Iron Management in iAVs

In traditional aquaponics systems, iron deficiency is a common challenge that requires supplementation, adding to the cost, time, and complexity of the system.  However, the Integrated AquaVegeculture System (iAVs) offers a simpler and more cost-effective solution to iron management.

This article explores how iAVs simplifies iron management and why it is a superior option for sustainable food production.

The Challenges of Iron in Traditional Aquaponics

In aquaponics, iron is available in two forms: soluble ferrous iron (Fe²⁺) and insoluble oxidized ferric iron (Fe³⁺).  While Fe²⁺ is readily available to plants, it is often oxidized to Fe³⁺ in aerobic environments and at circumneutral pH, making it less bioavailable1.  Traditional aquaponics systems typically operate at a pH closer to 7 and remove a significant portion of the fish waste, which contains iron.

Additionally, these systems do not use soil, necessitating iron supplementation to meet plant requirements1.

The iAVs Advantage

The iAVs approach differs from traditional aquaponics in several key aspects that contribute to better iron management:

1. Utilization of Fish Waste:  In iAVs, all fish waste is utilized, ensuring that the iron present in the waste is not removed from the system1.
2. Optimal pH:  iAVs maintains a pH of 6.4, which is more conducive to iron availability compared to the higher pH levels in traditional aquaponics3.
3. Soil Integration:  The use of soil in iAVs allows for the presence of microbes and siderophores, which increase the availability of iron to plants3.  Plants have evolved over millions of years to thrive in soil, making it the most natural and effective medium for their growth.

These factors combine to create a system that does not require additional iron supplementation, simplifying the process and reducing costs.

Organic Matter

The enhanced presence and accessibility of iron (Fe) in iAVs, as compared to traditional aquaponic systems, can be attributed to the presence of soil organic matter.  This organic matter is instrumental in chelating micronutrients, thereby improving their availability for plant uptake.  Chelation refers to the process of binding micronutrients to organic compounds, which prevents their absorption in less accessible forms.  Additionally, soil microbes contribute to the solubility of micronutrients, further increasing their availability to plants.

The Role of Microbes and Siderophores

In iAVs, the presence of soil fosters the growth of beneficial microbes, such as bacteria from the genera Pseudomonas, Bacillus, Enterobacter, Streptomyces, Gliocladium, and Trichoderma4.  These microbes produce siderophores, which are compounds that chelate and solubilize Fe³⁺, making it more accessible to plants3.

Furthermore, bacterial populations in the rhizosphere can convert nutrients, including iron, into forms that are more readily available for root uptake4.  This microbial activity enhances iron availability without the need for external supplementation.

Understanding Iron Uptake in Plants

Most plants employ acidification and reduction.  This method involves several steps to make iron more accessible:

1. Acidification of the Rhizosphere: The plant releases protons into the soil, lowering the pH around its roots.  This acidification helps dissolve iron compounds in the soil, making iron more available.
2. Reduction of Iron Ions: Once the iron is more soluble, Fe3+ ions are reduced to Fe2+ ions by a membrane-bound enzyme known as Fe(III)-chelate reductase.
3. Uptake of Iron: The reduced Fe2+ ions are then absorbed into the root cells through specific iron-regulated transporters.

Response to Iron Deficiency
In conditions where iron is scarce, plants can enhance their iron uptake mechanisms.  For example, plants might increase the secretion of chelators, pump more protons to acidify the soil further, boost the activity of ferric reduction oxidases to convert more Fe3+ to Fe2+, and enhance the function of ferrous transporters in the root plasma membrane.  These adaptations ensure that plants can maintain adequate iron levels even when it is limited in the environment.

Reduced Iron Requirements in iAVs

Research conducted on iAVs concludes that iron levels in fish feed could be reduced to 25% of the levels typically used in traditional aquaponics.  This reduction is possible due to the efficient utilization of iron within the iAVs, thanks to the optimal pH, soil integration, and the presence of beneficial microbes and siderophores.

Growing Fruiting Plants Without Supplementation

One of the noteworthy benefits of iAVs in comparison to traditional aquaponics lies in its capacity to facilitate the growth of fruit-bearing plants by relying exclusively on fish food, thereby eliminating the necessity for supplemental additives.

In traditional aquaponics, the nutrient profile often falls short of what is required for fruiting plants, necessitating external inputs to meet their nutritional needs.  This is particularly true for elements like potassium, calcium, and iron, which are critical for fruit development and overall plant health.

In contrast, iAVs leverages the natural soil ecosystem, which includes a diverse array of microbes and organic matter that continuously break down and recycle nutrients.  This process ensures a steady and balanced supply of essential nutrients, including those required for fruiting plants.  The soil-based system in iAVs mimics natural growing conditions more closely than the soilless media used in traditional aquaponics, providing a more comprehensive nutrient profile.

Conclusion

The Integrated AquaVegeculture System (iAVs) offers a simpler and more cost-effective approach to iron management compared to traditional aquaponics. * Research has shown that the amount of iron lost in the solid ‘waste’ can be as high as 99%.  By utilizing fish waste, maintaining an optimal pH, and integrating soil to support beneficial microbes and siderophores, iAVs creates an environment that promotes efficient iron utilization.

This eliminates the need for additional iron supplementation, reducing costs and simplifying the overall management of the system.

*Palm, Harry W., et al. “Coupled aquaponics systems.” (2019): 163-199.