Yield and Nutrients Leaf Content of Butterhead Lettuce <i>(Lactuca Sativa)</i> in Response to Fish Nutrient Solution in a Small Scale of Aquaponic Systems

Two lettuce cultivars exhibiting differential levels of tolerance to thiobencarb in soil and nutrient solution assays were examined. Seedlings of ‘Dark Green Boston’ (BOS), a susceptible cultivar, were found to show significant inhibitions in foliar growth compared to the tolerant ‘Great Lakes 366’ (GLA). Reductions of 57% occurred in BOS leaf dry weights at rates of 3 μM thiobencarb as soon as 4 days after treatment. In addition, growth abnormalities including fused leaves were observed in the BOS cultivar, indicating inhibition early in leaf development at the meristem. Twenty-nine and 22% of applied14C-thiobencarb was absorbed from nutrient solution by BOS and GLA, respectively. This difference is probably due to BOS having a 50% greater root system at the time of treatment. Greater absorption and accumulation of radioactivity in the leaves, as well as significantly greater amounts of parent14C-thiobencarb in the foliage of BOS compared to GLA (30 and 19%, respectively) may account for the selectivity observed. Metabolism of14C-thiobencarb occurred within 1 day in both cultivars, with the apparent production of herbicide conjugates accounting for more than 90% of the extracted radiolabel 12 days after treatment. A thiobencarb sulfoxide metabolite was not identified in these studies, indicating sulfoxide production is not a mechanism of selectivity in lettuce.

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Predictive Equations for Butterhead Lettuce (Lactuca Sativa, cv. Flandria) Root Surface Area Grown in Aquaponic Conditions

Horticulturae ◽

10.3390/horticulturae5020039 ◽

2019 ◽

Vol 5 (2) ◽

pp. 39 ◽

Cited By ~ 1

Author(s):

Pamela A. Schwartz ◽

Tyler S. Anderson ◽

Michael B. Timmons

Keyword(s):

Surface Area ◽

Lactuca Sativa ◽

Nutrient Utilization ◽

Root Surface ◽

Root Surface Area ◽

Fresh Weight ◽

Predictive Equations ◽

Recirculating Aquaculture ◽

Butterhead Lettuce ◽

Fish Tank

Aquaponic systems are becoming more prevalent and have led to accurate mass and energy balance models that allow nutrient utilization to be maximized and plant and fish systems to be coupled or complimentary. Such models still do not address the potential of using the plant side as both the primary nitrification system and as a sink for the nitrate being produced from the fish system. However, using the plants as the nitrification system for the fish waste requires a better understanding and quantification of the nitrification capacity of the plant system. A series of experiments were conducted using butterhead lettuce (Lactuca sativa, cv. Flandria) in deep water culture rafts. Plants were grown under two growing conditions and were evaluated based upon harvestable weight. Treatment 1 (H5) consisted of a standard hydroponic nutrient solution maintained at pH 5.8, while treatment 2 (A7) consisted of an aquaponic waste solution maintained at pH 7.0. The aquaponic conditions were created from a fish rearing system using koi (Cyprinus carpio) that was continuously recirculated between the designated plant tubs and the fish tank with an in-line bead filter to capture and mineralize fish solids. The total root surface area was not significantly different between treatments, but the ratio of root surface area to root fresh weight was different, suggesting that aquaponic roots are finer than hydroponic roots. Predictive equations were developed to correlate root surface area to shoot or root fresh weight, which can be used to design the nitrification component for a recirculating aquaculture system (RAS), as part of an integrated aquaponic system.

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