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Controlled Environment Food Production for Urban Agriculture

September 2019
HortScience: a publication of the American Society for Horticultural Science 54(9):1448-1458

DOI:10.21273/HORTSCI14073-19

Authors:

Christopher J. Currey

Iowa State University

Hye-Ji Kim

AeroFarms

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The recent increased market demand for locally grown produce is generating interest in the application of techniques developed for controlled environment agriculture (CEA) to urban agriculture (UA). Controlled environments have great potential to revolutionize urban food systems, as they offer unique opportunities for year-round production, optimizing resource-use efficiency, and for helping to overcome significant challenges associated with the high costs of production in urban settings. For urban growers to benefit from CEA, results from studies evaluating the application of controlled environments for commercial food production should be considered. This review includes a discussion of current and potential applications of CEA for UA, references discussing appropriate methods for selecting and controlling the physical plant production environment, resource management strategies, considerations to improve economic viability, opportunities to address food safety concerns, and the potential social benefits from applying CEA techniques to UA. Author’s viewpoints about the future of CEA for urban food production are presented at the end of this review.

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HORTSCIENCE 54(9):1448–1458. 2019. https://doi.org/10.21273/HORTSCI14073-19

Controlled Environment Food

Production for Urban Agriculture

Celina G

omez

Environmental Horticulture Department, University of Florida, 1549 Fiﬁeld

Hall, Gainesville, FL 32611

Christopher J. Currey

Department of Horticulture, Iowa State University, 008 Horticulture Hall,

Ames, IA 50011

Ryan W. Dickson

Department of Horticulture, University of Arkansas, PTSC 311, Fayetteville,

AR 72701

Hye-Ji Kim

Department of Horticulture and Landscape Architecture, Purdue University,

625 Agriculture Mall Drive, West Lafayette, IN 47907

Ricardo Hern

andez

Department of Horticultural Sciences, North Carolina State University, 2721

Founders Drive, Suite 170, Raleigh, NC 27695

Nadia C. Sabeh

Dr. Greenhouse, Inc., 930 Alhambra Boulevard, Suite 260, Sacramento, CA 95816

Rosa E. Raudales

Department of Plant Science and Landscape Architecture, University of

Connecticut, 1376 Storrs Road, Storrs CT 06269

Robin G. Brumﬁeld

Department of Agriculture, Food and Resource Economics, Rutgers

University, 55 Dudley Road, New Brunswick, NJ 08901

Angela Laury-Shaw

Department of Food Science and Human Nutrition, Iowa State University,

2577 Food Sciences Building, 536 Farm House Lane, Ames, IA 50011

Adam K. Wilke

Iowa State University Extension and Outreach, 418 East Hall, Ames, IA 50011

Roberto G. Lopez

Department of Horticulture, Michigan State University, 1066 Bogue Street,

East Lansing, MI 48824

Stephanie E. Burnett

School of Food and Agriculture, The University of Maine, 5722 Deering Hall,

Orono, ME 04469

Additional index words. economics, food safety, food security, greenhouse, plant factory,

review, sole-source lighting, and supplemental lighting

Abstract. The recent increased market demand for locally grown produce is generating

interest in the application of techniques developed for controlled environment agriculture

(CEA) to urban agriculture (UA). Controlled environments have great potential to

revolutionize urban food systems, as they offer unique opportunities for year-round

production, optimizing resource-use efﬁciency, and for helping to overcome signiﬁcant

challenges associated with the high costs of production in urban settings. For urban

growers to beneﬁt from CEA, results from studies evaluating the application of controlled

environments for commercial food production should be considered. This review includes

a discussion of current and potential applications of CEA for UA, references discussing

appropriate methods for selecting and controlling the physical plant production environ-

ment, resource management strategies, considerations to improve economic viability,

opportunities to address food safety concerns, and the potential social beneﬁts from

applying CEA techniques to UA. Author’s viewpoints about the future of CEA for urban

food production are presented at the end of this review.

The term controlled-environment agricul-

ture (CEA) was ﬁrst introduced in the 1960s

and refers to an intensive approach for con-

trolling plant growth and development by

capitalizing on advanced horticultural tech-

niques and innovations in technology (Hodges

et al., 1968). Controlled environments (CEs)

provide advantages to predict plant responses

to their environment and increase production

efﬁciency, optimize plant yield, and improve

product quality. They play a key role in the

commercial production of ornamental plants

and vegetable crops and in the production of

young plant material from seed, cuttings, or

tissue-culture (Jensen, 2002; Kozai and Niu,

2016a). The recent increase in market demand

for locally grown produce is generating interest

in applying CEA practices to urban agriculture

(UA), including small- (e.g., in-home produc-

tion or indoor gardens), medium- (e.g., com-

munity gardens), or large-scale commercial

operations [e.g., rooftop greenhouses or

warehouse-based indoor ‘‘plant factories’’

(PFs), sometimes referred to as vertical, ware-

house, or container farms] (Eaves and Eaves,

2018; Jansen et al., 2016).

Before land and labor shortages prompted

by the Industrial Revolution forced food pro-

duction to move away from cities, agriculture

was central to urban environments and their

planning (Vitiello and Brinkley, 2014). Al-

though some efforts were made to promote UA

by documenting health, educational, and social

beneﬁts, urban food production was viewed

mostly as a strategy to reduce pressure on the

public food supply during hardships such as

war (Hynes and Howe, 2004; Lawson, 2005).

However, recent shifts in consumption pat-

terns are allowing UA to make a comeback

through its concerted efforts to address sus-

tainability issues in our food system (e.g.,

reduced dependence on fossil fuels, increased

food security) and promote social and envi-

ronmental cohesion (Peterson et al., 2015).

CEs have tremendous potential for commer-

cial urban food production. The high plant

density and year-round production attainable

with CEA optimize space use and can help

overcomechallenges associated with costs and

availability of land in urban settings. More-

over, soilless culture systems allow plants to

grow in nonconventional spaces, as opposed to

fertile soil, while maximizing use of available

resources (e.g., water and nutrients). For a

comprehensive review of the beneﬁts from

CEA in UA, see Kozai and Niu (2016b) and

Takagaki et al. (2016).

For UA producers to beneﬁt from CEA,

results from studies evaluating the applicabil-

ity of CEs for commercial food production

should be considered. Although proﬁtability

will typically depend on the local demand and

supply of food, location, population density,

facility design, and crops produced, prelimi-

nary research suggests that economic sustain-

ability for commercial CEA requires careful

consideration of capital investment and

operating costs, production volume, product

quality and consistency, and local market

trends (Al-Kodmany, 2018; Kozai et al.,

2016). A review of key studies, followed by

1448 HORTSCIENCE VOL. 54(9) SEPTEMBER 2019

a discussion of current and potential applica-

tions regarding opportunities and limitations of

commercial CEA for urban food production

follows.

Physical Environment

Production environment. A key beneﬁt of

CEA is the ability to modify production

environments to maximize plant quality and

yield, extend growing seasons, and enable crop

production in unfavorable climatic conditions

(e.g., wind, rain, extreme temperature, and

limited light). Greenhouses and PFs are the

most common types of CEs used in UA.

Following the construction of an efﬁcient

transportation system after World War II, most

commercial greenhouses in the United States

settled in rural locations with favorable cli-

mates (e.g., high-light, moderate temperatures)

or near large markets to improve economic

viability (Nelson, 2012). Therefore, it is not

uncommon for greenhouse-grown food crops

to travel long distances before reaching con-

sumers (Weber and Matthews, 2008). How-

ever, increasing interest in local food systems

is bringing attention to the impact that green-

house gas emissions associated with food pro-

duction against long-distance distribution

channels (i.e., ‘‘food miles’’) have on our food

chain. Although some argue that reducing

‘‘food miles’’ is necessary to improve the

sustainability of our food chain (Morgan, 2009;

Paxton, 1994), others call attention to the fact that

several key transportation factors (e.g., vehicle

efﬁciency, infrastructure, alternative fuels) affect

the sustainability of many CEs typically used in

UA (Coley et al., 2009; Mundler and Rumpus,

2012). However, the potential for reducing

environmental impacts from UA needs to be

assessed from a broad perspective, including

evaluating the life cycle assessment (LCA) of a

product and incorporating socioeconomic factors

(Edwards-Jones et al., 2008).

Greenhouses built on vacant rooftops of

city buildings have become popular in recent

years as they capitalize on sunlight to pro-

duce plant products in close proximity to

consumers. In addition, because rooftops

represent close to one fourth of residential

and nonresidential urban areas, they have

signiﬁcant potential to contribute to the

expansion of UA (Getter and Rowe, 2006).

Nonetheless, important economic aspects of

producing in rooftop greenhouses should be

considered, as they may require special con-

struction materials, components, and struc-

tural support to satisfy building codes and

withstand strong wind loads and substantial

sun exposure (Meier et al., 2013). Numerous

studies assess the impact of building rooftop

greenhouses in urban settings from an eco-

nomic (Benis et al., 2018; Sany

e-Mengual

et al., 2015), environmental (Jones and

Gilbert, 2018; Nadal et al., 2017; Sanjuan-

Delm

as et al., 2018; Sany

e-Mengual et al.,

2018), social (Davis, 2011), and educational

(Nadal et al., 2017; Sany

e-Mengual et al.,

2014) perspective. In addition, a number of

commercial operations have demonstrated

the economic viability of rooftop green-

houses for urban food production (e.g.,

Gotham Gree n Farms, Luf a Farms). Fur-

thermore, rooftop greenhouse designs can

include photovoltaic systems and rainwater

harvesting strategies, increasing their poten-

tial to expand sustainable UA production

practices.

In contrast, the economic sustainability of

indoor PFs has demonstrated to be more

challenging, in part due to their dependence

on electricity to run all systems (Banerjee and

Adenaeuer, 2014). Indoor PFs are widely

used in Asia and are gaining popularity in

the United States and European countries for

producing high-value crops such as leafy

greens (Kozai et al., 2016). However, most

countries successfully adopting PFs for fresh

food production have land and/or environ-

mental limitations, which, coupled with

food-safety concerns, justify the high pro-

duction costs. However, preliminary research

suggests that some U.S. consumers are not

willing to pay higher prices for indoor-grown

produce (Coyle and Ellison, 2017; Short

et al., 2018).

Production systems. Production systems

for CEA typically consist of soilless culture,

with or without the use of an organic or

inorganic substrateand with active application

of water and fertilizer, typically provided with

a dilute nutrient solution. Hydroponic pro-

duction is a type of soilless culture in which

plant roots are suspended in either a static,

continuously aerated nutrient solution, or in a

continuous ﬂow or mist (Jones, 2014). The

terms ‘‘soilless culture’’ and ‘‘hydroponics’’

often are used interchangeably, especially

when using substrates that are chemically inert

and provide little nutrient supply or retention.

Crop production using soilless culture or

hydroponics has several potential beneﬁts

compared with traditional ﬁeld production,

including isolation from soil or water-borne

issues (e.g., nematodes, salinity, or heavy

metals) and an improved ability to control

water and nutrient uptake. For comprehensive

reviews about the beneﬁts of using soilless

culture in CEA, see Raviv et al. (2019) and

Jones (2014). Crops produced using soilless

culture often are grown in containers, troughs,

or bags with a limited volume, allowing for

efﬁcient root-zone management. Argo and

Fisher (2002), Bunt (1988), and Raviv et al.

(2019) list common sources of nutrients in

soilless culture, which include the raw irriga-

tion water, fertilizers either dissolved in the

irrigation water or incorporated into a sub-

strate, substrate components, and amendments

used to adjust substrate pH. Raviv et al. (2019)

also discuss common irrigation and fertiliza-

tion equipment used for container production

systems, including overhead, drip, and sub-

irrigation systems. Nelson (2012) provides a

detailed review of management strategies

across soilless culture systems, including strat-

egies on system design, substrates, water and

fertilizer, production environment, and mar-

keting and business planning.

Substrate selection is a critical aspect of

soilless culture. Primary substrate compo-

nents (i.e., >40% of the substrate volume)

often consist of organic materials with low

bulk density and high water holding capacity,

such as peatmoss and coconut coir ﬁber

(Argo and Fisher, 2002). Conversely, sec-

ondary components (i.e., <40% substrate

volume) often include materials such as

expanded minerals (e.g., perlite and vermic-

ulite), clays, sand, and composts that increase

drainage and cation exchange capacity to

increase aeration and nutrient retention. Sev-

eral authors have reviewed the most common

organic and inorganic components of sub-

strates, manufacturing, and cultural plant pro-

duction advantages and disadvantages to using

different materials (Bunt, 1988; Burnett et al.,

2016; Raviv et al., 2019).

Hydroponic systems commonly used in

UA differ in their design and suitability for

certain crops and production scenarios. The

most common hydroponic systems include

nutrient-ﬁlm technique (NFT), deep-water

culture (DWC; also known as deep-ﬂow

technique, raft, raceway, or ﬂoating hydro-

ponics, among others), and aggregate cul-

ture. NFT consist of crops grown in sloped

troughs where a thin ﬁlm of nutrient solution

ﬂows (either continuously or intermittently)

over the roots, whereas DWC systems con-

sist of crops grown with their roots contin-

uously submerged in a nutrient solution.

Aggregate culture consists of growing crops

in bagged substrates (e.g., rockwool or co-

conut coir slabs) or containers (e.g., Dutch/

Bato buckets) with the nutrient solution

applied using drip emitters. Typically,

NFT and DWC systems are used for short-

term, non-fruiting crops such as leafy greens

and herbs, whereas long-term fruiting crops

such as tomato (Lycopersicon esculentum),

cucumber (Cucumis sativus), sweet pepper

(Capsicum annuum), and strawberry (Fra-

garia ·ananassa) are usually grown in

aggregate culture. Several authors have

reviewed speciﬁc plant species, water and

nutrient management, structural design, and

economic considerations for producing

crops in NFT and DWC (Blok et al., 2017;

Walters and Currey, 2015), and aggregate

culture (Raviv et al., 2019; Sonneveld and

Voogt, 2009).

Soilless culture and hydroponic systems

used in CEs also provide opportunities for

producing medicinal and pharmaceutical

crops with high quality, purity, consistency,

bioactivity, and biomass (Hayden, 2006;

Lopez and Runkle, 2017; Papadopoulos

et al., 2001; Potter, 2014). Hayden (2006)

Received for publication 22 Mar. 2019. Accepted

for publication 22 May 2019.

We gratefully acknowledge support from the US

Department of Agriculture National Institute of

Food and Agriculture, Multistate Research Project

NE1835: Resource Optimization in Controlled

Environment Agriculture and thank Dr. A.J. Both

for his valuable review.

Current address: University of Minnesota Water

Resources Center, 183 McNeal Hall, 1985 Buford

Avenue, St. Paul, MN 55108.

Corresponding author: E-mail: cgomezv@uﬂ.edu.

HORTSCIENCE VOL. 54(9) SEPTEMBER 2019 1449

REVIEWS

and Maggini et al. (2014) discuss the ad-

vantages of using hydroponic systems for

producing medicinal crops commonly

grown in CEs. Moreover, despite being

regulated as an illicit crop in many coun-

tries, production of cannabis (Cannabis

sativa) using soilless culture in CEs has

increased and gained signiﬁcant public at-

tention in recent years, particularly in

Europe and North America. Cultivation,

processing, and regulation of cannabis for

medicinal use is reviewed by Potter (2014).

Aquaponic production, integrating hydro-

ponic systems with aquaculture (i.e., ﬁsh

production), recently has increased in popu-

larity for UA (dos Santos, 2016). Aquaponics

involves converting water and organic waste

produced by cultivated ﬁsh or crustaceans

into nutrient solutions used for hydroponic

plant production. Potential beneﬁts of aqua-

ponics include the ability to increase

resource-use efﬁciency (e.g., shared startup,

operating, and infrastructure costs) and im-

prove sustainability (e.g., reduced water use

and waste discharge to the environment)

while simultaneously producing ﬁsh and food

crop commodities (Tyson et al., 2011). Recir-

culating the nutrient solution between the

hydroponic and aquaculture production com-

ponents, essentially forming a completely

closed system, is termed ‘‘coupled’’ aqua-

ponics. Due to the technical challenges with

maintaining appropriate chemical and bio-

logical properties in a recirculating solution,

‘‘decoupled’’ aquaponics has been proposed

as a more efﬁcient alternative to ‘‘coupled’’

aquaponics. In ‘‘decoupled’’ aquaponics, the

aquaculture efﬂuent is collected and supple-

mented with speciﬁc nutrients for higher

yield of ﬁsh and hydroponic food crops

(Kloas et al., 2015). However, commercial

applications of ‘‘decoupled’’ aquaponics are

still under development. Although integrated

aquaponic production systems have been

used for over 30 years, the commercial

application of aquaponics is relatively new

to UA. For a comprehensive review on the

history of aquaponics see Palm et al. (2018).

For appropriate functioning, aquaponic

systems require balancing multiple factors,

including solution pH (Wongkiew et al.,

2017a; Zou et al., 2016), plant and animal

density (Buzby and Lin, 2014; Hussain et al.,

2014, 2015), solution ﬂow rates (Hussain

et al., 2015; Khater and Ali, 2015; Wongkiew

et al., 2017b), economics (Quagrainie et al.,

2018; Tokunaga et al., 2015), system conﬁg-

uration (Klemencic and Bulc, 2015; Monsees

et al., 2017), and food safety considerations

(Elumalai et al., 2017; Pantanella et al., 2015).

Several authors have reviewed system types,

management, and potential proﬁtability of

aquaponic production systems (Blidariu and

Grozea, 2011; Lewis et al., 1978; Love et al.,

2015).

Leaf chlorosis and/or reduced yields are

reported for some crops grown in aquaponics,

such as tomato (unpublished data) and egg-

plant (Solanum melongena) (Roosta and

Mohsenian, 2015). However, supplementing

aquaponic solutions with potassium, sulfur,

iron, and manganese may alleviate crop

growth and yield losses associated with

nutritional deﬁciencies (Rakocy et al., 2004,

2006; Roosta and Hamidpour, 2011).

Technologies

Electric lighting. The daily light integral

(DLI) requirement of food crops commonly

grown in CEs typically ranges from 12 to 30

mol·m

‒2

·d

‒1

(Dorais et al., 2017). Greenhouse

production located in regions with consider-

able seasonal variation in solar radiation

typically relies on supplemental lighting to

increase DLI (Faust and Logan, 2018). Fur-

thermore, solar spectrum can vary depending

on location, season, and time of day; how-

ever, in general, it is composed of 0.1%

ultraviolet-B (280–315 nm), 5% ultraviolet-

A (315–400 nm), 19% blue (400–500 nm),

25% green (500–600 nm), 26% red (600–700

nm), 25% far-red (700–800 nm) (extracted

from Kotilainen et al., 2018). High-pressure

sodium (HPS) lamps are the most common

type of electric light source used in commer-

cial greenhouses, whereas metal halide lamps

are used occasionally because of their higher

blue light output (Menard et al., 2006; Nelson

and Bugbee, 2014). However, the use of

light-emitting diodes (LEDs) in CEs has

substantially increased in recent years

(Lopez and Runkle, 2017; Mitchell et al.,

2015).

Research comparing LED and HPS lamps

as supplemental lighting sources mainly fo-

cuses on: 1) evaluating potential reductions

in energy consumption; and 2) understanding

the effects of light spectra on plant growth,

morphology, and quality. Although HPS

lamps have a set spectrum that typically is

composed of approx. 5% blue, 49% green,

39% red, and 7% far-red (measurements from

a 600-W HPS ﬁxture; P.L. Light Systems

Inc., Beamsville, ON, Canada), LED ﬁxtures

can have different color diodes to achieve

customized spectra. However, the most com-

mon LED ﬁxtures available for plant lighting

contain mainly red and blue diodes (10% to

25% blue diodes), with some ﬁxtures in-

cluding a small number of far-red and/or

white diodes. For a review of different uses,

ﬁxture characteristics, and application of

LEDs for supplemental lighting in CEA see

Lopez and Runkle (2017) and Mitchell et al.

(2015).

Although initial efforts to produce high-

value food crops in warehouse-based PFs

used water-cooled HPS lamps, challenges

associated with their economic and thermal

management negate the application of these

lamps for sole-source lighting in multitiered

PFs (Mitchell and Stutte, 2015). Fluorescent

lamps have been commonly used for indoor

CEA for many years. However, with increas-

ing light efﬁcacy (mmol·J

‒1

), capital cost

reductions, and widespread availability,

LEDs are becoming the light source of choice

for PFs. In fact, introducing commercial

LEDs as plant lighting sources was a major

contributing factor to the renewed interest in

CEA for urban food production. This is

because LED ﬁxtures typically have lower

electric power requirements per unit of grow-

ing area (kW·m

‒2

) and deliver high light

intensities with small amounts of radiant heat

delivered to crops, theoretically resulting in

signiﬁcant savings for energy-intensive in-

door food production. In addition, by maxi-

mizing photon capture efﬁciency using

‘‘precision’’ or ‘‘smart’’ lighting’’ such as

targeted (Poulet et al., 2014), intracanopy

(Dueck et al., 2012; G

omez and Mitchell,

2016; Massa et al., 2005), or dynamic

(Clausen et al., 2015; Pinho et al., 2012;

van Iersel, 2017; van Iersel and Gianino,

2017; van Iersel et al., 2016; Weaver et al.,

2019) LED lighting, efﬁciency of production

systems can signiﬁcantly increase. For a

comprehensive review of the adoption of

LEDs in UA see Gupta (2017).

Carbon dioxide (CO2) enrichment. In

closed environments with high planting den-

sities (typical for greenhouses and PFs), the

concentration can rapidly drop below

the ambient concentration (approx. 400

mmol·mol

‒1

), requiring supplemental CO

injection to avoid limiting photosynthesis

and plant growth. Enrichment up to 800

mmol·mol

‒1

is typically cost-effective to pro-

mote photosynthesis and growth of most

plants grown in CEs (Both et al., 2017).

However, enrichment strategies and beneﬁts

depend on, among others: plant species, tar-

get CO

concentration, environmental con-

trol strategies for light, ambient temperature,

and humidity, and the cost and source of CO

injection (e.g., equipment and electricity)

(Both et al., 2017). Indoor CO

concentration

can be increased by releasing pure gas or by

producing CO

from fuel combustion. When

using the latter approach, carbon monoxide

and ethylene production are also important

factors to consider with CO

enrichment, as

they can be toxic to plants at relatively low

concentrations and may result from inefﬁ-

cient fuel combustion or by improperly ad-

justed burners (Nelson, 2012).

Several studies report responses of differ-

ent food crops to CO

enrichment. Generally,

studies suggest that doubling ambient CO

levels increases lettuce yield by 25 to 60%

(Chagvardieff et al., 1994; P

erez-L

opez et al.,

2015). Conversely, some report small or non-

signiﬁcant differences in lettuce fresh and dry

mass grown under elevated CO

(>800 ppm)

compared with ambient levels (Fu et al., 2015;

Mortensen, 1994; Park and Lee, 2001). Yield

(kg per plant) of strawberry plants grown in

CEs signiﬁcantly increases by doubling the

ambient CO

concentration (Enoch et al.,

1976; Sun et al., 2012). For cucumber, sup-

plemental nitrate enhances the positive effects

of CO

enrichment on fruit yield (Dong et al.,

2017; Enoch et al., 1976). However, Peet

(1986) found no response to cucumber pro-

duction under an elevated CO

concentration.

Similarly, although some studies report to-

mato yield increases with CO

enrichment

(Calvert and Slack, 1975), others have re-

ported increased individual fruit mass and

number of high-rated fruits, but no increase

in total yield (Peet and Willits, 1984).

1450 HORTSCIENCE VOL. 54(9) SEPTEMBER 2019

Heuvelink and Kierkels (2015) reported

that in general, CO

enrichment from 400 to

1000 mmol·mol

‒1

in CEs can increase total

yield by 35 to 50%. For comparison, yield

increases with higher DLIs are often linear,

as commonly observed in yield differences

between greenhouse crops produced during

spring-to-summer vs. fall-to-winter seasons

(Acock et al., 1971; Cockshull, 1992;

Kubota et al., 2016). Also, responses to

enrichment are species-speciﬁc and

concentrations above 1000 mmol·mol

‒1

are

not typical for commercial production, since

several studies have shown little or no

additional beneﬁt at higher concentrations

(Calvert and Slack 1975; Enoch et al., 1976;

Peet and Willits, 1984). Furthermore, crops

with high harvest indices (dry mass of

harvestable organs/total plant biomass of

plant) such as leafy greens beneﬁt most from

enrichment, as increases in photosyn-

thesis directly affect the harvestable portion

of the plant (i.e., leaves). In contrast, bene-

ﬁts from CO

supplementation are less

signiﬁcant with fruiting crops because in-

creased photosynthesis does not directly

translate into increased fruit yield.

Humidity control. In CEs, the areal hu-

midity (both absolute and relative) is affected

by several factors, such as plant transpiration

rate, irrigation strategy, inﬁltration and ven-

tilation, and active systems used to humidify

or dehumidify the air (von Caemmerer and

Baker, 2007). Managing humidity is essential

for optimal plant growth and development,

but it is often the hardest environmental

parameter to fully control in CEs. Although

relative humidity is the most common mea-

sure of humidity, it is not indicative of the

plant’s relationship to humidity. Vapor pres-

sure deﬁcit (VPD) is the driving force of

water loss from a leaf, and therefore, it is a

more accurate measure of humidity in CEs. A

review of the thermodynamic properties of

moist air and their effect on plant growth in

CEs can be found in Hanan (1997) and Kozai

et al. (2016).

Plant transpiration generally increases

linearly with increasing VPD, radiation, and

air speed. Therefore, all factors indirectly

affect nutrient uptake, leaf temperature, and

overall plant growth and development. For

leafy greens and culinary herbs grown in

CEs, high VPDs are desirable to prevent

calcium deﬁciencies such as tipburn (Frantz

et al., 2004; Goto and Takakura, 1992). For

CE-grown tomato, VPDs in the range of 0.5

to 1.0 kPa are positively correlated with

increases in fruit yield and stomatal conduc-

tance, and reductions of blossom-end rot and

fungal diseases (Barker, 1990; Guichard

et al., 2005; Leonardi et al., 1999; Shamshiri

et al., 2018; Zhang et al., 2017). Studies also

report that low nighttime VPDs enhance

calcium uptake of young and inner straw-

berry leaves (Bradﬁeld and Guttridge, 1979;

Choi et al., 1997), whereas VPDs <0.1 kPa

for at least 3 h each night help prevent

calcium deﬁciencies in strawberries pro-

duced under environments with high daytime

VPD (Kroggel and Kubota, 2017).

Under high-humidity conditions in CEs,

water vapor has to be removed from the air to

maintain desirable humidity levels. The

lowest-cost, lowest-energy method of dehu-

midiﬁcation is ventilation, which is the ex-

change of indoor air with outdoor air, either

with fans or vents (Wang et al., 2016).

Ventilation works best when outside air is

dry and cool. Therefore, in northern climates

during winter conditions, ventilation is

mainly used for dehumidiﬁcation. However,

if the outside air is too cold, simultaneous

heating is needed to maintain the desired air

temperature. Alternatively, if the outside air

is too hot, cooling will be needed, usually

with an air conditioner (common practice for

PFs) (Kozai et al., 2016). Growers typically

make economic decisions to balance the cost

of temperature control with the beneﬁts of

lower humidity obtained by ventilation.

Kubota et al. (2006) reports that under typical

semiarid midday weather, humidity control

inside the greenhouse is very efﬁcient. In

contrast, humidity control in greenhouses

located in continental climates is challenging

in the winter months when using ventilation

(Kubota et al., 2006). Therefore, the common

humidity set point in greenhouses located in

continental climates is 80 to 85% relative

humidity (K€

orner and Challa, 2003).

Ventilation is not desirable in PF opera-

tions due to reductions in CO

-use-efﬁciency

from venting out supplemental CO

and the

potential introduction of pests from the out-

doors (Kozai, 2013). For that reason, de-

humidiﬁcation with air conditioning is

typically used in PFs, as opposed to ventila-

tion in greenhouses. However, reports using

an internal dehumidiﬁcation system in the

greenhouse (dehumidiﬁer or heat pump) in-

dicate reductions in energy consumption

compared with the venting-heating technique

(de Zwart, 2014; Valli

eres et al., 2014).

Furthermore, several studies have evaluated

night-time greenhouse dehumidiﬁcation us-

ing a heat pump to prevent condensation on

foliage (Boulard et al., 1989; Campen et al.,

2003; Chass

eriaux and Gaschet, 2011;

Migeon et al., 2012), preventing venting the

greenhouse during the night to reduce the

consumption of energy by conditioning (re-

heating) the air. In some instances, night-time

heat-pump dehumidiﬁcation requires up to ﬁve

times less energy than the common venting-

heating technique (Chass

eriaux et al.,

2014). Furthermore, proof-of-concept stud-

ies demonstrate the feasibility of using

desiccant-based systems to absorb moisture

from the greenhouse environment during

periods with high humidity (Davies, 2005;

Lychnos and Davies, 2012; Mei and Dai,

2008).

Transpiration increases the amount of

water in the air and increases the energy

content (i.e., enthalpy) of the air. Heating,

ventilation, and air conditioning systems are

able to cool the air (remove energy) while

lowering the humidity (dehumidiﬁcation). In

PFs, it is not uncommon for the energy input

from transpiration (i.e., latent heat) to be

larger than the energy input from electric

equipment (i.e., sensible heat) (Graamans

et al., 2017). When sizing a heating, ventila-

tion, and air conditioning system, it is impor-

tant to consider 1) the increase in humidity in

the air from plant transpiration; 2) the evap-

orative cooling effect of plant transpiration;

and 3) the resulting increase in latent and

decrease in sensible heat that has to be

removed from the growing environment.

Resource Management

Resource cycling and environmental

footprint of CEA in UA. Recent LCA studies

in urban settings provide insights in the

carbon footprint of several CE systems.

Sany

e-Mengual et al. (2015) report that the

environmental impact of a rooftop green-

house in a city is higher at the construction

stage and lower during the cultivation and

transportation stages compared with a multi-

span greenhouse in a rural area. Goldstein

et al. (2016) concludes that the overall

environmental impact of urban CEA depends

on the local energy costs and production

materials, and suggest that CEA for urban

food production might be better-adapted to

mild climates. While results from these pro-

jects cannot be extrapolated to all locations or

CEA structures, they underline the impor-

tance of breaking down environmental foot-

print and costs by processes in the supply

chain and location.

CEA is energy intensive. Some studies

conclude that the establishment and infrastruc-

ture of CEA in cities can have a high envi-

ronmental and economic footprint (Coley

et al., 2009; de Villiers et al., 2011; Mundler

and Rumpus, 2012). In addition, the energy

requirement for heating in northern climates

can be high. Therefore, some debate whether

reducing distance from source to consumer

justiﬁes the high-energy footprint of CEA in

urban settings (Goldstein et al., 2016; Sany

Mengual et al., 2015; Weber and Matthews,

2008). Alternative energy resources, such as

geothermal, solar, wind, and hydropower, can

be an improvement over traditional carbon-

based energy sources. Nonetheless, local land

and infrastructure design need to be consid-

ered in the overall footprint of a production

system.

Soilless culture requires less water than

soil-based agriculture. However, environ-

mental gains from the overall net effect of

water consumption in UA remain to be de-

termined, considering that the irrigation efﬁ-

ciency (kg·m

‒3

) and indirect water use (e.g.,

for cooling and heating) depends on the

system infrastructure, irrigation design, and

location, among other production factors.

The multidimensional concept of water foot-

print considers the whole supply chain, as

well as geographical and temporal parame-

ters. Hoekstra et al. (2011) deﬁne water

footprint of a product as ‘‘the total volume

of fresh water that is used directly or in-

directly to produce the product.’’ In urban

CEs, the water footprint of the whole system

must be considered to measure the true

impact on water resources. Rainwater and

HORTSCIENCE VOL. 54(9) SEPTEMBER 2019 1451

wastewater are potential water sources for the

production system. However, it is unknown

how capturing rainwater in urban environ-

ments may affect the entire water system

(Goldstein et al., 2016; Hoekstra et al., 2011).

In addition, wastewater must be treated to

reduce human health risks from pathogens,

pharmaceuticals, or excess salts, which can

be energy-intensive. Goldstein et al. (2016)

show that the total amount of water and

nutrient use per crop for production in CEA

can be lower compared with conventional

agriculture. Nonetheless, until indirect ef-

fects on the overall water system are

accounted for, the net effect on water con-

sumption in urban setting is unknown.

Fertilizer applications in CEA are more

efﬁcient compared with ﬁeld production be-

cause of targeted applications (in time and

space) and the physical ease of recirculating

nutrient solutions (Goldstein et al., 2016). In

urban environments, human food waste could

be used as fertilizer sources for plant pro-

duction (Chiew et al., 2015; Sp



angberg et al.,

2014). However, while integrating solid and

liquid waste to supply nutrients for UA is

technically feasible, its implementation and

technology requires maximum integration to

make it economically feasible (Villarroel

Walker et al., 2014).

Economic Environment

Although buying local food products may

not be economically cost-effective in terms of

comparative advantages, consumer groups

endorse UA for a number of reasons, such as

to support local economies, promote environ-

mental sustainability, and reduce food insecu-

rity by providing access to local, fresh food in

inner-city food deserts (Ikerd, 2017; Peterson

et al., 2015; Scharber and Dancs, 2015; Steele,

2017). Although interest in UA is growing,

few studies evaluate its cost effectiveness. For

example, studies compare rooftop green-

houses with other rooftop production systems,

but not to the cost of greenhouse production in

rural areas (Quagrainie et al., 2018; Tokunaga

et al., 2015). There is a need for research that

accurately assesses the return on investment

and LCA of various types and sizes of CE

systems for UA (Al-Kodmany, 2018).

The number of urban farms is currently

low due to the many challenges faced by

urban growers, such as tight regulations,

zoning restrictions, limitations to water ac-

cess, and high capital and operating costs

(e.g., land and electricity), among others

(Reisman, 2012; Steele, 2017). In addition,

shade from tall buildings and skyscrapers is

particularly problematic with growing plants

in cities, partly explaining the increasing

interest in rooftop greenhouses in urban

settings. However, rooftop greenhouses have

higher capital costs compared with standard

ground-based greenhouses. An alternative to

overcoming issues associated with shade is to

produce in PFs, but this increases production

costs even further because of the need for

adequate environmental control (Banerjee

and Adenaeuer, 2014). These high costs have

kept the number of urban farms small. For

UA to be viable, CEs must derive proﬁts from

extending the economic beneﬁt to the local

community, or by focusing on targeted sales

to markets that can pay high prices

(Brumﬁeld and Singer, 2018; Singer and

Brumﬁeld, 2017).

UA can bring value to local communities

by providing opportunities for strengthening

social bonds, expressing and maintaining cul-

tural heritage, and engaging in activities pro-

moting social and political change (Steele,

2017). A social business model offers oppor-

tunities for alternate funding sources from

schools, governmental programs, or donors

particularly interested in education, research,

or community development. Some businesses

have reduced labor costs through the assis-

tance or use of volunteers (Reisman, 2012).

In addition, commercial CE businesses with

an integrated educational component offer

the social beneﬁt of providing job training

and skill development for individuals. For

example, CEA offers students opportunities

to learn about food systems, nutrition, tech-

nology, and environmental sustainability,

as well as teaching skills in customer ser-

vice, leadership, marketing, and fundraising

(Steele, 2017).

Consumer sociodemographic background

typically drives preferences and willingness

to pay for local food products. Yue and Tong

(2009) show that urban consumers are more

likely to buy locally grown produce com-

pared with rural consumers. Therefore, due to

the high costs associated with CEs for urban

food production, some urban growers target

high-value niche products (e.g., microgreens

and heirloom tomatoes), charging premium

prices to cover the added costs of operating in

the city. To increase proﬁtability, urban

growers also target high-end restaurants and

supermarkets, whose customers are prepared

to pay a premium price for locally-grown

produce (Sace and Natividad, 2015).

Potential Improvement of Product

Quality in CEA

Increasing awareness of health and well-

ness has generated signiﬁcant interest in the

nutritional composition and health-promoting

compounds of fruits and vegetables. The

contribution of UA to human health can be

signiﬁcant because urban settings may provide

easier access to fresh food (Orsini et al., 2013).

Fruits and vegetables are excellent sources of

selected minerals, vitamins, and antioxidants,

and their impacts on human health are affected

by environmental and cultural factors (Bian

et al., 2015; Bjorkman et al., 2011). In

contrast, harmful substances such as nitrate

also can accumulate in these commodities,

negatively affecting product quality (Colla

et al., 2018). Environmental and cultural

factors inﬂuencing mineral and phytochemical

content of fruits and vegetables include light

(intensity, quality, and duration), CO

concen-

tration, water availability, fertilization, and

pH, as well as plant species, cultivar, and

plant developmental stage (Bjorkman et al.,

2011; Kopsell and Kopsell, 2008; Vicente

et al., 2009). Using CEs provide opportunities

for improving the quality of horticultural

commodities through precise control and ma-

nipulation of these factors. For example, plant

phytochemicals serve functional roles in re-

sponse to environmental stress, and many of

the compounds protecting plant cells also

protect human cells (Demmig-Adams and

Adams, 2002). Thus, environments inducing

plant protection can stimulate accumulation

of nutritional compounds of interest to con-

sumers.

Although high light intensities are associ-

ated with phytochemical accumulation, main-

taining high light with sole-source or

supplemental lighting in CEs increases oper-

ating costs and may induce photoinhibition

(Bian et al., 2015). Therefore, optimum light

intensities should be considered to avoid these

issues while maximizing phytochemical accu-

mulation. Increasing light intensity across the

range of 100 to 400 mmol·m

–2

·s

–1

increases

accumulation of lutein and b-carotene in kale

(Brassica oleracea) (Lefsrud et al., 2006) and

spinach (Spinacea oleracea) (Li et al., 2011)

grown indoor with LEDs. Similarly, increas-

ing light intensity with supplemental HPS

lamps increases nutritional quality of vegeta-

bles grown in the greenhouse. For example,

increasing light intensity increases sugar con-

tent in tomato (Dorais and Gosselin, 2002) and

soluble sugars in lettuce (Fu et al., 2012).

Additionally, chicory (Cichorium endivium),

lettuce, mizuna (Brassica rapa var. niposin-

ica), and chard (Beta vulgaris subsp. vulgaris)

grown at a high light intensity contain higher

total phenolic content compared with those

grown at lower intensities (Colonna et al.,

2016).

Manipulating light spectra also affects the

quality of plant products, even at low light

intensities. Although various light sources

are used to grow plants in CEs, the narrow-

band light output produced by LEDs offer the

opportunity to manipulate spectra to control

ﬂavor, pigmentation, and other consumer-

desired traits in CE-grown plants. While

promising, there are inconsistent results on

the effects of light spectra on crop quality,

partly due to the complex interactions of

multiple factors, including plant genetics

and environmental conditions (e.g., temper-

ature, light intensity). For a review on the

application of light spectra to manipulate

product quality of key crop species see Bian

et al. (2015), Carvalho and Folta (2014),

Mitchell et al., (2015), and Samuolien_

et al. (2017).

High CO

concentration can also impact

plant phytochemical and nutritional com-

pounds. Based on a meta-analysis using

published literature, Dong et al. (2018) sur-

veyed the effect of elevated CO

on the

nutritional quality of vegetables. The authors

concluded that in general, elevated CO

has

potential to improve the quality of vegetable

crops by increasing fructose, glucose, total

soluble sugar, total antioxidant capacity, total

phenols, total ﬂavonoids, ascorbic acid, and

calcium (Dong et al., 2018). Water and

1452 HORTSCIENCE VOL. 54(9) SEPTEMBER 2019

nutrient availability also affect the quality of

plant products. Crops grown under water

deﬁcit tend to have higher nutrient content

than those grown under abundant water,

although this may partly be due to an increase

in concentration per unit dry mass (Bjorkman

et al., 2011). Reducing irrigation increases

glucosinolate content and total carotenoids in

cabbage (Brassica oleracea) and pak choi

(Brassica rapa subsp. chinensis), respec-

tively, compared with well-watered plants

(Hanson et al., 2009; Radovich et al., 2005).

In addition, manipulating the nutrient solu-

tion in soilless culture can help regulate

secondary metabolite production in fruits

and vegetables (Borgognone et al., 2016;

Colla et al., 2013; Fallovo et al., 2009).

Similarly, controlling the EC of the nutrient

solution affects the composition and concen-

tration of fruit phytochemicals (Colla et al.,

2013; Rouphael et al., 2012; Wu and Kubota,

2008).

Food Safety

Food safety risks for urban food produc-

tion are triggered by microbiological, chem-

ical, or external contaminants within the

system. All of these risks can be prevented,

minimized or reduced through proper train-

ing, documentation, policies, and resources.

The Centers for Disease Control and Pre-

vention reported that an estimated 48 million

people (one in six U.S. residents) suffer from

a food-borne illness each year (Scallan et al.,

2011); 128,000 are hospitalized, and 3000 die

each year from foodborne diseases. Between

1998 and 2008, 46% of all food-borne ill-

nesses reported were associated with fruits,

vegetables, and nuts (Painter et al., 2013).

Contamination of fruits and vegetables pro-

duced in the United States is one of the most

important issues for the food industry sector

(Centers for Disease Control and Prevention,

2011). After recent high-proﬁle outbreaks

associated with fresh-cut produce (Centers

for Disease Control and Prevention, 2011;

Food and Drug Administration, 2018),

widespread scrutiny of the U.S. fruit and

vegetable supply underscores a growing

concern regarding the awareness of and

adherence to best practices by growers and

processors.

Typically, fruits and vegetables grown in

CEs are perceived to have fewer potential

food safety concerns than ﬁeld-grown pro-

duce due to their isolation from the soil and

wild animals. However, human pathogens

can still be introduced into CE production

systems from various sources including wa-

ter, substrates, and human contact (Olaimat

and Holley, 2012; Shaw et al., 2016). In

addition, because CEA often uses recirculat-

ing nutrient solutions, human pathogens can

be introduced into the solutions (i.e., agricul-

tural water or nutrients) and rapidly spread

throughout the production system. Research

in hydroponic systems show if Escherichia

coli O157:H7, E.coli non-O157 STEC, and

Salmonella are introduced into systems over

a short period of time (48 h), these microor-

ganisms can survive and multiply (Shaw

et al., 2016). Orozco et al. (2008) reported

that 2.8% of tomatoes harvested from a

greenhouse were contaminated with Salmo-

nella and 0.7% with E. coli, whereas other

environments and materials within the green-

house tested positive for Salmonella included

puddles, soil, cleaning cloths, and sponges.

Food safety–relevant contamination of

produce can occur during production, har-

vest, processing, wholesale storage, distribu-

tion, retail, and preparation (i.e., food service

or in-home). Contamination also can be

caused by physical aspects (i.e., substrate,

water, air, harvesting/processing equipment),

animals (i.e., wild or domesticated), or hu-

man handlers (Food and Drug Administra-

tion, 2018). All growing materials (e.g.,

substrates, seeds, fertilizers) should be ob-

tained from vendors who can provide evi-

dence of following Good Manufacturing

Practices, including careful monitoring of

personnel, physical plant and grounds main-

tenance, sanitary operations, equipment and

utensils, processing controls, warehouse and

distribution, and holding and distribution of

human food for use in animal food (Food and

Drug Administration, 2017).

Pathogens of greatest concern in produce

include viruses (Hepatitis A and norovirus),

parasites (Cryptosporidium), and bacteria in-

cluding Bacillus cereus,Clostridium spp., E.

coli STEC, Listeria monocytogenes,Salmo-

nella spp., Yersinia enterocolitica,Shigella

spp., and Campylobacter spp. (Beuchat 2002;

Harris et al., 2003; Olaimat and Holley,

2012). It is important to note that Salmonella

spp. and E. coli O157:H7 are consistently

associated with outbreaks of food-borne ill-

ness, and Listeria monocytogenes has been

implicated in fewer, but particularly large,

produce-related outbreaks (Olaimat and Hol-

ley, 2012). In addition to microbiological

food safety concerns, chemical and heavy

metal concerns must be considered for urban

food production. These contaminants can be

introduced in the water throughout the grow-

ing cycle and can cause harm to consumers if

ingested in large amounts (United States

Geological Survey, 2013).

Water is an essential component in all

production systems and many foodborne

outbreaks are associated with water contam-

inated with E.coli O157:H7, Salmonella,

and Cyclospora (Hedberg and Osterholm,

1993). Furthermore, water sources can be

categorized as low risk or high risk. While

municipal water sources are considered low-

risk due to daily testing by cities and

municipalities for E. coli, surface water

sources (e.g., ponds, streams) are high-risk

since they are not regularly tested by a

government body. Therefore, the end user

is responsible for testing and results are

more easily inﬂuenced by watershed activ-

ities and seasonal variation. Lopez-Galvez

et al. (2014) showed that the prevalence of

Salmonella spp. was 7.7% in irrigation

water samples and 62.5% in reclaimed water

sources for tomatoes grown hydroponically

in greenhouses.

Social Environment

Humans and social systems are an impor-

tant component of the horticultural industry

(Lohr and Relf, 2000; Relf and Lohr, 2003).

However in 2012, there were slightly more

than threemillion growers in the United States,

which accounted for less than 2% of the

population (United States Department of Ag-

riculture, 2014). This relatively recent discon-

nect from food production presents questions

concerning the role of horticultural systems in

human well-being, particularly involving the

role of UA to provide services which promote

public health and other social beneﬁts (Brown

and Jameton, 2000; Relf, 1992).

CEA is an important ﬁeld with many

unique facets. However, to date, the role of

humans, social beneﬁts, and communities

with access to CE systems has not been

thoroughly studied. Although we understand

that urban food production can increase food

access in cities, questions remain as to what

extent CEA may alter social connections,

community capitals, and education in both

positive and negative ways (Eigenbrod and

Gruda, 2015). By extrapolating from the

available literature about urban horticultural

production, we hypothesize that urban CE

systems can have beneﬁts for community

food security, agricultural education, and

horticultural therapy. For example, integrat-

ing CEA and UA has great potential to serve

extreme-poverty areas by providing job op-

portunities and access to fresh food that can

support a healthy diet (Bohm, 2017; Specht

et al., 2014). In addition, hands-on teaching

tools, facilitated through demonstrations of

CE systems within schools and classrooms,

allow students direct access to understand the

process of food crop production. Previous

research has shown that school gardens pos-

itively impact student attitude toward vege-

tables (Lineberger and Zajicek, 2000).

Furthermore, students experiencing hands-

on gardening opportunities in school exhibit

more positive outlooks toward school

(Waliczek et al., 2001). In addition, CEA

may hold beneﬁts to increase access to

horticultural therapy. In settings such as

prisons (Rice and Remy, 1994) and rehabil-

itation centers (Wichrowski et al., 2005),

horticultural therapy facilitates both psycho-

logical and physiological healing and recov-

ery (Lewis, 1994; Simson and Straus, 1997).

By incorporating CE technologies into social

institutions such as prisons, hospitals, or

nursing homes, we may realize additional

social beneﬁts beyond the individual connec-

tion to plants. Furthermore, increasing re-

habilitation time reduce taxpayer burden for

social systems and promote overall human

health and wellbeing in society.

Author’s Viewpoints

Long-term success and economic viabil-

ity of CEs used for food production largely

will depend on future trends in consumer

preferences and market demand for agricul-

tural products produced in urban settings.

HORTSCIENCE VOL. 54(9) SEPTEMBER 2019 1453

The efﬁciency of most urban CE systems

will be improved by optimizing resources to

maximize crop production and quality. For

example, as LED technologies continue to

increase in efﬁcacy and decrease in cost,

more CE operations will adopt the technol-

ogy to reduce electrical costs and/or to

improve product quality. Horticultural-

grade LED ﬁxtures are expected to be

classiﬁed in two main groups: 1) relatively

affordable ﬁxtures with ﬁxed spectra, often

ﬁxed emission rate (light output), high

efﬁcacy, and simple on/off controllers; and

2) custom-made ﬁxtures with advanced

controllers to manipulate emission rate,

spectral control, and/or with sensor integra-

tion. The economic value to end-users will

determine ﬁxture applicability. Nonethe-

less, HPS lamps will continue to be widely

used for greenhouse supplemental lighting

due to their lower initial capital cost and

acceptable efﬁcacy compared with LEDs

(approx. 1.7 to 1.9 vs. 2.4 to 3.0 mmol·J

‒1

for some LEDs).

Future research evaluating ‘‘dynamic’’

control of CO

enrichment will help reduce

the long-term adaptation to high CO

con-

centration, which over time, diminishes the

positive impacts of CO

enrichment in CEs.

Studies focused on changing concentration

levels during the daytime and/or manipulat-

ing the environment to increase CO

uptake

during speciﬁc times of the day will be

helpful in furthering our understanding about

the potential beneﬁts of using CO

enrich-

ment in CEs. Further studies focusing on

breeding or sink-source relationships may

elucidate ways in which CO

enrichment

can increase yield by ensuring translocation

of photoassimilates to the harvestable portion

of plants. Humidity control will continue to

be an important challenge in CE production.

However, with the continued technological

development of dehumidiﬁcation systems

(e.g., heat pumps and desiccants), mainly

driven by their use in commercial buildings,

their adoption in CEs is expected to increase,

especially with the worldwide expansion of

PFs and potential adoption by some green-

house facilities.

The applicability of CEA in urban settings

as a solution to current challenges in our

food-supply chain will be context-dependent.

For example, from a food safety perspective,

CEs provide more physical and environmen-

tal control compared with ﬁeld-based pro-

duction systems. Therefore, given the risks

associated with foodborne illness outbreaks

coming from large-scale outdoor farms, pro-

duction in CEs may offer consumers peace of

mind in their produce purchases.

Although few studies have evaluated

food safety risk factors that could cause a

foodborne illness in CEs, food safety should

be a priority in all production systems

growing edible products. Education about

proper fresh produce handling from farm to

fork can help prevent food safety contam-

ination within CEA systems. Considering

the wide variations in production systems,

food safety programs for CEA could focus

on four main areas: substrate, water and

nutrient solutions, facilities, and people.

Prevention of foodborne microorganisms,

chemicals, and contaminants from entering

into a CE system should be the focus of

training and protocols. Employees within

production facilities should be trained on

how to properly sanitize the facilities, tools,

and equipment, along with personal health

and hygiene (i.e., washing stations, rest-

rooms, clothing, sickness and injury poli-

cies). Strict visitor policies minimizing

introductions of food safety risks to the

crops (e.g., hand washing, disposable boo-

ties, no-touching policies) should also be

implemented.

Regarding the sustainability of CEA,

local and regional limitations and resource

availability must determine the net environ-

mental and economic impacts of CEs in

urban environments. The integration of wa-

ter, energy, nutrients, and plant production in

cities could help promote the local food

movement (e.g., eliminate food deserts, fresh

produce with large carbon-footprints) by de-

livering a neutral net carbon and water

footprint. However, the footprint for crop

production will depend on the crop and

location, factors that are not commonly

considered when assessing the environmental

and economic beneﬁts of CEA for urban food

production. Consideration should be given to

the fact that goods already ﬂow in and out of

cities; limiting these ﬂows may result in

negative side-effects for UA. Although sci-

entists have advanced our understanding in

CEA and many discuss the potential of in-

tegrating resources in built settings, few have

investigated a truly integrated system in

which waste is captured and processed in situ

to supply water, nutrients, and energy to local

CE operations. Engineers and horticulturists

must work together to improve system per-

formance at the establishment and production

stages, and design truly integrated and efﬁ-

cient systems. Potential areas of work include

infrastructure design and materials, energy

production, storage and usage, and closing

water, energy, and nutrient loops.

Speciﬁc outcomes from CEA to human

wellbeing, social systems, and urban com-

munities remain to be determined. As de-

scribed above, research suggests many

potential beneﬁts from integrating CEA

and UA. For example, non-commercial,

small-scale CE systems may become avail-

able for display and hands-on teaching in

classrooms and community centers. How-

ever, to incorporate CEA into social sys-

tems, plant scientists should be actively

engaged in understanding and assessing

human issues in our food chain. This

allows an important unanswered gap in

advancing interdisciplinary social sci-

ences and may provide research opportu-

nities to increase urban CEA for social

sustainability and community resilience.

Urban areas involve a diversity of inter-

acting human components and the future of

CEA for food production must consider

these important social environments.

Conclusions

UA will continue to increase in impor-

tance as populations move into cities and the

demand for local food increases. Although

currently it is not uncommon for UA to take

place on relatively inexpensive land in the

urban core (e.g., public land or city-owned

properties that are economically rented to

reduce the municipal maintenance burden),

CE food production for UA is expected to

expand to land that is signiﬁcantly more

expensive than rural farming land. Therefore,

one of our goals as CEA researchers will be to

continue exploring how to make UA as

economically, socially, and environmentally

sustainable as possible. For example, we will

try to recommend the most effective lighting

sources available as we continue to explore

ways to improve the efﬁciency of implement-

ing LED lighting. We will also assist growers

in managing available resources to reduce

negative impacts of agriculture on the urban

environment. We may do this by helping

growers select irrigation systems and fertil-

izers that will result in less leaching and

runoff. This is particularly important in an

urban setting so that UA does not contribute

to storm-water management issues. We also

hope to identify crops that are economically

viable to grow in an urban environment,

considering external competition and market

trends. Furthermore, our research efforts

should consider all energy inputs to ensure

that local products truly have a lower carbon

footprint compared with crops produced out-

doors and shipped to the city. Lastly, we must

consider that UA creates green spaces in

areas with very few plants, allowing city-

dwellers to connect with how their produce is

grown. This human connection to plants and

food is a major beneﬁt of UA that warrants

our support so that urban producers can

beneﬁt from CEA.

Literature Cited

Acock, E., D.A. Charkes-Edwards, D.J. Fitter,

D.W. Hand, J. Ludwig, J. Warren-Wilson,

and A.C. Withers. 1971. The contribution of

leaves from different levels within a tomato

crop to canopy net photosynthesis: An exper-

imental examination of two canopy models. J.

Expt. Bot. 29:815–827.

Al-Kodmany, K. 2018. The vertical farm: A review

of developments and implications for the ver-

tical city. Buildings 8(24):1–36.

Argo, W.R. and P.R. Fisher. 2002. Understanding

pH management for container-grown crops.

Meister Publishing, Willoughby, OH.

Barker, J.C. 1990. Effects of day and night humid-

ity on yield and fruit quality of glasshouse

tomatoes (Lycopersicon esculentum Mill). J.

Hort. Sci. 65:323–331.

Banerjee, C. and L. Adenaeuer. 2014. Up, up and

away! The economics of vertical farming. J.

Aging Stud. 2:40–60.

Benis, K., I. Turan, C. Reinhart, and P. Ferr~

ao.

2018. Putting rooftops to use—A cost-beneﬁt

analysis of food production vs. energy genera-

tion under Mediterranean climates. Cities

78:166–179.

Beuchat, L.R. 2002. Ecological factors inﬂuencing

survival and growth of human pathogens on

1454 HORTSCIENCE VOL. 54(9) SEPTEMBER 2019

raw fruits and vegetables. Microbes Infect.

4:413–423.

Bian, Z.H., Q.C. Yang, and W.K. Liu. 2015.

Effects of light quality on the accumulation of

phytochemicals in vegetables produced in con-

trolled environments: A review. J. Sci. Food

Agr. 95:869–877.

Bjorkman, M., I. Klingen, A.N.E. Birch, A.M.

Bones, T.J.A. Bruce, T.J. Johansen, R. Meadow,

J. Molmann, R. Seljasen, L.E. Smart, and D.

Stewart. 2011. Phytochemica ls of Brassicaceae

in plant protection and human health - Inﬂuences

of climate,environment and agronomic practice.

Phytochemistry 72:538–556.

Blidariu, F. and A. Grozea. 2011. Increasing the

economic efﬁciency and sustainability of in-

door ﬁsh farming by means of aquaponics:

Review. Animal Sci. Biotech. 44:1–8.

Blok, C., B.E. Jackson, X. Guo, P.H.B. de Visser,

and L.F.M. Marcelis. 2017. Maximum plant

uptakes for water, nutrients, and oxygen are not

always met by irrigation rate and distribution in

water-based cultivation systems. Front. Plant

Sci. 8:562.

Bohm, M. 2017. Urban agriculture in and on

buildings in North America: The unfulﬁlled

potential to beneﬁt marginalized communities.

Built Environ. 43:343–363.

Borgognone, D., Y. Rouphael, M. Cardarelli, L.

Lucini, and G. Colla. 2016. Changes in bio-

mass, mineral composition, and quality of

cardoon in response to NO

–

:Cl

–

ratio and

nitrate deprivation from the nutrient solution.

Front. Plant Sci. 7:978.

Both, A.J., J.M. Frantz, and B. Bugbee. 2017.

Carbon dioxide enrichment in controlled envi-

ronments, p. 82–86. In: R. Lopez and E. Runkle

(eds.). Light management in controlled envi-

ronments. Meister Media Worldwide, Wil-

loughby, OH.

Boulard, T., A. Baille, J. Lagier, M. Mermier, and

E. Vanderschmitt. 1989. Water vapour transfer

in a plastic house equipped with a dehumidiﬁ-

cation heat pump. J. Agr. Eng. Res. 44:191–

204.

Bradﬁeld, E.G. and C.G. Guttridge. 1979. The

dependence of calcium transport and leaf tip-

burn in strawberry on relative humidity and

nutrient solution concentration. Ann. Bot.

43:363–372.

Brown, K.H. and A.L. Jameton. 2000. Public

health implications of urban agriculture. J.

Public Health Policy 21:20–39.

Brumﬁeld, R.G. and C. Singer. 2018. Economics of

Urban Ag: Targeting high-value, niche markets

or products, and adapting a social business

model can help urban greenhouses derive

proﬁt. Produce Grower October, 18–20.

Bunt, A.C. 1988. Media and mixes for container-

grown plants. Unwin Hyman Ltd., London,

UK.

Burnett, S.E., N.S. Mattson, and K.A. Williams.

2016. Substrates and fertilizers for organic

container production of herbs, vegetables, and

herbaceous ornamental plants grown in green-

house in the United States. Scientia Hort.

208:111–119.

Buzby, K.M. and L.-S. Lin. 2014. Scaling aqua-

ponic systems: Balancing plant uptake with ﬁsh

output. Aquacult. Eng. 63:39–44.

Calvert, A. and G. Slack. 1975. Effects of carbon

dioxide enrichment on growth, development

and yield of glasshouse tomatoes. I. Responses

to controlled concentrations. J. Hort. Sci.

50:61–71.

Campen, J.B., G.P.A. Bot, and H.F. De Zwart.

2003. Dehumidiﬁcation of greenhouses at

northern latitudes. Biosyst. Eng. 86:487–493.

Carvalho, S.D. and K.M. Folta. 2014. Environmen-

tally modiﬁed organisms—expanding genetic

potential with light. Crit. Rev. Plant Sci.

33:486–508.

Centers for Disease Control and Prevention. 2011.

Investigation of outbreak of infections caused by

Salmonella Saintpaul. 5 Dec. 2017. <http://

www.cdc.gov/salmonella/saintpaul/jalapeno/>.

Chagvardieff, P., T. D’aletto, and M. Andr

e. 1994.

Speciﬁc effects of irradiance and CO

concen-

tration doublings on productivity and mineral

content in lettuce. Adv. Space Res. 14:269–

275.

Chass

eriaux, G. and O. Gaschet. 2011. A multi-

function dehumidifying heat pump for green-

houses. Acta Hort. 893:469–476.

Chass

eriaux, G., E. Chantoiseau, C. Migeon, and

P.E. Bournet. 2014. A dehumidiﬁcation strat-

egy to avoid condensation on plants and spare

energy in greenhouse. Acta Hort. 1037:453–

460.

Chiew, Y.L., J. Sp



angberg, A. Bakyb, P.A. Hans-

son, and H. J€

onssona. 2015. Environmental

impact of recycling digested food waste as a

fertilizer in agriculture—A case study. Resour.

Conserv. Recycling 95:1–14.

Choi, J.H., G.C. Chung, and S.R. Suh. 1997. Effect

of night humidity on the vegetative growth and

the mineral composition of tomato and straw-

berry plants. Scientia Hort. 70:293–299.

Clausen, A., H.M. Maersk-Moeller, J. Corﬁxen

Soerensen, B.N. Joergensen, K.H. Kjaer, and

C.O. Ottosen. 2015. Integrating commercial

greenhouses in the smart grid with demand

response based control of supplemental light-

ing. Proc. Intl. Conf. Ind. Technol. Mgt. Sci.

199–213.

Cockshull, K.E. 1992. Crop environments. Acta

Hort. 312:77–85.

Coley, D.A., M. Howard, and M. Winter. 2009.

Local food, food miles and carbon emissions: A

comparison of farm shop and mass distribution

approaches. Food Policy 34:150–155.

Colla, G., H.J. Kim, M.C. Kyriacou, and Y.

Rouphael. 2018. Nitrate in fruits and vegeta-

bles. Scientia Hort. 237:221–238.

Colla, G., Y. Rouphael, M. Cardarelli, E. Svecova,

E. Rea, and L. Lucini. 2013. Effects of saline

stress on mineral composition, phenolics acids

and ﬂavonoids in leaves of artichoke and

cardoon genotypes grown in ﬂoating system.

J. Sci. Food Agr. 93:1119–1127.

Colonna, E., Y. Rouphael, G. Barbieri, and S. De

Pascale. 2016. Nutritional quality of ten leafy

vegetables harvested at two light intensities.

Food Chem. 199:702–710.

Coyle, B.D. and B. Ellison. 2017. Will consumers

ﬁnd vertically farmed produce ‘‘out of reach’’?

Choices 32:1–8.

Davies, P.A. 2005. A solar cooling system for

greenhouse food production in hot climates.

Sol. Energy 79:661–668.

Davis, B.E. 2011. Rooftop hospital gardens for

physical therapy: A post-occupancy evalua-

tion. Health Environ. Res. Design J. 4:14–43.

de Villiers, D.S., H.C. Wien, J.E. Reid, and L.D.

Albright. 2011. Energy use and yields in

tomato production: Field, high tunnel and

greenhouse compared for the northern tier of

the USA (upstate New York). Acta Hort.

893:373–380.

de Zwart, H.F. 2014. Energy conserving dehumid-

iﬁcation of greenhouses. Acta Hort. 1037:203–

210.

Demmig-Adams, B. and W.W. Adams. 2002.

Antioxidants in photosynthesis and human

nutrition. Science 298:2149–2153.

Dong, J., X. Li, W. Chu, and Z. Duan. 2017. High

nitrate supply promotes nitrate assimilation and

alleviates photosynthetic acclimation of cu-

cumber plants under elevated CO

. Scientia

Hort. 218:275–283.

Dong, J., N. Gruda, S.K. Lam, X. Li, and Z. Duan.

2018. Effects of elevated CO

on nutritional

quality of vegetables: A review. Front. Plant

Sci. 9:924.

Dorais, M. and A. Gosselin. 2002. Physiological

response of greenhouse vegetable crops to

supplemental lighting. Acta Hort. 580:59–67.

Dorais, M., C.A. Mitchell, and C. Kubota. 2017.

Lighting greenhouse fruiting vegetables, p.

159–169. In: R. Lopez and E. Runkle (eds.).

Light management in controlled environments.

Meister Media Worldwide, Willoughby, OH.

dos Santos, M.J.P.L. 2016. Smart cities and urban

areas—Aquaponics as innovative urban agri-

culture. Urban For. Urban Green. 20:402–406.

Dueck, T.A., J. Janse, B.A. Eveleens, F.L.K.

Kempkes, and L.F.M. Marcelis. 2012. Growth

of tomatoes under hybrid LED and HPS light-

ing. Acta Hort. 952:335–342.

Eaves, J. and S. Eaves. 2018. Comparing proﬁt-

ability of greenhouse to a vertical farm in

Quebec. Can. J. Agr. Econ. 66:43–54.

Edwards-Jones, G., L.M. Canals, N. Hounsome, M.

Truninger, G. Koerber, B. Hounsome, P. Cross,

E.H. York, A. Hospido, K. Plassmann, I.M.

Harris, R.T. Edwards, G.A.S. Day, A.D.

Tomos, S.J. Cowell, and D.L. Jones. 2008.

Testing the assertion that ‘local food is best’:

The challenges of an evidence-based approach.

Trends Food Sci. Technol. 19:265–274.

Eigenbrod, C. and N. Gruda. 2015. Urban vegeta-

ble for food security in cities. A review. Ag.

Sust. Dev. 35:483–498.

Elumalai, S.D., A.M. Shaw, D.A. Pattillo, C.J.

Currey, K.A. Rosentrater, and K. Xie. 2017.

Inﬂuence of UV treatment on the food safety

status of a model aquaponic system. Water

9:27.

Enoch, H.Z., I. Rylski, and M. Spigelman. 1976.

enrichment of strawberry and cucumber

plants grown in unheated greenhouses in Israel.

Scientia Hort. 5:33–41.

Fallovo, C., Y. Rouphael, M. Cardarelli, E. Rea, A.

Battistelli, and G. Colla. 2009. Yield and

quality of leafy lettuce in response to nutrient

solution composition and growing season. J.

Food Agr. Environ. 7:456–462.

Faust, J.E. and J. Logan. 2018. Daily light in-

tegral: A research review and high-resolution

maps of the United States. HortScience

53:1250–1257.

Food and Drug Administration (FDA). 2017. Cur-

rent good manufacturing practice, hazard anal-

ysis, and risk-based preventive controls for

human food. 5 Aug. 2018. <https://www.ac-

cessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/

CFRSearch.cfm?CFRPart=117>.

Food and Drug Administration (FDA) 2018.

Guide to minimize food safety hazards of

fresh-cut produce: Draft guidance for in-

dustry. 10 Dec. 2018. <https://www.fda.-

gov/downloads/Food/GuidanceRegulation/

GuidanceDocumentsRegulatoryInformation/

UCM623718.pdf>.

Frantz, J.M., G. Ritchie, N.N. Cometti, J. Robin-

son, and B. Bugbee. 2004. Exploring the limits

of crop productivity. Beyond the limits of

tipburn in lettuce. J. Amer. Soc. Hort. Sci.

129:331–338.

Fu, W., P. Li, Y. Wu, and J. Tang. 2012. Effects of

different light intensities on anti-oxidative

enzyme activity, quality and biomass in lettuce.

HortScience 39:129–134.

HORTSCIENCE VOL. 54(9) SEPTEMBER 2019 1455

Fu, Y., L. Shao, H. Liu, H. Li, Z. Zhao, P. Ye, P.

Chen, and H. Liu. 2015. Unexpected decrease

in yield and antioxidants in vegetable at very

high CO

levels. Environ. Chem. Lett. 13:473–

479.

Getter, K.L. and D.B. Rowe. 2006. The role of

extensive green roofs in sustainable develop-

ment. HortScience 41:1276–1285.

Goldstein, B., M. Hauschild, J. Fern

andez, and M.

Birkved. 2016. Testing the environmental per-

formance of urban agriculture as a food supply

in northern climates. J. Clean. Prod. 135:984–

994.

G

omez, C. and C.A. Mitchell. 2016. Physiological

and productivity responses of high-wire tomato

as affected by supplemental light source and

distribution within the canopy. J. Amer. Soc.

Hort. Sci. 141:196–208.

Goto, E. and T. Takakura. 1992. Promotion of Ca

accumulation in inner leaves by air supply for

prevention of lettuce tipburn. Trans. ASAE

35:641–645.

Graamans, L., A. van den Dobbelsteen, E. Meinen,

and C. Stanghellini. 2017. Plant factories; crop

transpiration and energy balance. Agr. Syst.

153:138–147.

Guichard, S., C. Gary, C. Leonardi, and N. Bertin.

2005. Analysis of growth and water relations of

tomato fruits in relation to air vapor pressure

deﬁcit and plant fruit load. J. Plant Growth

Regul. 24:201–213.

Gupta, D. 2017. Light emitting diodes for agricul-

ture, Smart lighting. Springer, Singapore.

Hanan, J.J. 1997. Greenhouses: Advanced technol-

ogy for protected horticulture. CRC Press,

Boca Raton, FL.

Hanson, P., R.-Y. Yang, L.-C. Chang, L. Ledesma,

and D. Ledesma. 2009. Contents of caroten-

oids, ascorbic acid, minerals and total glucosi-

nolates in leafy brassica pakchoi (Brassica

rapa L. chinensis) as affected by season and

variety. J. Sci. Food Agr. 89:906–914.

Harris, L.J., J.N. Farber, L.R. Beuchat, M.E. Parish,

T.V. Suslow, E.H. Garrett, and F.F. Busta.

2003. Outbreaks associated with fresh produce:

Incidence, growth and survival of pathogens in

fresh and fresh-cut produce. Compr. Rev. Food

Sci. Food Saf. 2:78–141.

Hayden, A.L. 2006. Aeroponic and hydroponic

systems for medicinal herb, rhizome, and root

crops. HortScience 413:536–538.

Hedberg, C.W. and M.T. Osterholm. 1993. Out-

breaks of food-borne and waterborne viral

gastroenteritis. Clin. Microbiol. Rev. 6:199–

210.

Heuvelink, E. and T.Kierkels. 2015.In greenhouses:

Plant physiology in greenhouses. Horti-Text

BV, Netherlands.

Hodges, C.N., J.E. Groh, and A.W. Johnson. 1968.

Controlled-environment agriculture for coastal

desert areas. Proc. Natl. Agr. Plastics Conf.

8:58–68.

Hoekstra, A.Y., A.K. Chapagain, M.M. Aldaya,

and M.M. Mekonnen. 2011. The water foot-

print assessment manual: Setting a global

standard. Earthscan, London, UK.

Hussain, T., A.K. Verma, V.K. Tiwari, C. Prakash,

G. Rathore, A.P. Shete, and K.K.T. Nuwansi.

2014. Optimizing koi carp, Cyprinus carpio

var. Koi (Linnaeus, 1758), stocking density and

nutrient recycling with spinach in an aquaponic

system. J. World Aquacult. Soc. 45:652–661.

Hussain, T., A.K. Verma, V.K. Tiwari, C. Prakash,

G. Rathore, A.P. Shete, and N. Saharan. 2015.

Effect of water ﬂow rates on growth of Cypri-

nus carpio var. koi (Cyprinus carpio L., 1758)

and spinach plant in aquaponic system. Aqua-

cult. Intl. 23:369–384.

Hynes, H.P. and G. Howe. 2004. Urban horticul-

ture in the contemporary United States: Per-

sonal and community beneﬁts. Acta Hort.

643:171–181.

Ikerd, J. 2017. The urban agriculture revival. J Agr.

Food Systems Community Dev. 7:13–16.

Jansen, G., N. Cila, M. Kanis, and Y. Slaats. 2016.

Attitudes towards vertical farming at home: A

user study. Proc. CHI Conf. Human Factors in

computing systems. CHI2016:3091–3098.

Jensen, M.H. 2002. Controlled environment agri-

culture in deserts, tropics, and temperate re-

gions: A world review. Acta Hort. 578:19–25.

Jones, C. and P. Gilbert. 2018. Determining the

consequential life cycle greenhouse gas emis-

sions of increased rooftop photovoltaic deploy-

ment. J. Clean. Prod. 184:211–219.

Jones, J.B., Jr. 2014. Complete guide for growing

plants hydroponically. CRC Press, Boca Raton,

FL.

Khater, E.G. and S.A. Ali. 2015. Effect of ﬂow rate

and length of gully on lettuce plants in aqua-

ponic and hydroponic systems. J. Aquac. Res.

Dev. 6:3.

Klemencic, A.K. and T.G. Bulc. 2015. The use of

vertical constructed wetland and ultrasound in

aquaponic systems. Environ. Sci. Pollut. Res.

Intl. 22:1420–1430.

Kloas, W., R. Groß, D. Baganz, J. Graupner, H.

Monsees, U. Schmidt, G. Staaks, J. Suhl, M.

Tschirner, B. Wittstock, S. Wuertz, A. Zikova,

and B. Rennert. 2015. A new concept for

aquaponic systems to improve sustainability,

increase productivity, and reduce environmen-

tal impacts. Aquacult. Environ. Interact. 7:179–

192.

Kopsell, D.A. and D.E. Kopsell. 2008. Genetic and

environmental factors affecting plant lutein/

zeaxanthin. Agro Food Ind. Hi-Tech 19:44–46.

K€

orner, O. and H. Challa. 2003. Process-based

humidity control regime for greenhouse crops.

Comput. Electron. Agr. 39:173–192.

Kotilainen, T., T.M. Robson, and R. Hern

andez. 2018.

Light quality characterization under climate

screens and shade nets for controlled-

environment agriculture. PLoS One 13:e0199628.

Kozai, T. 2013. Resource use efﬁciency of closed

plant production system with artiﬁcial light:

Concept, estimation and application to plant

factory. Proc. Jpn. Acad. 89:447–461.

Kozai, T. and G. Niu. 2016a. Plant factory as a

resource-efﬁcient closed plant production sys-

tem, p. 69–90. In: T. Kozai, G. Niu, and M.

Takagaki (eds.). Plant factory: An indoor ver-

tical farming system for efﬁcient quality food

production. Academic Press, San Diego, CA.

Kozai, T. and G. Niu. 2016b. Role of the plant

factory with artiﬁcial lighting (PFAL) in urban

areas, p. 7–33. In: T. Kozai, G. Niu, and M.

Takagaki (eds.). Plant factory: An indoor ver-

tical farming system for efﬁcient quality food

production. Academic Press, San Diego, CA.

Kozai, T., W. Fang, C. Chun, Q. Yang, Y. Tong, R.

Cheng, C. Kubota, and C. Lu. 2016. PFAL

business and R&D in the world: Current status

and perspectives, p. 35–8. In: T. Kozai, G. Niu,

and M. Takagaki (eds.). Plant factory: An

indoor vertical farming system for efﬁcient

quality food production. Academic Press, San

Diego, CA.

Kroggel, M.A. and C. Kubota. 2017. Controlled

environment strategies for tipburn management

in greenhouse strawberry production. Acta

Hort. 1156:529–536.

Kubota,C.,S.Yokoi,M.Hayashi,Y.Fukuda,andS.

Sase. 2006. Using ventilation-evapotranspiration-

temperature-humidity (VETH) chart software for

developing a strategy for evaporative cooling of

semiarid greenhouses. Acta Hort. 719:483–490.

Kubota, C., M. Kroggel, A.J. Both, and M. Whalen.

2016. Does supplemental lighting make sense

for my crop?-Empirical evaluations. Acta Hort.

1134:403–411.

Lawson, L. 2005. City bountiful: A century of

community gardening in America. University

of California Press, Berkley, CA.

Lefsrud, M.G., D.A. Kopsell, D.E. Kopsell, and

J. Curran-Celentano. 2006. Irradiance levels

affect growth parameters and carotenoid

pigments in kale and spinach grown in a

controlled environment. Physiol. Plant.

127:624–631.

Leonardi, C., A. Baile, and S. Guichard. 1999.

Effects of fruit characteristics and climatic

conditions on tomato transpiration in a green-

house. J. Hortic. Sci. Biotechnol. 74:748–756.

Lewis, C.A. 1994. Human health and well-being:

The psychological, physiological, and socio-

logical effects of plants on people. Acta Hort.

391:31–40.

Lewis, W.M., J.H. Yopp, H.L. Schramm, and A.M.

Brandenburg. 1978. Use of hydroponics to

maintain quality of recirculated water in a ﬁsh

culture system. Trans. Amer. Fish. Soc.

107:92–99.

Li, J., S. Hikosaka, and E. Goto. 2011. Effects of

light quality and photosynthetic photon ﬂux on

growth and carotenoid pigments in spinach

(Spinacia oleracea L.). Acta Hort. 907:105–

110.

Lineberger, S.E. and J.M. Zajicek. 2000.

School gardens: Can a hands-on teaching

tool affect students’ attitudes and behaviors

regarding fruit and vegetables? HortTech-

nology 10:593–597.

Lohr, V.I. and P.D. Relf. 2000. An overview of the

current state of human issues in horticulture in

the United States. HortTechnology 10:27–33.

Lopez, R.G. and E. Runkle. 2017. Light manage-

ment in controlled environments. Meister Me-

dia Worldwide, Willoughby, OH.

Lopez-Galvez, F., A. Allende, F. Pedrero-Salcedo,

J.J. Alarcon, and M.I. Gil. 2014. Safety assess-

ment of greenhouse hydroponic tomatoes irri-

gated with reclaimed and surface water. Int. J.

Food Microbiol. 191:97–102.

Love, D.C., J.P. Fry, X. Li, E.S. Hill, L. Genello, K.

Semmens, and R.E. Thompson. 2015. Com-

mercial aquaponics production and proﬁtabil-

ity: Findings from an international survey.

Aquaculture 435:67–74.

Lychnos, G. and P.A. Davies. 2012. Modelling and

experimental veriﬁcation of a solar-powered

liquid desiccant cooling system for greenhouse

food production in hot climates. Energy

40:116–130.

Maggini, R., C. Kiferle, and A. Pardossi. 2014.

Hydroponic production of medicinal plants, p.

91–116. In: D.A.M. Pereira (ed.). Medicinal

plants: Antioxidant properties, traditional uses

and conservation strategies. Nova Science Pub-

lishers, Inc., Hauppauge, NY.

Massa, G.D., C.A. Mitchell, J.C. Emmerich, and

R.C. Morrow. 2005. Development of a recon-

ﬁgurable LED plant-growth lighting system for

equivalent system mass reduction in an ALS.

35th International Conference on Environmen-

tal Systems. Rome, Italy. SAE Technical Paper

No. 2005–01–2955.

Mei, L. and Y.J. Dai. 2008. A technical review on

use of liquid-desiccant dehumidiﬁcation for

air-conditioning application. Renew. Sustain.

Energy Rev. 12:662–689.

Meier, S., K. Ackerman, E. Dahlgren, and X. Xu.

2013. Sustainable urban agriculture: Conﬁrming

1456 HORTSCIENCE VOL. 54(9) SEPTEMBER 2019

viable scenarios for production. New York State

Energy Research and Development Authority. 7

May 2019. <https://www.nyserda.ny.gov/-/me-

dia/Files/Publications/Research/Environmental/

Sustainable-Urban-Agriculture.pdf>.

Menard, C., M. Dorais, T. Hovi, and A. Gosselin.

2006. Developmental and physiological re-

sponses of tomato and cucumber to additional

blue light. Acta Hort. 711:291–296.

Migeon, C., A. Pierart, D. Lemesle, A. Travers, and

G. Chass

eriaux. 2012. A dehumidifying heat

pump for greenhouses. Acta Hort. 952:485–

492.

Mitchell, C.A. and G.W. Stutte. 2015. Sole-source

lighting for controlled-environment agriculture.

NASA Technical Reports. 5 Aug. 2018. <https://

ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/

20150009399.pdf>.

Mitchell, C.A., J.F. Burr, M.J. Dzakovich, C.

G

omez, R. Lopez, R. Hern

andez, C. Kutoba,

C.J. Currey, Q. Meng, E.S. Runkle, C.M.

Bourguet, R.C. Murrow, and A.J. Both. 2015.

Light-emitting diodes in horticulture. Hort.

Rev. 43:1–87.

Monsees, H., W. Kloas, and S. Wuertz. 2017.

Decoupled systems on trial: Eliminating bot-

tlenecks to improve aquaponic processes. PLoS

One 12:e0183056.

Morgan, K. 2009. Feeding the city: The challenge

of urban food planning. Intl. Plann. Stud.

14:341–348.

Mortensen, L.M. 1994. Effects of elevated CO

concentrations on growth and yield of eight

vegetable species in a cool climate. Scientia

Hort. 58:177–185.

Mundler, P. and L. Rumpus. 2012. The energy

efﬁciency of local food systems: A comparison

between different modes of distribution. Food

Policy 37:609–615.

Nadal, A., P. Llorach-Massana, E. Cuerva, E. L

opez-

Capel, J.I. Montero, A. Josa, J. Rieradevall, and

M. Royapoor. 2017. Building-integrated rooftop

greenhouses: An energy and environmental as-

sessment in the Mediterranean context. Appl.

Energy 187:338–351.

Nelson, J.A. and B. Bugbee. 2014. Economic

analysis of greenhouse lighting: Light emitting

diodes vs. High intensity discharge ﬁxtures.

PLoS One 9(6):e99010.

Nelson, P.V. 2012. Greenhouse operation and

management. 7th ed. Prentice Hall. Upper

Saddle River, NJ.

Olaimat, A.N. and R.A. Holley. 2012. Factors

inﬂuencing the microbial safety of fresh pro-

duce: A review. Food Microbiol. 32:1–19.

Orozco, L., L. Rico-Romero, and E.F. Escartin.

2008. Microbiological proﬁle of greenhouses in

a farm producing hydroponic tomatoes. J. Food

Prot. 71:60–65.

Orsini, F., R. Kahane, R. Nono-Womdim, and G.

Gianquinto. 2013. Urban agriculture in the

developing world: A review. Agron. Sustain.

Dev. 33:695–720.

Painter, J.A., R.M. Hoekstra, T. Ayers, R.V. Tauxe,

C.R. Braden, F.J. Angulo, and P.M. Grifﬁn.

2013. Attribution of foodborne illnesses, hos-

pitalizations, and deaths to food commodities

by using outbreak data, United States, 1998–

2008. Emerg. Infect. Dis. 19:407–415.

Palm, H.W., U. Knaus, S. Appelbaum, S. Goddek,

S.M. Strauch, T. Vermeulen, M.H. Jijakli, and

B. Kotzen. 2018. Towards commercial aqua-

ponics: A review of systems, designs, scales,

and nomenclature. Aquacult. Intl. 26:813–

842.

Pantanella, E., M. Cardarelli, E. Di Mattia, and G.

Colla. 2015. Aquaponics and food safety:

Effects of UV sterilization on total coliforms

and lettuce production. Acta Hort. 1062:71–76.

Papadopoulos, A.P., X. Luo, S. Leonhart, A.

Gosselin, K. Pedneault, P. Angers, L. Gau-

dreau, and M. Dorais. 2001. Soilless green-

house production of medicinal plants in North

Eastern Canada. Acta Hort. 554:297–304.

Park, M.H. and Y.B. Lee. 2001. Effects of CO

concentration, light intensity and nutrient level

on growth of leaf lettuce in a plant factory. Acta

Hort. 548:377–384.

Paxton, A. 1994. The food miles report: The

dangers of long distance food transport. Safe

Alliance, London, UK.

Peet, M.M. 1986. Acclimation to High CO

Monoecious Cucumbers. Plant Physiol. 80:59–

62.

Peet, M.M. and D.H. Willits. 1984. CO

enrich-

ment of greenhouse tomatoes using a closed-

loop heat storage: Effects of cultivar and

nitrogen. Scientia Hort. 24:21–32.

P

erez-L

opez, U., J. Miranda-Apodaca, M. Lacuesta,

A. Mena-Petite, and A. Mu~

noz-Rueda. 2015.

Growth and nutritional quality improvement in

two differently pigmented lettuce cultivars

grown under elevated CO

and/or salinity. Sci-

entia Hort. 195:56–66.

Peterson, H.H., M.R. Taylor, and Q. Baudouin.

2015. Preferences of locavores favoring com-

munity supported agriculture in the United

States and France. Ecol. Econ. 119:64–73.

Pinho, P., T. Hyt€

onen, M. Rantanen, P. Elomaa,

and L. Halonen. 2012. Dynamic control of

supplemental lighting intensity in a greenhouse

environment. Light. Res. Technol. 45:295–304.

Poulet, L., G.D. Massa, R.C. Morrow, C.M. Bour-

get, R.M. Wheeler, and C.A. Mitchell. 2014.

Signiﬁcant reduction in energy for plant-

growth lighting in space using targeted LED

lighting and spectral manipulation. Life Sci.

Space Res. 2:43–53.

Potter, D.J. 2014. A review of the cultivation and

processing of cannabis (Cannabis sativa L.) for

production of prescription medicines in the

UK. Drug Test. Anal. 6:31–38.

Quagrainie, K.K., R.M.V. Flores, H.-J. Kim, and

V. McClain. 2018. Economic analysis of aqua-

ponics and hydroponics production in the US

midwest. J. Appl. Aquacult. 30:1–14.

Radovich, T.J.K., M.D. Kleinhenz, and J.G.

Streeter. 2005. Irrigation timing relative to

head development inﬂuences yield compo-

nents, sugar levels, and glucosinolate concen-

trations in cabbage. J. Amer. Soc. Hort. Sci.

130:943–949.

Rakocy, J.E., M.P. Masser, and T.M. Losord. 2006.

Recirculating aquaculture tank production sys-

tems: Aquaponics–integrating ﬁsh and plant

culture. Southern Regional Aquaculture Center

Publication no. 454.

Rakocy, J.E., R.C. Shultz, D.S. Bailey, and E.S.

Thoman. 2004. Aquaponic production of tila-

pia and basil: Comparing a batch and staggered

cropping system. Acta Hort. 648:63–69.

Raviv, M., J.H. Lieth and A. Bar-Tal. 2019. Soiless

culture: Theory and practice. Elsevier, San

Diego, CA.

Reisman, A. 2012. A greenhouse in the city: The

uses and roles of community-oriented urban

greenhouses. Tufts University, Medford, MS

Thesis.

Relf, D. 1992. The role of horticulture in human

well-being and social development. Timber

Press, Portland, OR.

Relf, P.D. and V.I. Lohr. 2003. Human issues in

horticulture. HortScience 38:984–993.

Rice, J.S. and L.L. Remy. 1994. Evaluating horticul-

tural therapy: The ecological context of urban jail

inmates. J. Home Consumer Hort. 1:203–224.

Roosta, H.R. and M. Hamidpour. 2011. Effects of

foliar application of some macro- and micro-

nutrients on tomato plants in aquaponic and

hydroponic systems. Scientia Hort. 129:396–

402.

Roosta, H.R. and Y. Mohsenian. 2015. Alleviation

of alkalinity-induced Fe deﬁciency in eggplant

(Solanum melongena L.) by foliar application

of different Fe sources in recirculating system.

J. Plant Nutr. 38:1768–1786.

Rouphael, Y., M. Cardarelli, L. Lucini, E. Rea, and

G. Colla. 2012. Nutrient solution concentration

affects growth, mineral composition, phenolic

acids and ﬂavonoids in leaves of artichoke and

cardoon. HortScience 47:1424–1429.

Sace, C. and E.P. Natividad, Jr. 2015. Economic

analysis of an urban vertical garden for hydro-

ponic production of lettuce (Lactuca sativa).

Intl. J. Contemporary Appl. Sci. 2:42–57.

Samuolien_

e, G., A. Brazaityt_

e, and V. Va

stakait_

2017. Light-Emitting Diodes (LEDs) for im-

proved nutritional quality, p. 149–190. In: S.D.

Gupta (ed.). Light emitting diodes for agricul-

ture: Smart lighting. Springer Nature, Singa-

pore.

Sanjuan-Delm

as, D., P. Llorach-Massana, A. Nadal,

M. Ercilla-Montserrat, P. Mu~

noz, J.I. Montero,

A. Josa, X. Gabarrell, and J. Rieradevall. 2018.

Environmental assessment of an integrated roof-

top greenhouse for food production in cities. J.

Clean. Prod. 177:326–337.

Sany

e-Mengual, E., P. Llorach-Masana, D. Sanjuan-

Delmas, J. Oliver-Sol

a, A. Josa, J.I. Montero,

and J. Rieradeva ll. 2014. The ICT A-ICP rooftop

greenhouse lab (RTG-Lab): Closing metabolic

ﬂows (energy, water, CO2) through integrated

rooftop greenhouses, p. 693–701. In: R. Rog-

gema and G. Keeffe (eds.). Finding spaces for

productive cities. VHL University of Applied

Sciences, Velp, Netherlands.

Sany

e-Mengual, E., J. Oliver-Sol

a, J.I. Montero,

and J. Rieradevall. 2015. An environmental and

economic life cycle assessment of rooftop

greenhouse (RTG) implementation in Barce-

lona, Spain. Assessing new forms of urban

agriculture from the greenhouse structure to

the ﬁnal product level. Intl. J. Life Cycle

Assess. 20:350–366.

Sany

e-Mengual, E., J. Martinez-Blanco, M.

Finkbeiner, M. Cerd

a, M. Camargo, A.R.

Ometto, L.S. Vel

asquez, G. Villada, S. Niza,

A.Pina,G.Ferreira,J.Oliver-Sol



a, J.I.

Montero, and J. Rieradevall. 2018. Urban

horticulture in retail parks: Environmental as-

sessment of the potential implementation of

rooftop greenhouses in European and South

American cities. J. Clean. Prod. 172:3081–3091.

Scallan, E., R.M. Hoekstra, F.J. Angula, R.V.

Tauxe, M. Widdowson, S.L. Roy, J.L. Jones,

and P.M. Grifﬁn. 2011. Foodborne illness

acquired in the United States-major pathogens.

Emerg. Infect. Dis. 17:7–15.

Scharber, H. and A. Dancs. 2015. Do locavores

have a dilemma? Economic discourse and the

local food critique. Agr. Human Values

33:121–133.

Shamshiri, R.R., J.W. Jones, K.R. Thorp, D.

Ahmad, H.C. Man, and S. Taheri. 2018. Re-

view of optimum temperature, humidity, and

vapour pressure deﬁcit for microclimate eval-

uation and control in greenhouse cultivation of

tomato: A review. Intl. Agrophys. 32:287–302.

Shaw, A., K. Helterbran, M.R. Evans, and C.

Currey. 2016. Growth of Escherichia coli

O157:H7, non-O157 Shiga toxin–producing

HORTSCIENCE VOL. 54(9) SEPTEMBER 2019 1457

Escherichia coli, and Salmonella in water and

hydroponic fertilizer solutions. J. Food Prot.

79:2179–2183.

Short, G., C. Yue, M. Abbey, N. Anderson, N.

Phelps, P. Venturelli, and Z. Vickers. 2018.

Consumer preferences for aquaponic produce:

Implications from an experimental auction.

Agribusiness 34:742–755.

Simson, S. and M. Straus. 1997. Horticulture as

therapy: Principles and practice. CRC Press,

Boca Raton, FL.

Singer, C. and R.G. Brumﬁeld. 2017. An economic

analysis of urban agriculture. Intl. J. Agr. Sci.

2:42–45.

Sonneveld, C. and W. Voogt. 2009. Plant nutrition

of greenhouse crops. Springer, Dordrecht,

Netherlands.



angberg, J., P. Tid



aker, and H. J€

onsson. 2014.

Environmental impact of recycling nutrients in

human excreta to agriculture compared with

enhanced wastewater treatment. Sci. Total

Environ. 493:209–219.

Specht, K., R. Siebert, I. Hartmann, U.B. Frei-

singer, M. Sawicka, A. Werner, S. Thomaier,

D. Henckel, H. Walk, and A. Dierich. 2014.

Urban agriculture of the future: An overview of

sustainability aspects of food production in and

on buildings. Agr. Human Values 31:33–51.

Steele, K. 2017. Urban farming: An introduction to

urban farming, from types and beneﬁts to

strategies and regulations. Vitalyst Health

Foundation, Phoenix, AZ.

Sun, P., N. Mantri, H. Lou, Y. Hu, D. Sun, Y. Zhu,

T. Dong, and H. Lu. 2012. Effects of elevated

and temperature on yield and fruit quality

of strawberry (Fragaria ·ananassa Duch.) at

two levels of nitrogen application. PLoS One

7(7):e41000.

Takagaki, M., H. Hara, and T. Kozai. 2016. Micro-

and mini PFALS for improving the quality of

life in urban areas, p. 91–104. In: T. Kozai, G.

Niu, and M. Takagaki (ed.). Plant factory: An

indoor vertical farming system for efﬁcient

quality food production. Academic Press, San

Diego, CA.

Tokunaga, K., C. Tamaru, H. Ako, and P.S. Leung.

2015. Economics of small-scale commercial

aquaponics in Hawai’i. J. World Aquacult. Soc.

46:20–32.

Tyson, R.V., D.D. Treadwell, and E.H. Simonne.

2011. Opportunities and challenges to sustain-

ability in aquaponic systems. HortTechnology

21:6–13.

United States Department of Agriculture (USDA).

2014. Farm demographics: U.S. farmers by

gender, age, race, ethnicity, and more. 22

Feb. 2018. <https://www.agcensus.usda.gov/

Publications/2012/Online_Resources/High-

lights/Farm_Demographics/Highlights_Farm_

Demographics.pdf>.

United States Geological Survey (USGS). 2013.

Contaminants found in groundwater. The

USGS Water Science School. Feb. 2018.

<https://water.usgs.gov/edu/groundwater-

contaminants.html>.

Valli

eres, M., D. De Halleux, M. Dorais, and S.

Bouzid. 2014. Comparison of two cooling

and dehumidifying methods for a semi-closed

organic tomato greenhouse. Acta Hort.

1037:611–616.

van Iersel, M.W. 2017. Optimizing LED lighting in

controlled environment agriculture, p. 59–80.

In: S.D. Gupta (ed.). Light emitting diodes for

agriculture: Smart lighting. Springer Nature,

Singapore.

van Iersel, M.W. and D. Gianino. 2017. An

adaptive control approach for light-emitting

diode lights can reduce the energy costs of

supplemental lighting in greenhouses. Hort-

Science 52:72–77.

van Iersel, M.W., G. Weaver, and M.T. Martin.

2016. A chlorophyll ﬂuorescence-based bio-

feedback system to control photosynthetic

lighting in controlled environment agriculture.

J. Amer. Soc. Hort. Sci. 141:169–176.

Vicente, A.R., G.A. Manganaris, G.O. Sozzi, and

C.H. Crisosto. 2009. Nutritional quality of

fruits and vegetables, p. 57–106. In: W.

Florkowski, R. Shewfelt, B. Brueckner, and

S. Prussia (eds.). Postharvest handling: A

systems approach. 2nd ed. Elsevier Inc. Aca-

demic Press, San Diego, CA.

Villarroel Walker, R.V., M.B. Beck, J.W. Hall, R.J.

Dawson, and O. Heidrich. 2014. The energy-

water-food nexus: Strategic analysis of technol-

ogies for transforming the urban metabolism. J.

Environ. Mgt. 141:104–115.

Vitiello, D. and C. Brinkley. 2014. The hidden

history of food system planning. J. Plann. Hist.

13:91–112.

von Caemmerer, S. and N. Baker. 2007. The

biology of transpiration. From guard cells to

globe. Plant Physiol. 143:3.

Waliczek, T.M., J.C. Bradley, and J.M. Zajicek.

2001. The effect of school gardens on chil-

dren’s interpersonal relationships and attitudes

toward school. HortTechnology 11:466–468.

Walters, K.J. and C.J. Currey. 2015. Hydroponic

greenhouse basil production: Comparing sys-

tems and cultivars. HortTechnology 25:645–

650.

Wang, J., Y. Tong, Q. Yang, and M. Xin. 2016.

Performance of introducing outdoor cold air for

cooling a plant production system with artiﬁ-

cial light. Front. Plant Sci. 7:270.

Weaver, G.M., M. van Iersel, and J.M. Velni. 2019.

A photochemistry-based method for optimiz-

ing greenhouse supplemental light intensity.

Biosyst. Eng. 182:123–137.

Weber, C.L. and H.S. Matthews. 2008. Food-miles

and the relative climate impacts of food choices

in the United States. Environ. Sci. Technol.

42:3508–3513.

Wichrowski, M., J. Whiteson, F. Haas, A. Mola,

and M.J. Rey. 2005. Effects of horticultural

therapy on mood and heart rate in patients

participating in an inpatient cardiopulmonary

rehabilitation program. J. Cardiopulm. Rehabil.

Prev. 25:270–274.

Wongkiew, S., Z. Hu, K. Chandran, J.W. Lee, and

S.K. Khanal. 2017a. Nitrogen transformations

in aquaponic systems: A review. Aquacult.

Eng. 76:9–19.

Wongkiew, S., B.N. Popp, H.J. Kim, and S.K.

Khanal. 2017b. Fate of nitrogen in ﬂoating-raft

aquaponic systems using natural abundance

nitrogen isotopic compositions. Intl. Biodete-

rior. Biodegradation 125:24–32.

Wu, M. and C. Kubota. 2008. Effects of high

electrical conductivity of nutrient solution and

its application timing on lycopene, chlorophyll

and sugar concentrations of hydroponic toma-

toes during ripening. Scientia Hort. 116:122–

129.

Yue, C. and C. Tong. 2009. Organic or local?

Investigating consumer preference for fresh

produce using a choice experiment with real

economic incentive. HortScience 44:366–

371.

Zhang, D., Q. Du, Z. Zhang, X. Jiao, X. Song, and

J. Li. 2017. Vapour pressure deﬁcit control in

relation to water transport and water produc-

tivity in greenhouse tomato production during

summer. Sci. Rep. 7:43461.

Zou, Y.N., Z. Hu, J. Zhang, C. Guimbaud, Q.S.

Wang, and Y.K. Fang. 2016. Effect of seasonal

variation on nitrogen transformations in aqua-

ponics of northern China. Ecol. Eng. 94:30–36.

1458 HORTSCIENCE VOL. 54(9) SEPTEMBER 2019

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Dec 2022
AGR HUM VALUES

Consumers have a growing desire to know where their food comes from and how it is produced, not only for health and safety reasons, but also to satisfy a nostalgia or a perception of “true”, “healthy”, “authentic” and “traceable”. The commercial urban agriculture sector attempts, at least in part, to respond to a growing demand from citizens for locally produced food and for local agriculture that can be signalled to consumers with the help of quality signs, such as reserved designations and added-value claims labels. To date, however, we can wonder about the issues of establishing an added-value claim “urban agriculture” to promote the distinction and development of food products from commercial urban agriculture. This study, using semi-directed interviews with 16 urban farmers and managers of urban agriculture businesses in Quebec, explores their perception of an added-value claim "urban agriculture" to certify their food products. The results of the thematic analysis carried out showing seven main issues, namely: notion of urbanity, sustainability of agricultural practices, valorization of hyper-locality, community, regulations, ownership concerns and relevance of the claim. These issues underline that the logic of commercial urban producers is not only mercantile but also community, social and environmental. In this sense, legislating a movement, under the establishment of a public food label to meet the market's needs and promote the development of this industry, can reveal the various forms of power, exclusion and inequality embedded in urban agriculture initiatives but also some niche opportunities for them. Thoughts are proposed to promote products from urban agriculture from the perspective of increasingly nurturing cities.

Modeling resource consumption and carbon emissions associated with lettuce production in plant factories

Article

Dec 2022
J CLEAN PROD

Economic Analysis of an Urban Vertical Garden for Hydroponic Production of Lettuce (Lactuca sativa)*

Article

Full-text available

Jul 2015

A household module of tropical greenhouse was constructed for leafy vegetable production. The system uses a 35-watt submersible pump to lift the nutrient solution up from the reservoir to the uppermost growing tubes that are configured vertically to accommodate more plants and have cutouts to hold plastic cups for seedlings to be grown hydroponically. The system costs PhP 50,000.00 and grows 560 plants with a net weight of 26.6 kg in 30 days after transplanting. When sold at PhP 150.00 per kg, an annual gross income of PhP 47,900.00 is obtained. A total cost of PhP 23,994.00 per year was determined when fixed cost of PhP 5,550.00 and variable cost of PhP 18,444.00 were added. Unit price, which is computed by dividing total variable cost by the total weight of lettuce per year, is PhP 57.78 per kg. Results revealed that the annual net income and gross margin is PhP 23,906.00 and PhP 29,456.20, respectively; payback period is 2.1 years; break-even point is 60.20 kg per annum; benefit-cost ratio of 1.56 and the net present worth of PhP 129,084.05 per year. These proved that the household module for hydroponic lettuce production is profitable to operate within the locality.

Effects of Elevated CO2 on Nutritional Quality of Vegetables: A Review

Article

Full-text available

Aug 2018

Elevated atmospheric CO2 (eCO2) enhances the yield of vegetables and could also affect their nutritional quality. We conducted a meta-analysis using 57 articles consisting of 1015 observations and found that eCO2 increased the concentrations of fructose, glucose, total soluble sugar, total antioxidant capacity, total phenols, total flavonoids, ascorbic acid and calcium (Ca) in the edible part of vegetables by 14.2%, 13.2%, 17.5%, 59.0%, 8.9%, 45.5%, 9.5% and 8.2%, respectively, but decreased the concentrations of protein, nitrate, carotenoids, magnesium, iron and zinc by 9.5%, 18.0%, 8.1%, 9.2%, 16.0% and 9.4%. The concentrations of titratable acidity, total chlorophyll, lycopene, anthocyanins, phosphorus, potassium, sulphur, copper and manganese were not affected by eCO2. Furthermore, we propose several approaches to improving vegetable quality based on the interaction of eCO2 with factors, i.e. species, cultivars, CO2 levels, growth stages, light, O3 stress, nutrient and salinity. Finally, we give a summary of the eCO2-effect on quality of three widely-cultivated crops, namely, lettuce, tomato and potato.

Light quality characterization under climate screens and shade nets for controlled-environment agriculture

Article

Full-text available

Jun 2018
PLOS ONE

Climate screens are typically used inside glass greenhouses to improve control of humidity and temperature, and thus reduce energy expenditure. Shade nets are more appropriate to use, either with or without polyethylene cladding, at locations less-reliant on climate control, but where protection against hail, wind and excessive solar radiation might be needed. In addition, insect screens and nets can be employed to hinder insect pests and other invertebrates entering either type of production environment, and to keep invertebrates used in pest management contained inside. Screens and nets both transmit sunlight in a wavelength-specific manner, giving them the potential to affect plant morphology and physiology. Screens and nets of various colours and nominal shading factors have been described and studied; however, detailed measurements of their spectral characteristics are scarce. We measured solar spectral photon-irradiance and its attenuation by climate screens, shade nets, insect nets, greenhouse glass, and polyethylene covers. Our aim was to elucidate the effects of different patterns, colours, and shading factors, on light quality in production environments. Our measurements reveal that there are large differences both in the fraction of global irradiance attenuated and spectral ratios received under materials that are otherwise superficially similar in terms of their appearance and texture. We suggest that the type of spectral characterization that we performed is required to fully interpret the results of research examining plant responses to different types of screen and net. These data on spectral irradiance would benefit material manufacturers, researchers, growers, and horticultural consultants, enabling material selection to better match the solutions sought by growers and their desired outcomes regarding plant performance.

Consumer preferences for aquaponic produce: Implications from an experimental auction

Article

Full-text available

Aug 2017

Aquaponics is the integration of aquaculture and hydroponics to grow fish and plants together in one system. Many producers in the northern United States are attracted to aquaponics for its potential to produce indoors year‐round. However, little is known about consumer preferences for products grown in aquaponic systems. To address this knowledge gap, we conducted an experimental auction to measure the impact of information about production method on consumers’ willingness‐to‐pay (WTP) for lettuce. For most participants, WTP was similar for both aquaponic and soil grown lettuce with overall average bids of $1.47 per 8 ounces and $1.48 per 8 ounces, respectively. Learning how samples were grown (either aquaponic or soil‐grown) rarely changed bids significantly, although on average, participants with environmental group membership lowered their bids for aquaponic lettuce samples. In general, higher frequency shoppers expressed higher average WTP for all types of lettuce. [Q100 Agriculture: General, Q220 Renewable Resources and Conservation: Fishery; Aquaculture]

Towards commercial aquaponics: a review of systems, designs, scales and nomenclature

Article

Full-text available

Jun 2018
AQUACULT INT

Aquaponics is rapidly developing as the need for sustainable food production increases and freshwater and phosphorous reserves shrink. Starting from small-scale operations, aquaponics is at the brink of commercialization, attracting investment. Arising from integrated freshwater aquaculture, a variety of methods and system designs has developed that focus either on fish or plant production. Public interest in aquaponics has increased dramatically in recent years, in line with the trend towards more integrated value chains, greater productivity and less harmful environmental impact compared to other production systems. New business models are opening up, with new customers and markets, and with this expansion comes the potential for confusion, misunderstanding and deception. New stakeholders require guidelines and detail concerning the different system designs and their potentials. We provide a definitive definition of aquaponics, where the majority (> 50%) of nutrients sustaining the optimal plant growth derives from waste originating from feeding aquatic organisms, classify the available integrated aquaculture and aquaponics (open, domestic, demonstration, commercial) systems and designs, distinguish four different scales of production (≤ 50, > 50–≤ 100 m2, > 100–≤ 500 m2, > 500 m2) and present a definite nomenclature for aquaponics and aquaponic farming allowing distinctions between the technologies that are in use. This enables authorities, customers, producers and all other stakeholders to distinguish between the various systems, to better understand their potentials and constraints and to set priorities for business and regulations in order to transition RAS or already integrated aquaculture into commercial aquaponic systems.

Review of optimum temperature, humidity, and vapour pressure deficit for microclimate evaluation and control in greenhouse cultivation of tomato: A review

Article

Full-text available

Mar 2018
INT AGROPHYS

Greenhouse technology is a flexible solution for sustainable year-round cultivation of Tomato (Lycopersicon esculentum Mill), particularly in regions with adverse climate conditions or limited land and resources. Accurate knowledge about plants requirements at different growth stages and light condition can contribute to design of adaptive control strategies for a more cost-effective and competitive production. In this context, different scientific publications have recommended different values of microclimate parameters at different growth stages of tomato. This paper provides a detailed summary of optimal, marginal and failure air and root-zone temperature, relative humidity and vapor pressure deficit for successful greenhouse cultivation of tomato. Graphical representation of membership function model to define optimality degrees of these three parameters are presented as a reference to determine how close a greenhouse microclimate is to the optimal condition. Several production constraints have been discussed to highlight the short and long-term effects of adverse microclimate condition on the quality and yield of tomato that are associated with the interactions between suboptimal parameters, greenhouse environment, and growth responses.

A photochemistry-based method for optimising greenhouse supplemental light intensity

Article

Apr 2019
BIOSYST ENG

Free download through early June 2019: https://authors.elsevier.com/a/1Yxy05Tbkk5R0V • Electricity use of greenhouse lights can be reduced using dimmable LEDs. • An optimization problem is formulated to minimize electricity use for lighting. • The problem is solved using a quick and computationally-simple algorithm. • Lettuce lighting requirements are simulated using typical meteorological year data. • Annual electricity costs can be reduced by an estimated 9.55% using this method. Supplemental lighting in greenhouses can increase crop growth, improving rates of greenhouse production. The advent of light-emitting diodes (LEDs) for photosynthetic lighting presents new opportunities for optimising greenhouse supplemental lighting control. Because LED light intensity can be controlled rapidly and precisely in real time, these lights can be controlled such that supplemental light is provided when it will be most efficiently used to drive photosynthesis. This approach to supplemental lighting control has the potential to reduce the electricity cost associated with greenhouse lighting while retaining the beneficial effects on crop growth, thereby decreasing the financial cost and improving the sustainability of greenhouse crop production. In this paper, an optimisation problem is formulated to minimise the total amount of electricity used by supplemental LED lights, subject to achieving a specified daily amount of photochemistry. An algorithm to solve the problem explicitly based on sufficient conditions for a global minimiser is developed. This method represents a computationally simple and broadly applicable means for minimising the amount of electricity required for supplemental lighting in greenhouses.

Daily Light Integral: A Research Review and High-resolution Maps of the United States

Article

Sep 2018
HORTSCIENCE

The National Renewable Energy Laboratory developed the National Solar Radiation Database to provide accessible solar radiation data to the research community for various uses. Previously, we created a series of monthly daily light integral (DLI) maps to provide a tool for horticulturists to estimate the potential growth and flowering responses for various plants throughout the year. The original DLI maps were based on solar radiation data from 239 sites recorded from 1961 to 1990. The DLI maps presented in this article were created from an updated database that included data from 1998 to 2009. This database provides higher resolution data modeled from satellite images of cloud cover. The data are presented in pixels with each pixel representing 100 km² of land across the lower 48 United States and Hawaii, whereas the Alaska data are 1600 km² pixels. The database provided global horizontal irradiance data that were converted to DLI (mol∙m–2∙d–1) using the conversion factor of 0.007265 mol (400–700 nm)·Wh–1 (400–2700 nm), which assumes that 45% of the solar radiation is in the photosynthetically active radiation (PAR, 400–700 nm) region and 4.48 μmol∙J–1 is the conversion from radiometric to quantum units. The updated DL1 maps provide more geographically precise data reflecting recent weather patterns. We present a comprehensive review of recent research exploring the growth and flowering responses of horticultural crops to DLI. © 2018, American Society for Horticultural Science. All rights reserved.

Greenhouses: Advanced Technology for Protected Horticulture

Book

Nov 2017

Joe J. Hanan

A greenhouse provides an essential means of livelihood to its owner and must be economically practical for the particular climate in which it stands. Greenhouses: Advanced Technology for Protected Horticulture addresses the major environmental factors of light, temperature, water, nutrition, and carbon dioxide, and features extensive discussions of greenhouse types, construction, and climate control. The book highlights technology such as hydroponics, computer control of environments, and advanced mathematical procedures for environmental optimization. Greenhouses: Advanced Technology for Protected Horticulture is the definitive text/reference for the science of greenhouse engineering and management. The author Dr. Joe J. Hanan, Professor Emeritus of Colorado State University, is the recipient of the Society of American Florists' (SAF) 2000 (Millenium) Alex Laurie Award for Research and Education. The Alex Laurie Award is presented annually to an individual who has made broad-scope, long-lasting contributions to the floriculture industry through research or education. The award is named for Alex Laurie, a professor at The Ohio State University, who pioneered work in many areas of floriculture. "Joe is one of the most precise floricultural researchers I have known," said Dr. Gus De Hertogh, Chairman of SAF's Research Committee. "That excellence is reflected in his latest book, Greenhouses, Advanced Technology for Protected Horticulture, which was published in 1998, nine years after his official 'retirement.'"

Nitrate in fruits and vegetables

Article

Jul 2018
SCI HORTIC-AMSTERDAM

The current article provides an updated review of scientific advances regarding nitrate accumulation in plant tissues and a critical examination of the genetic, agroenvironmental and postharvest factors that can modulate nitrate levels in a wide range of horticultural crops, including herbs, roots and tubers, inflorescences, buds, seeds, stems, and leafy vegetables, fungi as well as fruits. A refined classification of horticultural crops is presented according to the nitrate content of their edible product. The role of plant cultivar/morphotype and tissue age in nitrate accumulation is discussed along with the physiological role of nitrate as osmoticum in maintaining turgor and driving leaf expansion under conditions of variable photosynthetic capacity. Nitrate accumulation is examined in respect to key cultural practices, such as the timing-rate-form of N application and the use of plant biostimulants (natural substances and microbial inoculants), as well as the potential interaction with other nutrients (e.g., P, Ca, Mo and Cl). The influence of environmental conditions during plant growth (light intensity, spectral quality, photoperiod, air and root-zone temperature and atmospheric CO2 concentration), harvest stage and diurnal timing of harvest is assessed. Postharvest storage conditions (temperature, light, and duration) are discussed in respect to their effects on the putative endogenous conversion of nitrate residues to nitrites. Several approaches that may be adopted to reduce nitrate content in vegetables, fruits and herbs are analysed and warranted future research subjects are identified.

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Plant extracts as antimicrobials in food products: mechanisms of action, extraction methods, and app...

A study on current and future realities for urban food security in South Africa         