Mineral Nutrient Concentration and Uptake of Tomato Irrigated with Recirculating Aquaculture Water as Influenced by Quantity of Fish Waste Products Supplied
M. R. McMurtry, D. C. Sanders, and P. V. Nelson
Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695-7609
Additional index words. biofiltration, hydroponics, integrated aquaculture, Lycopersicon esculentum Mill., Oreochromis mossambicus (Peters), Oreochromis niloticus (L.), sand culture.
Abstract
Fish and tomato (Lycopersicon esculentum Mill.) production were linked in a recirculating water system. Fish (tilapia) were fed a commercial diet with 32% protein. Tomato cultivars Laura and Kewalo were grown during summer 1988 and spring 1989, respectively, in a Raleigh, N.C., greenhouse. Plants were grown in biofilters at 4 plants m-2 and surface irrigated 8 times daily with water pumped from an associated fish tank.
Four tank to biofilter ratios were established by varying the filter size. Each system received identical nutrient inputs and an equal quantity of water was applied per plant. Biofilter drainage returned to the tanks. Biological filtration, aeration, and mineral assimilation by plants maintained water quality within limits for tilapia.
All nutrients were assimilated above deficiency levels. Tissue concentrations of N, P, K, and Mg were not limiting. Calcium was low and S was high when their sole nutrient source was fish waste.
Micronutrients were assimilated in excess of sufficiency, but toxicity was not seen. Irrespective of yield, metabolic products of each kg increase in fish biomass provided sufficient nutrient for 2 tomato plants for a period of three months. Under reduced growth rates of mature fish, K became limiting.
Alterations in fish feed mineral nutrient content are suggested which better meet plant requirements and still remain within the range of fish needs.
Introduction
Recirculating aquacultural water has considerable potential for hydroponic cultivation of higher plants (Lewis et al., 1978, 1981; Watten and Busch, 1984; Rakocy, 1989a, 1989b). Dissolved and suspended organic materials accumulate rapidly in aquaculture systems and must be removed for efficient fish production (Nair, et al., 1985). Nitrates and phosphates accumulate in filtered recirculatory fish culture systems (Balarin and Haller, 1982; Watten and Busch, 1984).
Hydroponic vegetable production has been demonstrated to control NO3– concentrations in recirculatory aquaculture water (Lewis et al., 1978, 1981; Watten and Busch, 1984; Rakocy, 1989a, 1989b; McMurtry et al., 1990a). Reciprocating biofilters, which alternately flood and drain, provide uniform distribution of nutrient-laden water within the filtration medium and improved aeration of the substrate with each dewatering which benefits both nitrifying bacteria and plant roots (Lewis et al., 1978; Paller and Lewis, 1982; Nair et al., 1985; Rakocy, 1989a, 1989b).
Other integrated fish-vegetable systems removed suspended solids from the water by sedimentation in clarifiers prior to plant application (Rakocy, 1989b). Removal of the solid wastes has resulted in insufficient residual nutrients for good plant growth. Acceptable fruit yields have previously only been achieved with substantial supplementation of plant nutrients (Lewis et al., 1978, 1981; Rakocy, 1989b).
The objective of this study was to determine mineral nutrient concentration, balance and accumulation in tomato grown in sand biofilters and irrigated with aquaculture wastes.
Materials and Methods
Olericulture was integrated with recirculatory aquaculture (McMurtry et al., 1990a, 1990b, 1990d). All-male hybrid tilapia were cultivated in tanks which were physically associated with a biofilter utilizing builder’s grade sand as substrate. Four tank to biofilter volume (BFV) ratios were selected as treatments (McMurtry et al., 1990a). The experiments were conducted in a double-layered polyethylene covered greenhouse in Raleigh, N.C.
The bacterial pathogen Pseudomonas solanacearum (Smith) Smith was anticipated and preplant fumigation of the sand with methyl bromide-chloropicrin (98-2) was made at 250 kg ha-1. Each biofilter was inoculated with 1.0 liter of Fritz-zyme #7 (a suspension of Nitrosomonas Winogradsky sp. and Nitrobacter Winogradsky sp.), and irrigated for 9 days prior to tomato planting.
Hybrid tilapia (Oreochromis mossambicus (Peters) x O. niloticus (L.)) were grown in the aquaculture component of the culture system (McMurtry et al., 1990a). The fish were fed a diet of modified Purina Fish Chow 5140, which had an analysis of 32% crude protein (McMurtry et al., 1990a). The rate of daily feed application was a variable percentage of standing fish biomass as influenced by age and mean individual weight (Pullen and Lowe-McConnell, 1982). The fish also grazed algae which grew in the water and on the tank walls. Standing fish biomass and feed rates were adjusted monthly (McMurtry et al., 1990a).
Irrigation water and sediment were drawn from the bottom of the fish tanks 8 times daily between dawn and sunset and pumped to the biofilter surface at a rate of 500 I m-2 of biofilter surface area per day (McMurtry et al., 1990a, 1990b). Water pH and elemental composition after a year of system operation were reported by McMurtry et al. (1990d). Specifics of fish and plant growth were previously reported (McMurtry et al., 1990a, 1990b).
Tomato seedlings were transplanted at 4 plants m-2 in each study resulting in 4, 6, 9, or 14 plants per biofilter. The fish tank size and stocking densities were held constant and fish biomass was maintained uniformly across treatments. Foliar tissue samples were taken at harvest of the first mature fruit. Plants infected with bacterial wilt were excluded from foliar tissue analysis.
The fourth whole compound leaf from the growing tip was collected from each plant and collectively analyzed for each biofilter. Fruit samples were taken from trusses 3 and 4 and combined for analysis. All aerial plant tissue was collected for analysis at the termination of the each crop.
Plant tissue and fish food analysis were conducted using the following procedures: atomic absorption spectrophotometry for K, Ca, Mg, Fe, Mn, Zn, and Cu; vanadomolybdophosphoric yellow procedure (Jackson, 1958) for P; a Kjeldahl procedure (Black et al., 1965) using a salicylic acid modification was used for N; a curcumin method (Grinstead and Snider, 1967) for B; and a turbidimetric procedure (Hunter, 1979) for S. All analyses are reported on a dry weight (DW) basis.
Total DW in each plant portion was calculated from the respective fresh weight DW ratio of representative tissue samples. Total plant mineral uptake was calculated from aerial whole plant and fruit DW, multiplied by the respective elemental concentrations in the assayed tissues. The percentage of elemental inputs assimilated by the plants was calculated from the above plant uptake (x100) divided by the summation of the respective elemental concentrations of each input, except those present in the water, multiplied by the respective input mass.
A randomized complete-block design with 4 replicates was used. Analyses were performed for factorial experiments with Statview™ 512+ on a PC; including Scheffe F-test, and single degree of freedom contrasts. When F-test values were significant, LSDs were calculated.
Experiment 1
Fish were stocked on 5 May 1988 and harvested on 23 August 1988 (McMurtry et al., 1990a). Tomato (Lycopersicon esculentum Mill. ‘Laura’) was transplanted 13 May 1988. This indeterminate greenhouse variety was grown single-stem and harvested through the fourth truss (McMurtry et al., 1990b). A cucumber crop was grown prior to Experiment 2, but results are not reported here.
Experiment 2
Fish were restocked 5 January and harvested on 27 May 1989 (McMurtry et al., 1990a). ‘Kewalo’ was planted 5 January, 1989. This semi-determinate, bacterial wilt-resistant variety was grown single-stem and harvested through the eighth truss (McMurtry et al., 1990b).
Results
Experiment 1
All leaf nutrient concentrations were above normal sufficiency levels except Ca. No differences in leaf nutrient concentrations occurred between treatments except for B (Table 1a). Boron concentrations differed at P=0.01 and were positively correlated to the level of boric acid amendment of the medium (McMurtry et al, 1990b). There were no visual deficiency or toxicity symptoms, although concentrations of Fe, Mn, Zn, and Cu were each approximately 5-fold sufficiency recommendations.
Concentrations of all mineral elements assayed in the fruit tissue differed between treatments but we could not identify a pattern of assimilation (Table 1b). Aerial whole plant concentrations of P decreased with increasing BFV (Table 1c). Generally, K, S, and Fe concentrations decreased with increasing BFV, while N, Mg, and Zn concentrations generally increased with BFV. Boron concentration increased with BFV and was directly correlated to treatment amendment level (McMurtry et al., 1990b).
- Minerals assimilated by all plants collectively in each biofilter increased with BFV (Table 2a). The percentage of total inputs assimilated by the plants also increased with BFV (Table 2b).
Experiment 2
The P and K concentrations in leaves decreased with increasing BFV while S, Cu, and B concentrations generally decreased with BFV (Table 3a). In general, Mg concentration in leaves increased with BFV. Levels of each element except N and K were found above sufficiency recommendations. N concentration was below deficiency levels in all treatments but showed no significant treatment effect. K concentration was above sufficiency levels in the 1:0.67 and 1:1.00 v/v ratios and below sufficiency but above deficiency levels in the 1:1.5 and 1:2.25 v/v ratios. No visible nutrient deficiency symptoms were seen. There was no visual evidence of toxicity symptoms although concentrations of Fe, Cu, and B were each approximately 4-fold, Mn 2 to 3-fold, and Zn 7 to 10-fold sufficiency levels.
Fruit K and S concentrations decreased with increasing BFV (Table 3b). Fruit Zn concentration increased with BFV while B concentration was highest in the intermediate treatment ratios.
Aerial whole plant Mg and Zn concentrations increased with BFV, while P, K, and B concentrations decreased with increasing BFV (Table 3c). Generally, Cu concentrations decreased with increasing BFV while Zn levels generally increased with BFV.
Uptake by the plants of all nutrients except K and Fe increased with BFV (Table 4a). The percentage of total inputs assimilated by the plants also increased with BFV (Table 4b).
Discussion
In agreement with earlier studies (McMurtry et al., 1990b), plant growth was adequately maintained on minimal N, P, and K nutrient levels probably due to the constant replenishment by recirculated aquacultural water (Lewis et al., 1978; Winsor et al., 1985). The proportional balance of N, P, and K in the aquaculture waste was adequate for tomato nutrition.
A slight increase in fish biomass and/or feed input rate in Experiment 2 would probably have raised all leaf tissue N concentrations to within “sufficiency” range. Tomatoes may have also assimilated N in organic amino acid forms. Ghosh and Burris (1950) found that tomatoes utilized alanine, glutamic acid, histidine, and leucine as effectively as inorganic N sources.
All water quality variables remained within acceptable levels for tilapia by circulation through the biofilters (McMurtry et al., 1990a). Nitrogenous compounds, which frequently limit production of fish in other recirculating systems (Lewis et al., 1978), never reached toxic levels (McMurtry et al., 1990a) and were apparently extracted by the plants (McMurtry et al., 1990a). Tomato fruit yields in Experiment 1 were considered to be acceptable from the first 4 trusses and production was greater in Experiment 2 (McMurtry et al., 1990b).
The growth of plants, their cation-anion balance, proton balance and composition of metabolic products are greatly influenced by the form of nitrogen absorbed (Coic et al., 1962). Much of the ammoniacal-N in the aquaculture water was not oxidized prior to irrigation of the biofilter as in other integrated systems, and was available for tomato assimilation. Acceptable fruit yields (McMurtry et al., 1990b) were partially attributed to plant availability of both NH4+ and NO3- ions, a condition which produces the greatest growth and protein production in most plants (Cox and Reisenauer, 1973; Haynes and Goh, 1978). Highest N uptake rates were observed by Blondel and Blanc (1973) when both N forms, NH4+-N and NO3–N were present in the nutrient solution.
Plant availability of NH4+-N at low concentrations, as in this system, may have stimulated NO3- reduction and thereby benefiting plant growth and yield (Kirkby and Hughes, 1970). Because the reduction of NO3- to NH3 in the plant requires energy, it may be theorized that with uptake of NH4+ energy is conserved and diverted to other metabolic processes including ion uptake and growth.
Earlier we reported that NO3- occurred at a much higher concentration than NH4+ (McMurtry et al., 1990a). High plant tissue concentrations of cations was attributed to the dominant NO3–N nutrition which stimulated uptake and translocation of cations as counter-ions (Blevins et al., 1974).
Following the reduction of NO3- in the plant, organic anions accumulate to balance the cation charge originally accompanying the NO3- ions (Dijkshoorn and Ismunadji, 1972). Under high fish growth (feed) rates, N, P, K and Mg availability were not limiting in any treatment. Irrespective of fruit yield (McMurtry et al., 1990b), metabolic by-products from each kg increase in fish biomass provided adequate nutrition for 2 tomato plants for a period of 3 months.
Under reduced feed rates applied to mature fish, we found that if we grew more than 1 plant per kg of standing fish biomass or the increase in fish biomass was less than 0.43 kg per plant then K became limiting. We concur with Rakocy (1989b) that optimum ratios between feed input rate, standing fish biomass, system water volume, and biofilter volume needs to be established for various combinations of fish and vegetable species.
The fish feed formulation employed in these studies appears to be relatively low in Ca if residual quantities alone are used to support plant growth. Amendment of the biofilter medium with CaMg(CO3)2 was ineffective in supplying Ca to the immediate crop. Subsequent application, as in Experiment 2, of CaO was made primarily to maintain the water above pH 5.5, and tissue Ca concentrations reflected this input.
The Ca component of the fish feed might be increased from 1.3% DW to approximately 3.0% DW to mitigate deficiencies in tomato crops irrigated with recirculatory aquaculture water. Available Mg levels in the fish wastes were adequately proportioned with respect to N, P and K. Plant tissue Mg concentrations were substantially greater in Experiment 2 probably as a result of CaMg(CO3)2 amendments made in Experiment 1.
Available S levels in the fish wastes were high relative to N, P and K. This suggests that the fish feed S concentration might be reduced from 1600 ppm to less than 800 ppm without detrimental effect on either fish or tomato production. Concentrations of Fe, Mn, Zn and Cu were high in all plant tissues but no toxicity symptoms were seen. A contributing factor to excess uptake of these elements, in addition to high availability levels, might be attributed to NO3- nutrition which stimulates organic anion synthesis and hence cation accumulation (Coic et al., 1962; Dijkshoorn and Ismunadji, 1972). Kirkby and Knight (1977) showed that when the cation level of a nutrient solution is maintained, plant tissue concentrations of cations and organic anions increase dramatically in response to NO3- nutrition.
Concentrations of Fe, Mn, Zn and Cu in the whole plant tissues were significantly higher than in the associated leaf or fruit tissues. This suggests that these metals were primarily incorporated into stem tissue. Tissue levels of Fe, and Cu per kg feed input were not found to substantially differ between Experiment 1 and 2 and suggests that plant assimilation rates paralleled feed input rates less fish assimilation.
Leaf tissue and whole plant Zn concentrations were very high in Experiment 1 and even greater in Experiment 2. This suggests that Zn was disproportionately high in the fish feed and that the plants were not capable of extracting Zn at a rate approaching that residual from the feed input minus fish assimilation regardless of BFV. Fish feed Zn concentration may be reduced from 65 ppm to approximately 10 ppm without detriment to the fish or plants.
Mineral uptake by the plants in Experiment 2 in excess of input quantities were found for K, Ca, Mg, S, Fe, Zn, Cu and B (Table 4b). This was attributed to the availability of residual nutrient from previous experiments including fish feed, dolomitic lime, and the root masses of prior crops.
Based on tomato nutrient assimilation rates, it would seem appropriate to modify fish feed composition as follows without adversely affecting plant growth: N increased by 5 to 10%; P reduced by 50%; K reduced by 30 to 50%; Ca increased by 200 to 300%; Mg and B unchanged; S reduced by 50%; Fe, Mn, and Cu reduced to 25%; and Zn reduced to 15% of feed concentrations used in this study.
Literature Cited
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Note: 4 Tables not yet added.
Additional Notes from the iAVs Research
| Element | N | P | K | Ca | Mg | Cl | S | Fe | Mn | Zn | Cu | B | Mo |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Fish Feed (%) | 4.65 | 0.88 | 1.20 | 1.31 | 0.28 | 0.6 | 1600 | 201 | 52 | 65 | 12 | 22 | 0.4 |