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Controlled Environment Food Production for Urban Agriculture

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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.
HORTSCIENCE 54(9):1448–1458. 2019.
Controlled Environment Food
Production for Urban Agriculture
Celina G
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
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
a discussion of current and potential applica-
tions regarding opportunities and limitations of
commercial CEA for urban food production
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
et al., 2015), environmental (Jones and
Gilbert, 2018; Nadal et al., 2017; Sanjuan-
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
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:
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.,
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).
Electric lighting. The daily light integral
(DLI) requirement of food crops commonly
grown in CEs typically ranges from 12 to 30
(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.,
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.
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
), 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
) 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
), requiring supplemental CO
injection to avoid limiting photosynthesis
and plant growth. Enrichment up to 800
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
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
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
Similarly, although some studies report to-
mato yield increases with CO
(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).
Heuvelink and Kierkels (2015) reported
that in general, CO
enrichment from 400 to
1000 mmol·mol
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
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
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,
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.
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
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
) 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
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
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-
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
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.,
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
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
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,
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
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.
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
for some LEDs).
Future research evaluating ‘‘dynamic’
control of CO
enrichment will help reduce
the long-term adaptation to high CO
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
during specific times of the day will be
helpful in furthering our understanding about
the potential benefits of using CO
ment in CEs. Further studies focusing on
breeding or sink-source relationships may
elucidate ways in which CO
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
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.
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.
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... Vertical farms, warehouses, and shipping containers, collectively encompassing indoor agriculture (IA), provide the opportunity to produce year-round where growing seasons, land access, or food system infrastructure are limiting [1,2]. Set apart from greenhouses for its sole use of artificial lighting systems, IA facilities enable precise control of environmental conditions, improving produce quality and annual yields beyond that possible under field conditions [3,4]. ...
... Set apart from greenhouses for its sole use of artificial lighting systems, IA facilities enable precise control of environmental conditions, improving produce quality and annual yields beyond that possible under field conditions [3,4]. In addition, these compact, closed systems offer more efficient use of resources such as land and water [5,6], contributing to a recent rising interest in producing leafy greens in IA [2]. Lettuce (Lactuca sativa) is particularly well-suited for IA production due to its compact growth, quick marketable biomass accumulation, and high market significance, enabling higher yield per area with efficient space utilization [1]. ...
... Parameters influential to plant growth, such as radiation duration, quantity, and quality; day and night temperatures; airflow; relative humidity (RH); vapor pressure deficit (VPD); and carbon dioxide (CO 2 ) concentration can all be precisely manipulated in IA [1][2][3][4]. and 'Sensation' at day/night temperatures (12 h/12 h) of 22/18 • C (20 • C MDT) or 18/16 • C (17 • C MDT) and under PPFDs of 150, 200, and 250 µmol·m −2 ·s −1 for the first 30 d after transplant (DAT) [19]. From 30-60 DAT, the plants were grown at 18/16 • C (17 • C MDT) or 18/14 • C (16 • C MDT). ...
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Lettuce (Lactuca sativa) is among the most consumed vegetables worldwide and is primarily field-grown; however, indoor agriculture enables year-round, precise production. Through precise manipulation of the mean daily temperature (MDT) and photosynthetic photon flux density (PPFD), crop color, morphology, and yield can be altered. Therefore, we quantified how MDT and PPFD interact and developed models predicting yield and economic viability. Eleven days after sowing, green butterhead lettuce ‘Rex’ and red oakleaf lettuce ‘Rouxaï RZ’ were transplanted into six deep-flow hydroponic tanks with day/night and MDTs of 22/15 °C (20 °C), 25/18 °C (23 °C), or 28/21 °C (26 °C), under light-emitting diodes providing a low or high PPFD of 150 or 300 µmol·m−2·s−1 for 17-h·d−1. As PPFD increased, shoot fresh mass (SFM) of ‘Rex’ increased by 29% (33.4 g). SFM of ‘Rouxaï RZ’ and shoot dry mass (SDM) of both cultivars was influenced by the interaction of MDT and PPFD. The greatest ‘Rouxaï RZ’ SFM (158.8 g) and SDM (6.42 g) were recorded at >20 °C MDT under the high PPFD; the lowest SFM (76.0 g) and SDM (3.17 g) occurred at 20 °C under the low PPFD. Similarly, ‘Rex’ SDM was greatest (7.36 g) and lowest (3.78 g) under the aforementioned MDTs and PPFDs. Increasing from the low to high PPFD increased tipburn incidence on ‘Rouxaï RZ’ from 0 to 25% and ‘Rex’ from 47 to 100%. ‘Rouxaï RZ’ had darker yellow-red foliage at lower MDTs under the high PPFD. A high MDT and low PPFD resulted in a lighter green. Finally, for the greatest SFM, while reducing energy costs as interpreted from the economic analysis, we recommend growing ‘Rex’ and ‘Rouxaï RZ’ under a PPFD of 150 and 300 µmol·m−2·s−1, respectively, at an MDT of 23 to 26 °C depending on the cost of temperature control.
... [18] [19]. Despommier [20] initially envisioned the benefits of using CEAs and vertical plant factories, which featured a closed system to relieve the problems of traditional agriculture in urban areas (i.e. ...
... Placing agriculture in urban areas enhances social interaction as individuals work together to produce crops [17]. Urbanized agricultural projects can be incorporated into facilities such as nursing homes, prisons, and hospitals, which provide additional social benefits for urban areas [19]. ...
... Controlled environment agriculture is known since a long time (Dalrymple, 1973). As the term implies, Controlled Environment Agriculture (CEA) allows farmers to control different variables of the growing environment such as temperature, humidity, carbon dioxide, nutrient concentration, and light to a more or lesser extent (Agrilyst, 2017;Gómez et al., 2019;Dalrymple, 1973) but also root zone, growth media and the atmosphere (Dalrymple, 1973). A controlled environment (CE) can be defined in a broad range from minimum protection of crops from e.g., wind, rain and snow (protected cropping in the field) to partially controlled in greenhouses and up to high end facilities with complete CE (light, atmosphere, root medium) (Dalrymple, 1973). ...
... We observed that occurrence of pests and diseases cannot be prevented (Goodman and Minner, 2019), especially if a standard plastic-/greenhouse or screenhouse is used as in our case. Our study suggests that food produce from hydroponic systems might be healthier in urban settings, but we need to account that even in CEA human pathogens from water, substrates and human contact can be introduced and impact human health (Gómez et al., 2019). The high energy demand of hydroponics systems in hot climates (Arizona) questions if it is a good alternative for open field vegetable production (Barbosa et al., 2015). ...
... Especially for food production with artificial light supply in urban agriculture [1,2] or in spaceflight environments [3,4], the light energy required for nutrient production is a critical factor for food production. Findings are used to discuss options to improve nutritional quality through a combination of informed crop choice and suitable growing conditions. ...
... These findings reported here can further inform the design of suitable growth protocols that optimize nutritional quality for the human consumer relative to the required light input for plant cultivation in controlled environments, including in locations with extreme climates or high levels of urbanization [1,2]. Duckweed is an attractive candidate for controlled growth environments and limited space, where this diminutive plant can be grown in shallow trays stacked vertically in multiple layers and supplied with lighting from energy-efficient light-emitting diodes [99]. ...
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Development of a nutritious, sustainable food source is essential to address worldwide deficiencies in human micronutrients. Aquatic floating plants (e.g., species in the family Lemnaceae, duckweeds) are uniquely suited for area-efficient productivity with exceptionally high rates of growth and nutritional quality. Here, we provide an overview of the role of dietary micronutrients (with a focus on carotenoids) in human health and the promise of Lemnaceae as sustainable crops. We examine the effect of growth light environment on plant biomass production and levels of the carotenoids zeaxanthin, lutein, and pro-vitamin A (β-carotene), as well as the antioxidant vitamin E (α-tocopherol), and protein. Data on each of these nutrients are reported on a plant dry biomass basis (as relevant for nutrition) as well as relative to the required input of light energy (as relevant to resource-use efficiency).
... Regional humidity, including the absolute and relative humidity, is affected by numerous factors, such as plant transpiration rates, irrigation strategies, infiltration, ventilation, and active systems for air humidification or dehumidification. The difference between saturation and actual air vapor pressure at a given temperature is represented by vapor pressure deficit (VPD) and that it is the most accurate parameter indicating leaf water loss and has a linear relationship with plant transpiration, nevertheless, relative air humidity (RH) remains the most commonly used indicator in horticulture (Gómez et al., 2019). In the plant factory, many vegetables suffer from tip burn, a common physiological disorder characterized by necrosis in margins of young developing leaves. ...
... The occurrence of leaf burn was also genotype-dependent, and the most common and severe in cruciferous leafy vegetables, especially flowering Chinese cabbage and radish (Table 2, Fig. 1). Extensive research has been conducted on the influence of LED light intensity, spectrum, and photoperiods in horticultural crop yield, nutritional quality, and pest and/or disease control, especially in the production of green leafy vegetables (Bian, Yang & Liu, 2015;Mitchell et al., 2015;Gómez et al., 2019). Sago (2016) reported that a positive relationship between light intensity and the tip burn occurrence in butterhead lettuce at PPFD 150, 200, 250, and 300 µmol m −2 s −1 . ...
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Plant factories that ensure the annual production of vegetable crops have sparked much attention. In the present study, thirty types of common vegetable crops from 25 species and eight families, were grown in a multi-layer hydroponic system in a closed-type plant factory to evaluate the adaptive performance. A total of 20 vegetable crops, belonging to 14 species and 4 families, unexpectedly exhibited different degrees of leaf margin necrosis in lower leaves firstly, then the upper leaves gradually. We defined this new physiological disorder as “leaf burn”. It occurred more commonly and severely in cruciferous leafy vegetables. Two different light intensities (150 and 105 µmol m ⁻² s ⁻¹ photosynthetic photon flux density (PPFD)), three photoperiod conditions (12, 10 and 8 h d ⁻¹ ) and two canopy relative air humidity (RH) (70% and 90% RH) were set to evaluate the suppression effects on leaf burn occurrence in two commercial flowering Chinese cabbage cultivars (‘Sijiu’ and ‘Chixin’), the special cruciferous vegetable in South China. We discovered that changing light conditions did not fully suppress leaf burn occurrence in the cultivar ‘Sijiu’, though lower light intensity and shorter photoperiod partly did. Interestingly, the occurrence of leaf burn was completely restrained by an increased canopy RH from 70% to 90%. Specifically, the low RH-treated seedlings occurred varying degree of leaf burn symptoms, along with rapidly decreased water potential in leaves, while the high RH treatment significantly lessened the drop in leaf water potential, together with increased photosynthetic pigment contents, net photosynthetic rate, stomatal conductance and transpiration rate, decreased leaf stomatal aperture and density, and thus reduced the incidence of leaf burn in ‘Sijiu’ and ‘Chixin’, from 28.89% and 18.52% to zero, respectively. Taken together, high canopy RH may favor maintaining leaf water potential and improving photosynthesis performance, jointly regulating leaf burn incidence and plant growth.
... It results from the decomposition process of organics by microorganisms in water. Nitrite usually does not cause water quality problems in FT because of the rapid conversion of nitrite to nitrate (Gómez et al 2019) and presumably due to aeration and vigorous stirring (Deswati & Sutopo 2022). The results of the statistical test of the best treatment for the concentration of nitrite is the P5 treatment. ...
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Feed is one of the factors that determine success in catfish Clarias batrachus farming, and it contributes about 60-70% to the production costs. Furthermore, feed waste is an obstacle in cultivation that requires the application of biofloc technology. The water quality parameters observed in this study were temperature, pH, dissolved oxygen (DO), ammonia, nitrite, and nitrate. This study aims to (1) analyze several parameters that affect water quality, and (2) obtain environmentally friendly catfish cultivation technology. A completely randomized design (CRD) was adopted with five treatments and three replications. The treatments include P1 (control), P2 (biofloc), P3 (biofloc+bio balls), P4 (biofloc+ carbonation), and P5 (biofloc+bio balls+carbonation). The results showed a temperature of 26.6-28.5°C, 6.875-8.5 pH, 3.95-8.75 mg L⁻¹ DO, 0.08-0.98 mg L⁻¹ ammonia, 0.41-0.91 mg L⁻¹ nitrite, and 9.23-11.4 mg L⁻¹ nitrate. These parameters met the water quality standard. The best treatment is P5, which is a combination of biofloc, carbonation, and bio-balls. Therefore, it is feasible to be applied to catfish farming.
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Producing enough healthy food for a globally growing urban population within planetary boundaries requires more resource-efficient and localized food production systems. Controlled-environmental food production systems (CEFPS) are a widely discussed new approach for sustainable food production in urban contexts. However, little research has addressed innovation processes of CEFPS in urban or rural areas. This paper aims to address this research gap by adapting an innovation system perspective, developing a conceptual framework for 'urban food production innovation systems' (UFoPrInS) and applying it to a paradigmatic case study in Berlin. Based on a content analysis of the relevant literature and 23 semi-structured expert interviews, we analyse (a) the main characteristics and (b) the key elements of the UFoPrInS and their relationships during different stages of the innovation process. The case results show that UFoPrInS faces various challenges related to possible structural failures that can occur in infrastructure, interactions, capabilities of actors and institutions. The current institutional framework at EU and national level was seen as the major barrier to innovations. To support new food production innovations, a comprehensive regulatory framework for CEFPS is needed that considers in an integrated approach the specifics of (1) the highly-intensive production processes, (2) the diverse types of products and (3) the urban location.
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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.
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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.
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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.
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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.
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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]
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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.
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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.
Free download through early June 2019: • 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.
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.
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.'"
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.