Abstract
A recent study by Sewilam et al., (2022) conducted a comparative analysis of a sand-based agricultural system. This commentary identifies a terminological inconsistency within the article, specifically the conflation of the proprietary commercial method “Sandponics” with the “Integrated Aqua-Vegeculture System” (iAVs). These methodologies employ different nutrient sources and operational principles. This conflation led to the omission of pertinent historical data from the literature review and the misattribution of system limitations. This paper clarifies the distinction between the two technologies and emphasizes the research by McMurtry et al., which addresses the research gap identified by Sewilam et al.
Keywords: iAVs, Sandponics, Integrated Aqua-Vegeculture System, Aquaponics, Closed-loop agriculture, Integrated Aquaculture Agriculture
1. Introduction
Precision in nomenclature is critical for the accurate assessment and classification of agricultural technologies. Sewilam et al., (2022) define their research focus by stating that “sandponics (SP), which is also referred to as an Integrated Aqua-Vegeculture system (iAVs),” is a technique that employs sand filtration in conjunction with fish effluents.
However, existing literature delineates “Sandponics” (a proprietary commercial system defined by Baba & Ikeguchi, 2015) and “Integrated Aqua-Vegeculture Systems (iAVs)” as distinct methodologies. This analysis examines the differences between these systems and illustrates how the interchangeable use of the terms has led to inaccuracies concerning the historical availability of data and the specific operational constraints of the studied system.
2. Defining the Distinct Systems
The literature indicates that the two terms describe systems with different nutritional inputs and mechanical configurations. While Sewilam et al., (2022) employ the term “Sandponics,” the experimental treatments described (specifically T2, T3, and T4) utilize the functional architecture of iAVs specifically, the application of aquaculture effluent onto sand beds for biofiltration and plant growth.
2.1. The Integrated Aqua-Vegeculture System (iAVs)
Developed and characterized across multiple studies (McMurtry et al., 1990b), the Integrated Aqua-Vegeculture system (iAVs) is a closed system of recirculating water linking fish production (aquaculture) with sand-cultured vegetable crops (olericulture) (McMurtry et al., 1990b). The system utilizes unfiltered fish effluent (including solids) pumped directly onto sand beds (as schematically shown in Figure 1) (McMurtry et al., 1997a). The sand beds serve simultaneously as the plant growth substrate or plant support (McMurtry et al., 1997a), a biofilter for the oxidation of reduced nitrogen compounds (McMurtry et al., 1997a), and a mechanism for particulate removal and the decomposition of waste solids (McMurtry et al., 1997a). The feasibility of the integrated system was demonstrated using no supplemental fertilization (McMurtry et al., 1990a), relying exclusively on the mineral nutrition provided only from fish wastes through biological cycles (McMurtry et al., 1993b).
Fig. 1. Original schematic of the iAVs method. This diagram illustrates the requisite aquaculture component and direct biological filtration that defines the system. Reproduced from McMurtry et al., (1990) with the purpose of critical comparison.
2.2. The Sandponics System
The term “Sandponics” is explicitly identified as a trademark or registered trademark of Sumitomo Electric Industries, Ltd. (Kanazawa et al., 2017).
The proprietary methodology referred to as “Sandponics” (Baba & Ikeguchi, 2015) is characterized by the use of external chemical inputs. It is described as a unique cultivation system developed by Sumitomo Electric, using sand as the primary medium (Baba & Ikeguchi, 2015). The system documentation explicitly lists the inclusion of a “Liquid fertilizer pump” and a “Liquid fertilizer Dilutor” (see Figure 2) to administer “Standard Sandponics fertilizer.” Furthermore, the operational protocol addresses agronomic challenges through chemical adjustment (Baba & Ikeguchi, 2015). This indicates a reliance on manual chemical intervention to manage water quality, rather than biological nitrification.
Fig. 2. Configuration of the Sandponics System. Reproduced from Baba and Ikeguchi (2015), “Industrial Cultivation Using the Latest Sandponics System,” SEI Technical Review, with the purpose of critical comparison.
Kanazawa et al., (2017) describe the evolution of this technology into “New Sandponics” (NSP) (see Figure 3). This configuration utilizes a basal tank to supply nutrients via the capillary action of an irrigation cloth. This reliance on chemical fertigation represents a fundamental divergence from the biological nutrient cycling inherent to iAVs.
Fig. 3: Development of Sandponics devices. Reproduced from Kanazawa (2017), “High Quality Agricultural Production Support System by Smart Sand Cultivation Device ‘New Sandponics’,” SEI Technical Review, with the purpose of critical comparison.
3. Evidence of Existing Literature and the Research Gap
The assertion by Sewilam et al., (2022) that “very little or no scientific literature about growing crops in sandponics systems hence, creating so many questions related to the operation, functionality, optimization, sand suitability, and system productivity” (Sewilam et al., 2022), is directly challenged by the substantial scientific record dating back to the 1980s.
By overlooking the terminology distinction, Sewilam et al., omitted the work of Dr. Mark McMurtry and colleagues at North Carolina State University (NCSU), which provides comprehensive, quantitative data on the exact methodology studied.
3.1. Documented System Functionality
Research on iAVs explicitly addressed the operational dynamics, nutrient cycling, and productivity of sand-based integrated systems, contradicting the claim that such data is absent.
- Feasibility and Operation: McMurtry et al., (1990) documented the integrated aquaculture-vegeculture system (iAVs) (McMurtry et al., 1990a, 1990b), which they described as a closed system of recirculating water (McMurtry et al., 1990a). This system utilized sand beds as a grow medium (McMurtry et al., 1990a) for the concurrent production of Blue Tilapia (McMurtry et al., 1990a) and vegetables, including tomato, cucumber, and bush bean (McMurtry et al., 1990a). The study successfully demonstrated that the vegetables grown in sand beds provided sufficient filtration of the recirculated water to maintain water quality acceptable for fish growth (McMurtry et al., 1993b). The crops achieved adequate mineral nutrition solely from fish wastes (McMurtry et al., 1990a) with no supplemental fertilization (McMurtry et al., 1990a).
- Sand Suitability and Substrate Mechanics: Sewilam et al., (2022) assert that “sand suitability” remains an open question due to scarce literature, specifically citing the difficulty of “suitable sand for crops that require cooler climates” as a system limitation. Contrary to this, McMurtry et al., (1990a) provided comprehensive technical specifications for the optimal growing medium, identifying “builder’s grade sand” (99.25% quartz, 0.75% clay) with a specific particle size distribution dominated by: medium sand (0.50–0.25 mm) at 21.0%, coarse (1.00–0.50 mm) at 38.3%, and very coarse (2.00–1.00 mm) (33.3%) fractions. This granulometry was engineered to optimize biofiltration and hydraulic conductivity. Longitudinal data confirmed that clogging was “never observed” over three years of operation, and percolation rates remained stable without channeling or anaerobic zones (McMurtry et al., 1990a). Thus, the parameters for sand suitability are well-established in the literature. The literature demonstrated that for optimal fish health and growth in the recirculating system utilizing hybrid tilapia (Oreochromis mossambicus x O. niloticus), water temperatures were kept above 25°C through the use of thermostatic aquaria heaters (McMurtry et al., 1990b; McMurtry et al., 1997a). Tilapia species (such as Oreochromis niloticus and hybrids) are classified as warm-water species (Diver, 2000; Abdelrahman, 2018) that are favored for tropical and sub-tropical regions (Abdelrahman, 2018) and inherently define the operating environment of the iAVs (McMurtry et al., 1994). Consequently, the system is inherently optimized for environments excluding those that necessitate specialized substrates tailored for maximizing crop production in ambient ‘cooler climates,’ rendering this specific concern redundant within the typical iAVs framework.
- Economic Viability: The accompanying projected economic returns analysis (McMurtry et al., 1997b), based on experimental results and current local market values (McMurtry et al., 1997b), established that the gross returns from this co-culture system… are on a par with traditional commercial greenhouse tomato production (McMurtry et al., 1997b). Specifically, the research projected that the annualized gross returns for the tilapia component alone were estimated to range from $110 to 143/m3 per year (McMurtry et al., 1997b). The projected annual gross returns for the tomato crop ranged from $50 to 102/m2 (McMurtry et al., 1997b). This comparison indicated that the overall system’s economic viability was comparable to commercial greenhouse operations, which Mickey et al., (1989) estimated to range from $77 to $157/m² annually (McMurtry et al., 1997b).
- Nutrient Dynamics: Sewilam et al., (2022) suggest a lack of data on crop performance in sand systems. However, McMurtry et al., (1993) provided a detailed analysis of mineral nutrient concentration and uptake (McMurtry et al., 1993a). The findings established that despite low absolute concentrations of dissolved nutrients (e.g., N, P, K, Mg), crop growth was maintained through the constant replenishment characteristic of the recirculating design (McMurtry et al., 1993a). The research also demonstrated that the percentage of total nutrient inputs assimilated by the plants increased in direct correlation with the Biofilter Volume (BFV) ratio (McMurtry et al., 1993a, 1993b).
- System Optimization: Sewilam et al., (2022) assert that “many questions regarding optimization” exist due to a lack of literature. Contrary to this, McMurtry et al., provided the foundational framework for optimization, characterizing it not as a missing dataset but as a dynamic interaction between four established variables: feed input rate, standing fish biomass, system water volume, and biofilter volume. McMurtry et al., (1997a) evaluated specific biofilter-to-tank ratios (0.67:1 to 2.25:1), demonstrating that the “optimum” ratio is context-dependent and determined by specific regional goals, such as prioritizing maximum fish yield versus water efficiency. The literature further details operational optimization strategies, including the regulation of ammoniacal-N via feed adjustments (McMurtry et al., 1990a), the necessity of continuous multi-cropping to maintain pH stability, and specific feed reformulations to align nutrient input with plant assimilation rates (McMurtry et al., 1993a).
- Water Efficiency: McMurtry et al., (1997b) quantified the water use efficiency of the system (McMurtry et al., 1997b). The daily water replacement rate (makeup water) ranged from 1.2% to 4.7% of the total system volume (McMurtry et al., 1997b). Beyond exchange rates, McMurtry et al., (1997b) quantified total food production efficiency (fish plus fruit) at 24.1 g/L of water consumed. This metric compares favorably to advanced traveling trickle irrigation (23.9 g/L) and dramatically outperforms traditional methods such as Egyptian tomato production (1.19 g/L) (McMurtry et al., 1997b). This data directly addresses the functionality metrics Sewilam et al., claim are missing.
3.2. Historical Context and Citation Record
The work conducted at North Carolina State University (NCSU) on the Integrated Aqua-Vegeculture System (iAVs), is widely recognized as foundational to the field of aquaponics (Abdelrahman, 2018; Diver, 2000; Marklin et al., 2013; Dutta et al., 2018; Ramsundar, 2015). Historical analyses identify this research as a primary source of scientific data on integrated fish/vegetable production between the late 1970s and 2000 (Martin, 2017; Greenfeld et al., 2019). The continued relevance and recognition of the NCSU model is evident in subsequent academic literature, as attested by numerous publications, which reference the iAVs model’s introduction of the first closed-loop aquaponic system (Marklin et al., 2013: Dutta et al., 2018; Martin, 2017; Greenfeld et al., 2019; Gott, 2019; Abdelrahman, 2018; Moldovan et al., 2015; Ramsundar, 2015).
The assertion that literature is sparse is not supported by the widespread citation of McMurtry’s work in subsequent bio-engineering and aquaculture studies. These citations confirm that the scientific community has long recognized the iAVs methodology as a distinct, well-characterized system. Consequently, the “research gap” identified by Sewilam et al., (2022) does not reflect an absence of scientific inquiry but rather the exclusion of the primary literature governing iAVs.
3.3. Consequential Methodological Divergence
The omission of the foundational literature resulted in significant methodological divergences that likely constrained the system’s performance in the Sewilam et al., (2022) study. Specifically, Sewilam et al., utilized irrigation drip lines with diaphragm emitters and limited water recirculation to two cycles per day. This contrasts fundamentally with the established Reciprocating Biofilter (RBF) technique detailed by McMurtry (1990b, 1997a), with high-frequency exchanges (5 to 8 times daily). McMurtry (1993a, 1997a) demonstrated the intermittent irrigation cycle provides a “constant replenishment” of nutrients, allowing crops to thrive on low concentrations. Furthermore, the RBF method was shown to reduce Total Ammoniacal Nitrogen (TAN) and nitrite concentrations by approximately 50% per cycle (McMurtry et al., 1990b, 1997a). By reducing the daily water processing volume by 50% to 85% relative to McMurtry’s parameters (McMurtry et al., 1997b), the methodology employed by Sewilam et al., represents a sub-optimal configuration that likely underreported the potential efficiency of the system.
4. Attribution of System Limitations
Sewilam et al., (2022) identify specific system limitations, including “crop nutritional deficiencies due to insufficient fertilizers” and a requirement for “specialized training.”
Regarding nutrition, the authors cite Makokha et al., (2020), who investigated an inorganic, fertigated sandponics system. Attributing limitations characteristic of synthetic formulations to the Integrated Aqua-Vegeculture System (iAVs) contradicts the system’s documented biological dynamics.
Robust data confirm that iAVs operates via strategic design (McMurtry et al., 1993b; 1997a) rather than passive reliance on inputs (McMurtry et al., 1997b). This methodology involves: (1) optimizing biofilter-to-tank ratios to maximize nutrient extraction and reduce TAN concentrations (McMurtry et al., 1993b, 1997a); (2) balancing nutrient loads by regulating feed input to ensure sufficiency (McMurtry et al., 1990a, 1993a); and (3) utilizing targeted mineral amendments to address specific imbalances (McMurtry et al., 1993a). Therefore, applying the limitations of an inorganic methodology to iAVs constitutes a critical misattribution.
Furthermore, the assertion that iAVs necessitates “specialized training” is demonstrably contradicted by the fundamental design objectives detailed in the literature. McMurtry et al., (1990a; 1997b) explicitly optimized the system for “functional simplicity” and “easy to maintain and operate” (McMurtry et al., 1997a). This operational ease is achieved through three mechanisms:
- Component Integration: The sand beds function simultaneously as biofilters, as substrate for vegetable growth, and as location for decomposition of waste solids, reducing mechanical complexity (McMurtry et al., 1997a, 1997b).
- Self-Regulating Chemistry: Unlike systems requiring base addition, iAVs demonstrates pH stability (~6.0) derived from the biological balance between nitrification (acidifying) and plant nitrate assimilation (alkalizing). This stability is supported by established physiological principles: the uptake of nitrate (NO3− ) anions by plant roots stimulates the release of hydroxyl (OH− ) or bicarbonate (HCO3−) ions (Marschner, 1995; Kirkby & Hughes, 1970), which effectively counteracts the acidity generated by microbial nitrification (McMurtry et al., 1990b; 1997a). Furthermore, the simultaneous availability of ammonium (NH4+ ) and nitrate (NO3− ) buffers the pH fluctuations typically associated with single-source nitrogen uptake (Haynes & Goh, 1978; McMurtry et al., 1990a), significantly reducing the need for external chemical management.
- Uniform Distribution: Reciprocating flood-and-drain cycles ensure uniform distribution of nutrient-laden water within the filtration medium during the flood cycle and improved aeration through complete atmosphere exchange with each dewatering (McMurtry et al., 1990a, 1990b, 1994, 1997a). This system feature allows vegetables to be grown using “traditional methods excluding any which would be harmful to either the fish or biofilter microbes” (McMurtry et al., 1994) rather than complex hydroponic protocols (McMurtry et al., 1994). The simplicity of operation (McMurtry et al., 1994) and the resulting maintenance of adequate nutrient levels limit or eliminate the need for fertilizer additions (McMurtry et al., 1997a). McMurtry et al., (1990a) provided a spatial analysis of nutrient distribution within the substrate (McMurtry et al., 1990a), documenting that nutrient concentrations in the sand medium generally increased nearest the irrigation furrow (within 50 mm or 1.97 in.) and toward the bed surface (McMurtry et al., 1990a). The accumulation near the furrow was linked to the fact that apparent cation exchange capacity (CEC) changes were greatest near the furrows (McMurtry et al., 1987, 1990a). This change was attributed to organic matter accumulating on the surface in these areas (McMurtry et al., 1987, 1990a).
Consequently, the literature describes a system intended for high labor efficiency and ease of operation, directly refuting the claim that specialized technical training is an inherent requirement.
5. Conclusion
Sewilam et al., (2022) conducted an investigation utilizing the functional architecture of the Integrated Aqua-Vegeculture System (iAVs) – specifically, the biological filtration of aquaculture effluent through sand beds – but failed to recognize the methodology’s historical context. This fundamental conflation of iAVs with “Sandponics” (a chemically fertigated system) led the authors to identify research gaps regarding optimization, sand suitability, and nutritional limitations that had already been exhaustively quantified and resolved by McMurtry et al., in the 1980s and 1990s.
The objective of this commentary is not merely to correct nomenclature, but to ensure that the robust, quantitative data existing on iAVs system performance is preserved for future research. The foundational literature provides proven metrics for biofiltration efficiency, water conservation, and economic viability for the advancement of resource-efficient agriculture in arid regions. Future studies must correctly identify and cite the iAVs methodology to build upon, rather than replicate, this established scientific record.
Competing Interests
The author serves as a volunteer administrator for iavs.info, an independent, non-commercial, public educational resource dedicated to archiving and clarifying the historical scientific development of the Integrated Aqua-Vegeculture System (iAVs). The preparation of this commentary received no external financial support. The analysis is based exclusively on a review of peer-reviewed scientific literature. The author’s motivation for this commentary is to ensure the accuracy of the scientific record regarding the distinction between biologically integrated systems (iAVs) and chemically fertigated methodologies (Sandponics).
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