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Use of hydroponics is increasing because of its ability to be used for year round vegetable production using an environmentally sustainable system. Management of solution pH is an important challenge in hydroponics systems. Our objective was to quantify the effects of various pH modifiers on growth and nutrient uptake of leafy greens and stability of nutrient solution’s pH. Lettuce, basil, and Swiss chard were transplanted into an Ebb and flow system, and nutrient solution pH was maintained using three different pH modifiers (pH Down, lime juice, or vinegar). The nutrient solution’s pH was maintained between 5.5 and 6.5. pH Down resulted in the most stable solution pH and required the least amount of product used when compared to lime juice and vinegar. The cost of using phosphoric acid or lime juice was greater than that of using vinegar. Vinegar reduced the yield of all crops in comparison to pH Down. When compared to pH Down, lime juice reduced the yield of basil and Swiss chard but not that of lettuce. Therefore, growers can use lime juice as an alternative to pH Down in lettuce production but not for basil and Swiss chard, while vinegar would not be recommended for any of the crops studied.
Content may be subject to copyright.
Journal of Horticultural Research 2019, vol. 27(1): 31-36
DOI: 10.2478/johr-2019-0004
*Corresponding author:
Hardeep SINGH*, Bruce DUNN, Mark PAYTON
Department of Horticulture and Landscape Architecture,
Oklahoma State University, Stillwater, OK 74078-6027, USA
Received: April 2019; Accepted: June 2019
Use of hydroponics is increasing because of its ability to be used for year round vegetable production
using an environmentally sustainable system. Management of solution pH is an important challenge in
hydroponics systems. Our objective was to quantify the effects of various pH modifiers on growth and
nutrient uptake of leafy greens and stability of nutrient solution’s pH. Lettuce, basil, and Swiss chard were
transplanted into an Ebb and flow system, and nutrient solution pH was maintained using three different
pH modifiers (pH Down, lime juice, or vinegar). The nutrient solution’s pH was maintained between 5.5
and 6.5. pH Down resulted in the most stable solution pH and required the least amount of product used
when compared to lime juice and vinegar. The cost of using phosphoric acid or lime juice was greater than
that of using vinegar. Vinegar reduced the yield of all crops in comparison to pH Down. When compared
to pH Down, lime juice reduced the yield of basil and Swiss chard but not that of lettuce. Therefore, growers
can use lime juice as an alternative to pH Down in lettuce production but not for basil and Swiss chard,
while vinegar would not be recommended for any of the crops studied.
Keywords: soilless culture, nutrients, lettuce, basil, Swiss chard, chlorophyll meter
By 2050, the human population is expected to
reach 8.9 billion (USAID 2004), and a major chal-
lenge for the increased population will be maintain-
ing the supply of fresh produce to ensure nutrient-
rich diets. Hydroponic or soilless production could
be an important solution to this problem because of
its higher yields and more nutritious food when
compared to soil production (Skagg 1996). Hydro-
ponics can be defined as a technique of growing
non-aquatic plants without soil in a nutrient solu-
tion with or without soilless substrate (Arancon et
al. 2015). Maintaining an adequate nutrient solu-
tion and pH level are often cited as major obstacles
to hydroponic production (Steiner 1961). Frick and
Mitchell (1993) indicated that pH of a hydroponic
nutrient solution fluctuates because of the unbal-
anced anion and cation exchange reaction with
roots and there is no buffering capacity in hydro-
ponics as in soil.
Plant essential nutrient availability varies with
pH. According to Resh (2004), slightly acidic pH is
optimum for hydroponic production because iron
(Fe), manganese (Mn), calcium (Ca), and magne-
sium (Mg) may form precipitates and become una-
vailable at pH above 7. Islam et al. (1980) reported
that at higher pH, the amount of Fe, Mn, Mg, potas-
sium (K), and Ca increased in the plants, but these
elements were not translocated to the shoot but in-
stead remained stored in the roots. Bugbee (2003)
also reported that availability of K and phosphorus
(P) is slightly reduced in a nutrient solution with
high pH. Dyśko et al. (2008) also reported that the
increase in nutrient solution’s pH led to the decrease
in available P for hydroponic production of tomato
(Solanum lycopersicum L.). Chen et al. (2016) also
reported a difference in nutrient uptake of lettuce
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32 H. Singh et al.
with solution pH when using wood vinegar.
Hochmuth (2001) recommended a nutrient solu-
tion’s pH of 5.5–6.5 for greenhouse hydroponic
production, whereas Resh (2004) recommended
a pH of 5.86.4. Ahn and Ikeda (2004) also re-
ported a pH of 57 as optimum for hydroponic cul-
tivation of Chinese chive (Allium tuberosum Rot-
tler ex Spreng.). Whipker et al. (1996) various
studies examining optimum pH for hydroponic let-
tuce (Lactuca sativa L.) production reported a de-
crease in leaf area, shoot dry weight, leaf length
and width, and stomatal conductance because of
the exposure to a suboptimal solution pH.
There are various chemicals that can be used
to lower the pH of a nutrient solution in hydropon-
ics. Burleigh et al. (2008) recommended the use of
citric acid (lime juice), acetic acid (vinegar), nitric
acid, phosphoric acid, and sulfuric acid for lower-
ing pH of the water used for plant cultivation.
Chen et al. (2016) also reported that pyroligneous
acid (wood vinegar) can be used for hydroponic
cultivation of lettuce at a rate of 0.25 ml·dm-3
while evaluating different strengths of wood vine-
gar as a pH buffer. Frick and Mitchell (1993) com-
pared the use of 2-(N-morpholino)ethanesulfonic
acid (MES) buffer and Amberlite DP-1 (cation-ex-
change resin beads, 1650 wet mesh, 8.1 mEq·g-1)
for stabilizing the pH of nutrient solution for the
production of mustard (Brassica juncea L.). The
concentration of chemicals used for pH stabiliza-
tion can also affect plant growth. Stahl et al.
(1999) used different concentrations of MES for
hydroponic culture and concluded that plant
growth was affected with increasing concentra-
tions. Stabilizing the pH of a nutrient solution is
necessary for optimum crop productivity in hydro-
ponics (Frick & Mitchell 1993). Identifying
a more economical and readily available product
for reducing the pH of the solution without reduc-
ing the crop yield would be beneficial to growers
(Kirimura & Inden 2005). Therefore, the objective
of this study was to evaluate the use of lime juice,
vinegar, and a commercial pH buffer (pH Down) as
pH modifiers in hydroponics and their effect on
plant growth, chlorophyll content, and nutrient up-
take of leafy greens.
Plant material and growth conditions
The research was conducted at the Department of
Horticulture and Landscape Architecture Research
Greenhouses in Stillwater, OK, under natural photo-
periods. Temperature was set at 21 °C/18 °C day/night
with a photosynthetic photon flux density (PPFD)
range of 600–1,200 μmol·m-2·s-1 at 1,200 HR.
Seeds of red lettuce ‘Oscarde’, basil (Ocimum basil-
icum L. ‘Citrus’) and Swiss chard (Beta vulgaris L.
‘Magenta Sunset’), were obtained from Johnny’s
Selected Seeds (Winslow, ME). Seeds were sown in
1.5 cm3 rockwool starter cubes (Gordan, Milton, ON)
on 2 February 2017. A styrofoam sheet was used to
support the plants, and 5 cm diameter slots were
drilled into the sheet with a spacing of 28 cm × 28 cm.
Upon obtaining two true leaves (March 6, 2017),
plants were transplanted into 5-cm net pots on Ebb
and flow tables (Gro Master, Maple Park (Virgil), IL).
Plants were randomly assigned to 1 of 30 net pots on
each of 3 tables resulting in 10 replicates of each crop
species per table. Each table was randomly as-
signed one of the three pH modifier treatments:
white vinegar (5% acidity; Wal-Mart Stores Inc.,
Bentonville, AR), lime juice (1.06 g·oz-1 citric
acid; Dr. Pepper Snapple Group, Plano, TX), and
pH Down (General Hydroponics, Santa Rosa, CA).
The lime juice was diluted to reach a pH of 2.5
similar to the other two products. The plants were
harvested 30 days after transplanting. The entire
experiment was repeated three times with planting
also occurring on 20 March and 25 April 2017 and
transplanting occurring on 25 April and 3 June
2017 for the second and third runs, respectively.
Fertilizers and EC
The nutrient solution was designed using a commer-
cially available soluble fertilizer (Peters 5-5.2-21.6,
J.R. Peters Allentown, PA), calcium nitrate (Amer-
ican Plant Products), and local tap water (EC =
0.5 mS·cm-2, pH = 7.8). Initial solutions were pro-
duced using manufacturer recommendations of
147.41 g·dm-3 of Peters and 97.52 g·dm-3 of cal-
cium nitrate. The hydroponics system had
a 141.4 dm3 of tank capacity and was circulated us-
ing a 189 dm3·min.-1 pump (Wayne, Harrison, OH).
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pH modifiers affect lettuce, basil, and Swiss chard 33
The EC and pH of the solution were measured every
other day using a pH/EC meter (Hanna Instruments,
Woonsocket, RI). The EC of the nutrient solution
was checked every other day to maintain the EC at
1.52.5 ds·m-1 and the pH at 5.56.5 by adding fer-
tilizer and pH solution.
Data Collection
At the end of the study, data were collected on fresh
shoot weight and dried shoot and root weight (plants
cut at substrate level and dried for 2 days at
56.6 °C). Three leaves (top, middle, and bottom)
from each plant were scanned using a SPAD-502
chlorophyll meter (SPAD-502, Konica Minolta, Ja-
pan) at the time of harvest. Dried shoot samples
were analyzed for nitrogen content by the Soil, Wa-
ter and Forage Analytical Laboratory (SWFAL) at
Oklahoma State University, using a LECO TruSpec
Carbon and Nitrogen Analyzer (LECO Corporation,
St. Joseph, MI).
The experimental design was a split-plot design
with 3 replications of 10 individual replicates per
species per run; Factors were pH-lowering products
(three levels) and species (three levels). Data were
subjected to an analysis of variance (ANOVA) us-
ing PROC MIXED with the LSMEANS statement
and DIFF option within the SAS/STAT software,
version 9.4 (SAS Institute, Cary, NC). Tests of sig-
nificance are reported at the 0.05, 0.001, and 0.0001
levels. Treatment means were separated using
Fisher’s protected least significance difference
(LSD) method. Statistical analyses were conducted
for each crop separately.
Effect of different pH products on nutrient solu-
tion’s pH
Nutrient solution’s pH increased on a near-liner
trend for all three modifiers; however, pH Down ap-
peared to plateau around a pH of 6.7 starting around
25 days (Fig. 1). The pH was in the required range
(5.56.5) throughout the growth cycle for treat-
ments using phosphoric acid, whereas for treat-
ments using lime juice and vinegar, the pH reached
7.5 at harvest (Fig. 1). Across the three experimental
runs, the total amount of lime, vinegar, and pH
Down used per run was 6,000 ml; 8,000 ml; and
600 ml, respectively.
Effect of different pH products on growth and
chlorophyll content of lettuce, basil, and Swiss
The fresh weight and dry shoot weight of lettuce
were significantly lower with vinegar than with the
other treatments, while there was no significant dif-
ference between lime juice and phosphoric acid (Ta-
ble 1). There was no significant difference in dry
weight of lettuce roots among the treatment groups.
The SPAD values were lowest for lime juice, and
there was no significant difference between vinegar
and phosphoric acid (Table 1).
The fresh and dry shoot weight of basil was
significantly greater for phosphoric acid than other
pH modifier treatments. The dry root weight of basil
was significantly lower for vinegar than other treat-
ments, whereas no significant difference was ob-
served between lime juice and phosphoric acid. The
SPAD values were significantly greater for phos-
phoric acid than for lime juice or vinegar (Table 2).
The fresh and dry shoot weight of Swiss chard
was greatest for plants grown with phosphoric acid
(Table 3). The dry weight of Swiss chard roots was
lowest using vinegar, whereas no significant differ-
ence was observed between among lime juice and
phosphoric acid. No significant difference was ob-
served for SPAD values among all three treatments
of Swiss chard (Table 3).
Effect of different pH products on nutrient con-
tent of lettuce, basil, and Swiss chard
Nitrogen (N) and K contents for lettuce and basil
were significantly lower for the lime and vinegar
treatments when compared to the phosphoric acid
treatment (Table 4). This corresponded to lower
SPAD values in both lime- and vinegar-treated nu-
trient solution when compared to that treated with
phosphoric acid. There was no significant differ-
ence in the P content among the different treatments
for either lettuce or basil; also, there was no signifi-
cant difference in N or K content among treatments
for Swiss chard (Table 4). Plant micronutrient con-
tent was not affected by pH buffer treatment (data
not presented).
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34 H. Singh et al.
Fig. 1. Nutrient solution’s pH before adjustment during the production of lettuce ‘Oscarde’, basil ‘Citrus’, and Swiss
chard ‘Magenta Sunset’
Table 1. Effects of different pH modifiers on ‘Oscarde’ lettuce growth and chlorophyll content after 30 days in Ebb
and flow system (n = 30)
Shoot FW (g)***z
Shoot DW (g)**
Root DW (g)NS
pH Down
235.9 ay
7.7 a
0.7 a
22.2 a
Lime juice
210.8 a
7.8 a
0.8 a
20.5 b
116.7 b
5.7 b
0.7 a
22.6 a
z indicates significant at or non-significant (NS) at *p ≤ 0.05, **p ≤ 0.001, or ***p ≤ 0.0001
y LS means within a column followed by same lowercase letter are not significantly different by pairwise comparison in mixed
model (p ≤
Table 2. Effects of different pH modifiers on ‘Citrus’ basil growth and chlorophyll content after 30 days in Ebb and
flow system (n = 30)
Shoot FW (g)***z
Root DW (g)*
pH Down
293.0 ay
4.2 a
26.0 a
Lime juice
213.6 b
4.3 a
24.5 b
151.8 c
3.3 b
23.6 b
Note: see Table 1
Table 3. Effects of different pH modifiers on ‘Magenta Sunset’ Swiss chard growth and chlorophyll content after 30
days in Ebb and flow system (n = 30)
Shoot FW (g)**z
Root DW (g)*
pH Down
187.7 ay
1.4 a
42.6 a
Lime juice
118.8 b
1.0 a
42.1 a
50.1 c
0.3 b
42.0 a
Note: see Table 1
Table 4. Effects of different pH modifiers on macronutrients element of lettuce ‘Oscarde’, basil ‘Citrus’, and Swiss
chard ‘Magenta Sunset’ (n = 3)
Nitrogen (%)
Phosphorus (%)
Potassium (%)
Swiss chardNS
Swiss chardNS
Swiss chardNS
pH Down
4.8 ay
5.2 a
4.3 a
0.7 a
1.3 a
0.4 a
6.2 a
0.8 a
2.1 a
Lime juice
4.4 b
4.2 b
4.5 a
0.7 a
1.3 a
0.4 a
6.0 b
0.6 b
2.2 a
4.8 a
4.2 a
4.1 a
0.7 a
1.3 a
0.5 a
6.1 b
0.7 b
2.1 a
Note: see Table 1
1 8 15 22 29
Lime Vinegar pH Down
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pH modifiers affect lettuce, basil, and Swiss chard 35
The authors hypothesize that the initial delay
in pH increase may be because the nutrient uptake
was less during the first week because of the small
size of the plant as well as a smaller leaf surface area
for transpiration of water. During the second week,
as the plants grew, more nutrients and water were
taken up. This may have led to an uneven uptake of
anions and cations, which is one of the causes of pH
change in a nutrient solution (Frick & Mitchell
1993). Chen et al. (2016) also reported that pH was
more stable during the first week of the growth cy-
cle but increased thereafter. In contrast to the results
of the present study, Lee and Lee (2006) reported
that because of balanced nutrient uptake during the
growth cycle, the nutrient solution pH remained sta-
ble during hydroponic production of leafy greens.
Because our water pH is alkaline (pH 7.8), adding
water to replenish levels in the tank increased the
pH. According to Sinclair and Eny (1946), juices
such as lemon juice consisting of citric acid can also
be used as an organic buffer to resist changes in the
pH when hydrogen or hydroxyl ions are added. In
this study, citric acid alone was only effective for
a day then the pH increased steadily, whereas with
pH Down, which also contains citric acid, ammo-
nium dihydrogenorthophosphate, and phosphoric
acid, the pH level did not fluctuate as rapidly and
stabilized at the end.
The color of leafy green vegetables is an im-
portant attribute affecting consumer preference (Ali
et al. 2009). Chlorophyll meters can be used to esti-
mate the greenness of leafy green vegetables as Col-
onna et al. (2016) used a SPAD meter to estimate
nitrogen (N) content of leaves as a nondestructive
method. Singh et al. (2019) reported that SPAD val-
ues ranged from 17 to 28 for different cultivars of
lettuce, which corresponded with our values, but
found ‘Oscarde’ to have a greater SPAD value. The
lower SPAD values for basil treated with lime juice
and vinegar corresponded to visual observations of
chlorosis and lower tissue N content. Chen et al.
(2016) found that use of wood vinegar at high con-
centrations (1 ml·dm-3) in hydroponic lettuce pro-
duction may lead to decreased nitrate-N uptake,
photosynthesis rate, and chlorophyll content.
In contrast, the lower SPAD values for lettuce
plants treated with lemon juice did not show evi-
dence of chlorosis, which may be the result of using
a red leafed cultivar.
Generally, inorganic acids such as nitric acid,
sulfuric acid, and phosphoric acid are used for re-
ducing and stabilizing the nutrient solution’s pH in
hydroponic production. This may also affect the nu-
trient composition of the solution as nitric acid may
contribute to the nitrate form of N and sulfuric acid
may contribute to sulfate ions and it would be hard
for a normal grower to calculate the amount of nu-
trients added every time the pH buffer is added
(Chen et al. 2016). Lei et al. (2004) reported hydro-
ponic vegetables to be higher in nitrate concentra-
tion as compared to soil grown vegetables, which is
harmful for human consumption. Greater leaf nitro-
gen and potassium values were observed for ‘Os-
carde’ and ‘Citrus’, which is not unexpected for pH
Down containing additional ammonium and phos-
phates. The additional nitrogen was unexpected for
vinegar, which is derived from ethanol to produce
acetic acid. Kirimura and Inden (2005) reported that
using safe, natural, and less-expensive acidic mate-
rial is more beneficial for hydroponic production as
compared to inorganic acids. This contradicts what
we found, as vinegar and lime juice reduced the plant
growth for ‘Citrus’ and ‘Magenta Sunset’ and re-
duced the plant quality in ‘Oscarde’ compared to pH
Down. The effect of lime juice and vinegar on basil
and Swiss chard may be due to the use of too high of
concentrations to maintain a desirable pH level.
From the results of the present experiment, lime
juice or pH Down can be used as a pH modifier for
hydroponic production of ‘Oscarde’ as chlorosis is
not prominent in red cultivars. For hydroponic pro-
duction of basil, only pH Down should be used, be-
cause the use of lime juice and vinegar leads to lower
SPAD values (chlorosis), less N uptake, and reduced
growth. For Swiss chard, pH Down would be recom-
mended for greater growth. For all three species, pH
Down had lower production costs of $2.60 compared
to $8 and $26.40 for vinegar and lime juice, respec-
tively, and had a greater affect at maintaining the pH.
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36 H. Singh et al.
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organic acids, concentrations, combination with
other buffering compound, or different cultivars of
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... The electrical conductivity (EC) and pH of nutrient solutions appear to affect the growth of some crops (e. g., Wu et al., 2004;Dewir et al., 2005;Samarakoon et al., 2006;Zhao et al., 2013;Singh et al., 2019). With regard to environmental effects, we already have shown that the medicinal plant Pinellia ternata Breit. is affected by the hydraulic conditions surrounding the corm (Eguchi et al., 2014), and the temperature surrounding the plant (Eguchi et al., 2016(Eguchi et al., , 2019. ...
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Medicinal plants (Pinellia ternata Breit.) were cultivated under four nutrient solution conditions, namely a pH of 4 and electrical conductivity (EC) of 2.2 mS cm⁻¹, pH of 4 and EC of 1.2 mS cm⁻¹, pH of 6 and EC of 2.2 mS cm⁻¹, and pH of 6 and EC of 1.2 mS cm⁻¹. Plants were grown for 15 weeks in phytotron glass rooms controlled at an air temperature of 25℃ and a relative humidity of 70%. The leaf number per plant was measured every week, the leaf chlorophyll content (SPAD) was measured at 100 d after planting, and the corm yield and the effective ingredient, namely araban, content in the corm were evaluated after 15 weeks of cultivation. No clear effects of the nutrient solution EC and pH on the corm growth, the corm quality, and leaf chlorophyll content were not observed in this experiment. The EC and pH of the nutrient solution will not affect the productivity of the P. ternate in the ranges of EC 1.2–2.2 mS cm⁻¹ and pH 4–6, respectively.
... The fluctuations of the pH were recorded in hydroponic system using CDPC matrix was studied and shown in Figures 3a and 3b. The recirculation of the hydroponic solution was continued to maintain the constant availability of nutrients and pH stabilisation [20]. The buffering was practiced using phosphoric acid and potassium carbonate and the pH was varied between 5.5 and 6.5 throughout the experimental period of 58 days in cycle-1. ...
In this research study, the feasibility of renewable energy based green house was investigated for sustainable food production under arid climatic conditions. The novel hybrid biomass based matrix (Coco Date Palm Coir matrix), was synthesized from locally available date palm tree fibers and coconut coir. The characterization of the matrix was done in terms of bulk density (0.09 g/cc), particle density (0.23 g/cc), porosity (61%), moisture content (37.4%) and water holding capacity (65.6%). The hydroponic system based greenhouse employing evaporative cooling based climate control technique is used for the identification and application of novel plant growth matrix for the successful demonstration of plant growth. The experimental trials were conducted over the one-year period with dedicated cycles with average 7-8 weeks duration. The experiments conducted verified the growth of Lettuce over two cycles and the plant growth rate and wet biomass are recorded and compared. The growth of the plant attained at the end of week 5 was 175 mm and the maximum growth of 293 mm at the end of 58 days.
... In comparison, the commercial fertiliser treatment tended to have the lowest pH readings (pH < 7; Fig. 6). Many leafy vegetables prefer a slightly acidic pH (Singh et al., 2019), and the pH in the BSF biochar treatment may be too high for the plants to tolerate. The high pH of the BSF biochar treatment may be a result of its high calcium content (7% DM; Table 1). ...
Anaerobic digestion produces large quantities of digestate as a by-product, which can potentially be applied as an organic fertilizer, but untreated anaerobic digestate (AD) may contain phytotoxins and the large volume of AD makes transportation and storage difficult. This study explored two relatively inexpensive processing methods to improve the agronomic performance of AD as a fertilizer via vegetable cultivation experiments. We first investigated the effect of dilution on AD’s performance using four leafy vegetables (Chinese spinach, water spinach, Chinese cabbage and lettuce). The optimal concentrations of the AD were 20–40% (v/v in 250 mL applications per single-plant pot) for all four vegetables based on shoot fresh weight and comparable to the control treatment using commercial fertilizer. AD application also introduced Synergistetes bacteria into the growing medium, but the overall bacterial diversity and composition were similar to those of the control treatment. Considering the nutrient separation in the liquid and solid fractions of AD and the need to reduce the volume, we then experimented with the recovery of nutrients from both the liquid and solid fractions by filtering AD using two types of wood-based biochar (100 g biochar: 1 L AD) before applying the AD-biochar residues as side dressing at 1% (w/w). Both types of biochar achieved yields comparable to the treatment using a commercial fertilizer for the three vegetables tested (kale, lettuce and rocket salad). Our results show that dilution and biochar filtration can improve the agronomic performance of AD, making it a sustainable substitute for commercial fertilizer.
This paper presents the study to determine the correlation of factors considered in developing a temperature control system that remotely controls the heating and cooling process of a hydroponic nutrient solution (HNS). The system incorporates the use of the Internet of Things (IoT), to remotely monitor, control, and acquire data. The ESP32 is used to provide IoT connectivity through the Blynk application. The temperature measurements were collected using the DS18B20 temperature sensor. The number of Peltier modules utilized for both heating and cooling cores varies from 1 to 4 units, as well as the volume of solution employed, varies between 1000 ml, 1500 ml, and 2000 ml, respectively. The heating and cooling performances were evaluated by determining the thermal equilibrium temperature meanwhile the correlation was analyzed using a fit regression model. The highest and lowest temperature recorded are 67.36 °C and 11.88 °C, respectively, with the uses of 4 Peltier modules as the temperature regulation core. Furthermore, the result reveals that the number of Peltier modules factor has significant affect (P < 0.05) on both of the heating and cooling capabilities of the system meanwhile the volume of the HNS factor is only significant for cooling performance (P = 0.023) compared to heating performance (P = 0.205). The correlation of the factors is represented by the regression model.KeywordsTemperature controlThermoelectric PeltierRegression analysisInternet of ThingsHydroponic nutrient management
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Rössler systems are introduced as prototype equations with the minimum ingredients for continuous time chaos. These systems are made up of three nonlinear ordinary differential equations that define a continuous-time dynamical system with chaotic dynamics due to the attractor's fractal features. Recently, the study on dynamics of fractional-order Rössler systems is attracting a lot of attention. In this study, the Rössler system of fractional order was numerically investigated. The existence, equilibrium points and their stability are also studied. The system is considered in the sense of Caputo fractional derivatives. In addition, an Adams-type predictor-corrector (ATPC) procedure is applied to the solutions of the system. The numerical result of the experiment shows that the system undergoes Hopf bifurcation for certain values. The result shows that selecting an appropriate value for the parameter can determine the stability of the region of our model. In conclusion, the study shows that the fractional order is very much stable than the integer order.KeywordsRössler systemStability analysisBifurcation analysisFractional order
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In this book, we have a publication: T.A. Nasibova, E.A. Garaev, G.R. Zeynalova, D.S. Gafarova, S.A. Pashayeva, N.S. Huseynova. Evaluation of heavy metals in Peganum harmala seeds.
Conference Paper
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The aim of this research was to compare the chemical composition and other characteristics of two liquid organic fertilisers - biogas digestate and pig slurry. Variations in chemical composition of tested fertilisers might have been caused by the use of animal feeding stuffs in pig farms and their quality. Nitrogen is one of the main factors shaping both soil fertility and crop productivity. Ntot and N-NH4 concentrations were lower in anaerobic digestate rather than in pig slurry. Therefore, the use of digestate fertilisers may require more labour force and higher energy costs as a result of a higher fertilisation rate. The forms of digestate Corg had shown a high level of humification, which may have a positive impact on soil. Keywords: liquid anaerobic digestate, pig slurry, nutrients.
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The biofloc technology (BFT) was proposed as an alternative to the conventional extensive and semi-extensive aquaculture production systems. In terms of expansion, conventional systems face serious challenges such as competition for land and water and environmental regulations related to discharge of effluents which contain excess organic matter, nitrogenous compounds and other toxic metabolites that might compromise the adjacent culture areas and boost the spread of disease (Browdy et al. 2012). Currently, BFT is used in the cultivation of commercial species such as penaeid shrimp and tilapia (Figure 1), and more recently, as a management tool during early cultivation during nursery phases. In recent times, as the aquaculture industry has faced diverse issues, in terms of diseases and reduced production yields, BFT was considered (and still is) the new “blue revolution”(Stokstad 2010). Such system originated in the 1970s for shrimp at the French Research Institute for Exploitation of the Sea (IFREMER), located in Tahiti, and in partnership with private companies
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Nutrient-film technique (NFT) trials were conducted to quantify the effect of two different water-soluble hydroponic fertilizers (5N–4.8P–21.6K and 5N–5.2P–21.6K) on different cultivars of lettuce ( Lactuca sativa ), basil ( Ocimum basilicum ), and swiss chard ( Beta vulgaris ). Results indicated swiss chard yield was affected only by cultivars, with Fordhook Giant producing the greatest fresh weight across fertilizer treatments. For lettuce production, interaction between fertilizers and cultivars was significant. ‘Mirlo’ and ‘Rubysky’ had greater growth compared with other cultivars in both fertilizers, whereas Dragoon performed well using 5N–4.8P–21.6K, but not 5N–5.2P–21.6K. For basil, dry weight production showed a significant interaction between fertilizers and cultivars. ‘Largeleaf’ produced greater dry weight with 5N–4.8P–21.6K, whereas ‘Lemon’ produced greater dry weight with 5N–5.2P–21.6K. For nutrient concentration of leaves, the concentrations were within the recommended range for lettuce when fertilized with 5N–5.2P–21.6K. Nutrient concentrations varied by nutrient from the recommended range for basil, but there was no significant difference between fertilizers. For swiss chard, the nutrient concentrations were in the recommended range and there was no difference between fertilizers. Therefore, growers may need to use more than one type of fertilizer for different lettuce and basil cultivars for optimum production, whereas swiss chard cultivars can be selected based on yield regardless of fertilizer.
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Greenhouse experiments with tomato were conducted in the years 2004-2006. The aim was to study the effect of nutrient solution pH on the availability of phosphorus in soilless culture of tomato. Tomato plants were grown on mats made of shredded rye straw, and on slabs of peat and rockwool. The plants were fertilized with a standard nutrient solution of different pH: 4.5, 5.0, 5.5, 6.0 and 6.5. Such different pH levels of the nutrient solution used in soilless culture modified the pH of the root growth zone. This effect was more evident in rockwool than in the organic media (especially straw). The phosphorus content in the root zone was closely associated with the pH value of the supplied nutrient solution and the kind of growing medium. Considerably lower concentrations of phosphorus were recorded in the organic media (straw, peat) than in rockwool. As the pH level of the nutrient solution increased, so did the pH of the root zone, whereas the amount of available P-PO4 decreased. The course of these changes was similar in all the substrates. However, the dynamics of the changes was weaker in the organic media. With an increase in the pH of the nutrient solution, the average phosphorus content in tomato leaves decreased. The P-PO4 concentration was higher in the leaves of tomato plants growing in rockwool compared to those in the organic media. A significantly higher marketable yield was obtained from tomato plants cultivated in rockwool than in the organic media. For all the growing media, the highest yield of tomatoes was obtained after feeding the plants with the nutrient solution of pH 5.5.
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A comparison was made to investigate the effects of two potting methods: coconut husk/ sphagnum moss and a plastic forestry tube with a peat-based medium (Sunshine® mix #1, Sungro Horticulture, Agawam, MA, USA), on the growth and yield of Romaine ‘Ridgeline’ and Buttercrunch ‘UH Manoa’ lettuce (Lactuca sativa) using a non-circulating hydroponics system. Two-week old lettuce seedlings were transplanted into 5 cm holes, 20 × 30 cm apart on polystyrene bead boards fitted on top of a 0.6 m wide, 1.2 m long and 25 cm deep hydroponics tanks. A standard hydroponics nutrient solution was prepared using Chem Gro® (Hydro-Gardens, Colorado Springs, CO) (8-15-36 + micronutrients), calcium nitrate [Ca(NO3)2] and magnesium sulfate (MgSO4). Each tank contained either one lettuce variety, replicated 12 times in completely randomized design. Growth and yields significantly increased in both lettuce varieties grown in coconut husk/sphagnum moss plugs which were attributed by their relatively greater water holding capacities and a more favorable media that allowed better root growth.
The nutritional composition of ten leafy vegetables (chicory, green lettuce, lamb’s lettuce, mizuna, red chard, red lettuce, rocket, spinach, Swiss chard, and tatsoi) and quality traits of the selected leafy vegetables in relation to the light intensity (low and high Photosynthetically Active Radiation; PAR) at time of harvest were determined. Irrespective of the light intensity at time of harvest, the highest leaf dry matter (DM), proteins, nitrate, P, K and Ca contents were observed in rocket followed by mizuna. The highest lipophilic antioxidant activity (LAA) was recorded in red lettuce and rocket, whereas ascorbic acid (AA) and total phenolic (TP) contents of red lettuce were higher compared to the other leafy vegetables. When leafy vegetables were harvested at low as opposed to high PAR, the leaf content was higher in DM, protein, K, Ca and Mg, hydrophilic antioxidant activity (HAA), and LAA by 12.5%, 10.0%, 12.6%, 23.7%, 14.1%, 11.9%, and 18.5%, respectively. The highest values in TP for chicory, green lettuce, lamb’s lettuce, mizuna, red chard, and red lettuce, were observed under high PAR.
This study was conducted to determine whether using wood vinegar instead of nitric acid to adjust the pH of nutrient solution in hydroponics had any effects on the lettuce. Photosynthesis, mineral elements, water absorption, and the growth of the lettuce were all comparable to those of lettuce in the control group, in which nitric acid was used to adjust the pH. Nitric acid was added to half a unit of Enshi formula to adjust the pH of the control group. The rates of growth, water and mineral element absorption, and photosynthesis were low in lettuce plants grown in nutrient solution with 1 ml L−1 wood vinegar. However, the lettuce grown in solutions with 0.25 ml L−1 wood vinegar showed no significant differences from the control group. Therefore, wood vinegar concentration of 0.25 ml L−1 was found to be sufficient to keep the pH of the nutrient solution within the optimum range for growth.
To establish an environment-friendly hydroponics system, the ion concentration control method for nutrient solution was developed.This demonstrated to be superior to the EC control method in respect to reduction of effluent and increase of yield. In this study, the technique for keeping a suitable pH value without using acid and/or alkali was examined; plants were cultivated under three concentrations of NH4-N. When the set point concentration of NH4-N was high, the pH value of nutrient solution fell rapidly after compensation of the component. However, when the set point of concentration of NH4-N was 5-8 mg l-1, the pH was rather stable. The pH value becomes stable when the ratio of NO3-N to NH4-N of nitrogen source is around 30 (total N: 120∼240 mg l-1). From the result of the comparative experiment on nutrient solution control methods on cucumber, it was suggested that new ideas on NH4-N supply should take into consideration of the ion concentration control method and that it includes not only set points of NH4-N concentration value but also the ratio of NH4-N to NO3 -N in the ion concentration.
The effect of 2(N‐morpholino)ethane)sulfonic acid (MES) on the growth of cucumber (Cucumis sativa L. var. Marketer) in hydroponic culture was determined at 0, 1, 5, and 10 mM concentrations. The effect of adding the MES to the solution at the time of transfer to hydroponic culture or waiting one week was also determined. MES was observed to strongly affect plant growth with increasing concentration in nutrient solution. Tissue and nutrient solution analysis determined that MES affects manganese (Mn) uptake. MES appears to be reduced by Mn, precipitating the Mn out of solution. The suitability of MES as a pH buffer in hydroponic culture is discussed in terms of this effect.