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Measuring Daily Light Integral in a Greenhouse

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In commercial greenhouses, several strategies can be used to help properly manage light levels throughout the day and seasonally. Some of the primary reasons why greenhouses manipulate light levels include temperature and irrigation management, photoperiod control, minimizing crop stress, and optimizing photosynthesis. Supplemental lighting with high-intensity discharge (HID) lamps can increase the light intensity a crop receives and improve and accelerate its growth and development. Retractable shade curtains and whitewash can reduce and scatter light intensity to create a more desirable growing environment during high-light periods. This publication examines the characteristics of greenhouse lighting and describes one management option, daily light integral (DLI). What Is Light and Why Is It Important? Light is a form of energy called electromagnetic radiation. Electromagnetic radiation, whether from sunlight or HID lamps [e.g., high-pressure sodium lamps (HPS) or metal halide] varies in duration (energy over time), quality (wavelength or color), and intensity (the amount of light at each wavelength or color). We will only focus on photosynthetically active radiation (PAR), which is light with a wavelength
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HO-000-W
Measuring Daily Light Integral in a Greenhouse
Ariana P. Torres and Roberto G. Lopez
Department of Horticulture and Landscape Architecture,
Purdue University
Purdue Department of Horticulture
and Landscape Architecture
www.hort.purdue.edu
Purdue Floriculture
owers.hort.purdue.edu
HO-238-W
Commercial Greenhouse Production
Purdue e xtension
In commercial greenhouses, several strategies can be used to help properly manage light levels
throughout the day and seasonally. Some of the primary reasons why greenhouses manipulate
light levels include temperature and irrigation management, photoperiod control, minimizing crop
stress, and optimizing photosynthesis.
Supplemental lighting with high-intensity discharge (HID) lamps can increase the light intensity
a crop receives and improve and accelerate its growth and development. Retractable shade
curtains and whitewash can reduce and scatter light intensity to create a more desirable growing
environment during high-light periods. This publication examines the characteristics of green-
house lighting and describes one management option, daily light integral (DLI).
What Is Light and Why Is It Important?
Light is a form of energy called electromagnetic radiation. Electromagnetic radiation, whether
from sunlight or HID lamps [e.g., high-pressure sodium lamps (HPS) or metal halide] varies in
duration (energy over time), quality (wavelength or color), and intensity (the amount of light at
each wavelength or color).
We will only focus on photosynthetically active radiation (PAR), which is light with a wavelength
between 400 to 700 nm — this also happens to be the light people can perceive. Increasing en-
ergy in the PAR range increases plant photosynthesis, (the plant’s most basic metabolic process).
Each crop species has an optimal light intensity that maximizes photosynthesis and plant growth.
When there is not enough light, growth and crop quality can decline; and if there is excessive
light, photosynthesis and growth will not increase despite the expense of keeping the lights on.
Measuring Light
The most common units for measuring light are the foot-candle (primarily in the United States)
and lux (primarily in Europe). It is important for growers to understand the limitations of these
units. Both units provide an instantaneous light intensity at the time the reading is taken. As we all
know, natural light levels are continuously changing and a single measurement in time does not
accurately represent the amount of light a plant has received in a day.
Just as important, foot-candles are “photometric” units based on the amount of visible light de-
tected by the human eye (primarily green light). That means foot-candles are focused on people
and not appropriate for indicating plant photosynthesis.
Most horticultural researchers measure instantaneous light in micromoles (μmol) per square
meter (m
-2
) per second (s
-1
), or: μmol·m
-2
·s
-1
of PAR. This “quantum” unit quanties the number of
photons (individual particles of energy) used in photosynthesis that fall on a square meter (10.8
square feet) every second. However, this light measurement also is an instantaneous reading.
HO-238-W Measuring Daily Light Integral in a Greenhouse
Purdue extension
2
Daily Light Integral
Daily light integral (DLI) is the amount of PAR received
each day as a function of light intensity (instantaneous
light: μmol·m
-2
·s
-1
) and duration (day). It is expressed
as moles of light (mol) per square meter (m
-2
) per day
(d
-1
), or: mol·m
-2
·d
-1
(moles per day).
The DLI concept is like a rain gauge. Just as a rain
gauge collects the total rain in a particular location over
a period of time, so DLI measures the total amount of
PAR received in a day. Greenhouse growers can use
light meters to measure the number of light photons
that accumulate in a square meter over a 24-hour
period.
Jim Faust and colleagues at Clemson University have
developed maps of monthly outdoor DLI throughout
the United States (Figure 1). These maps illustrate
how latitude, time of year, length of day (photoperiod),
and cloud cover inuence DLI and vary from 5 to 60
mol∙m
-2
∙d
-1
.
In a greenhouse, values seldom exceed 25 mol∙m
-2
∙d
-1
because of greenhouse glazing materials and super-
structure, the season (which affects the sun’s angle),
cloud cover, day length (photoperiod), shading, and
other greenhouse obstructions, such as hanging
baskets.
The Importance of DLI in
Greenhouse Production
DLI is an important variable to measure in every
greenhouse because it inuences plant growth, de-
velopment, yield, and quality. For example, DLI can
inuence the root and shoot growth of seedlings and
cuttings, nish plant quality (characteristics such as
branching, ower number and stem thickness), and
timing. Commercial growers who routinely monitor
and record the DLI received by their crops can easily
determine when they need supplemental lighting or
retractable shade curtains.
This is especially true for growers in northern
latitudes where the majority of crops are propagated
from December to March and naturally occurring
outdoor DLI values are between 5 to 30 mol·m
-2
·d
-1
.
Furthermore, these values can be 40 to 70 percent
Figure 1. Maps of monthly outdoor DLI throughout the United States.
Source: Mapping monthly distribution of daily light integrals across the contiguous United States (Pamela C. Korczynski,
Joanne Logan, and James E. Faust; Clemson University, 2002)
Purdue extension
HO-238-W Measuring Daily Light Integral in a Greenhouse
3
lower because of shading from greenhouse glazing,
structures, and hanging baskets. These obstructions
can result in an average DLI as low as 1 to 5
mol·m
-2
·d
-1
.
There are devices that automatically measure and
calculate the DLI your greenhouse crops are receiv-
ing. One of these is the WatchDog weather station
manufactured by Spectrum Technologies (Figure 2).
This instrument is portable and should be placed next
to your crop to determine the DLI for that particular
area. Some models can be connected to download
data automatically to a computer.
Another method to measure DLI is to use a light
quantum sensor connected to a data logger or com-
puter (Figure 3). The sensor measures instantaneous
light intensity (preferably in µmol
.
m
-2.
s
-1
) at some de-
ned interval (such as once every 15 to 60 seconds),
which allows you to calculate DLI. Table 1 on page 4
provides DLI calculations based on average hourly
foot-candles or μmol·m
-2
·s
-1
of PAR measurements.
No matter which sensors you use, it is important to
keep all light sensors level and clean to assure ac-
curate readings.
DLI Recommendations
Plants grown under light-limiting conditions (a low
DLI), typically have delayed growth and development.
Research conducted at Michigan State University
indicated that maintaining a DLI between 4 to 11
mol·m
-2
·d
-1
during stage 2 (callusing) and stage 3
(root development) accelerates propagation of petu-
nia and New Guinea impatiens cuttings (Figure 4).
Experiments with these petunias and New Guinea
impatiens have shown that, as propagation DLI
increases, rooting, biomass accumulation (root and
shoot growth), and quality (reduced stem elongation)
generally increase, while subsequent time to ower
generally decreases. Similarly, experiments with
seedlings of celosia, impatiens, salvia, marigold, and
Figure 2. WatchDog weather stations contain light sensors
and automatically calculate DLI.
Figure 3. A light quantum sensor connected to a computer
can measure and record instantaneous light levels
throughout the day. These values can then be used to
calculate the DLI received by the crops using Table 1.
viola showed that quality parameters at transplant
increased when DLI increased up to 12 mol·m
-2
·d
-1
.
Based on this research, we recommend that
greenhouse growers provide a minimum of 10 to
12 mol·m
-2
·d
-1
of light during the nish stage to
produce many shade-intolerant oriculture crops.
But remember, DLI requirements differ between
greenhouse crops as outlined in Table 2 on pages
5-7. Some growers separate their oriculture crops
by DLI requirements. Crops with a DLI requirement
of 3 to 6 mol·m
-2
·d
-1
are considered low-light crops,
Figure 4. Influence of propagation daily light integral (DLI)
on root development and liner marketability in New Guinea
Impatiens (Lopez and Runkle, 2008).
HO-238-W Measuring Daily Light Integral in a Greenhouse
Purdue extension
Step 1
Determine the average number
of foot-candles per hour. Take the
hourly foot-candle averages for the
day, add them, and then divide this
sum by 24.
For example, you have 24 hourly foot-candle readings:
0 + 0 + 0 + 0 + 0 + 5 + 12 + 21 + 40 + 43 + 159 + 399 + 302 +
461 + 610 + 819 + 567 + 434 + 327 + 264 + 126 + 15 + 4 + 0 =
4,408 foot-candles
4,408 foot-candles ÷ 24 hours = 184 foot-candles per hour
Step 2
Convert foot-candles per hour to
PAR (µmol.m
-2
.s
-1
) based on light
source. Do this by multiplying foot-
candles per hour by a factor for the
light source.
Sunlight has 0.20 foot-candles per
µmol.m
-2
.s
-1
. HPS lamps have 0.13
foot-candles per µmol.m
-2
.s
-1
.
Using the same example as above, the PAR for crops receiv-
ing natural sunlight would be calculated like this:
184 foot-candles per hour x 0.20 foot-candles per µmol.m
-2
.s
-1
= 36.8 µmol.m
-2
.s
-1
For HPS lamps, the PAR would be:
184 foot-candles per hour x 0.13 foot-candles per µmol.m
-2
.s
-1
= 23.9 µmol.m
-2
.s
-1
Step 3
Convert PAR to DLI. Do this by
using the following equation:
PAR (µmol
.
m
-2.
s
-1
) x 0.0864
The 0.0864 factor is the total num-
ber of seconds in a day divided by
1,000,000
For crops receiving natural sunlight:
36.8 µmol.m
-2
.s
-1
x 0.0864 = 3.2 mol
.
m
-2.
d
-1
For crops receiving HPS lighting:
23.9 µmol.m
-2
.s
-1
x 0.0864 = 2.1 mol
.
m
-2.
d
-1
Table 1. Converting Foot-Candles to PAR and DLI
This table shows how to calculate from foot-candles to PAR (µmol.m-2.s-1), and from PAR to daily light integral [DLI (mol·m-
2·d-1)] for sunlight and high-pressure sodium lamps (HPS).
Note that the conversion factor from foot-candles to PAR depends on the light source.
4
6 to 12 mol·m
-2
·d
-1
are medium-light crops, 12 to 18
mol·m
-2
·d
-1
are high-light crops, and those requiring
more than 18 mol·m
-2
·d
-1
are considered very high-
light crops.
Supplemental Lighting
Under light-limiting conditions (such as during the
winter in temperate climates), most greenhouse
crops benet from supplemental lighting. But remem-
ber, supplemental lighting is generally worthwhile
only when increased photosynthesis leads to greater
revenue (such as more turns of plugs, cutting liners
or more cut owers).
The practice of using HID lamps to supplement
natural sunlight during periods of inclement weather
or short days allows growers to increase productivity
and plant quality. HPS or metal halide lamps typically
provide between 250 and 750 foot-candles (33 to 98
μmol·m
-2
·s
-1
).
HPS lamps that deliver 400 foot-candles (52 μmol·m
-
2
·s
-1
) for 12 hours provide a DLI of 2.3 mol·m
-2
·d
-1
.
This is a relatively small amount of light compared
to the DLI provided by the sun (Figure 1). Without
supplemental photosynthetic lighting, greenhouse
crops in the northern half of the United States often
receive insufcient light (<10 mol·m
-2
·d
-1
) for several
months of the year.
The percentage of U.S. greenhouse acreage using
supplemental lighting is increasing, but it is still low
— estimated at 10 to 20 percent in the northern half
of the United States. Generally, the high investment
and installation costs for HID lamps are a limitation
for greenhouse growers.
In some areas of the country, electricity costs can
be prohibitive during daily peak energy demands.
In 2004, it was estimated that the average cost
of supplemental lighting was $0.052 per square
foot per week across the United States. Some of
the perceived drawbacks to using HID lamps for
supplemental lighting, such as heavy ballasts and
high energy consumption, are decreasing as lighting
technologies improve.
In the future, light emitting diodes (LEDs) may re-
place HID lamps because they are more energy-ef-
cient, reduce energy costs, provide more options for
control of crop characteristics, are safer to operate,
and reduce light pollution. However, supplemental
lighting from LEDs is now extremely expensive and
likely won’t be practical in most greenhouse produc-
tion situations until 2015 or beyond.
Purdue extension
HO-238-W Measuring Daily Light Integral in a Greenhouse
5
Table 2. DLI Requirements for Various Greenhouse Crops
Minimum aceptable quality
Good quality
High quality
1=Requires ample water to perform well at high-light levels.
2=Requires cool or moderate temperatures to perform well at high-light levels.
3=Stock plants perform well under higher light levels than nished plants.
Species
Average Daily Light Integral (Moles/Day)
Greenhouse
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Ferns (Pteris Adiantum)
Maranta
Phalaenopsis (orchid)
Saintpaulia
Spathiphyllum
Forced hyacinth
Forced narcissus
Forced tulip
Aglaonema
Bromeliads
Caladium 1 1 1
Dieffenbachia
Dracaena
Nephrolepsis
Streptocarpus
Hosta 1 1 1
Hedera (English ivy)
Begonia (heimalis)
Sinningia
Schlumbergera 2 2 2 2 2 2 2
Cyclamen
Exacum
Heuchera
Coleus (shade)
Impatiens, New Guinea
Iris, Dutch (cut owers)
Kalanchoe
Lobelia 2 2 2 2
Primula
Impatiens
Pelargonium peltatum (Ivy geranium)
Begonia (brous)
Senecia (dusty miller)
Fuchsia 2 2 2 2
Euphorbia (poinsettia) 3 3 3
Hydrangea
HO-238-W Measuring Daily Light Integral in a Greenhouse
Purdue extension
Lilium (asiatic and oriental)
Lilium longiorum (easter lily)
Ageratum
Antirrhinum
Chrysanthemum (potted)
Dianthus
Gazania
Gerbera
Hibiscus rosa-siniensis
Lobularia
Pelargonium hororum (zonal gera-
nium)
Rose (miniature potted)
Salvia splendens
Schefera
Angelonia
Aster
Salvia farinacea
Iberis
Catharanthus (vinca)
Celosia
Chrysanthemum (garden)
Coleus (sun)
Coreopsis
Cosmos
Croton
Dahlia
Echinacea
Ficus bejaminia
Gaura
Gomphrena
Hemerocallis
Lantana
Lavendula (lavender)
Tagetes (marigold)
Petunia
Phlox (creeping)
Rudbeckia
Scaevola
Sedum
Thymus
Verbena
Viola (pansy) 2 2
Table 2. DLI Requirements for Various Greenhouse Crops (continued)
6
Species
Average Daily Light Integral (Moles/Day)
Greenhouse
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Purdue extension
HO-238-W Measuring Daily Light Integral in a Greenhouse
Zinnia
Alstroemeria (cut ower)
Capsicum (pepper)
Chrysanthemum (cut ower)
Dianthus (carnation)
Gladiolus (cut ower)
Lycopersicon (tomato)
Rose (cut ower)
Source: James E. Faust, Ball Red Book.
Table 2. DLI Requirements for Various Greenhouse Crops (continued)
7
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References
Department of primary industries. 2005. Light in
greenhouses. NSW Australia. 24 February 2009.
www.dpi.nsw.gov.au/agriculture/horticulture/green-
house/structures/light.
Fausey, B.A., R.D. Heins, and A.C. Cameron. 2005.
Daily light integral affects owering and quality of
greenhouse-grown Achillea, Gaula, and Lavandula.
HortScience 40:114−118.
Faust, J.E. 2001. Light, p. 71−84. D.Hamrick, (ed.).
Ball Redbook: Crop Production, Ball Publishing,
Batavia, IL.
Fisher, P., C. Donelly and J. Faust. 2001. Evaluating
supplemental light for your greenhouse. 24 Febru-
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OFAlight.pdf.
Korczynski, P.M., J. Logan, and J.E. Faust. 2002.
Mapping monthly distribution of daily light integrals
across the contiguous United States. HortTechnol-
ogy 12:12−16.
Lopez, R.G. and E.S. Runkle. 2008. Photosyntetic
daily light integral during propagation inuences
rooting and growth of cuttings and subsequent de-
velopment of New Guinea impatiens and petunia.
HortScience 43:2052−2059.
Pramuk, L.A. and E.S. Runkle. 2005. Photosyn-
thetic daily light integral during the seedling stage
inuences subsequent growth and owering of
Celosia, Impatiens, Salvia, Tagetes, and Viola.
HortScience 40:1336-1339.
Runkle, E. 2006. Technically speaking: Daily light
integral dened. Greenhouse Product News. 24
February 2009. www.gpnmag.com/articles/070_
gpn1106.pdf.
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what your DLI is? Greenhouse Product News 24
February 2009. www.gpnmag.com/Do-You-Know-
What-Your-DLI-Is-article7530.
Runkle, E. 2006. Technically speaking: Light it up!
Greenhouse Product News 24 February 2009.
www.gpnmag.com/articles/lightitupjuly2006.pdf.
Species
Average Daily Light Integral (Moles/Day)
Greenhouse
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
... Plants can also be categorized into very low light, low light, moderate light, high light, and very high light responses. Based on this classification, a tabulated classification of generalized responses of various greenhouse crops to daily light integrals can be found in [16,23]. Plants can grow in a wide range of DLI and a deviation of 0.1 mol/d should not disqualify a plant from thriving. ...
... Early attempts to generate contextual PAR simulated maps were incorporated in Ecotect, a software that is currently defunct, which utilized a simplified calculation that derives directly from solar irradiance. More recently, methodologies [24] and applications [25] are leveraging the overlap between visible wavelength range and photosynthetically active wavelength range of the solar spectrum, and, by utilizing conversion factors based on [26] and [23] they outline a way to simulate PAR and DLI more accurately. This methodology allows the incorporation of context geometries and materials' properties in a micro-scale level. ...
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The deliberate introduction of vegetation in urban environments, referred to as urban greening, is known to improve outdoor thermal comfort and mitigate the effects of Urban Heat Island in cities. Urban greening can be applied on ground level or elevated parks, roof tops, and building facades. The main parameters that affect plant growth are space, light, water, humidity, oxygen, carbon dioxide, mineral elements, and temperature. Of these parameters, light and temperature are the ones more unlikely to be supplemented in a non-controlled urban setting. This research presents the development of an automated workflow that facilitates design decisions on vegetation growth potential and vegetation species selection within their climatic and geometrical context. This novel scripting-based prototype uses hourly radiation results to extract location specifications, such as photoperiod, hardiness zone, and hourly annual Daily Light Integral values on a user-defined grid. It then seamlessly compares the data against seasonal light and soil temperature requirements of listed cultivars to evaluate their suitability within the constraints of the analysis area. A basic plant dataset is created that is open to expansion based on plants growth data availability. This automated workflow can be employed by agriculturalists, urban planners, and landscape designers to perform vegetation selection for applications such as urban greening in dense contexts or vertical farms.
... The DLI has proven to be a very useful and reliable tool for greenhouse cultivation, allowing growers to assess their light requirements with a simple quantity, similar to a "rain gauge" that accumulates all the PAR photons received in an area each day [27,28]. For northern latitudes where the natural light varies considerably throughout the year, the DLI can help determine the need for supplementary lighting and the strategy to use, either to reach an intensity threshold or to extend the photoperiod [29][30][31][32]. ...
... An adequate PVR requires considering the shading effect that the integrated PV will have inside the greenhouse and its impact on the light levels for the crop. Plant species with a low (5-10 mol·m -2 ·d -1 ) and moderate light needs (10-20 mol·m -2 ·d -1 ) are more tolerant to shading compared to plants with high (20-30 mol·m -2 ·d -1 ) or very high (DLI > 30 mol·m -2 ·d -1 ) requirements [28][29][30][31][32]. Greenhouses in southern Europe with a PVR,% between 10% and 15% showed a very small decrease in the crop yields, even when cultivating shade-intolerant plants like tomatoes [66,69]. ...
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High efficacy LED lamps combined with adaptive lighting control and greenhouse integrated photovoltaics (PV) could enable the concept of year-round cultivation and become a feasible option even in the harsh climate of the Nordic countries. Meteorological satellite data of this region was analyzed in a parametric study to evaluate the potential of these technologies. The generated maps showed monthly average temperatures fluctuating from -20°C to 20°C throughout the year. The natural photoperiod and light intensity also changed drastically, resulting in monthly average daily light integral (DLI) levels ranging from 45-50 mol·m-2·d-1 in summer and contrasting with 0-5 mol·m-2·d-1 during winter. To compensate, growth room cultivation independent from outdoor conditions could be used in winter. Depending on the efficacy of the lamps, the electricity required for sole-source lighting at 300 µmol·m-2·s-1 for 16 hours would be between 1.4 and 2.4 kWh·m-2·d-1. Greenhouses with supplementary lighting could help start the cultivation earlier in spring and extend it further into autumn. The energy required for lighting highly depends on several factors such as the natural light transmittance, the light threshold settings and the lighting control protocol, resulting in electric demands between 0.6 and 2.4 kWh·m-2·d-1. Integrating PV on the roof or wall structures of the greenhouse could offset some of this electricity, with specific energy yields ranging from 400 to 1120 kWh·kWp-2·yr-1 depending on the region and system design.
... Toplam günlük ışık gereksinimi, bitki türlerine göre önemli oranda değişiklik gösterebilmektedir. Toplam günlük ışık gereksinimi değerleri; düşük olan bitkilerde (birçok ev bitkisi) 3-6 molˑm -2 gün -1 , orta olan bitkilerde (çoğu yıllık bitkiler) 6-12 molˑm -2 gün -1 , yüksek olan bitkilerde (çok yıllık bitkiler ve sebzeler) ise en düşük 12 molˑm -2 gün -1 değerlerinin dikkate alınması önerilmektedir (Mattson, 2015;Torres and Lopez, 2012). ...
... mol·m −2 gün −1 , 2.1-1.3 mol·m −2 gün −1 , 2.2-1.1 mol·m −2 gün −1 olarak belirlenmiştir. Sera bitkileri için en az olması gereken 10-12 mol·m −2 gün −1 ve en yüksek domates verimi için 20-30 mol·m −2 gün −1 günlük ışık birikimi önerileri (Dayıoğlu ve Silleli, 2012;Torres and Lopez, 2012;Mattson, 2015) dikkate alındığında, A ve B tipi ışık kaynaklarının söz konusu yerleşim sonuçlarının bu istekleri rahatlıkla karşıladığı yani yerleşim durumuna göre hem tam yapay hem de tamamlayıcı fotosentez aydınlatma uygulamalarında kullanılabileceği görülmektedir. C ve D tipi ışık kaynaklarının ise yalnızca tamamlayıcı fotosentez aydınlatma uygulamalarında kullanılabileceği söylenebilir. ...
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... Summer growing seasons in the Rocky Mountain West have highintensity sunlight, especially at higher elevations (Curtis and Grimes, 2004). Crops in high tunnels and greenhouses receive a lower daily light integral and reduced air movement compared with those in the field, which often results in significantly longer stems (Torres and Lopez, 2010;Wien, 2009;Wien and Pritts, 2009). The type of market and market demand will influence a grower's target stem length. ...
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The objective of this study was to determine best production practices for five different specialty cut flower species at an altitude of 7200 ft. Region-specific information about cut flower production is important because of unique environmental conditions. We grew five specialty cut flower species in two different growing environments: a greenhouse and a high tunnel. Flowers were grown year-round in the greenhouse and during late spring through fall in the high tunnels. We also used pinching as another production method for the potential increase in branching. The goals were to test the effects of species, growing environment, and pinching on the days from sowing to harvest, stem length, number of stems cut per plant, and marketable yield. Experiments were conducted at the University of Wyoming Laramie Research and Extension Center in Laramie, WY, to assess the potential for producing specialty cut flowers for local consumption. The species used in this study included ‘Princess Golden’ pot marigold ( Calendula officinalis ), ‘Lucinda Mix’ stock ( Matthiola incana ), ‘Double Mix’ strawflower ( Helichrysum bracteatum ), ‘Dara’ ornamental carrot ( Daucus carota ), and ‘Celway Mix’ cockscomb ( Celosia argentea ). Results showed significant species × environment and season interactions, indicating the importance of species and production practice selections. We successfully sold the cut flowers to the university student farm for community-supported agriculture shares and farm market sales, as well as to a local florist for use in floral arrangements. This study concluded that careful species selection for season and growing environment is essential for the successful integration of these niche cut flowers into current or future greenhouse and high-tunnel production in Wyoming.
... Potassium has influenced photosynthetic rate, stomatal conductance, water movements (turgor regulation and osmotic adjustment) and enzyme activation which affects adenosine triphosphate (ATP) production in plants(Chen et al., 2013). Subsequently, the ATP will regulate the rate of photosynthesis(Torres & Lopez, 2010). ...
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Gynura procumbens is an herbaceous plant. Despite the progressive reports on the pharmacological properties, many are overlooking at the importance of agronomic requirements, such as fertilization, to produce high phytochemical content which have not been conclusively concluded. The study was carried out to examine the effects of N and K interaction on physiological and phytochemical quality; to identify compositions of phytochemicals, and to determine marker compounds. Physiological and phytochemical attributes were recorded in three harvests of triplicate samples to exhibit the trend for plant quality, and statistically analyzed. Generally, N and K interaction have affected phytochemical content significantly (p<0.05) with stronger effect on physiological and biochemical attributes (p<0.01). The results have demonstrated that the following combination of fertilizer, 0 kg/ha N and 30 kg/ha K; and 90 kg/ha N and 0 kg/ha K are high and low, respectively affecting metabolite content in the plant. Lowest rate of N, moderate of K had produced significant phytochemical contents. Meanwhile, caffeic acid and kaempferol were demonstrated as marker compounds in this study. Thus, phytochemical content can be further established through the selection of appropriate N and K rates and proper abiotic stress interaction.
... The light environment needs to be optimized to ensure desirable growth and reduce electricity consumption in indoor CE systems. The effects of the light intensity or photosynthetic photon flux density (PPFD) on the growth of tomato seedlings (Fan et al., 2013;O'Carrigan et al., 2014) and mature fruiting plants (Dorais, 2003;Torres and Lopez, 2011;Hao et al., 2017) have been studied. In general, an increase in the PPFD or daily light integral (DLI) increases the biomass and flower developmental rate (Uzun, 2006;Fan et al., 2013;Gómez and Mitchell, 2015). ...
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Indoor growing systems with light-emitting diodes offer advantages for the growth of tomato seedlings through uniform and optimized environmental conditions which increase consistency between plants and growing cycles. CO2 enrichment has been shown to improve the yield of crops. Thus, this research aimed to characterize the effects of varied light intensities and CO2 enrichment on the growth, morphology, and production efficiency of tomato seedlings in indoor growing systems. Four tomato cultivars, “Florida-47 R,” “Rebelski,” “Maxifort,” and “Shin Cheong Gang,” were subjected to three different daily light integrals (DLIs) of 6.5, 9.7, and 13 mol m–2 d–1 with a percent photon flux ratio of 40 blue:60 red and an end-of-day far-red treatment of 5 mmol m–2 d–1. The plants were also subjected to three different CO2 concentrations: 448 ± 32 (400-ambient), 1010 ± 45 (1000), and 1568 ± 129 (1600) μmol mol–1. Temperature was maintained at 24.3°C ± 0.48/16.8°C ± 1.1 (day/dark; 22.4°C average) and relative humidity at 52.56 ± 8.2%. Plant density was 1000 plants m–2 until canopy closure. Morphological measurements were conducted daily to observe the growth response over time. In addition, data was collected to quantify the effects of each treatment. The results showed increases in growth rate with increases in the DLI and CO2 concentration. In addition, CO2 enrichment to 1000–1600 μmol mol–1 increased the light use efficiency (gDM mol–1 applied) by 38–44%, and CO2 enrichment to 1600 μmol mol–1 did not result in any additional increase on shoot fresh mass, shoot dry mass, and stem extension. However, the net photosynthetic rate obtained with 1600 μmol mol–1 was 31 and 68% higher than those obtained with 1000 and 400 μmol mol–1, respectively. Furthermore, the comparison of the light and CO2 treatment combinations with the control (13 mol m–2 d–1–400CO2) revealed that the plants subjected to 6.5DLI–1600CO2, 9.7DLI–1000CO2, and 9.7DLI–1600CO2 treatment combinations exhibited the same growth rate as the control plants but with 25–50% less DLI. Furthermore, two treatment combinations (13.0DLI–1000CO2 and 13.0DLI–1600CO2) were associated with the consumption of comparable amount of energy but increased plant growth by 24–33%.
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Carnarvon has a hot, semi-arid climate with high temperatures and solar radiation during spring–summer, which damages crops and limits the production season for the local vegetable industry. Protective cultivation is one of the promising approaches to mitigate these adverse weather conditions and avoid the resulting damage to vegetable crops. This study, which is part of the protected cropping research program for vegetable crops in Western Australia, was conducted to understand how the shade nets of a protective net house modify the microenvironment affecting the growth, physiology, and fruit yield of eggplants, a model vegetable crop. The eggplant crop was grown under four light regimes, i.e., three shade factors (11%, 21%, 30%) and the open field. There were three replicated blocks under each light regime and four eggplant varieties that were randomized within the replicated blocks. Other experimental conditions, e.g., fertilising, irrigation, pest, and disease management and other cultural practices were identical across light regimes. The results showed that shade nets created different microenvironments inside the net house, with a large variation in the light intensity, affecting photosynthetic-related traits. Eggplants grew taller and bushier and gave higher fruit yield under shade compared to the open field. Overall, our data suggest that the 21% shade net appeared to be the most suitable for growing eggplants during the autumn to early spring period in Carnarvon. The future perspective of protected cropping technology for vegetable crop production in Carnarvon is also discussed.
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The phenological responses of Capsicum annuum var. glabriusculum (Cag) plants were documented, tracking the seasonal climatic trend in the Sonoran Desert. Plants exhibited a relatively fast seasonal phenological transition in synchrony with fast shifts in solar radiation, air temperatures, relative humidity, and rainfalls. Plants developed under significant levels of shade throughout their phenological stages; however, the increase of sunlight penetration and rising air temperatures during the mid-winter period suggests an early photonic/thermal stimulation effect, which could drive the transition between dormancy and budburst. Early buds outbreak can occur in some individuals. First leaves development suggests a strategic phenological/ecophysiological transitional interruption can occur to cope with drought conditions during the spring period. During rainy summer-autumn plants fully grew either vegetative only or vegetative/reproductively. The CO2 assimilation curves in response to light suggest that plants are photosynthetically adapted to photonic flux in the low-intermediate range. Leave's diurnal gas exchange responded differentially under contrasting levels of sunlight, temperatures, and vapor pressure deficit, depending on the plant's phenological stage. Ecosystem-level dataset suggests that duration of air temperature thresholds and significant variation in precipitation peaks during seasons transition could drive subtle timeline shifts between succession/extension of phenological stages and consequently in the forest mass productivity.
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The growth and development of Achillea xmillefolium L. 'Red Velvet', Gaura lindheimeri Engelm. & Gray 'Siskiyou Pink' and Lavandula angustifolia Mill. 'Hidcote Blue' were evaluated under average daily light integrals (DLIs) of 5 to 20 mol·m-2·d-1. Plants were grown in a 22 ± 2°C glass greenhouse with a 16-h photoperiod under four light environments: 50% shading of ambient light plus PPF of 100 μmol·m -2·s-1 (L1); ambient light plus PPF of 20 μmol·m-2·s-1 (L2); ambient light plus PPF of 100 μmol·m-2·s-1 (L3); and ambient light plus PPF of 150 μmol·m-2·s-1 (L4). Between 5 to 20 mol·m-2·d-1, DLI did not limit flowering and had little effect on timing in these studies. Hence, the minimum DLI required for flowering of Achillea, Gaura and Lavandula must be <5 mol·m-2·d-1, the lowest light level tested. However, all species exhibited prostrate growth with weakened stems when grown at a DLI of about 10 mol·m-2·d-1. Visual quality and shoot dry mass of Achillea, Gaura and Lavandula linearly increased as DLI increased from 5 to 20 mol·m-2·d -1 and there was no evidence that these responses to light were beginning to decline. While 10 mol·m-2·d-1 has been suggested as an adequate DLI, these results suggest that 15 to 20 mol·m-2·d-1 should be considered a minimum for production of these herbaceous perennials when grown at about 22°C.
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A majority of commercial propagation of herbaceous ornamental cuttings occurs during the winter when the photosynthetic daily light integral (DLI) is relatively low. We quantified how the mean DLI influenced rooting and subsequent growth and development of two popular vegetatively propagated species, New Guinea impatiens (Impatiens hawkeri Bull.) and petunia (Petunia ·hybrida hort. Vilm.-Andr.). Three cultivars of each species were propagated under a mean DLI ranging from 1.2 to 10.7 molm-2d-1. Cuttings were rooted in a controlled greenhouse environment maintained at 24 to 25 8C with overhead mist, a vapor-pressure deficit of 0.3 kPa, and a 12-h photoperiod. Rooting and growth evaluations of cuttings were made after 8 to 16 d. In a separate experiment, rooted cuttings under DLI treatments were then transplanted into 10-cm containers and grown in a common greenhouse at 21 ± 2 8C under a 16-h photoperiod to identify any residual effects on subsequent growth and development. In both species, rooting, biomass accumulation, and quality of cuttings increased and subsequent time to flower generally decreased as mean propagation DLI increased. For example, root number of petunia 'Tiny Tunia Violet Ice' after 16 days of propagation increased from 17 to 40 as the propagation DLI increased from 1.2 to 7.5 molm-2d-1. In addition, cutting shoot height decreased from 6.3 to 4.5 cm, and root and shoot dry biomass of cuttings harvested after 16 days of propagationincreased by 737% and 106%, respectively. Subsequent time to flower for 'Tiny Tunia Violet Ice' from the beginning of propagation decreased from 50 to 29 days as propagation DLI increased from 1.4 to 10.7 molm-2d-1 regardless of the DLI provided after propagation. In New Guinea impatiens 'Harmony White', root and shoot dry weight of cuttings increased by 1038% and 82%, respectively, and subsequent time to flower decreased from 85 to 70 days as the propagation DLI increased from 1.2 to 10.7 molm-2d-1. These experiments quantify the role of the photosynthetic DLI during propagation on the rooting and subsequent growth and development of vegetatively propagated herbaceous ornamental cuttings.
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The photosynthetic daily light integral (DLI) dramatically increases during the spring when the majority of bedding plants are commercially produced. However, the effects of DLI on seedling growth and development have not been well characterized for most bedding plant species. Our objectives were to quantify the effects of DLI on growth and development of Celosia , Impatiens , Salvia , Tagetes , and Viola during the seedling stage and determine whether there were any residual effects of DLI on subsequent growth and development after transplant. Seedlings were grown in growth chambers for 18 to 26 days at 21 °C with a DLI ranging from 4.1 to 14.2 mol·m –2 ·d –1 . Average seedling shoot dry weight per internode (a measure of quality) increased linearly 64%, 47%, 64%, and 68% within this DLI range in Celosia , Impatiens , Tagetes , and Viola , respectively. Seedlings were then transplanted to 10-cm containers and grown in a common environment (average daily temperature of 22 °C and DLI of 8.5 mol·m –2 ·d –1 ) to determine subsequent effects on plant growth and development. Flowering of Celosia , Impatiens , Salvia , Tagetes , and Viola occurred 10, 12, 11, 4, and 12 days earlier, respectively, when seedlings were previously grown under the highest DLI compared with the lowest. Except for Viola , earlier flowering corresponded with the development of fewer nodes below the first flower. Flower bud number and plant shoot dry weight at first flowering (plant quality parameters) decreased as the seedling DLI increased in all species except for flower number of Tagetes . Therefore, seedlings grown under a greater DLI flowered earlier, but plant quality at first flowering was generally reduced compared with that of seedlings grown under a lower DLI.
Article
The photosynthetic daily light integral (DLI) dramatically increases during the spring when the majority of bedding plants are commercially produced. However, the effects of DLI on seedling growth and development have not been well characterized for most bedding plant species. Our objectives were to quantify the effects of DLI on growth and development of Celosia, Impatiens, Salvia, Tagetes, and Viola during the seedling stage and determine whether there were any residual effects of DLI on subsequent growth and development after transplant. Seedlings were grown in growth chambers for 18 to 26 days at 21 degrees C with a DLI ranging from 4.1 to 14.2 mol.m(-1).d(-1). Average seedling shoot dry weight per internode (a measure of quality) increased linearly 64%, 47%, 64%, and 68% within this DLI range in Celosia, Impatiens, Tagetes, and Viola, respectively. Seedlings were then transplanted to 10-cm containers and grown in a common environment (average daily temperature of 22 degrees C and DLI of 8.5 mol.m(-2).d(-1)) to determine subsequent effects on plant growth and development. Flowering of Celosia, Impatiens, Salvia, Tagetes, and Viola occurred 10, 12, 11, 4, and 12 days earlier, respectively, when seedlings were previously grown under the highest DLI compared with the lowest. Except for Viola, earlier flowering corresponded with the development of fewer nodes below the first flower. Flower bud number and plant shoot dry weight at first flowering (plant quality parameters) decreased as the seedling DLI increased in all species except for flower number of Tagetes. Therefore, seedlings grown under a greater DLI flowered earlier, but plant quality at first flowering was generally reduced compared with that of seedlings grown under a lower DLI.
Article
The daily light integral (DLI) is a measurement of the total amount of photosynthetically active radiation delivered over a 24-hour period and is an important factor influencing plant growth over weeks and months. Contour maps were developed to demonstrate the mean DLI for each month of the year across the contiguous United States. The maps are based on 30 years of solar radiation data for 216 sites compiled and reported by the National Renewable Energy Lab in radiometric units (watt-hours per m-2·d-1, from 300 to 3,000 nm) that we converted to quantum units (mol·m-2·d-1, 400 to 700 nm). The mean DLI ranges from 5 to 10 mol·m-2·d-1 across the northern U.S. in December to 55 to 60 mol·m-2·d-1 in the southwestern U.S. in May through July. From October through February, the differences in DLI primarily occur between the northern and southern U.S., while from May through August the differences in DLI primarily occur between the eastern and western U.S. The DLI changes rapidly during the months before and after the vernal and autumnal equinoxes, e.g., increasing by more than 60% from February to April in many locations. The contour maps provide a means of estimating the typical DLI received across the U.S. throughout the year.
Evaluating supplemental light for your greenhouse
  • P Fisher
  • C Donelly
  • J Faust
Fisher, P., C. Donelly and J. Faust. 2001. Evaluating supplemental light for your greenhouse. 24 February 2009. http://extension.unh.edu/Agric/AGGHFL/ OFAlight.pdf.
Technically speaking: Daily light integral defined
  • E Runkle
Runkle, E. 2006. Technically speaking: Daily light integral defined. Greenhouse Product News. 24 February 2009. www.gpnmag.com/articles/070_ gpn1106.pdf.
Ball Redbook: Crop Production
  • J E Faust
Faust, J.E. 2001. Light, p. 71−84. D.Hamrick, (ed.). Ball Redbook: Crop Production, Ball Publishing, Batavia, IL.
Technically speaking: Do you know what your DLI is? Greenhouse Product News 24
  • E Runkle
Runkle, E. 2006. Technically speaking: Do you know what your DLI is? Greenhouse Product News 24 February 2009. www.gpnmag.com/Do-You-Know-What-Your-DLI-Is-article7530.
Technically speaking: Light it up! Greenhouse Product News 24
  • E Runkle
Runkle, E. 2006. Technically speaking: Light it up! Greenhouse Product News 24 February 2009. www.gpnmag.com/articles/lightitupjuly2006.pdf. Species Average Daily Light Integral (Moles/Day)