MOHAMMAD AYUB,1 CLAUDE E. BOYD, AND DAVID TEICHERT-CODDINGTON. Department of Fisheries and Allied Aquacuhures, Alabama Agricultural ...
The Progressive Fish-Cultwist 55:210-213, 1993
Effects of Urea Application, Aeration, and Drying on Total Carbon Concentrations in Pond Bottom Soils MOHAMMAD AYUB,1 CLAUDE E. BOYD, AND DAVID TEICHERT-CODDINGTON
Department of Fisheries and Allied Aquacuhures, Alabama Agricultural Experiment Station Auburn University. Alabama 36849, USA Abstract.—Aerated ponds did not accumulate as much carbon in bottom soils as control ponds. Application of urea to manured ponds did not accelerate carbon loss from bottom soils. When ponds were drained for fish harvest, appreciable carbon was eroded from the surface layers of bottom soil. Further decomposition of soil carbon occurred during the 5-week drying period between crops. Within-pond variation in soil carbon concentration was high; a technique for selecting replication and sample size requirements for experiments on changes in bottom soil carbon concentration is provided. Excessive accumulation of organic matter in soils of aquaculture ponds is detrimental. High concentrations of soil organic matter increase oxygen demand and favor development of reducing conditions. In anaerobic soils, microbial activity releases reduced chemical compounds, such as Fe2+, Mn 2 +, NC>2~, H2S, and CH4, which may be toxic to aquatic animals (Boyd 1990). Avnimelech and Zohar (1986) found that when reduced microenvironments developed in intensive aquaculture ponds, growth offish was retarded. Although there is little information on maximum tolerable concentrations of organic matter in pond soils, a study by Banerjea (1967) suggested that organic carbon concentrations above 2.5% were associated with low yields of fish from unaerated and manured ponds in India. Organic carbon (OQ concentrations increase over time in aquaculture ponds, but few data are available to indicate the rate of increase. In Mississippi ponds used to raise channel catfish (Ictalurus punctatus), OC concentrations increased at a rate of about 10% of initial concentration per year as ponds aged (Tucker 1985). Organic carbon concentration increased from 1.54% at the beginning of one crop to 1.88% at the beginning of the next crop in channel catfish ponds at Auburn, Alabama (Gately 1990). Boyd (1974) showed that concentrations of organic matter were higher in older sport-fish ponds than in newer ones. About 1
Present address: Department of Fisheries, Government of Punjab, 2- Sanda Road, Lahore, Pakistan.
50% of the ponds contained more than 1.5% soil OC. Because organic matter accumulates in pond soils and high OC concentrations may be detrimental to environmental quality and fish growth in ponds, techniques for reducing OC concentrations would be useful. Several techniques are thought to reduce OC concentrations in pond soils. One common technique is to remove sediment from ponds (Boyd 1992). However, unless the sediment is disposed of properly, it can contaminate natural waters. Draining ponds also removes considerable amounts of bottom soil particles (Schwartz and Boyd 1993), but suspended matter in pond effluents can pollute natural waters. Drying of pond bottom soils between crops improves contact with the air, and the higher concentrations of oxygen in air, as compared with water, may enhance microbial oxidation of organic matter in fallow pond bottoms (Arenas and De La Lanza 1981; Boyd 1990, 1992). Ghosh and Mohanty (1981) suggested that aeration increased dissolved oxygen concentrations at the pond bottom and enhanced microbial oxidation of organic matter. There also is preliminary evidence from shrimp farming that application of nitrogen fertilizer to ponds stimulates microbial activity and encourages decomposition of organic matter (Peterson and Daniels 1992). Organic carbon concentrations obviously can be reduced by sediment removal, but few data to support the other practices are available. Experiments conducted in ponds of the El Carao National Fish Culture Research Center near Comayagua, Honduras, provided opportunity to study changes in pond soil carbon concentrations affected by nitrogen supplementation of manure applications, aeration, and draining and drying of ponds. Ponds are 1,000 m 2 in area and about 80 cm in average depth. In the urea experiment, six ponds were stocked with Nile tilapia (Tilapia nilotica) at 10,000/hectare and jaguar guapote (Cichlasoma managuense) at 500/hectare. Chicken litter was applied to all ponds at 750 kg dry weight/hectare weekly. Three ponds were treated
210
211
TECHNICAL NOTES
2.0
M • MANURE
M+U • MANURE + UREA
n-3
aa
aa
m.
1.0
M
cc
5 W
d!
M M+U 5-15 cm
M+U
0-5 cm OA
2>0
r
TT a
b
(-)-BEFORE DRAINING (*) - AFTER DRAINING
A -AERATED
2.0 —
-
I
I -1 +1 *5 DAY HR WKS
a ^ ^§
1.0L- U U U
1.0 -1
+1 +5
DAY HR WKS
C- CONTROL
-
C
i
n-3 b
r J.
b
a
t ii
1 A
C
a
1 A
0-5 cm 5-15 cm 5-15 cm 0-5 cm FIGURE 1.—Changes in organic carbon concentrations in: I. manured ponds and ponds treated with manure plus urea; II. ponds with bottoms dried between crops; III. aerated and control ponds. Nine samples were taken from 0-5-cm and 5-15-cm depths on each sampling date. Number of ponds per treatment (n) is given in the figure. In I and III, shaded bars represent the initial concentrations and open bars give concentrations at the end of the experiments. Vertical lines in ends of bars represent 95% confidence intervals for the means. Two bars indicated by the same lower case letter do not differ significantly at the 5% level of probability (comparison valid only for bars within a set).
weekly with urea at 22 kg/hectare. The experiment lasted 126 d. Ponds were then drained for fish harvest, bottoms were left dry for 35 d, and ponds were refilled. In the aeration experiment, six ponds were stocked with 20,000 Nile tilapia/hectare and with jaguar guapote at 500/hectare. All ponds received chicken litter weekly at 1,000 kg dry weight/ hectare for 2 months. Manuring was then halted, and a pelleted 20% protein feed was applied 6 d/week at 3% of body weight per day. Three ponds were aerated for the last 127 d of the 148-d-long experiment with one, 0.5-hp (0.37 kW) verticalpump aerator (Air-o-lator Corp., Kansas City, Missouri) per pond; three ponds were unaerated controls. Data on fish production in the ponds and further details on management procedures may be found in Teichert-Coddington et al. (1991, 1992). Pond bottom soils were sampled on the day that fish were stocked and on the day before ponds were drained for harvest. For the drying experiment, ponds were drained and samples were taken after 1 h and after 5 weeks. Ponds were divided into nine equal quadrants, and one soil sample
was obtained at random from each quadrant with a 4-cm-diameter core sampler. Samples were frozen, frozen soil was pushed out of sampling tubes, and cores were sectioned to provide samples from 0-5-cm and 5-15-cm layers. Samples were ovendried at 65°C, pulverized with mortar and pestle to pass a 60-mesh screen, and analyzed for total carbon with an induction-type carbon analyzer (model EC-12, Leco Corp., St. Joseph, Michigan). Quality control for carbon analyses followed recommendations of Boyd and Tucker (1992). All analyses for a particular treatment and sampling date were averaged and 95% confidence limits for the means were calculated. Statistical comparisons of treatment means were made with /-tests and Duncan's new multiple-range test (Steel and Torrie 1980). The carbon analyzer measures both inorganic and organic carbon in samples. However, tests of samples from all ponds with hydrochloric acid (Jackson 1958) failed to reveal the presence of calcium carbonate, so samples were assumed to contain only organic carbon.
212
TECHNICAL NOTES
1.00-
O
0.80-
*
0.60
o »2 ponds °-3pond» • 0.05). Thus, application of nitrogen fertilizer did not stimulate microbial activity and increase the decomposition of organic matter in pond bottom soils. When ponds were drained at the end of the urea experiment (Figure 1), there was an immediate reduction in the carbon concentration of the 0-5cm layer (P < 0.05). This resulted from erosion of paniculate matter from the bottom by water currents and the loss of these particles from the pond in discharge. The loss of organic matter during draining is a positive influence on the pond environment, but the organic matter may be released into natural water where it can be considered a potential pollutant. Further loss of carbon was affected by microbial decomposition in both the 0-5-cm and 5-15-cm layers during the dry period (Figure 1). When the soil dried, deep cracks
developed. This process improved contact with air and enhanced microbial activity. Roughly onehalf of'the loss of carbon resulted from draining and one-half occurred during the dry period. During the urea experiment, the average carbon content of the 0-15-cm layer of the six ponds increased from 1.45% to 1.51%. The average carbon concentration in this layer after draining and 5 weeks of drying was 1.41%. Thus, an amount of carbon approximately equal to the quantity accumulated during the experiment was removed or decomposed during draining and drying. Studies to determine the optimum length of the drying period would be useful, because it may not be necessary to dry pond bottoms for 5 weeks to appreciably lower organic matter concentrations. Both aerated and control ponds had increases in carbon in the 0-5-cm layer (Figure 1), but the largest increase incurred in control ponds. In the 5-15-cm layer, carbon increased in the control ponds but not in the aerated ponds. Thus, carbon should not increase as rapidly in aerated ponds as unaerated ponds. Nevertheless, a drying period is
TECHNICAL NOTES
recommended even for aerated ponds, because aeration did not completely prevent carbon accumulation; the amount of accumulation was simply less in the aerated ponds. Experiments to detect changes in concentrations of carbon in ponds must take into account the high degree of variability in carbon concentrations within ponds. Coefficients of variation (100-SO/mean) for sets of nine samples from single ponds on single dates in this experiment ranged from 20% to 50%. Gately (1990) found similar variation in samples from ponds on the Fisheries Research Unit at Auburn University. In order to provide an assessment of variation in carbon concentrations in pond soil useful in design of future experiments, we used a two-stage nested (hierarchical) linear statistical model to estimate components of variance for the carbon data from the ponds (Howe and Meyers 1970; Gill 1978). These variance components were then used to determine the relationship among detectable change in carbon concentration (P < 0.05), number of samples per pond, and number of ponds per treatment (Figure 2). In order to detect a change of 0.200.30% in carbon—for example, an increase from 1.50% to 1.70% or 1.80%—at least three ponds per treatment and eight samples per pond will be required. We used three ponds per treatment and nine samples per pond and were able to show some differences. Acknowledgments. —This research was supported by Pond Dynamics/Aquaculture Collaborative Research Support Program (CRSP) funded by the U.S. Agency for International Development; Direccion General de Recursos Naturales Renovables, Secretatia de Recursos Naturales, Honduras; and Auburn University.
References Arenas. V., and G. De La Lanza. 1981. Effect of dried and cracked sediment on the availability of phosphorus in a coastal lagoon. Estuaries 4:206-212. Avnimelech, Y., and G. Zohar. 1986. The effect of local anaerobic conditions on growth retardation in aquaculture systems. Aquaculture 58:167-174. Banerjca, S. M. 1967. Water quality and soil condition of fish ponds in some states of India in relation to fish production. Indian Journal of Fisheries 14:113144. Boyd, C. E. 1974. Lime requirements of Alabama fish ponds. Alabama Agricultural Experiment Station, Auburn University Bulletin 459.
213
Boyd, C. E. 1990. Water quality in ponds for aquaculture. Alabama Agricultural Experiment Station, Auburn University, Auburn. Boyd, C. E. 1992. Shrimp pond sediment and sediment management.Pages 166-18\ in]. Wyban,editor. Proceedings of the special session on shrimp farming. World Aquaculture Society, Baton Rouge, Louisiana. Boyd, C. E., and C. S. Tucker. 1992. Water quality and pond soil analyses for aquaculture. Alabama Agricultural Experiment Station, Auburn University, Auburn. Gately, R. J. 1990. Organic carbon concentrations in bottom soils of ponds. Master's thesis. Auburn University, Auburn, Alabama. Ghosh, S. R., and A. R Mohanty. 1981. Observations on the effect of aeration on mineralization of organic nitrogen in fish pond soil. Bamidgeh 33:5056. Gill, J. L. 1978. Design and analysis of experiments, volume 1. Iowa State University Press, Ames. Howe, R. B., and R. H. Meyers. 1970. An alternative to Satterwaite's test involving positive linear combinations of variance components. Journal of the American Statistical Association 65:404-412. Jackson, M. L. 1958. Soil chemical analysis. PrenticeHall, Englewood Cliffs, New Jersey. Peterson, J., and H. Daniels. 1992. Shrimp industry perspectives on soil and sediment management. Pages 166-181 in J. Wyban, editor. Proceedings of the special session on shrimp fanning. World Aquaculture Society, Baton Rouge, Louisiana. Schwartz, M. R, and C. E. Boyd. 1993. Effluent quality during harvest of channel catfish from watershed ponds. Progressive Fish-Culturist 55. Steel, R. G. D., and J. H. Torrie. 1980. Principles and procedures of statistics, 2nd edition. McGraw-Hill, New York. Teichert-Coddington, D., B. W. Green, and M. I. Rodriquez. 1991. Supplementation of nitrogen fertilization of organically-fertilized ponds. Pages 18-21 in H. S. Egna, M. McNamara, and N. Weidner, editors. 8th annual administrative report. Oregon State University, Pond Dynamics/Aquculture Collaborative Research Program 1990, Corvallis. Teichert-Coddington, D., B. W. Green, and M. I. Rodriquez. 1992. Yield improvement by maintaining critical oxygen concentrations in tilapia ponds. Pages 17-20 in H. S. Egna, M. McNamara, and N. Weidner, editors. 9th annual administrative report. Oregon State University, Pond Dynamics/Aquaculture Collaborative Research Program 1991, Corvallis. Tucker, C. S. 1985. Organic matter, nitrogen, and phosphorus content of sediments from channel catfish, Icialwrus punctatus, ponds. Mississippi Agricultural and Forestry Experiment Station, Research Report 10, Mississippi State University, Mississippi State.
