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American Journal of Agricultural Science
2015; 2(5): 196-202
Published online September 20, 2015 (http://www.aascit.org/journal/ajas)
Keywords Lettuce Production,
Recirculating Hydroponic
System,
Tropical Greenhouse,
Growth and Yield,
Urban Vertical Garden
Received: July 28, 2015
Revised: August 29, 2015
Accepted: August 30, 2015
Lettuce Production in a Recirculating Hydroponic System*
Chito F. Sace1, Jaypee H. Estigoy
2
1CLSU Hydroponics and Aquaponics Technologies, Institute for Climate Change and
Environmental Management, Central Luzon State University, Science City of Muñoz, Nueva
Ecija, Philippines 2Agricultural Science and Technology School, Central Luzon State University, Science City of
Muñoz, Nueva Ecija, Philippines
Email address [email protected] (C. F. Sace), [email protected] (J. H. Estigoy)
Citation Chito F. Sace, Jaypee H. Estigoy. Lettuce Production in a Recirculating Hydroponic System.
American Journal of Agricultural Science. Vol. 2, No. 5, 2015, pp. 196-202.
Abstract A recirculating hydroponic system was constructed in an urban vertical garden to
determine the growth and yield of lettuce. The system used a 35-watt submersible pump to
lift the nutrient solution from the reservoir to the uppermost growing tubes which were
vertically configured to move the solution in circles. All lettuce seedlings were planted in
plastic cups containing non-soil media of coco peat, fine sand, ricehull and carbonized
ricehull and seated on growing tubes where thin film of nutrient solution pass through. The
system is enclosed in a tropical greenhouse that protects the plants from the elements.
Results showed that lettuce variety Carlo Rossa tolerated an environment beyond the
optimal and remained productive throughout the six growing seasons even at temperature
of 25 to 35 °C and relative humidity of 50 to 88 %. The taste and tenderness of the harvest
were highly acceptable to local consumers when harvested 30 days after transplanting even
when sold at P150.00 per kilogram. The system costs P50,000.00 and can accommodate
560 plants resulting to a plant density of 48.6 hills per square meter per cropping. The
average weight per plant was 48 g and the net weight was 26.6 kg per harvest or about 2.33
kg per square meter of greenhouse floor area. When adjusted to annual basis, a gross
income of P47,900.00 is obtained. The system has a total cost of P23, 994.00 per year
when fixed cost of P5,550.00 and operating cost of P18,444.00 were added. An annual net
income of P23, 906.00 was computed when total cost is subtracted from the gross income
while the annual gross margin was P29,456.00 when the total variable cost is deducted
from the gross income. Payback period, the length of time it will take for the investment to
return to its original cost, was 2.1 years when the initial cost was divided by the net
income. Unit price is only P57.80 per kg when the total variable cost is divided by the total
weight of lettuce. It is recommended to establish a high end market that will be willing to
pay a higher price in exchange of safe and sustained supply of quality harvest, increase
plant density, and optimize all inputs to maximize profit.
1. Introduction
The National Nutrition Month is being celebrated every July in the Philippines. The
celebration is led by the National Nutrition Council (NNC) since 1974 by virtue of
Presidential Decree No. 491 and is punctuated with various activities all aimed at
improving the nutritional status of Filipinos, particularly in preventing malnutrition and
*Portion of the research conducted in the project titled “Hydroponic System as Smart Farming Technique for Vegetable
Crops Production” at Central Luzon State University, Science City of Muñoz, Nueva Ecija, Philippines; funded by the
Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development
American Journal of Agricultural Science 2015; 2(5): 196-202 197
other non-communicable diseases (Gavilan, 2015; Crisostomo,
2014). The NNC’s main task is to craft an enabling policy-
making atmosphere by utilizing every plausible strategy and
approach in planning, implementation, monitoring and
evaluation, and surveillance for national and local applications
(Gavilan, 2015).
Under the umbrella of the Department of Health, NNC
works with other government agencies such as Food and
Nutrition Research Institute, Department of Social Welfare and
Development and the Department of Education (DepEd) in
launching nationwide media campaign. The OMG! (Oh My
Gulay! or Oh My Vegetables!), for example, was launched
with celebrities as role models to efficiently propel a paradigm
shift about vegetable consumption among younger generation.
Another program called the Pinggang Pinoy (Filipino Plate)
was also initiated to convey a model of an easy to understand
food guide for the consumption of right proportions of various
food groups (Crisostomo, 2014). Likewise, the DepEd issued
the Memorandum 191, series 2013 to implement Gulayan sa
Paaralan Program in all elementary and secondary schools
nationwide to address poverty and malnutrition and promote
vegetable production and consumption among school children
(DepEd, 2013).
The Philippine Council for Agriculture, Aquatic and Natural
Resources Research and Development of the Department of
Science and Technology (DOST-PCAARRD) also participated
in the celebration by embarking on programs called smarter
agriculture. Smarter agriculture involves the utilization of
advanced production systems, such as hydroponics and
aquaponics, as mitigation and adaptation techniques against
climate change aimed at increasing agricultural productivity in
urban and rural areas. A demonstration farm and experimental
station is being developed at Central Luzon State University,
Science City of Muñoz, Nueva Ecija where modules of
production are built for different scales of investment. The
station intends to develop technology packages for increased
production of high-value vegetables like tomato, melon,
cucumber, bell pepper, leafy vegetables and herbs in protected
structure. The station has a number of tropical greenhouses
that are used to demonstrate continuous production using
earth’s limited resources in limited footprint. Training, seminar
and workshop are conducted and several educational materials
are produced to promote the technologies. Today, the station is
frequently visited by students, educators, investors, farmers
and researchers from different institutions and agencies.
2. Materials and Methods
Lettuce (Lactuca sativa), considered one of the most
important salad crops in the Philippines, requires partial
shade to grow well in warm climates (Agri-Mixph, 2013;
DAFF, South Africa). Lettuce is a good source of vitamin
A, potassium, as well as several other vitamins and
nutrients (Barry, 1996). However, contaminated lettuce is
often a source of bacterial, viral and parasitic outbreaks in
humans, including Escherichia coli and Salmonella when
not carefully produced (Davis, and Kendall, 2014).
2.1. Seed Germination
Lettuce seeds, acquired from a reliable seed distributor,
were uniformly sown on styrofoam box seedbed containing
an equal ratio (1:1:1:1) of coconut peat, fine sand, rice hull
and carbonized rice hull as growing media. The seeds were
covered with thin layer of similar substrates and regularly
sprayed with hydroponic nutrient solution with an EC of 1.0
to 1.3 mS/cm. The technique provided high germination
percentage of about 80-90%.
Table 1. Description of the greenhouse.
Type of structure: Quonset-type
Classification: Tropical greenhouse for leafy vegetable production
Model: Household module
Dimension: 2.5 m high x 3.2 m wide x 3.6 m long
Sides and roof cover: Three layers of cover (insect-proof net, ultra-violet resistant plastic film and 60% gray net shading)
Metal frame: Galvanized iron pipe; Diameter =1/2-inch and 3/4-inch; Schedule 20
Fertigation unit: Submersible pump; 35-watt, AC
Growing systems: Growing tubes on vertical frame, side walls and horizontal frames
Type of system: Recirculating, allows nutrient solution to cascade from the uppermost growing tubes and down to the gravel beds and drain back
to the tank
2.2. Transplanting
Fourteen (14) days after emergence, the seedlings were
transplanted on perforated plastic cups which contain holes at
the bottom and side and were filled with the same mixture of
substrates used in the seedbed. The cups were placed on
individual cutouts of the growing tubes. Plants were watered
three times a day for three days. The system is kept running
with pump continuously lifting the nutrient solution allowing
the roots to avail of the nutrients.
2.3. Production System
A production system, enclosed in a tropical greenhouse
measuring 2.5 m high x 3.2 m wide x 3.6 m long, has frames
made from galvanized iron pipes bended and welded together
to form a Quonset-type structure (Figure 1). The structure has
three roof covers: the insect-proof net in the inner, the ultra-
violet-resistant plastic film in the middle and the gray woven
net shade on the outer that offer strength and improve
aerodynamics to withstand strong wind gust and heavy rain. A
198 Chito F. Sace and Jaypee H. Estigoy: Lettuce Production in a Recirculating Hydroponic System
footbath is installed at the entrance door to disinfect the
footwear (Bucklin, 2008).
The system is run by a 35-watt submersible pump that lifts
the nutrient solution to the uppermost layer of the growing
tubes. A vertical frame, the prototype that serves as laboratory
module, measuring 1.6 m high x 0.6 m wide x 0.8 m long lies
at the rear end of the structure. Below the frames are gravel
beds that measure 0.20 m deep, 0.50 m wide and 3.60 m long.
The system contains 560 plastic cups where lettuce plants were
transplanted. Table 1 provides more detailed description.
Figure 1. Schematic diagram of the greenhouse showing the components of the production system.
Five layers of growing tubes rest securely on the frame
(Figure 2a). The growing tubes which are made of 2-inch
diameter PVC pipes are interconnected by rubber hose
containing cutouts and where plastic cups containing
growing media are seated. The growing media is a mixture of
coconut peat, fine sand, rice hull and carbonized rice hull.
Each cup has holes on the side and bottom to permit capillary
action as well as to allow the plant roots to extend into the
duct and make contact with the nutrient solution. This is
achieved as thin film of the nutrient solution passes through
each tube allowing each plant to absorb the required elements
then flow by gravity to the next layer. Another two layers of
growing tubes hang on the left and right side walls while
three tubes of the same type also lie on the horizontally
frames in both sides of the greenhouse. Part of the solution
enters through a small tube of the float switch assembly
(Figure 2b). The assembly which controls the switching
mechanism of the low-head submersible pump that runs
intermittently every 15 minutes is fixed on the vertical frame.
Figure 2. The interior of the structure showing the growing tubes (a) and the float switch (b).
2.4. Nutrient Solution Management
The nutrient solution is the heart of hydroponics.
Maintaining its quality at optimal level is crucial because it
determines the success or failure of any system. Parameters
such as electric conductivity (EC), pH, temperature and
dissolve oxygen (DO) must be carefully managed (Jensen,
American Journal of Agricultural Science 2015; 2(5): 196-202 199
1991).
The nutrient solution was formulated and mixed in 1:1:98
ratio of Solution A, Solution B and water to make a 100-L
sulution in the reservoir. For this system with a 50-L
reservoir, 0.5 L of Solution A and 0.5 L of Solution B were
mixed with a 49 L of clean water. The volume of the nutrient
solution in the reservoir was maintained throughout the
growing periods by adding water and appropriate amount of
Solution A and Solution B every day.
A pen-type meter was used to maintain the following
values: EC - 1.0 to 1.3 mS/cm; pH - 5.8 to 6.8; DO > 5 ppm.
Sulfuric acid (H2SO4) was used to bring pH down and potash
to bring the pH up at optimal level.
2.5. Other Cultural Practices
Temperature inside and outside the production system
were monitored daily using a thermometer while a
mechanical hygrometer was used to monitor the relative
humidity. Unchlorinated water supply in the area which
originated from deepwell was used. After harvest, nutrient
solution was replaced and reused to fertilize open field crops
like dragon fruit, papaya and other herbs.
Whitefly, aphids and spider mites sometimes cause
damage to the crop. These pests were controlled easily by
alternately spraying mixture of extracts of capsicum and
allium with dishwashing liquid in water.
3. Results and Discussion
3.1. The Lettuce Variety
Lettuce (Lactuca sativa), just like other traditional leafy
vegetables, are the core in the dietary requirements of rural
and urban households in the Philippines. Traditional types of
lettuce were domesticated or having been cultivated for
several decades or centuries ago. This crop possibly
originated from Asia and was used in Egypt around 4,500
BC. During the era of Christianity, the Romans grew
different types of lettuce resembling the present romaine
cultivars. By 7th
century A.D, China was one of the earliest
countries to consume lettuce. Today, lettuce is quite essential
salad vegetable and garnishing for other food preparations
(DAFF, South Africa, 2010)
Carlo Rossa (Figure 3), a variety under Lollo Rossa, is a
popular heat tolerant variety tested in the locality. Forming a
circular crown of heavily frilled medium green leaves tipped
with a strong, warm red tinge, the variety is resistant to
bolting (Allied Botanical Corporation, 2012).
Figure 3. The quality of lettuce (variety Carlo Rossa) at harvest.
3.2. Environmental Factors
Lettuce is either grown in hydroponic or geoponic
systems both in the open field and in protected cultivation.
In tropical regions, greenhouse is used to protect the crop
from pest, severe solar radiation, heavy rain and strong
wind. Studies show that lettuce grows best in geoponic
system at pH ranging from 6.0 to 6.8 (Agri-Mixph, 2013)
and grows best at temperature ranging from 12 to 20 oC.
Some varieties can withstand heat better than others, high
temperature results to stunted growth and bitterness of
leaves. Other varieties are rarely grown to maturity as they
become bitter and unsalable because of bolting. In
temperate regions, controlling temperature extremes is the
primary reason for greenhouse cultivation (Hickman, 2010).
There are other advantages of growing lettuce in protected
cultivation, namely: improved quality and quantity of
harvest, reduced risk of pest infestation, minimal water
utilization, and efficient use of fertilizers (Zabeltitz, 1997).
The design of the system played a significant role in
sustaining the water and nutrient requirement of each crop.
Central to this is maintaining the water quality parameters
such as pH, EC, temperature and dissolved oxygen to
optimum levels. Using the principle of “one-pump rule”,
nutrient-enriched water is regularly recirculated into the
system from the uppermost growing tube allowing the same
200 Chito F. Sace and Jaypee H. Estigoy: Lettuce Production in a Recirculating Hydroponic System
to cascade to the tank. Evapotranspiration reduced the
volume to about 10-20% throughout the growing period and
needed to be replenished daily with water quality
parameters maintained to the optimum.
Water is one of the major limiting factors to crop
production and directly affects crop productivity of leafy
vegetables. Particularly in lettuce, water stress can easily
disfigure the leaf as a reaction to unsuitable environmental
condition. Leafy vegetables, such as lettuce generally
contains more or less 90% of water therefore it should be
sufficiently sustained for proper growth and development.
3.2.1. Temperature
Producing the crop in tropical countries, farmers are
normally confronted with high temperature and several
other environmental constraints brought by the changing
environment such as water scarcity and frequent occurrence
of pest and diseases. In the Philippines, lettuce grows at its
best and is productive during rainy season (June to October)
and windy season (November to February) with
temperatures ranging from 25 to 35oC. During dry season
(March to May), lettuce becomes less productive as
temperature is even higher ranging from 29-38oC. This
range is almost the same level inside the greenhouse
(AVRDC, 2006). In recent months, temperature even rise to
above 40oC.
Temperature was above the optimum requirement of crop
throughout the six growing seasons. Result showed that
temperature inside the greenhouse ranged from less than 25
to about 35oC while temperature outside the greenhouse
ranged from 25 to 33oC. The change in temperature causes
the solution to spike. It was recorded that the hottest was
during the latter part of November 2014 while coolest was
during mid-January 2015. The structural design of the
structure has minimum control over high temperature, a
common and perennial problem in tropical countries.
Temperature inside the greenhouse was higher than that of
the temperature outside (Figure 4). Nonetheless, the
shading net and outer layer roof cover reduce the amount of
solar radiation entering the greenhouse. The silver-gray net
is made of material proven to reduce solar radiation by as
much as 30-40% thereby preventing accumulation of heat.
As one of the major factors in lettuce production, the
temperature of the solution affected the dry mass of the
lettuce plant, while air temperature inside the greenhouse
significantly affected growth over time (Thompson et al.,
1998). Consequently, plants were harvested as early as it
reaches the edible leaf size to avoid bolting that cause bitter
taste. Results also revealed that during these months, lettuce
is still productive and profitable even in unsuitable
temperature.
Figure 4. Weekly average temperature from October 2014 to March 2015.
3.2.2. Relative Humidity
Relative humidity (RH), defined as the presence of water
vapor in the air to the greatest amount possible at the same
temperature, influenced the growth and yield of lettuce. It is
expressed as percentage of the ratio of the actual water
vapor pressure to the saturation vapor pressure. Scientists
recognize the indirect effect of RH on the leaf growth
where biochemical process happen resulting to cell
enlargement. The cells enlarge because of high turgor
pressure and less transpiration. Transpiration happens very
slowly when RH is high which may result in plant tissue
damage if in case environmental changes occur.
Results revealed that lettuce relatively met suitable RH
during November 2014 to February 2015 ranging from 50
to 88 % (Figure 5). Hence, lettuce was able to grow and
develop instead of spending energy to pump water into the
air.
American Journal of Agricultural Science 2015; 2(5): 196-202 201
Figure 5. Weekly average relative humidity from October 2014 to March 2015.
3.3. Potential Harvest
Lettuce was harvested every 30 days after transplanting.
Seedlings, which were propagated 12 days prior to
harvesting, were transplanted right after harvest to have a
continuous production. From October 2014 to March 2015, a
record of the weight of harvest was kept as shown in Table 2.
The harvest was sold at the local market at prevailing price.
Average weight was computed by dividing the total weight of
leaves by the total number of plants and was used as basis in
the computation of income and in the economic analysis.
The harvest was highest during the month of January with
28,003 g and was lowest during March with 26,003 g.
Temperature and RH were most favorable to the growth and
development of lettuce during January and was quite
unfavorable during the month March.
Table 2. Yield of lettuce during the growing seasons.
Months Yield, g Average yield, g
October 26,552 47.41
November 27,013 48.24
December 27,020 48.25
January 28,003 50.01
February 26,704 47.69
March 26,003 46.43
Average yield, g
48.00
3.4. Simple Cost and Return Analysis
The module has an initial cost of P50,000.00 and grows
560 plants resulting to a plant density of 48.6 hills per square
meter per cropping. Using the results of six growing seasons,
a net weight of 26.6 kg was obtained when harvested 30 days
after transplanting or about 2.33 kg per square meter of
greenhouse floor area. The module obtained an annual gross
income of P47,900.00 when produce is sold at P150.00 per
kg. A simple cost and return analysis was presented when
these data were adjusted to annual basis (Table 3).
A total cost of P23, 994.00 per year was determined when
fixed cost of P5, 550.00 and variable cost of P18, 444.00
were added. Average interest on investment and depreciation
comprised the fixed costs. Average interest on investment
was computed by multiplying the average of the initial cost
and salvage value by 12 % interest rate resulting to P3,300.00
per annum. Likewise, depreciation was computed by dividing
the difference of initial cost and salvage value by the life
span of 20 years. Unit price, which is computed by dividing
total variable cost by the total weight of lettuce per year, is P
57.78 per kg.
Table 3. The potential income, total fixed cost, total variable cost, total cost
of operation and cost and return analysis of the system.
ITEMS ANNUAL COST, P
A. Gross income 47,900.00
B. Fixed Costs
1. Average interest in investment 3,300.00
2. Depreciation 2,250.00
Sub-total 5,550.00
C. Variable Costs
1. Repair and Maintenance 996.00
2. Seeds 2,160.00
3. Labor 10,800.00
4. Electricity 1,464.00
5. Nutrient solution 624.00
6. Miscellaneous 2,400.00
Sub-total 18,444.00
D. Total Costs = (B + C) 23,994.00
E. Net income = (A – D) 23,906.00
F. Gross margin = (A – C) 29,456.00
G. Payback Period = (IC / E) 2.1 years
Results revealed that the net income was P23,906.00 when
the total cost is subtracted from the gross income while the
gross margin was P29,456.20 when the total variable cost is
subtracted from the gross income. The payback period or the
length of time it will take for the investment to return its
original cost is 2.1 years when the initial cost is divided by
the annual gross income.
202 Chito F. Sace and Jaypee H. Estigoy: Lettuce Production in a Recirculating Hydroponic System
4. Summary, Conclusions and
Recommendation
In summary, lettuce is still profitable to produce in the
locality using recirculating hydroponic system despite the
problems posed by high temperature and low relative
humidity. Growth and development of lettuce can also be
attained if water quality parameters are maintained in the
optimum. More income can be derived from the system when
sold at reasonably higher price.
It is recommended to establish a high end market that will
be willing to pay a higher price in exchange for safe and
sustained supply of quality harvest. Increasing plant density,
which is permissible in hydroponics, can also increase the
productivity of the system. Adding more growing tubes and
by hanging more plants in the structural frames will increase
the number of plant in the floor space of the structure.
Optimizing every material used in the construction of the
system will minimize its initial cost. Minimizing the inputs of
production will also maximize profit at the same time add
more value to water and fertilizer at the same time increasing
the productivity of the system.
Acknowledgement
The authors wish to acknowledge the Philippine Council
for Agriculture, Aquatic and Natural Resources Research and
Development of the Department of Science and Technology
for funding this research, the Central Luzon State University
for the support during the conduct of the research, the
members of the project team for the cooperation and
diligence.
References
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