Lettuce is a cool season vegetable often produced in greenhouses and other protective structures to meet market demands. Greenhouses are being increasingly adopted in warm climate zones where excessive heat often leads to physiological disorders of lettuce, such as tipburn and premature bolting. Greenhouse lettuce growers in warm climates need cultivar recommendations that can help improve production without ignoring marketability. In the current study, eighteen lettuce cultivars were grown in deep water culture and evaluated for growth, bolting, and tipburn in a greenhouse in Auburn, AL, starting on 30 June and 19 August 2016. Based on the severity of bolting and tipburn, nine cultivars were then selected and evaluated on 17 November 2016 for sensory attributes and marketability by 50 untrained consumer panelists. Cultivars ‘Adriana’, ‘Aerostar’, ‘Monte Carlo’, ‘Nevada’, ‘Parris Island’, ‘Salvius’, ‘Skyphos’, and ‘Sparx’ were selected as having higher heat tolerance than cultivars ‘Bambi’, ‘Buttercrunch’ ‘Coastal Star’, ‘Flashy Trout Back’, ‘Green Forest’, ‘Green Towers’, ‘Jericho’, ‘Magenta’, and ‘Truchas’. Higher crispness, lower bitterness, higher overall texture, and higher overall flavor each correlated to higher marketability, regardless of cultivar, but the strongest predictor of marketability was overall flavor. Overall flavor and overall texture were more strongly correlated to marketability than bitterness and crispness, respectively, suggesting that broader sensory categories may better capture human sensory perceptions of lettuce than narrower categories. Cultivars ‘Aerostar’, ‘Monte Carlo’, ‘Nevada’, ‘Parris Island’, ‘Rex’, ‘Salvius’, and ‘Sparx’ performed well in a hot greenhouse and were preferred by consumers. This step-wise experiment could be an adaptable tool for determining highest performing cultivars under any given production constraint, without ignoring marketability.

Biofloc technology involves the manipulation of the culture system’s carbon: nitrogen ratio to promote bacterial community growth to convert toxic nitrogenous wastes and organics into functional microbial protein; this protein can then be used as a food source and mediate water quality. Biofloc systems have several advantages, which include improved biosecurity, feed conversion, water use efficiency, and nutrient processing. Analyzing the nutritional value and the relationship between high production of aquacultural practices using biofloc is essential. Many studies have demonstrated that biofloc increases the growth of aquatic species by acting as a food source or providing bioactive compounds. Other than this, the beneficial micro-organisms in biofloc systems contain compounds such as organic acids that could resist the growth of pathogenic microbes. They will also serve as a natural probiotic and increase the immunity and survival of fish and shrimp. This technology could be useful for further integration within many aspects of aquaculture production when microbial interactions are considered. However, future studies must fully understand the principles and mechanisms behind the benefits of interactions between biofloc and cultured fish and crustacean species.

Decoupled aquaponic systems are gaining popularity as a way to manage water quality in aquaponic systems to suit plant and fish growth independently. Aquaponic systems are known to be deficient in several plant-essential elements, which can be affected by solution pH to either increase or decrease available nutrients. To determine the effect of pH in a decoupled aquaponic system, a study was conducted using aquaculture effluent from tilapia culture tanks at four pH treatments: 5.0, 5.8, 6.5, and 7.0, used to irrigate a cucumber crop. Growth and yield parameters, nutrient content of the irrigation water, and nutrients incorporated into the plant tissue were collected over two growing seasons. pH did not have a practical effect on growth rate, internode length or yield over the two growing seasons. Availability and uptake of several nutrients were affected by pH, but there was no overarching effect that would necessitate its use in commercial systems. Nutrient concentrations in the aquaculture effluent would be considered low compared to hydroponic solutions; however, elemental analysis of leaf tissues was within the recommended ranges. Research into other nutrient sources provided by the system (i.e., solid particles carried with the irrigation water) would provide further information into the nutrient dynamics of this system.

Aquaponic is a relatively new system of farming, which has received much research attention due to its potential for sustainability. However, there is no consensus on comparability between crop yields obtained from aquaponics (AP) and conventional hydroponics (cHP). Meta-analysis was used to synthesize the literature on studies that compared crop yields of AP and cHP. Factors responsible for differences were also examined through subgroup analysis. A literature search was conducted in five databases with no time restriction in order to capture any publication on AP and cHP crop yield comparisons. The search was, however, limited to journal and conference articles published in English. Study characteristics and outcome measures of food crops were extracted. A natural log response ratio effect size measure was used to transform study outcomes. An unweighted meta-analysis was conducted through bootstrapping to calculate overall effect size and its confidence interval. Between-study heterogeneity (I²) was estimated using a random effects model. Subgroup and meta-regression were used to assess moderators, in an attempt to explain heterogeneity in the effect size. The results showed that although crop yield in AP was lower than conventional cHP, the difference was not statistically significant. However, drawing conclusions on the overall effect size must be done with caution due to the use of unweighted meta-analysis. There were statistically significant effects of aquatic organism, hydroponic system type, and nutrient supplementation used in the studies on crop yield comparisons. Nutrient supplementation, particularly, led to on average higher crop yield in AP relative to cHP. These findings are a vital information source for choosing factors to include in an AP study. These findings also synthesize the current trends in AP crop yields in comparison with cHP.

Using aquaculture effluent (AE) to fertigate plants is gaining popularity worldwide. However, in substrate-based systems, the choice of substrate is essential due to their effects on crop productivity. Differences in the retention of nutrients by substrates makes it necessary to assess suitability for use in AE. This study was conducted from January to July in 2016 and September to October in 2019 to evaluate greenhouse-grown Beit Alpha cucumber (Cucumis sativus L. ‘Socrates’) performance fertigated with AE in pine bark or perlite substrates, grown either as one plant or two plants per pot. A 2 × 2 factorial arrangement in a randomized complete block design with four replications for each season was used. The substrate effect on yield in 2016 depended on the density and season. The pooled yield over seasons in 2016 showed pine bark had a significantly higher yield than perlite by 11% in one plant per pot but lowered by the same amount in two plants per pot. In 2019, pine bark significantly reduced the leachate pH in both plant densities and reduced the leachate EC by about 15% in two plants per pot. The foliar boron was occasionally below sufficiency whilst manganese was above sufficiency in pine bark due to its inherently low pH. We conclude that the effect of the substrates on cucumber yield fertigated with AE is dependent on the season and the number of plants per pot. Therefore, due to the local availability of pine bark, it could be a potential substitute for perlite especially when using one plant per pot for AE. In addition, pine bark could be used as an intermediate substrate to reduce the pH in AE for downstream use.

Nutrient film technique (NFT) is a popular, ergonomic, hydroponic system, but is not often used in commercial aquaponic systems due to lower efficiency in overall nutrient removal. Experiments were conducted to assess if NFT lettuce production could be improved by exchanging aquaculture effluent more frequently, and if so, determine the optimal water exchange rate. The AE was taken from a biofloc-based nile tiapia production system. Treatments consisted of increasing hydraulic retention time (HRT (d)) viz: four-, eight-, twelve-, or sixteen-day water exchanges arranged in a randomized complete block design with five blocks. In one trial (trial 1) where iron (Fe) was not supplemented, there was one replication. There were three replications for the second trial with iron supplementation. The analysis of lettuce plant size index and chlorophyll index (SPAD units) in trial 1 was statistically different among the HRTs beginning 14 days after planting, exhibiting negative linear trends with increasing HRT. However, most foliar micronutrients were borderline sufficient, and all treatments showed foliar Fe deficiency. After iron supplementation (trial 2), lettuce plant chlorophyll and size index exhibited quadratic trends with increasing HRT on 14 and 21 DAP, respectively. In trial 2, plant fresh mass decreased linearly from 162.1 g/head to 147.1 g/head, with increasing HRT. Furthermore, iron supplementation eliminated Fe deficiencies in the plants albeit only up to 14 DAP. Our findings suggest that shorter hydraulic retention times provide a solution to using the NFT system in aquaponics especially with iron supplementation.