Abstract
The aquaculture industry generates significant nutrient-rich wastewater that is released into streams and rivers causing environmental concern. The objective of this controlled environment study was to evaluate the effect of waste shrimp water (SW), vermicompost (VC), at rates of 10%, 20%, 40%, and 80% by volume alone or in combination with SW, controlled-release fertilizer (CRF), and water-soluble fertilizer (WSF) on bell peppers (Capsicum annuum L.) cv. X3R Red Knight. Application of VC at 80% or SW alone increased yields relative to unfertilized control. Combined applications of VC and SW increased yields compared with VC alone. Overall, total yields were greatest in the chemical fertilizer treatments (CRF and WSF) and least in the unfertilized control. SW and VC increased growth medium pH relative to the unfertilized control or to the chemical fertilizer treatments. In pepper fruits, the greatest nitrogen (N) content was found in the CRF treatment, although it was not different from VC at high rates or WSF treatments. Phosphorus concentration in peppers was greatest in the CRF treatment, less in all VC or SW treatments, but not different from unfertilized control or WSF treatment. Iron, magnesium (Mg), and zinc concentrations in peppers were greatest in CRF treatment but not different from control or WSF treatments. Overall, N accumulation in peppers was negatively correlated to growth medium pH and calcium (Ca); phosphorus (P) in peppers was negatively correlated to growth medium pH, Ca, and sodium (Na), whereas potassium (K) in peppers was negatively correlated to growth medium P, Mg, and Na. Results indicated: 1) SW may not be a viable pepper nutrient source; (2) SW can provide a similar nutrient supply as VC; and (3) chemical fertilizers can provide higher pepper yields compared with SW or VC alone or in combination.
Mississippi is the largest catfish producer and one of the largest fresh water farm-raised shrimp producers in the United States. These industries generate significant nutrient-rich wastewater that may currently be released into streams and rivers.
In aquaculture systems, fish or shrimp feed costs are ≈50% of total costs in modern high-volume fed monospecies aquaculture (Neori et al., 2004). However, some feed is not used and becomes waste. In addition, fish excretia is also a significant waste; this causes effluent discharge concerns. Rising fish or shrimp feed costs and environmental issues surrounding aquaculture systems are two important barriers for further increases in aquaculture production (Neori et al., 2004).
Research on finding new uses of the wastewater from shrimp aquaculture systems would be beneficial to the aquaculture industry and to the environment. In addition, it also may stimulate the development of shrimp-based aquaponics systems. Aquaponics is a system that combines recirculating fish aquaculture with a plant hydroponic system. The possibilities for integrating the aquaculture and hydroponic systems have been investigated in the past (Hargreaves et al., 1991; Naegel, 1977; Pierce, 1980; Rakocy, 1992; Seawright et al., 1998; Watten and Busch, 1984). It is based on the idea that vegetable hydroponics could be used for removing excess nutrients from aquaculture effluents. In the process of using the aquaculture effluent, high-value vegetables or other crops could be produced. In general, researches were conducted to establish 1) the optimal ratio of fish to plants; 2) which nutrients should be supplemented to the plants; and 3) maintaining proper salt and pH conditions for the fish and for the plants. However, like with the aquaponics system, most of the research was focused on tilapia-based aquaculture, suitable only for warm climates or for controlled environmental conditions (Rafiee and Saad, 2005; Rakocy, 1992; Seawright et al., 1998; Watten and Busch, 1984), and there is no research dealing with shrimp-based effluents. There are no reports on shrimp-based aquaponics systems. Fish-based aquaponics systems have been developed by several universities in the United States, but these systems are mainly tilapia-based (Watten and Busch, 1984). One reason for tilapia's popularity is tilapia are resilient and fed at high rates with commercially manufactured complete diets, which results in higher mineral and organic nutrient concentrations in tilapia tanks.
The objective of this study was to evaluate SW as a nutrient source for bell peppers, applied either alone or in combination with VC, and compare these treatments with traditional chemical fertilizer application.
Materials and Methods
Experiment.
Controlled environment condition experiment with bell peppers (Capsicum annuum L.) cv. X3R Red Knight was conducted using completely randomized design with four replications. Peppers were started from certified seed in 36-cell trays filled with growth medium (Metromix 300; Sun Gro Horticulture, Bellevue, WA). When plants reached 6 to 8 cm, they were transplanted in 3-gallon 1400 series pots. The experiment was conducted in a greenhouse at the North Mississippi Research and Extension Center in Verona (lat. 34°43′22″ N, long. 88°43′22″ W) with natural daylight and no supplemental lighting with 22 to 30 °C day temperatures and 18 to 22 °C night temperatures.
The 12 treatments (Table 1) consisted of untreated control (irrigated with tap water); SW (irrigated only with SW); VC at 10%, 20%, 40%, and 80% by volume, either alone or in combination with SW; CRF (Osmocote Plus N:P:K at 15:9:12; Scotts-Sierra Horticultural Products Co., Marysville, OH), and WSF (greenhouse-grade general purpose fertilizer N:P:K at 20:20:20; Scotts-Sierra Horticultural Products Co.). The WSF treatment was fertilized with 100 mg·kg−1 of N with 1100 mL of WSF when other treatments received either tap water or SW. The untreated control had 2800 g of growth substrate in each pot. Vermicompost was added to the growth medium once by volume and mixed thoroughly before transplanting peppers.
Mean total fruit weight, number of fruits, and pepper fruit weight from the 12 treatments.z
The SW was provided by Lauren Farms, Leland, MS. Nutrient concentration of SW was as follows in mg·kg−1: NO3-N (28–30), P (3.6), K (8.3), Ca (56), Na (65), Mg (17), iron (0.06), zinc (0.02), boron (0.32), and copper was under detection limit of inductively coupled argon plasma spectrometer (ICAP). The VC was obtained from Church Hill Worm Farm (Church Hill, MS). Nutrient concentration of VC was as follows: N 1.48%, P 3.85%, and K 0.41%.
Approximately 55 d were needed from transplanting for peppers to become green and 77 d to become red. Harvesting was done on a continual basis by picking marketable red peppers, taking fresh weight, and drying them in a drying oven at 68 °C for 72 h for dry weight and nutrient analysis. Subsamples of dried peppers were taken, ground, and analyzed for nutrient content at the Mississippi State Soil Testing laboratory. Immediately after the last harvest, growth medium from each pot was sampled; samples were dried at room temperature and sent for analysis of residual phyto-available nutrients using the Lancaster soil test method (Cox, 2001). Tissue and soil extracts were measured on ICAP (Perkin Elmer, Norwalk, CT).
Statistical analysis.
The effect of 12 treatments on several nutrient concentrations in soil and tissue was determined by conducting a one-way analysis of variance using the GLM procedure of SAS (SAS Institute Inc., 2008). The effect of treatments was significant (P < 0.05) on all but two responses and further multiple means comparison was done using the least significant difference method at the 1% level. A 1% level was used to protect Type I experimentwise (family) error rate from overinflation resulting from the relatively large number of treatments. For all responses, normal distribution and constant variance assumptions on the error terms were verified by constructing a normal probability plot of the residuals and a plot of residuals vs. fitted values, respectively (Montgomery, 2009); and appropriate transformation was applied when violated. Correlation analyses of nutrients in soil and tissue were also conducted to determine if nutrient concentrations in peppers can be predicted from those in the growth medium.
Results
Effects on yields.
Overall, total pepper yields, number of fruits per plant, and average fruit weight were highest in the chemical fertilizer treatments (CRF and WSF) and lowest in unfertilized controls (Table 1). Application of SW increased yields relative to the control. The combination of SW and VC at 10% further increased yields relative to their application alone. Yields at the SW applied alone were greater than that from VC alone at 10% to 80%. Overall, the combination of SW and VC increased yields, but yields and average fruit weight were still below those at chemical fertilizer treatments (SLF or WSF). It is evident that nutrient availability from SW or VC applied alone or in combination could not match CRF or WSF nutrient availability for bell peppers.
Effects on pH and residual nutrients.
Treatments had significant effect on growth medium pH and residual nutrients measured at harvest (Table 2). Generally, all SW and VC treatments had higher pH, untreated control and WSF had lower pH, and the CRF treatment had the lowest pH. Results demonstrated SW or VC applied alone or in combination may raise growth medium pH, whereas CRF can lower it. Interestingly, concentrations of soil P, Ca, Mg, and zinc at harvest were greater in VC at 80% or SW plus VC at 80% than in chemical fertilizer treatments. Concentrations of K were highest in the CRF, less in VC 80%, and relatively low in WSF treatments. Higher yields in chemical fertilizer treatments could be from two factors: (1) better match between nutrient availability and pepper plant requirements; and/or (2) insufficient N availability from SW or VC applications. The results suggest that SW and VC application to bell peppers must be supplemented with another N source.
Mean nutrient concentrations in the growth medium from the 12 treatments.z
Effect on nutrient content of peppers and nutrient removal with fruits.
Pepper nutrient content was also affected by the treatments (Table 3). Peppers in CRF and SW alone treatments had higher N content compared with peppers in untreated control. Peppers in CRF also had higher P content relative to most other treatments, although not different from untreated control or from WSF. Potassium content in peppers in the VC 10% treatment was higher than in chemical fertilizers but not different from the untreated control. Peppers in untreated control had higher Mg concentration than peppers in chemical fertilizer treatments.
Mean nutrient content of pepper fruits from the 12 treatments.z
The concentration of iron in pepper fruits in the SW and in all VC plus SW treatments was lower than in the control and lower than in the chemical fertilizer treatments (Table 3). The concentration of manganese (Mn) in pepper fruits in the SW, in the VC plus SW treatments, in the VC at 20% and VC at 80% was lower than in the control and lower than in the CRF treatments. The concentration of zinc in peppers in the SW and in the VC at 10% plus SW was lower than in the control and lower than in the CRF treatment (Table 3).
Generally, removal of nutrients [N, P, K, Ca, Mg, sulfur (S), iron (Fe), Mn, zinc (Zn), copper (Cu), and boron (B)] with pepper fruits (a function of nutrient content and pepper yields) was greatest in chemical fertilizer treatments and least in untreated control (Table 4). However, removal of K, Ca, and Mg with peppers in some other fertility treatments was not different from chemical fertilizer treatment.
Mean nutrient uptake by pepper from the 12 treatments.z
Correlations between nutrient concentrations in peppers and residual nutrients in the growth medium.
Nitrogen in peppers and N removal were negatively correlated with growth medium pH and Ca but positively correlated with growth medium K (Table 5). Phosphorus content in peppers was negatively correlated with growth medium pH, Ca, and Na, whereas P removal was negatively correlated with growth medium pH and Ca and positively with K. Potassium in peppers was negatively correlated with growth medium P and Na, whereas K removal was negatively correlated with growth medium Ca and positively correlated with growth medium K. Calcium in peppers was negatively correlated with growth medium K; Ca removal was negatively correlated with growth medium Na. Magnesium in peppers was negatively correlated with growth medium P, K, and Zn, whereas Mg removal was negatively correlated with growth medium Ca and positively correlated with Na. Sulfur in peppers was negatively correlated with growth medium pH and Na; S removal was negatively correlated with growth medium pH and Ca and positively correlated with K.
Correlation coefficients between nutrients in the soil (columns) and nutrient content in pepper and nutrient uptake by pepper (rows).
Iron in peppers was negatively correlated with growth medium pH, Ca, Mg, and Na, and Fe removal was negatively correlated with growth medium pH and Ca and positively correlated with K. Manganese in peppers was negatively correlated with growth medium pH, P, Ca, Mg, Zn, and Na, whereas Mn removal was negatively correlated with growth medium pH, K, and Ca. Zinc in peppers was negatively correlated with growth medium pH and Na and positively correlated with K, whereas Zn removal was negatively correlated with growth medium pH, K, and Ca. Copper in peppers was negatively correlated with growth medium pH, Ca, and Na and positively correlated with K, whereas Cu removal was negatively correlated with growth medium pH, and Ca was positively correlated with K. Boron in peppers was positively correlated with growth medium P and Zn, and B removal was negatively correlated with growth medium pH, and Ca was positively correlated with K (Table 5).
Discussion and Concluding Remarks
To our knowledge, this is the first study using SW as a nutrient source for bell peppers. We found only one report on using SW as nutrient source for vegetables. Castellani et al. (2009) evaluated SW producing hydroponic lettuce and watercress. The authors found SW was not sufficient to support lettuce growth but did meet the nutrient demand of watercress (Castellani et al., 2009). Their study and results from our study seem to suggest SW alone may not be sufficient to meet nutrient requirements of fast-growing vegetables.
Aquaponics research has intensified in recent years throughout the world. There have been reports from countries with various climates such as the United Kingdom (Price, 2009), Canada (Savidov et al., 2007), and Saudi Arabia (Al-Hafedh et al., 2008). In the United States, significant research has been conducted at the University of Virgin Islands (UVI) by Dr. James Rakocy, who has developed a commercial-scale aquaponic system (Rakocy, 1997) based on earlier research by Watten and Busch (1984). The system developed at the UVI has been modified and used by commercial entities in the United States (Rakocy et al., 2004). Apparently, further research is needed on using waste SW to develop a shrimp-based aquaponics system. Our results indicate bell peppers may not be suitable for a SW aquaculture system; however, other vegetables or herbs that have less nutrient requirements might be suitable.
Dufault and Korkmaz (2000) used biosolids from shrimp aquaculture as fertilizer for bell peppers grown on loamy sand soil and compared it with SRF (Osmocote). The authors found increased bell pepper yields with an increase in shrimp aquaculture biosolid; however, the greatest yields were achieved in SRF treatment. Similar to results from this study, the authors found an increase in soil nutrients, Na, and salinity with increased rates of SW biosolids (Dufault and Korkmaz, 2000).
This is also the first study to evaluate combined application of SW and VC to peppers. Previous research demonstrated addition of VC can significantly increase pepper yields (Arancon et al., 2004; Huerta et al., 2010), which is logical because VC adds nutrients to soil or growth medium and improves soil physical and biological characteristics. However, other authors did not find increase in pepper yields as a result of VC application at 20% by volume to the growth medium (Bachman and Metzger, 2008). The latter finding is similar to that in our study; addition of 10%, 20%, or 40% of VC did not increase yields relative to untreated control.
Results from this study demonstrated that concentration of the nutrients in the growth medium measured at harvest cannot be a good predictor for the concentration of the nutrients in peppers, because there were no significant correlations between these two measurements. Of all the measured nutrients, only the nutrient removal of K was mostly correlated with the concentration of K in the growth medium at harvest.
Results indicated: 1) SW may not be a viable nutrient source for peppers; 2) SW can provide a similar nutrient supply as VC; 3) chemical fertilizers can provide greater pepper yields compared with SW or VC alone or in combination; and 4) except for K, nutrient concentration in the growth medium measured at harvest may not be a good predictor of nutrient accumulation in bell peppers.
Literature Cited
Al-Hafedh, Y.S., Alam, A. & Beltagi, M.S. 2008 Food production and water conservation in a recirculating aquaponic system in Saudi Arabia at different ratios of fish feed to plants JWAS 39 510 520
Arancon, N.Q., Edwards, C.A., Atiyeh, R. & Metzger, J.D. 2004 Effects of vermicomposts produced from food waste on the growth and yields of greenhouse peppers Bioresour. Technol. 93 139 144
Bachman, G.R. & Metzger, J.D. 2008 Growth of bedding plants in commercial potting substrate amended with vermicompost Bioresour. Technol. 99 3155 3161
Castellani, D., Camargo, A.F.M. & Abimorad, E.G. 2009 Aquaponics: Use of the effluent from the secondary nursery of Macrobrachium amazonicum for the production of hydroponic lettuce (Lactuca sativa) and watercress (Rorippa nasturtium aquaticum) Bioikos. 23 67 75
Cox, M.S. 2001 The Lancaster soil test method as an alternative to the Mehlich 3 soil test method Soil Sci. 166 484 489
Dufault, R.J. & Korkmaz, A. 2000 Potential of biosolids from shrimp aquaculture as a fertilizer in bell pepper production Compost Sci. Util. 8 310 319
Hargreaves, J.A., Rakocy, J.E. & Bailey, D.S. 1991 Effects of diffused aeration and stocking density on growth, feed conversion, and production of Florida red tilapia in cages J. World Aquacult. Soc. 22 24 29
Huerta, E., Vidal, O., Jarquin, A., Geissen, V. & Gome, R. 2010 Effect of vermicompost on the growth and production of amashito pepper, interactions with earthworms and rhizobacteria Compost Sci. Util. 18 282 288
Montgomery, D.C. 2009 Design and analysis of experiments 7th Ed Wiley New York, NY
Naegel, L.C.A. 1977 Combined production of fish and plants in a re-circulating water Aquaculture 10 17 24
Neori, A., Chopin, T., Troell, M., Buschmann, A.H., Kraemer, G.P., Halling, C., Shpigel, M. & Yarish, C. 2004 Integrated aquaculture: Rationale, evolution and state of the art emphasizing seaweed biofiltration in modern mariculture Aquaculture 231 361 391
Pierce, B. 1980 Water re-uses aquaculture systems in two greenhouses in northern Vermont Proc. World Maric. Soc. 11 118 127
Price, C. 2009 A sustainable option for local food production. Fish Farmer 32(1) Edinburgh: Special Publications. 32 34
Rafiee, G. & Saad, C.R. 2005 Nutrient cycle and sludge production during different stages of red tilapia (Oreochromis sp.) growth in recirculating aquaculture system Aquaculture 244 109 118
Rakocy, J.E. 1992 Feasibility of using vegetable hydroponics to treat aquaculture effluents 347 350 Blake J., Donald J. & Magett W. Proc. of the 1991 national workshop, 29–31 July 1991, Kansas City, MO.Am. Soc. Agri. Engin. St. Joseph, MI
Rakocy, J.E. 1997 Integrating tilapia culture with vegetable hydroponics in recirculating systems 163 184 Costa Pierce B.A. & Rakocy J.E. Tilapia aquaculture in the Americas Vol. 1 World Aquaculture Society Baton Rouge, LA
Rakocy, J.E., Bailey, D.S., Shultz, R.C. & Thoman, E.S. 2004 Update on tilapia and vegetable production in the UVI aquaponic system 676 690 New dimensions on farmed tilapia. Proc. of the Sixth International Symposium on Tilapia in Aquaculture Manila, Philippines
SAS Institute Inc 2008 SAS OnlineDoc 9.2 SAS Institute Inc. Cary, NC
Savidov, N.A., Hutchings, E. & Rakocy, J.E. 2007 Fish and plant production in a recirculating aquaponic system: A new approach to sustainable agriculture in Canada Acta Hort. 742 209 222
Seawright, D.E., Stickney, R.R. & Walker, R.B. 1998 Nutrient dynamics in integrated aquaculture hydroponics system J. Aquac. 160 215 237
Watten, B.J. & Busch, R.L. 1984 Tropical production of tilapia (Sarotherodon aurea) and tomatoes (Lycopersicon esculentum) in a small-scale recirculating water system Aquaculture 41 271 283