Aquaponics · Plant production and nutrient management
Plant production in aquaponics
Plants use dissolved nutrients from the fish cycle, but do not replace solids separation or biofilters. Successful cultivation comes from suitable cultures, healthy roots, sufficient light and a controlled nutrient balance.
Clearly delineate system functions
1. What plants do in aquaponics
The plant area is a hydroponic production unit supplied with treated water from fish farming. Plants primarily absorb dissolved ions and convert some of them into harvestable biomass. Actual performance depends on growth, cultivated area, light, temperature, root health and nutrient availability.
Plant absorption
Removes dissolved nutrients from the water only to the extent that the crop actually grows.
Biofiltration
Nitrifying microorganisms oxidize TAN and nitrite. This protective function must not be attributed to plants.
Solids treatment
Settable and suspended substances are deposited or specifically mineralized in front of sensitive root zones.
Terminology correction: Cultivated plants are not blanket “natural filters”. They are a biological nutrient sink with fluctuating performance and their own production logic.
Plan material routes in a comprehensible way
2. From fish feed to harvest
Lining is the central external material input. Only a proportion of the nutrients contained reach the plant in an immediately available form. A further portion remains bound in fish biomass, solids or microbial biomass or leaves the system via discharges.
Balance sheet instead of gut feeling: Feed quantity, plant area and harvest mass are documented together. A high nitrate concentration does not prove either complete plant nutrition or a good overall balance.
Bringing biology and business together
3. Select cultures appropriately
| Cultural group | Typical suitability | Planning risk |
|---|---|---|
| Leaf salads and Asian salads | Short culture time, comparatively moderate nutrient requirements, good for stable series. | Bolting, tipburn, root diseases and loss of quality in heat. |
| Herbs | Basil, mint or parsley can achieve high product values. | Observe species-specific temperature, light and harvesting guidelines. |
| fruit vegetables | Tomato, cucumber or pepper are possible with controlled supplementation. | High need for light, potassium, calcium and culture management. |
| Special and aquatic plants | Only with a defined production target, safe marketing and suitable hydraulics. | Not automatically edible, economical or compatible with the fish system. |
No universal list: The right culture depends on climate, system architecture, sales, food safety and available nutrient supply.
Distinguish between concentration and availability
4. Assess nutrient supply correctly
| nutrient | Function | Typical management question |
|---|---|---|
| Nitrogen | leaf and shoot growth; Nitrate is often easy to measure. | Is the concentration appropriate for the culture or does nitrate accumulate due to insufficient intake? |
| Phosphorus | Energy transfer, root and generative growth. | How much remains bound in solids and can be mineralized in a controlled manner? |
| Potassium | Water balance, enzyme activity, quality and fruit production. | Is the feed input sufficient or is a fish-friendly supplement required? |
| Calcium and magnesium | Cell walls, photosynthesis and numerous metabolic processes. | Do water source, buffering and supplementation match plant intake? |
| Iron and trace elements | Chlorophyll formation and enzyme functions. | Are the form, dosage and pH range available for plants and acceptable for fish? |
Electrical conductivity and nitrate alone do not describe a complete nutrient solution. Leaf appearance, growth, yield, water analysis and, if necessary, tissue analysis must be evaluated together.
A common compromise or separate setpoints
5. pH, temperature and conductivity
pH
Affects nutrient availability, nitrification and non-ionized ammonia levels. Make changes slowly and in a balanced manner.
Temperature
Must suit fish, biofilter and culture at the same time. Decoupled systems allow separate setpoints.
E.C
Shows the sum of dissolved ions, but not their composition. High EC can also arise from unwanted salt accumulation.
Measuring rule: Document measurement method, unit, sampling point and time of day. Trends are usually more meaningful than individual values.
Translating energy into sellable biomass
6. Light and climate determine the recording
Without sufficient photosynthetically active radiation, a plant cannot utilize available nutrients at the expected rate. Daylight total, photoperiod, temperature, humidity and air movement together determine growth, transpiration and quality formation.
Too little light
Slow growth, low nutrient uptake and weak plants can occur despite high water values.
Too high a load
Heat and high evaporative demand can stress calcium transport, leaf quality and water balance.
Ensure oxygen and hygiene
7. Healthy root zone instead of raw mud
Roots require oxygen, appropriate flow and mechanical protection. Solids introduced increase the microbial oxygen demand, promote deposits and can clog pipes or root areas.
- Sufficiently remove solids in front of NFT and DWC modules.
- Check dead zones, blockages and overflows regularly.
- Observe root color, smell, temperature and dissolved oxygen.
- Hygienically remove dead roots and crop residues.
Raw sludge is not plant fertilizer: Recovery of bound nutrients requires a controlled treatment and release step.
Choose culture method according to function
8. Media bed, NFT, DWC and vertical modules
| Procedure | Strength | Critical point |
|---|---|---|
| Media bed | Buffering, versatile and clear for small systems. | Solids accumulation, uneven flow and maintenance access. |
| NFT | Low water volume and good accessibility for light crops. | Very sensitive to pump failure, clogging and unfiltered solids. |
| DWC | Large water volume and easily scalable for leaf crops. | Ventilation, hygiene and reliable pre-filtration. |
| Vertical modules | High space utilization and flexible arrangement. | Uneven light and water distribution, maintenance and energy expenditure. |
Merge demand and entry
9. Balance plant area and feed load
The design must neither be based solely on tank volume nor solely on square meters. Feed quantity and composition determine the potential nutrient input; Crop type, growth phase, climate and harvest sequence determine intake.
Undersupply
Lack, weak growth and low harvest despite stable fish farming.
Oversupply
Accumulation of dissolved substances, increasing water change requirements or quality risks.
Season change
Harvesting, new planting and weak winter light significantly change the intake in the short term.
Systematically limit the causes of deficiency
10. Symptoms are not yet a diagnosis
| Observation | Possible causes | Exam |
|---|---|---|
| Chlorosis | Nutrient deficiency, unfavorable pH, root damage or light stress. | Check leaf position, water analysis, roots and flow. |
| marginal necrosis | Calcium transport, salt stress, climate or rapid growth rate. | Check temperature, humidity, EC, flow and culture management. |
| Withering | Pump failure, root damage, heat or line blockage. | Check hydraulics and oxygen supply immediately. |
| Low yield | Lack of light, wrong crop choice, nutrient imbalance or disease. | Connect yield data with climate, water and crop data. |
Do not fertilize blindly: Supplementation without diagnosis can cause salt accumulation or stress fish and biofilters.
Protect food and equipment
11. Plant health and food safety
- Bring young plants, substrates and equipment into the system in a controlled manner.
- First limit pests through hygiene, monitoring and biological or mechanical measures.
- Only use plant protection products if they are legally permissible and evaluated for fish, biofilters and harvested products.
- Consider water source, crop hygiene, traceability and applicable food law.
Special caution: A product approved for greenhouse crops is not automatically suitable for a circulatory system with fish.
Run operations based on data
12. Monitoring, harvesting and incident planning
| Control panel | Record regularly | Prepare reaction |
|---|---|---|
| plant population | Set, variety, planting date, losses, fresh mass and quality. | Adjust crop plan and plant area. |
| Water and climate | pH, EC, temperature, oxygen, relevant ions, light and air climate. | Define boundaries, test sequence and responsible persons. |
| Hydraulics | Flow, pumps, levels, filters and blockages. | Provide emergency power, replacement pump, overflow and alarm. |
| Hygiene | Root condition, pests, disease symptoms and cleanings. | Arrange quarantine, removal and safe disposal. |
Comprehensible technical basis
13. Specialist sources
- Somerville, C. et al. (2014): Small-scale aquaponic food production, FAO Technical Paper 589.
- Lobanov, V.P. et al. (2021): Improving Plant Health Through Nutrient Remineralization in Aquaponic Systems, Frontiers in Plant Science.
- Bartelme, R.P. et al. (2018): Stripping Away the Soil: Plant Growth Promoting Microbiology in Aquaponics, Frontiers in Microbiology.
- FAO (2016): Report of the FAO Technical Workshop on Advancing Aquaponics.
- Goddek, S. et al. (2015): Challenges of Sustainable and Commercial Aquaponics, Sustainability 7, 4199–4224.
Limit of validity: Guideline values must always be compared with culture, variety, fish species, system architecture, climate, water source, analytics, food safety and applicable law.