Dewatering Aquaculture Effluent For The Hydroponic Production of Pak Choi (Brassica rapa chinensis) and Production of Vegetable Seedlings

Dewatering Aquaculture Effluent For The Hydroponic Production of Pak Choi (Brassica rapa chinensis) and Production of Vegetable Seedlings

Summary

Integrated production systems are necessary from an production perspective because the nutrient output from one system can provide essential nutrient inputs for another. Treated aquaculture effluent has demonstrated potential as a nutrient source for vegetable crop production. The discharged waste could be collected and treated as an on-farm resource to integrate aquaculture and horticulture. Separating the liquid and solid component in discharged aquaculture effluent creates two resources for plant production. Geotextile technology provides a practical method to capture and treat discharged aquaculture effluent after it leaves the fish production system, but we found no research evaluating plant growth response to the liquid or solid component created by geotextile technology. This proposed research project was interdisciplinary and evaluated practical methods with existing technology to determine if the liquid and solid component of discharged aquaculture effluent would benefit plant production.

Objectives/Performance Targets

Objective 1 evaluated the liquid component leaching from a geotextile bag dewatering discharged aquaculture effluent as a nutrient source for hydroponic production of pak choi (Brassica rapa chinensis).

Objective 2 assessed the AE solids retained in the geotextile bag as a substrate component for tomato, bell pepper, and pak choi transplant production.

Objective 3 evaluated growth response of two pak choi cultivars to leachate exiting a geotextile bag treating discharged aquaculture effluent from a moderate-sized recirculating aquaculture facility.

Accomplishments/Milestones

Objective 1
Leachate exiting the geotextile bag had sufficient dissolved nutrients for hydroponic production of pak choi. The pH of the leachate was high (>8.0) requiring the addition of citric acid to lower pH levels to more optimal plant production ranges of 6.0 – 6.5. Plant tissue analysis indicated all four pak choi cultivars responded well to the leachate in the ebb and flow system.

Objective 2
Tomato seedling growth response was negatively affected when greater than 25% (by volume) dewatered solids was incorporated into the potting mix. Increased amounts of dewatered solids negatively impacted physical and chemical parameters of the container substrate. However, tomato seedlings responded well to <15% (by volume) of dewatered solids incorporated into the mix. Water source did not affect final plant growth parameters at harvest when 10% of the container volume was replaced with dewatered solids. This indicates the solids captured from the fish production system could be used to produce tomato transplants without the additional input of commercial fertilizer.

Pak choi growth response was improved when grown in commercial substrate partially replaced with dewatered aquaculture effluent at 10 to 25% container volume. In addition growth response improved when water soluble fertilizer was used to irrigate plants compared to municipal water.

Pepper growth response was dependent on the combination of substrate and water regime. When comparing pepper growth within each type of substrate, the pepper growth was unaffected by water source in substrates with 10 to 50% (by volume) replacement of commercial potting mix with dewatered aquacutlure effluent. Plants grown in the commercial potting mix alone benefited from the water soluble fertilizer compared to municipal water, only. But when comparing pepper growth within each water regime, pepper plants fertigated with the water soluble fertilizer generally grew better when commercial potting mix was replaced with ?10% (by volume) dewatered aquaculture effluent. When municipal water was applied to substrates, pepper plant growth was best when commercial potting mix was replaced with 10% (by volume) dewatered aquaculture effluent. It appears a producer could replace commercial potting mix with 10% dewatered aquaculture effluent and not have to use a commercial fertilizer to produce pepper transplants. The nutrients in the dewatered aquaculture effluent are sufficient for plant growth.

Objective 3
This project will begin summer 2013.

Impacts and Contributions/Outcomes

This project has demonstrated the leachate created by geotextile technology treating discharged aquaculture effluent can be used to grow pak choi. In addition, the solids retained in the geotextile bag can partially replace commercial potting mix to produce containerized vegetable plants. The plant growth response to the amount of dewatered aquaculture effluent used to partially replace commercial potting mix is species dependent, but in general our observations suggest <20% container volume can be replaced. These experiments suggest aquaculture effluent should be captured and treated to create a resource for an integrated production facility.

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