Al3+ 1995). The role of Al(OH)3 in controlling phos- = 109 phorus concentration in acidic soil is illustrated in (H+ )3 Example 1.1. (Al3+ ) = (10−6 )3 (109 ) = 10−9 M Phosphate adsorption by iron and aluminum ox- ides and hydroxides decreases with decreasing pH. Al3+ will react with phosphate to form However, this phenomenon does not diminish phos- AlHPO4 ·2H2 O, and as Al3+ is precipitated in the re- phate precipitation as illustrated in Example 1.1. action, more Al(OH)3 will dissolve so AlPO4 ·2H2 O  Nutrient Cycling 7 will continue to precipitate. At equilibrium, the to zooplankton, fish, and other organisms. When phosphorus concentration will be: these organisms die, they settle to the pond bottom and become organic matter containing phosphorus. (Al3+ )(H2 PO4 − ) Thus, pond bottom soils contain organic phospho- = 10−2.5 (H+ )2 rus, but no references to typical concentration ranges (10−6 )2 (10−2.5 ) 10−14.5 could be found. The upper, 20-cm sediment layer in (H2 PO4 − ) = = = 10−5.5 M ponds at the E. W. Shell Fisheries Center at Auburn (10−9 ) (10−9 ) University has a dry bulk density 1500 kg/m3 and (3.16 × 10−6 M)(30.98 g P/mole)(10−3 ) 2% organic matter (Munsiri et al. 1995). If organic = 0.032 mg P/L matter phosphorus concentration is about the same as for dead plankton (around 0.5%), then soil would Calcium phosphate compounds are found in neu- contain about 100 mg/kg P bound in organic matter. tral and basic soils (Brady 2002). The most stable The role of sediment in removing phosphorus calcium phosphate compound is the mineral apatite from pond water was demonstrated by measuring that occurs in several forms. A representative form, phosphorus concentrations in water and sediment of hydroxyapatite, and its dissolution equation are as research ponds at Auburn University (Masuda and follow: Boyd 1994a). These ponds had been treated with fertilizers for 20 years, and ponds had been drained Ca5 (PO4 )3 OH + 7H+ = 5Ca2+ + 3H2 PO4 − + H2 O after each growing season. At sampling, pond water K = 1014.46 contained 0.252 g/m2 P, while sediment (to a 20 cm depth) contained 132.6 g/m2 P (Table 1.1). Phos- At the same calcium concentration, phosphorus phorus in sediment accounted for about two-thirds solubility from hydroxyapatite is low at pH 7 and phosphorus applied to ponds. Fish harvest typically decreases with increasing pH (Fig. 1.4). At the same removes 20–30% phosphorus applied to ponds in pH, phosphorus concentration will decrease with feeds and fertilizers (Boyd and Tucker 1998). Thus, a greater calcium concentration. relatively small phosphorus amount was discharged Calculations for preparing Figure 1.4 were based from ponds in water. It had either been absorbed by on the equilibrium constant for pure, crystalline alu- soil or removed from ponds in fish biomass. minum and calcium phosphate forms. In pond wa- Soil in ponds at Auburn University contained ters, amorphous aluminum and calcium phosphate roughly 1000 mg/kg P, sediment pore water con- forms precipitate. These forms gradually transform tained about 1 mg/L SRP, water at the soil-water to crystalline form, but amorphous forms are more interface had 0.1 mg/L SRP, and the water column soluble than crystalline forms (Bennett and Adams had 0.04 mg/L SRP (Masuda and Boyd 1994b). 1976). Thus, phosphate solubility in water is some- Thus, relatively little phosphorus bound in sediment what greater than indicated in Figure 1.4. Concen- is available at any one time to phytoplankton in the trations at equilibrium with amorphous forms, nev- water column. In traditional agriculture, fertilizer is ertheless, will be quite low. mixed into soil, and an equilibrium develops be- At pH 6.5–7, Al3+ , Fe3+ , and Ca2+ concentrations tween phosphate bound in soil and SRP in the pore are lowest. Thus, phosphate solubility from minerals water—the same as happens in pond bottom soils. in pond soil will be greatest in this pH range. Put However, in terrestrial systems, plant roots grow another way, the tendency for phosphate applied in throughout the soil mass and have easy access to fertilizer to be bound in soil as iron, aluminum, and phosphorus dissolved in pore water. When plants re- calcium phosphates will be lowest at pH 6.5–7.0. move phosphorus from pore water, equilibrium can Nevertheless, even though bottom soil might have a be quickly reestablished by soil phosphorus disso- pH 6.5–7.0, most phosphate applied to such ponds lution. In ponds, phytoplankton grow in the upper, in fertilizer will be sequestered in sediment (Masuda illuminated water stratum, and when they remove and Boyd 1994a). phosphorus from the water, phosphorus replacement Phytoplankton absorbs phosphorus, and some of is logistically much more difficult than in terrestrial this phosphorus is transferred through the food web soils as is illustrated in Figure 1.5. 8 General Fertilization Concepts Table 1.1. Distribution of Soil and Water Phosphorus within Different Pools and Fractions for a Fishpond at Auburn, Alabama. Phosphorus Pool Phosphorus Fraction Amount (g/m2 ) Percentage (%) Pond watera Total phosphorus 0.252 0.19 Soluble reactive phosphorus 0.019 0.01 Soluble nonreactive phosphorus 0.026 0.02 Particulate phosphorus 0.207 0.16 Soilb,c Total phosphorus 132.35 99.81 Loosely bound phosphorus 1.28 0.96 Calcium-bound phosphorus 0.26 0.20 Iron- and aluminum-bound phosphorus 17.30 13.05 Residual phosphorusd 113.51 85.60 Pond Total phosphorus 132.60 100.00 a Average pond depth = 1.0 m. b Soil depth = 0.2 m. c Soil bulk density = 0.797 g/cm3. d Phosphorus removed by perchloric acid digestion. PHYTOPLANKTON LAND PLANT Phytoplankton in surface water AIR WATER Convection source of P and site Distance between and diffusion of plant uptake P INTERFACE Diffusion SOIL SOIL P PORE WATER P P ROOTS IN CLOSE CONTACT WITH P Figure 1.5. Illustration of pathway of phosphorus (P) from soil to site of plant absorption in pond soil and terrestrial soil.  Nutrient Cycling 9 When phosphorus fertilizer is applied to a pond, phytoplankton quickly remove some applied phos- phorus, but most is usually adsorbed by sediment 0.5 Total phosphorus (Boyd et al. 1980). Soluble phosphorus concentra- Particulate phosphorus tions reach pretreatment concentrations within a few days (Fig. 1.6). Moreover, when phytoplankton die, Phosphorus concentration (mg/L) 0.4 settle to the bottom, and are decomposed, phos- phorus contained in them is quickly adsorbed by sediment. Granular phosphorus fertilizers such as triple su- 0.3 perphosphate and ammonium phosphates used for pond fertilization do not dissolve quickly while set- tling through the water column (Boyd 1981). If 0.2 broadcast over the water surface, granules mainly dissolve after settling to the pond bottom, and phos- phorus is quickly adsorbed by pond soil. Granular fertilizers should first be mixed in a bucket of water 0.1 and allowed to dissolve for 30 minutes to 1 hour be- fore being splashed over the pond surface. By doing this, a greater phosphorus proportion will dissolve in 0.0 the water column increasing opportunity for phos- J J A S O N phorus absorption by phytoplankton (Boyd 1981). Because of their high density (≈1.4 g/mL), liquid Figure 1.6. Average concentrations of total fertilizers also should be premixed with water and and particulate phosphorus in two fertilized applied over the pond surface (Boyd and Hollerman fishponds. Vertical arrows indicate fertilizer application dates. 1981). As frequently recommended, but seldom used, an alternative to predissolving granular fertilizers is to apply them on an underwater platform (Fig. 1.7). 20–30 cm Fertilizer Underwater platform Figure 1.7. Underwater platform for applying fertilizers to ponds. 10 General Fertilization Concepts The fertilizer phosphorus dissolves in water and is pond fertilization rates could be established using mixed throughout the pond by water currents. Usu- soil test data for nutrients, but more work is needed ally, one platform is sufficient for 2–3 ha of water to perfect this methodology. At present, the most surface area. reliable technique is to base phosphate fertilizer Some pond fertilizer vendors offer a highly water- application rates on amounts that have provided soluble fertilizer containing phosphorus as finely good fish production in previous research. Work at pulverized ammonium or potassium phosphate. This Auburn University (Wudtisin and Boyd 2005) sug- fertilizer can be broadcast over pond surfaces, and it gested periodic applications of about 3 kg P2 O5 /ha will dissolve before sinking to the bottom (Rushton will provide enough phosphorus for good sportfish and Boyd 2000; Tepe and Boyd 2001). Controlled- production in ponds that have been limed to neu- release fertilizers can be made by coating fertil- tralize soil acidity and provide total alkalinity of izer granules with a copolymer shell, for example, 30–40 mg/L. Tilapia production about 1000 kg/ha one product is coated with dicyclopentadiene and was obtained in ponds at Auburn University treated glycerol ester (Boyd and Tucker 1998). Water dif- with 9 kg P2 O5 /ha per application at 2-week inter- fuses through the shell and fertilizer dissolves in vals (Boyd 1976). However, in Israel, pond water the moisture inside the shell. Nutrients are gradu- contains much more calcium than ponds at Auburn ally released through microscopic pores in the shell. University, and almost three times as much phospho- Copolymer is applied in layers; the more layers, rus was needed to obtain similar tilapia production the slower the release rate. Initial nutrient release (Hepher 1962). rate is not great enough to elicit a phytoplankton There are few places in the world where opti- bloom. However, if an ordinary fertilizer is used to mum fertilizer rates have been determined for ponds, initiate the phytoplankton bloom, a single applica- but the nature of the soil and water can provide tion of controlled-release fertilizer can maintain a a clue. Ponds with acidic soils that have not been phytoplankton bloom for an entire growing season limed will require more phosphorus than ponds with (Rushton and Boyd 1995; Kastner and Boyd 1996). acidic soils that have been limed to provide a near The main disadvantage to highly water-soluble and neutral pH. Ponds with soils and waters of basic controlled-release fertilizers is their high cost. reaction and high calcium concentration will tend Phosphate fertilizers must be applied to ponds at to need more phosphorus than ponds with neutral fairly frequent intervals (usually, every 2–4 weeks) soils and moderate calcium concentrations in water. to maintain phytoplankton blooms. Even after years Pond soils with large amounts of iron and aluminum of fertilization, phosphorus release from bottom oxides—such as many tropical soils—will tend to soils usually is not adequate to maintain phytoplank- strongly fix phosphorus. Boyd and Munsiri (1996) ton blooms. For example, an experiment was con- found the ability of pond soils in Thailand to bind ducted at Auburn University in which fertilization phosphorus increased with increasing clay content. was halted in some ponds that had been regularly Sandy soils would tend to fix less phosphorus than fertilized for 15 years (Swingle et al. 1963). Dur- clayey soils. ing the first year without phosphate fertilization, Eren et al. (1977) reported soil P concentrations fish production declined to typical levels for un- increased over time in fertilized ponds in Israel and fertilized ponds. Another study conducted in Israel suggested phosphorus application could be lowered (Hepher 1966) demonstrated phosphorus release in older ponds. Boyd and Munsiri (1996) found from sediment of fertilized ponds was only about soils with higher phosphorus concentrations tended 20% of the phosphorus amount needed to maintain to have higher water-soluble equilibrium concentra- enough phytoplankton productivity for desired fish tions. This also suggests phosphorus adsorption by production. soil probably will decline as soils accumulate phos- Because of strong phosphorus uptake by sedi- phorus. Nevertheless, most studies have shown pond ment, water analysis is not a good indicator of phos- soils are a sink for fertilizer phosphorus, and phos- phorus that should be applied to ponds in fertilizers. phate must be applied on a regular basis to maintain A recent study (Banerjee et al. 2009) demonstrated phytoplankton blooms.  Nutrient Cycling 11 measuring total nitrogen—exclusive of N2 —that has P in been used in a few pond fertilization studies. In most inflow Fertilizer pond fertilization research, analyses have focused on the plant-available nitrogen forms—ammonia nitro- gen and nitrate nitrogen. Unionized NH3 is toxic to fish, and the NH3 –N Inorganic P proportion in a sample may be estimated from the P in plants in water following relationship: P in animals NH3 + H2 O = NH4 + + OH− K = 10−4.74 Inorganic P in organic P in soil matter and Tables giving the proportion of NH3 –N to TAN at microbes different water temperatures and pHs are available, P in outflow for example, see Boyd and Tucker (1998). The NH3 and harvested proportion rises with increasing pH, and excessive fish fertilization with urea or ammonium fertilizers can cause fish toxicity (Boyd et al. 2008). Nitrite also is Figure 1.8. Phosphorus cycle in a fertilized toxic to fish, but nitrite is not used as a fertilizer, and pond. natural nitrite sources seldom are elevated enough to be problematic in fertilized ponds. Nitrogen fertilizers for ponds include ammonium and nitrate compounds, urea, and organic matter The phosphorus dynamics in fishponds are illus- (Boyd and Tucker 1998). Urea quickly hydrolyzes trated in Figure 1.8. in water as follows: 1.2.2 Nitrogen CO(NH)2 + H2 O −−− −−→ 2NH3 + CO2 Urease Forms in Water Nitrogen, like phosphorus, occurs in water in several Organic matter applied as fertilizer is decomposed forms: nitorgen gas (N2 ), ammonia (NH3 ), ammo- by saprophytic microorganisms with ammonia nitro- nium (NH4 + ), nitrite (NO2 − ), nitrate (NO3 − ), sol- gen release. uble organic nitrogen compounds, and nitrogen in particulate organic matter. Nitrogen gas concentra- Plant Uptake tion is not measured in pond waters, but the con- Phytoplankton and other plants absorb ammonium centration will usually be near saturation (Boyd and and nitrate from water. These ionic nitrogen forms Tucker 1998). The common procedures for measur- are used by the plant to make amino acids, which are ing ammonia nitrogen do not distinguish between protein components. To make amino acids, ammo- NH3 and NH4 + ; both are measured together, and nia must be combined with organic carbon com- results reported as total ammonia nitrogen (TAN) pounds originating from photosynthesis. Thus, if or ammonia nitrogen (Eaton et al. 2005). Nitrite plants make amino acids using nitrate as the ni- and nitrate each usually are measured separately. trogen source, nitrate must be reduced to ammonia Organic nitrogen is present in soluble and particu- nitrogen via the nitrate reductase pathway (Devlin late form, and for pond fertilization purposes, the 1969). It is energetically more efficient for plants two fractions are not separated. The common way to use ammonia rather than nitrate as a nitro- to measure organic nitrogen in pond water is the gen source. Nevertheless, most plants, including Kjeldahl nitrogen procedure, one version that mea- phytoplankton, apparently can and do use ammo- sures only organic nitrogen (Eaton et al. 2005). nium and nitrate. There is some anecdotal evidence Gross and Boyd (1998) described a method for that, however, brackish water pond fertilization with 12 General Fertilization Concepts nitrate is more effective than fertilization with urea most organisms have similar carbon concentrations, or ammonium in encouraging diatom production. the C:N ratio varies greatly among organisms. Some organic matter can be decomposed quicker Natural Sources and more completely than others by organisms of de- Rainwater contains nitrate because electrical activ- cay. In general, decomposition rate declines in the ity oxidizes small amounts of gaseous nitrogen to following order: sugars and starches > proteins > nitrate, and nitrous oxides from air pollution are cellulose > fats and oils > waxes > hemicelluloses oxidized to nitric acid. Rainwater also may con- and lignins (Boyd 1995). The protoplasmic fraction tain some ammonia resulting from air pollution decomposes faster than the structural fraction, and and other terrestrial sources (Boyd 2000). Runoff nitrogen is associated mainly with the protoplasmic dissolves and suspends nitrogen compounds from fraction. Thus, materials with a narrow C:N ratio watersheds before entering ponds. In addition, cer- decompose faster and more completely than mate- tain bacteria and blue-green algae species have the rials with a wide C:N ratio. Moreover, organisms ability to fix nitrogen. The most well-known nitro- of decay use a portion of the nitrogen from organic gen fixers in pond waters are blue-green algae of residues to make their biomass, and a narrow C:N the genus Anabaena that contain heterocysts. When ratio favors a greater ammonia nitrogen release to N-fixing organisms die and decompose, nitrogen in the environment (nitrogen mineralization) than does them is converted to plant-available form. Ammo- a wide C:N ratio (Boyd 1995). Nitrogen may be re- nium and nitrate presence will suppress nitrogen fix- moved from the environment (immobilized) by mi- ation (Bothe 1982), but nitrogen fixation rates up to croorganisms decomposing a material of wide C:N about 60 mg/m2 /d have been reported in aquaculture ratio (see Example 1.2). ponds (Lin et al. 1988). The nitrogen fixation rate increases when the N:P ratio is low. At N:P ratios Example 1.2. Illustration of mineralization and above 13, no nitrogen fixation was detected (Findlay N immobilization: et al. 1994). Organic matter is present in pond sediment re- Bacteria contain about 50% carbon and 10% ni- sulting from organic matter sedimentation entering trogen, and they convert about 5% organic carbon ponds from watersheds and sedimentation of plank- to carbon in bacterial biomass during decomposi- ton remains (including nitrogen fixing organisms) tion. A highly decomposable organic matter residue and other organisms. Sediment organic matter de- (1000 g; 45% C; 1% N) contains 450 g C and 10 g N. composition is an ammonia nitrogen source to the The nitrogen amount mineralized during complete water column. residue decomposition will be calculated. Mineralization of Organic Nitrogen r 450 g C × 0.05 = 22.5 g bacterial carbon (45 g Cycles for carbon and nitrogen are intertwined, and bacteria) r 45 g bacteria × 0.1 = 4.5 g bacterial nitrogen it is not possible to discuss one independently of r 10 g in residue − 4.5 g bacterial nitrogen = the other. Plants and animals comprise 40–50% car- bon (dry weight basis), but their nitrogen content 5.5 g N mineralized. may vary from 10%, and most nitrogen in biomass is in protein amino acids (Boyd 1990). Suppose residue had only 0.4% nitrogen or 4 g Most animals and bacteria including actino- N in 1 kg residue, then residue would contain 0.5 g mycetes, contain 8–12% nitrogen on a dry weight less nitrogen than needed by the bacteria to quickly basis. Higher plants have a large amount of struc- decompose it. tural material (cellulose, hemicellulose, and lignin); hence, they have lower nitrogen concentrations— Organic matter decomposition is oversimplified usually, about 1–4%. Phytoplankton cells have less in Example 1.2 because all organic residue is as- structural material than found in higher plants, and sumed to decompose. In reality, the most reactive nitrogen concentration usually is 8–10%. Because organic matter (labile fraction) decomposes within  Nutrient Cycling 13 a few weeks or months, while more resistant organic Decomposition of the fresh organic matter labile matter (refractory fraction) decomposes over a much fraction occurs mainly in the flocculent layer (F hori- longer time (Boyd 1995). The partially decomposed zon) and in the So horizon (Fig. 1.9). Ammonia ni- products of organic matter, including those from trogen mineralized within F and So horizons can dead decomposer organisms, and excretions from enter the water and be recycled for use again by decomposer organisms react to form complex, high- phytoplankton and other plants. It is doubtful that molecular weight compounds known collectively as much nitrogen mineralized by anaerobic decompo- humus. The humus fraction is relatively stable and sition within deeper pond soil layers enters the water decomposes at a steady rate over a long time. The column. C:N ratio of fresh organic residues may vary greatly, The nitrogen mineralized in pond bottoms in- but the C:N ratio in soil that results mainly from the creases as ponds age, and after as little as 5–10 humus fraction usually is around 8–12 (Brady 2002). years, nitrogen amount entering some ponds from Organic matter concentration typically is low in pond soil allows nitrogen fertilization rates to be re- new pond bottoms, because the O and A horizons of duced or suspended (Swingle et al. 1963; Boyd and the area to be the pond bottom usually are removed. Tucker 1998). The pond bottom lies in the B horizon that has a lower organic matter concentration than typically Nitrification found in the O and A horizons (Brady 2002). A Ammonia nitrogen is oxidized to nitrate nitrogen by soil profile develops above the original bottom soil nitrifying bacteria. These chemoautotrophic bacteria in ponds because of sedimentation (Munsiri et al. use energy released from ammonia oxidization to re- 1995). This profile usually is discernable within 2–3 duce carbon dioxide to organic carbon. The process years, and well developed within 5–10 years. The is in some ways analogous to photosynthesis, ex- horizons are described in Figure 1.9. cept dissolved oxygen is used rather than produced. WATER HORIZON CHARACTERISTICS FLOCCULENT LAYER Water with high concentration of mineral F and organic solids, aerobic Oxidized (aerobic) So MIXED POND SOIL PROFILE SEDIMENT S Sediment with high water content and LAYER Reduced low dry bulk density, abundant organic (anaerobic) Sr matter, well stirred by physical and SEDIMENT biological agents, thin aerobic surface but anaerobic below MATURE STABLE SEDIMENT M Sediment with medium water content and intermediate dry bulk density, abundant organic matter, not stirred, MT anaerobic TRANSITIONAL T Transition between M and P horizons LAYER with characteristics intermediate PT between M and P horizons, not stirred, anaerobic ORIGINAL, UNDISTURBED POND BOTTOM P Low water content and high bulk density, usually compacted, low organic matter, not stirred, anaerobic Figure 1.9. Horizons in a pond bottom soil (sediment) profile. 14 General Fertilization Concepts Organic carbon yield per unit ammonia nitrogen ox- as the carbon source, and N2 as the resulting idized is low; hence, nitrification is not a significant nitrogenous gas: organic carbon source. The nitrification process occurs in two steps. In the 6NO3 − + 5CH3 OH → 5CO2 + 3N2 ↑ +7H2 O first step, Nitrosomonas bacteria oxidize ammonia + 6OH− nitrogen to nitrite: Of course, organic carbon sources other than − + NH4 + 1.5O2 → NO2 + 2H + H2 O methanol usually are present in pond soils and waters. Denitrification occurs only in the absence of In the second step, Nitrobacter bacteria oxidize molecular oxygen, so it is restricted to the nitrite to nitrate: hypolimnion of stratified, eutrophic water bodies or the anaerobic sediment layer. Gases resulting from NO2 − + 0.5O2 → NO3 − this process diffuse into the air, but ammonia pro- duced in denitrification is in equilibrium with am- The combined equation for nitrification is: monium remaining in water. Denitrification is an important process in aquacul- NH4 + + 2O2 → NO3 − + 2H+ + 2H2 O ture ponds, because it removes considerable nitrogen (Hargreaves 1998). Denitrification rates measured in channel catfish ponds at Auburn University averaged Nitrification requires dissolved oxygen—4.57 mg 38 mg N/m2 /d during summer—equal to a nitrogen oxygen for 1 mg/L ammonia nitrogen oxidized to ni- loss of 11.48 kg N/ha or about 20% nitrogen input trate. Thus, nitrification occurs only in the water col- in feed (Gross et al. 2000). Fertilized ponds usually umn and in the soil F and So horizons. Nitrification have much lower nitrogen inputs than channel cat- rate may be considerable—amounts of nitrate nitro- fish ponds, but the percentage fertilizer nitrogen loss gen production by this process have been reported through denitrification is likely similar. to reach 0.5 mg/L/d or more in ponds (Hargreaves Hydroxyl ion from denitrification can react with 1998). carbon dioxide to form bicarbonate (a contributor to Nitrification is an acidic reaction because the hy- alkalinity) as follows: drogen ion produced in this process neutralizes al- kalinity. The hydrogen ion resulting from oxidiza- OH− + CO2 − = HCO3 − tion of 1 mg/L ammonia nitrogen will neutralize 7.14 mg/L total alkalinity (reported as equivalent Thus, denitrification is a basic reaction. If nitrifi- CaCO3 ). It follows ammonium-based nitrogen fer- cation and denitrification are perfectly linked, that is, tilizers and urea that hydrolyze to release ammonia nitrate for denitrification originated in nitrification, that will have an acidic reaction—they are called the denitrification process could only restore half the acid-forming fertilizers. alkalinity consumed in nitrification. This is true be- cause each mole of ammonia nitrogen oxidized in ni- Denitrification trification results in 2 mol of hydrogen ion, whereas Certain bacteria, called denitrifying bacteria, can use denitrification produces only 1 mol of hydroxyl ion oxygen from nitrate and nitrite as a substitute for for each mole of nitrate nitrogen reduced. molecular oxygen in respiration (organic matter ox- idation). Nitrate and nitrite are reduced to gaseous Ammonia Volatilization form, usually N2 , but N2 O or NH3 also may be den- Ammonia in water diffuses into the air. The rate this itrification end products (Metting 1993). The equa- process occurs increases in response to greater wa- tion most commonly used to describe denitrifica- ter temperature, TAN concentration, surface water tion uses nitrate as the oxygen source, methanol pH, and turbulence caused by wind or other factors  Nutrient Cycling 15 (Hargreaves 1998; Boyd 2000). Gross et al. (1999) driven cycle. The nitrogen cycle is predominately a reported ammonia volatilization rates 9–71 mg biologically driven cycle. N/m2 /d from ponds at the E.W. Shell Fisheries Center at Auburn University. The greatest rates were 1.2.3 Carbon reported for ponds with TAN concentrations 4 or Inorganic carbon is needed in ecosystems in large 5 mg/L on windy days when pH was >8.5 and wa- amounts, because it is used in photosynthesis to ter temperature >25◦ C. The lowest reported rate make organic carbon compounds that become plant of 9 mg N/m2 /d is equal to an ammonia diffusion biomass, some of which is transformed via the food loss of 2.7 kg N/ha in 1 month. Thus, ammonia web to animal biomass. Plant and animal biomass volatilization represents an important nitrogen loss eventually become organic matter, and organic car- from aquaculture ponds. bon is recycled to carbon dioxide by microbial ac- tivity. The carbon cycle is illustrated in Figure 1.11. Nitrogen Cycle There is not convincing evidence that insufficient The processes and pathways discussed previously inorganic carbon availability is a common limiting can be combined to depict the pond nitrogen cycle factor in aquatic ecosystems. In pond fertilization, (Fig. 1.10). It is interesting to note the pond nitrogen carbon usually is not added to ponds like is done cycle is essentially a miniature version of the global with nitrogen and phosphorus for the sole purpose nitrogen cycle frequently depicted in discussions of of increasing their availability to plants. Of course, biogeochemical nutrient cycling. It also is instruc- organic carbon is present in organic matter used in tive to contrast the nitrogen and phosphorus cycles some ponds as fertilizer, and inorganic carbon is in- in a pond. Although phosphorus is a key nutrient in cluded in agricultural limestone that is frequently ponds—probably more important as a pond fertilizer applied to acidic ponds. Organic carbon impor- than nitrogen—its cycle is primarily a chemically tance in ponds was alluded to in the nitrogen cycle NH3 in air N2 in air Nitrogen in inflow Fertilizer (N) Nitrate N Ammonia N Organic N (D) in plants N2 (E) (N Organic N F) N in organic in animals matter and (D) (D) microbes Nitrogen outflow and Figure 1.10. Nitrogen cycle in harvested fish a fertilized pond. 16 General Fertilization Concepts of which plants are made and as the energy source C in inflow CO2 in Organic in plant respiration. Organic matter originating in Liming air fertilizer photosynthesis enters the food web in which it is the material source of organic compounds comprising the energy source and biomass of animals. In respiration, organic carbon is oxidized to car- Organic C CO2 in in plants bon dioxide and water with the release of bio- water logically available energy. Ecologically, respiration HCO3– /CO32– is the reverse of photosynthesis, but the two pro- in water cesses are very different with respect to biochemi- Organic C cal pathways. Moreover, organic matter decomposi- in animals tion by saprophytic organisms is nothing more than Limestone, respiration. silicates, and C in organic feldspars in matter and Plant-Available Carbon sediment microbes Phytoplankton and other aquatic plants can use car- bon dioxide or bicarbonate as carbon sources for photosynthesis. The atmosphere is a vast carbon C in outflow dioxide reservoir. But carbon dioxide concentration and harvested in the atmosphere is rather low, and free CO2 equi- fish librium concentration in water is equally low. For example, at 25◦ C, free CO2 concentration in pure Figure 1.11. Carbon cycle in a fertilized pond. water is only 0.46 mg/L (Boyd and Tucker 1998). Carbon dioxide reacts with minerals in the earth’s crust such as limestone, calcium silicate, and feldspars to yield bicarbonate (Morel and Hering discussion, and the importance of carbon dynamics 1993; Ittekkot 2003). Using calcium carbonate to in fertilized pond management likely is greater than represent limestone, reactions are as follows: it often is credited with being. CaCO3 + CO2 + H2 O = Ca2+ + 2HCO3 − Photosynthesis Photosynthesis by green plants is the most funda- CaSiO3 + 2CO2 + 3H2 O = Ca2+ + 2HCO3 − mental biological process in nature, because it is the + H4 SiO4 primary source of nearly all organic matter. The only NaAlSi3O8 + CO2 + 5.5H2 O = Na2+ + HCO3 − other organic matter source—and a very minor one + 2H4 SiO4 + 0.5Al2 Si2 O5 (OH)4 at that—is organic matter produced by chemoau- totrophic microorganisms such as those that oxidize Bicarbonate resulting from these reactions con- ammonia nitrogen, ferrous iron, and sulfide. tributes alkalinity to water. Limestone and calcium Aquatic plants remove carbon dioxide from wa- silicate dissolution also contribute an amount of total ter during daylight hours and reduce it to organic hardness equal to total alkalinity. carbon using light energy captured by photosynthet- Total alkalinity concentration in water at equi- ically active pigments. The familiar photosynthesis librium with solid phase CaCO3 and normal at- reaction is: mospheric CO2 usually is about 60 mg/L. How- ever, alkalinity at equilibrium would depend on ac- 6CO2 + 6H2 O = C6 H12 O6 + 6O2 tual carbon dioxide concentration in the atmosphere that varies with location and is steadily increasing Sugars produced in photosynthesis are the build- from atmospheric pollution. The greater the carbon ing blocks for synthesizing all organic compounds dioxide in water, the more calcium carbonate will  Nutrient Cycling 17 dissolve. On the other hand, removing carbon diox- ide from the system will cause calcium carbonate to 100 precipitate. Total alkalinity = 50 mg/L Natural water total alkalinity varies greatly from place to place from differences in types and amounts 50 of source minerals in soils and geological forma- tions. Moreover, water carbon dioxide concentra- Available carbon dioxide (mg/L) tion does not entirely depend on atmospheric carbon dioxide concentration—organic matter decomposi- 0 tion is a major carbon dioxide source in water. 6 7 8 9 Although carbon dioxide reacts with water to form pH bicarbonate: 50 pH = 7.0 CO2 + H2 O = HCO3 − + H+ 40 30 This reaction is acidic and forces pH down rather 20 than creating alkalinity. There is, however, a rela- tionship between bicarbonate concentration, carbon 10 dioxide concentration, and pH that can be expressed 0 as follows:  +   0 100 200 300 H HCO3 − Total alkalinity (mg/L) = 10−6.35 (CO2 ) Figure 1.12. Available carbon dioxide This expression reveals several facts. At pH 6.35, concentration. (A) In water of 50 mg/L total molar bicarbonate and carbon dioxide concentra- alkalinity and different pHs. (B) In water of pH = 7.0 and different total alkalinity tions are equal—molar carbon dioxide concentra- concentrations. tion is greater than bicarbonate at lower pH while the opposite is true at higher pH. The carbon diox- ide concentration at a given pH will increase with total carbon at pH 10.33. Aquatic plants can grow increasing total alkalinity (bicarbonate), but de- in water with pH > 8.3 that contains no free carbon crease with increasing pH at a given bicarbonate dioxide, because they have an enzyme system allow- concentration. These relationships are illustrated in ing them to remove carbon dioxide from bicarbonate Figure 1.12. according to the equation below: There is no free carbon dioxide in water ≥pH 8.3 (Boyd 2000). In addition, above pH 8.3, bicarbonate 2HCO3 − = CO2 + CO3 2− + H2 O dissociates as follows: Each carbon dioxide molecule obtained by plants HCO3 − = H+ + CO3 2− K = 10−10.33 results in forming one carbonate ion. Carbonate hy- drolyzes as illustrated below: The mass action expression is:    CO3 2− + H2 O = HCO3 − + OH− + H CO3 2− = 10−10.33 (HCO3 − ) The pH rises because hydroxyl ions increase dur- ing hydrolysis. Although carbonate hydrolysis re- From this expression, it can be seen as pH in- sults in forming bicarbonate, the reaction can only creases above 8.3, molar carbonate concentration replace half the bicarbonate removed by plants. increases relative to bicarbonate and reaches 50% Photosynthesis can cause pH to rise well above 18 General Fertilization Concepts 8.3, and a considerable bicarbonate amount may be 1.2.4 Other Nutrients transformed to carbonate. Of course, at night, pho- In addition to nitrogen and phosphorus, potassium tosynthesis stops, and the carbon dioxide return to is considered a primary nutrient in fertilizers for water by respiration transforms carbonate back to agronomic crops (Jones 1979). However, there are bicarbonate. When pH drops below 8.3, free carbon no studies revealing a need to include potassium dioxide will accumulate in water. in fertilizers for freshwater ponds or coastal ponds Plant-available carbon dioxide is mainly a func- filled from estuaries or the sea. However, in inland tion of total alkalinity concentration, pH, and water shrimp culture in low salinity water, potassium, and temperature (Saunders et al. 1962). Table 1.2 pro- sometimes magnesium, concentrations often are so vides factors for estimating available carbon dioxide low the resulting major cation imbalance leads to from the three variables. At a given pH and temper- low shrimp survival and growth (Roy et al. 2010). ature, available carbon dioxide will increase with Potassium fertilizer (muriate of potash (KCl)) and greater total alkalinity. For example, at 20◦ C and a potassium magnesium sulfate product marketed pH 7.0, available carbon dioxide would be 6 mg/L under the name K-Mag R are commonly applied to at a total alkalinity 20 mg/L, but 15 mg/L at a total increase potassium and magnesium concentrations alkalinity 50 mg/L. However, at a pH 9, available in inland shrimp ponds (Boyd et al. 2007; Pine and carbon dioxide concentration would decline to 4.6 Boyd 2010). mg/L and 11.5 mg/L, respectively. Water temper- Potassium fertilization studies to promote phy- ature effect on available carbon dioxide is rather toplankton growth do not include potassium defi- minor compared to pH effect. ciency investigations in waters with < 2.5 mg/L K Liming is a common practice in pond aquaculture (Viriyatum and Boyd 2011). Thus, in some waters, (see Chapter 4). Pulverized limestone or lime made potassium possibly is a limiting factor for phyto- by burning limestone in a kiln is applied to ponds to plankton and fish production. neutralize acidity in bottom soil and increase total al- Potassium fertilizers are highly soluble, but potas- kalinity concentration and available carbon dioxide sium can be removed from water by bottom soils. in water. Soils can absorb potassium and other cations on Table 1.2. Factors for Converting Total Alkalinity to Milligrams of Available Carbon per Liter. Temperature (◦ C) pH 5 10 15 20 25 30a 5.0 8.19 7.16 6.55 6.00 5.61 5.20 5.5 2.75 2.43 2.24 2.06 1.94 1.84 6.0 1.03 0.93 0.87 0.82 0.78 0.73 6.5 0.49 0.46 0.44 0.42 0.41 0.40 7.0 0.32 0.31 0.30 0.30 0.29 0.29 7.5 0.26 0.26 0.26 0.26 0.26 0.26 8.0 0.25 0.25 0.25 0.24 0.24 0.24 8.5 0.24 0.24 0.24 0.24 0.24 0.24 9.0 0.23 0.23 0.23 0.23 0.23 0.23 Source: Saunders et al. (1962). Multiply factors by total alkalinity. a Estimated by extrapolation.  Nutrient Cycling 19 negatively charged sites of clay minerals and organic Micronutrients, and especially iron, may be limit- particles. Exchangeable cations that are attracted to ing to phytoplankton in brackish water and seawater charged sites on soils can be readily exchanged with ponds and possibly in freshwater ponds with high other cations in water. Some soils, however, can ab- pH. Iron, manganese, zinc, and copper, the com- sorb potassium by a noncation exchange process, mon cationic micronutrients are quite insoluble at and potassium will be strongly fixed and unavail- pH > 5. Thus, adding mineral salts of these cations able. These differences result primarily from soil is not likely to increase concentrations greatly (Boyd clay mineralogy. Kaolinite and a few other clay 2000). Cationic micronutrients may be chelated minerals (1:1 types) are made up of one tetrahedral with citric acid, ethylenediaminetetraacetic acid, (silica) sheet combined with one octahedral (alu- triethanolamine, lignin sulfate, or other chelating mina) sheet. The structure is fixed, and minerals do agents to make them at least temporarily soluble in not expand when wetted. Cations and water cannot water (Boyd and Tucker 1998). Nevertheless, there enter between layers of 1:1-type clays (Brady 2002). has been little interest in applying cationic micronu- Smectite, vermiculite, and illite are clays made up trients to ponds for phytoplankton growth. of a silica sheet sandwiched between two alumina Two main anionic micronutrients affecting plant sheets (2:1-type clay minerals). Smectite and ver- growth are boron and silicon (for diatoms in shrimp miculite expand when wetted, and cations and water ponds). Sodium borate (borax) is a readily soluble can enter between layers (Dixon and Nash 1968). boron source (Boyd and Tucker 1998). Borate ion Cation exchange capacities of 2:1-type clays are would not be appreciably adsorbed by bottom soil much greater than for 1:1-type clays (Brady 2002). and would be lost from ponds primarily in outflow. Also, 2:1-type clays can fix cations within spaces be- Silicon can be provided by applying sodium silicate tween layers, and cations retained within the spaces or calcium silicate, but silicon from these sources between layers are largely unavailable biologically would not be highly soluble in waters of pH < 9 (Sparks 2000). (Boyd 2000). Boron has seldom been used in pond Boyd et al. (2007) showed a pond soil with fertilization, but shrimp ponds in South and Central a cation exchange capacity of 31 mEq/100 g in America often are fertilized with silicate. which most of the clay fraction consisted of smec- tite adsorbed 136 mg/kg K by cation exchange and REFERENCES 330 mg/kg K were adsorbed by fixation within the interlayers of clay minerals over 8 months. How- Banerjee, A., G.N. Chattopadhyay, and C.E. Boyd. 2009. Determination of critical limits of soil nutri- ever, in a potassium fertilization pond study with ents for use in optimizing fertilizer rates for fish- soils having a CEC of 5 mEq/100 g and containing ponds in red, lateritic soil zones. Aquacultural Engi- kaolinite clay, only about 70 mg/kg K was removed neering 40: 144–148. from water by soil over 7 months (Viriyatum and Bennett, A.C. and F. Adams. 1976. Solubility and sol- Boyd 2011). Thus, substantial potassium can be re- ubility product of dicalcium phosphate dehydrate in moved from water even by a soil containing 1:1 clay aqueous solutions and soil solutions. Soil Science minerals and with a low cation exchange capacity. Society of America Proceedings 40: 39–42. Potassium fertilizers would need to be applied at Bothe, H. 1982. Nitrogen fixation. In: N.G. Carr and frequent intervals just as is done with nitrogen and B.A. Whitton (eds.) The Biology of Cyanobacte- phosphorus fertilizers. ria. University of California Press, Berkley, CA, Calcium and magnesium are secondary nutrients pp. 87–104. Boyd, C.E. 1972. Sources of carbon dioxide for nui- in fertilizers for agronomic crops. Phytoplankton sance blooms of algae. Weed Science 20: 492–497. growth in pond waters with low calcium and mag- Boyd, C.E. 1976. 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Rice, and A.E. Green- Kastner, R.J. and C.E. Boyd. 1996. Production of sun- berg (eds.) 2005. Standard Methods for the Examina- fish (Lepomis spp.) in ponds treated with controlled- tion of Water and Wastewater, 21st edition. American release fertilizers. Journal of the World Aquaculture Public Health Association, Washington, DC. Society 27: 228–234.  Nutrient Cycling 21 Lal, R. and P.A. Sanchez. 1992. Myths and science of Polisini, J.M., C.E. Boyd, and B. Didgeon. 1970. Pro- soils of the tropics. Special Publication Number 29, ductivity and nutrient relationships in an oligotrophic Soil Science Society of America, Madison, WI. South Carolina pond. Oikos 21: 343–346. Lin, C.K., V. Tansakul, and C. Apinhapath. 1988. Redfield, A.C. 1934. On the proportions of organic Biological nitrogen fixation as a source of nitrogen deviations in sea water and their relation to the com- input in fishponds. In: R.S.V. Pullen, T. Bhukaswan, position of plankton. In: R.J. Daniel (ed.) James K. Tonguthai, and J.L. Maclean (eds.) The Second Johnstone Memorial Volume. University Press of International Symposium on Tilapia in Aquaculture. Liverpool, Liverpool, pp. 177–192. ICLARM Conference Proceedings 15, Department Roy, L.A., D.A. Davis, I.P. Saoud, C.A. Boyd, H.J. of Fisheries, Bangkok, Thailand and International Pine, and C.E. Boyd. 2010. Shrimp culture in in- Center for Living Resources Management, Manila, land low salinity waters. Reviews in Aquaculture 2: Philippines, pp. 53–58. 191–208. Masuda, K. and C.E. Boyd. 1994a. Phosphorus frac- Rushton, Y. and C.E. Boyd. 1995. New opportunities tions in soil and water of aquaculture ponds built on for sportfish pond fertilization. Alabama Agricul- clayey, Ultisols at Auburn, Alabama. Journal of the tural Experiment Station, Auburn University, Al- World Aquaculture Society 25: 379–395. abama. Highlights of Agricultural Research 36: Masuda, K. and C.E. Boyd. 1994b. Chemistry of sedi- 11–12. ment pore water in aquaculture ponds built on clayey, Rushton, Y. and C.E. Boyd. 2000. A comparison Ultisols at Auburn, Alabama. Journal of the World of water-soluble fertilizer with liquid fertilizer for Aquaculture Society 25: 396–404. sportfish pond fertilization. North American Journal Metting, F.B., Jr. (ed.) 1993. Soil Microbial Ecology. of Aquaculture 62: 212–218. Marcel Dekker, New York. Saunders, G.W., F.B. Trama, and R.W. Bachmann. Miller, W.E., T.E. Maloney, and J.C. Greene. 1974. 1962. Evaluation of a modified C-14 technique Algal productivity in 49 lake waters as determined for shipboard estimation of photosynthesis in large by algal assays. Water Research 8: 667–679. lakes. Great Lakes Research Division, Publica- Morel, F.M.M. and J.G. Hering. 1993. Principles and tion No. 7, University of Michigan, Ann Arbor, Applications of Aquatic Chemistry. John Wiley & MI. Sons, New York. Sparks, D.L. 2000. Bioavailability of soil potassium. Mortimer, C.H. 1954. Fertilizers in fishponds. Fisheries In: M.E. Summer (ed.) Handbook of Soil Science. Publication Number 5, Her Majesty’s Stationery CRC Press, Boca Raton, FL, pp. D38–D53. Office, London. Swingle, H.S., B.C. Gooch, and H.R. Rabanal. 1963. Munsiri, P., C.E. Boyd, and B.F. Hajek. 1995. Physical Phosphate fertilization of ponds. Proceedings An- and chemical characteristics of bottom soil profiles nual Conference Southeastern Association Game in ponds at Auburn, Alabama, USA, and a proposed and Fish Commission 17: 213–218. method for describing pond soil horizons. Journal of Tepe, Y. and C.E. Boyd. 2001. A sodium nitrate- the World Aquaculture Society 26: 346–377. based, water-soluble fertilizer for sportfish ponds. Nadis, S. 1998. Fertilizing the sea. Scientific American North American Journal of Aquaculture 63: 328– 277: 33. 332. Odum, E.P. 1975. Fundamentals of Ecology, 2nd edi- Viriyatum, R. and C.E. Boyd. 2011. Re-evaluation tion. Holt Rinehardt and Winston, New York. of potassium fertilization of bluegill, Lepomis Pais, I. and J.B. Jones, Jr. 1997. The Handbook of Trace macrochirus, ponds. Journal of the World Aquacul- Elements. Saint Lucie Press, Boca Raton, FL. ture Society 42: 332–338. Pine, H.J. and C.E. Boyd. 2010. Adsorption of magne- Wudtisin, W. and C.E. Boyd. 2005. Determination of sium by bottom soils in inland brackish water shrimp the phosphorus fertilization rate for bluegill ponds ponds in Alabama. Journal of the World Aquaculture using regression analysis. Aquaculture Research 36: Society 41: 603–609. 593–599.