Water: Effects of Irrigation With Saline Water On Crop Growth and Yield in Greenhouse Cultivation
Water: Effects of Irrigation With Saline Water On Crop Growth and Yield in Greenhouse Cultivation
Water: Effects of Irrigation With Saline Water On Crop Growth and Yield in Greenhouse Cultivation
Article
Effects of Irrigation with Saline Water on Crop
Growth and Yield in Greenhouse Cultivation
Hakkwan Kim 1 , Hanseok Jeong 1, *, Jihye Jeon 2 and Seungjong Bae 1
1 Institute of Green Bio Science and Technology, Seoul National University, Gangwon 25354, Korea;
hkkimbest@snu.ac.kr (H.K.); bsj5120@snu.ac.kr (S.B.)
2 Water Quality Assessment Research Division, National Institute of Environmental Research, Incheon 22689,
Korea; coramdeo8587@gmail.com
* Correspondence: jeonghanseok@gmail.com; Tel.: +82-33-339-5816; Fax: +82-33-339-5830
Abstract: Since the salinity of irrigation water is a critical constraint to the production of certain
vegetable crops, salinity has been considered as one of the most important factors of irrigation water.
The objective of this study was to investigate the response of lettuce and Chinese cabbage to various
salinity levels of irrigation water in greenhouse cultivation. A pot experiment was conducted with
different salinities under a glasshouse condition in Korea. A completely randomized experimental
design was used with three replications. The analysis results of crop growth and yield of lettuce and
Chinese cabbage indicated that the factors that were more significantly affected by saline irrigation
water were crop yields rather than crop components such as number of leaves, leaf length, and leaf
width. In this study, the point of salt concentration during an increase in salinity levels of irrigation
water (ECw ) at which yield starts to decline was determined to be 0.9 and 1.5 dS/m for lettuce and
Chinese cabbage, respectively. Furthermore, the present study demonstrated that the continuous
irrigation of saline water under greenhouse conditions could lead to a significant increase in electric
conductivity (ECe ) level and Na+ concentration in soil, as well as Na+ concentration in leaves of crops.
1. Introduction
Greenhouse cultivation is a widely used farming system to provide a controlled environment
suitable for optimal crop production [1]. For this reason, greenhouse crop production is now a steadily
growing agricultural sector throughout the world with an estimated 405,000 ha of greenhouses spread
all over the world [2]. In the Republic of Korea, the total area covered under greenhouse cultivation
is approximately 93,551 ha, accounting for 82,997 ha for vegetable crops and 2958 ha for flowers [3].
Recently, the Korean government is planning on constructing 5185 ha of new greenhouses for growing
horticultural crops including vegetable crops in the reclaimed land. In the reclaimed land, saline
water can be used for irrigation due to the absence or limited supply of fresh water. In addition, the
groundwater used for irrigating greenhouses near the coastal areas is frequently saline [4].
The use of saline irrigation water has an adverse effect on soil–water–plant relations, occasionally
severely restricting the normal physiological activity and productive capacity of the crops [5,6]. Under
high salinity level, the crop growth, leaf surface expansion, and primary carbon metabolism of many
crops are negatively affected due to osmotic effect, water deficit, nutritional imbalance, and oxidative
stress [7]. Several crops are sensitive to salinity and the negative effect on growth leads to the decrease
in potential profits. For this reason, salinity has been considered as one of the most important factors
of irrigation water [8]. Irrigating saline water can also result in salt accumulation in soil, leading to the
decrease in yield and deterioration in soil resource [9,10]. In particular, under greenhouse conditions,
the salinity problem is a critical constraint to vegetable production due to rapid accumulation of salts
in soil [11,12].
There have been several studies on the effects of saline irrigation water on plant systems in
greenhouses [13,14]. In the study by Reina-Sanchez et al. [15], effects of salinity on tomato fruit yield
have been quantified in experiments under greenhouse and soil-less cultivation with four salinity levels
in Malaga, Spain. Lee et al. [16] quantified the impact of saline irrigation water on chrysanthemums in
a greenhouse in Athens, Georgia. Rameshwaran et al. [12] investigated effects of different irrigation
regimes with salinity treatments using a drip irrigation system for two pepper varieties in the
greenhouse in Antalya, Turkey. Feigin et al. [17] tested the response of lettuce and Chinese cabbage to
the combination of a wide range of salinity and potassium nitrate levels in the greenhouse using an
aero-hydroponic system. Garrido et al. [18] evaluated physiological, phytochemical, and structural
changes in lettuce by salt stress in a soilless system. In Korea, land constructed by land reclamation
projects was mainly used to produce paddy rice. Thus, while many studies have focused on identifying
the response of paddy rice under salinity stress [19–21], there still is a lack of information on effects of
using saline irrigation water on the growth and yield of crops grown under greenhouse conditions.
Despite the number of studies on the subject, the sensitivity and tolerance of crops to salinity
level may vary depending on meteorological and soil conditions in the region, as well as the irrigation
method [22,23]. It is also recommended that a seawater or brackish water desalination system be used
to solve the salinity problems of irrigation water and soil in greenhouses located in coastal areas [24].
In designing the desalination system, the target salinity level for irrigation water substantially affects
the cost of the product water. Thus, it is important to examine the salt tolerance of crops grown
in greenhouse conditions and to determine the optimal salinity of irrigation water to minimize the
negative impacts on crop production, and at the same time maximize the economic benefits. The
objective of this study, therefore, was to investigate the response of vegetable crops to different salinity
levels of irrigation water under greenhouse conditions in order to determine the target salinity level
for a desalination system and to further our understanding of soil–water–plant relations.
relative humidity in the greenhouse were monitored daily during the experimental period. Daily
averages of temperature and relative humidity were 31.3 ˝ C and 21.9%, respectively. Fertilizer was
not applied to all treatments. The experiments for lettuce and Chinese cabbage were conducted
twice. The soils in each pot, however, were not changed after finishing the first experiment. After the
removal of crops at the end of the first experiment, the seeds of vegetables were again sown in the
same soil to investigate the long-term effects of saline irrigation water and the salinity accumulation
in soil and crops.
Table 2. Planting and harvesting dates for each vegetable during the experiment period.
Total Amount of
Vegetable Experiment Seeding Date Harvesting Date
Irrigation Water
First 19.June 2015 6 August 2015 5.6 L
Lettuce
Second 7 August 2015 24 September 2015 5.9 L
First 5 June 2015 10 July 2015 5.0 L
Chinese cabbage
Second 24 July 2015 28 August 2015 3.6L
2.2.2. Soil
Soil samples were taken from depths of 0–20 cm from each pot at the end of the second experiment,
and the samples were analyzed for chemical properties with the soil analysis methods of the American
Society of Agronomy (ASA) and Soil Science Society of America (SSSA) [27]. The chemical analyses
included pH, electrical conductivity of the saturated-soil extract (ECe ), cation exchange capacity (CEC),
T-N, T-P, phosphorus pentoxide (P2 O5 ), organic matter (OM) as well as exchangeable cations including
Ca2+ , Mg2+ , Na+ , and K+ .
3.1. Lettuce
Table 4. Average water quality of irrigation water for lettuce over the experiment period.
3.1.2. Soil
The ECe values ranged from 6.77 (TR#01) to 18.21 (TR#04) dS/m. As the salinity of irrigation
water (ECw ) increased, ECe tended to increase except for the case of TR#05 (Table 5). Compared to
the initial soil before irrigation (Table 1), the concentration of Na+ in soil increased in all treatments
(Table 5). A notable change in Na+ was observed in TR#05, where water of a high salinity level
was irrigated. These results indicated that the use of saline irrigation water results in an increase in
soil salinity.
the highest leaf number was observed in TR#04, followed by TR#03 and TR#05, TR#02, and TR#01,
whereas the highest leaf number of the second experiment was found in TR#03, followed by TR#01
and TR#02, TR#04, and TR#05. Andriolo et al. [13] reported that the number of lettuce leaves was not
affected by salinity treatments. While in the first experiment, the highest values for leaf length and
width were observed in TR#01, in the second experiment, they were found in TR#03.
Table 5. Chemical properties of the sampled soils at the end of the second lettuce experiment.
Table 6. ANOVA and post-hoc test of growth components, yield, and Na+ concentration in lettuce.
Leaf Number Leaf Length Leaf Width Fresh Weight (g) Na+ (mg/kg)
Treatments
(ea) (cm) (cm)
Total Shoot
First experiment
L-TR#01 22.0 ˘ 1.0a 18.2 ˘ 2.1a 18.5 ˘ 0.5a 133.3 ˘ 6.4a 120.3 ˘ 3.2a 7398.7 ˘ 2467.8a
L-TR#02 22.3 ˘ 0.6a 17.3 ˘ 0.3a 17.6 ˘ 1.4a 137.7 ˘ 9.1a 124.7 ˘ 9.6a 8508.9 ˘ 3391.8a
L-TR#03 22.7 ˘ 1.5a 17.7 ˘ 0.8a 17.6 ˘ 1.3a 141.7 ˘ 7.6a 128.7 ˘ 10.0a 8928.0 ˘ 343.0a
L-TR#04 23.3 ˘ 1.5a 16.6 ˘ 0.7a 17.7 ˘ 2.0a 136.0 ˘ 8.2a 123.7 ˘ 13.6a 9476.2 ˘ 3075.2a
L-TR#05 22.7 ˘ 0.6a 17.9 ˘ 1.8a 18.1 ˘ 0.6a 138.0 ˘ 5.3a 128.3 ˘ 4.7a 9646.1 ˘ 1147.7a
F 0.579 0.590 0.281 0.502 0.441 0.301
p 0.685 0.677 0.884 0.735 0.777 0.871
Second experiment
L-TR#01 19.0 ˘ 2.5a 17.7 ˘ 1.1a 20.8 ˘ 0.4a 144.5 ˘ 7.8abc 130.0 ˘ 5.7ab 7457.1 ˘ 157.5a
L-TR#02 19.0 ˘ 0.0a 17.6 ˘ 0.8a 20.2 ˘ 1.5a 146.7 ˘ 2.5bc 127.0˘3.6ab 10,679.2˘1242.4b
L-TR#03 20.5 ˘ 0.7a 18.3 ˘ 0.1a 21.1 ˘ 0.7a 152.0 ˘ 4.2c 134.0 ˘ 2.8b 12,848.0 ˘ 748.6bc
L-TR#04 18.3 ˘ 1.2a 17.8 ˘ 0.5a 19.3 ˘ 1.0a 133.7 ˘ 3.8ab 116.3 ˘ 6.8a 13,513.9 ˘ 589.1bc
L-TR#05 18.0 ˘ 0.0a 17.0 ˘ 0.6a 20.2 ˘ 1.1a 131.7 ˘ 5.5a 117.7 ˘ 6.1ab 13,689.1 ˘ 1090.5c
F 1.860 1.805 0.975 0.690 5.105 19.855
p 0.221 0.221 0.472 0.005 0.024 0.000
Different letters indicate significant differences by Turkey’s honestly significant difference test at p < 0.05
Up to an irrigation salinity of 0.9 dS/m (TR#03), both total and shoot fresh weight yields gradually
increased along with the escalation of salinity level, while salinity levels above 0.9 dS/m reduced
total and shoot fresh weight yields (Table 6). The highest shoot and total fresh weight yields in both
experiments were all observed in TR#03. Significant differences (p < 0.05) among the treatments were
found in total and shoot fresh weight yields of the second experiment, whereas significant differences
were not observed in the first experiment. This result demonstrated that the yield of lettuce was
affected by the salinity of irrigation water, and the negative effect of ECw level was found at salinity
levels above 0.9 dS/m. Previous studies [13,14] described that the decrease in crop yields with the
increase in the salinity of irrigation water was caused by disturbances in physiological and biochemical
activities under saline conditions. In this study, a similar trend was observed in the second experiment.
Based on statistical results, the point of salt concentration during an increase in salinity levels of
irrigation water (ECw ) at which yield starts to decline was determined to be 0.9 dS/m. This value
agreed with the value reported by Maas and Grattan [25], but was lower than the values of 2.0 and
1.1 dS/m reported by Andriolo et al. [13] and Ünlükara et al. [14], respectively.
results from the first experiment, the concentration of Na+ increased in all treatments of the second
experiment. The greatest difference between the first and second experiments was found in TR#05
(4043.0 mg/kg), followed by TR#04 (4037.7 mg/kg), TR#03 (3920.0 mg/kg), TR#02 (2170.3 mg/kg),
and TR#01 (58.4 mg/kg). These results indicated that the saline irrigation water led to the increase
in Na+ concentration in the leaves and that the continuous use of saline irrigation water caused Na+
accumulation in leaves of lettuce.
Table 7. Average water quality of irrigation water for Chinese cabbage over the experiment period.
3.2.2. Soil
The results for soil analysis showed that the increase in salinity level of irrigation water (ECw ) led
to an increase in ECe (Table 8). The concentration of Na+ in soil also increased compared to the initial
condition of soil before irrigation (Tables 1 and 8). A remarkable difference in Na+ concentration was
found in TR#05 where water with a high salinity level was irrigated. Like the lettuce experiment, these
results demonstrated that the use of saline irrigation water caused an increase in salinity level (ECe )
and Na+ concentrations in soil.
Table 8. Chemical properties of the sampled soils at the end of the second Chinese cabbage experiment.
width, no significant differences were found among the treatments (Table 7). However, in the second
experiment, there were no significant differences in leaf number, length, or width among the treatments.
In the first experiment, both shoot and total fresh weight yields tended to gradually increase up to
an irrigation salinity of 1.5 dS/m (TR#04), and decreased after that point (Table 9). There were
significant differences (p < 0.05) in shoot fresh weight among the treatments in both experiments
where, in the second experiment, a decrease in shoot and total fresh weight yields was observed at
salinity levels above 0.3 dS/m (TR#01). Based on statistical analysis, the salinity of irrigation water
at which yield reduces for Chinese cabbage was determined to be 1.5 dS/m in this study because
a significant decrease in shoot fresh weight yield was found between TR#4 (1.5 dS/m) and TR#5
(1.9 dS/m) in the first experiment. This value was higher than the value (1.2 dS/m) reported by Maas
and Grattan [25]. Furthermore, the present study showed that the salinity of irrigation water at which
yield reduces can vary depending on the duration of saline irrigation water supply. The results from
the second experiment demonstrated that the reduction in Chinese cabbage yield was found at a low
salt conservation (0.3 dS/m) due to continual supplement of saline irrigation water, although not at a
statistically significant level.
Table 9. ANOVA and post-hoc test of growth components, yield, and Na+ concentration in
Chinese cabbage.
Leaf Number Leaf Length Leaf Width Fresh Weight (g) Na+ (mg/kg)
Treatments
(ea) (cm) (cm)
Total Shoot
First experiment
C-TR#01 23.3 ˘ 0.6a 25.9 ˘ 0.8a 18.4 ˘ 0.6a 189.3 ˘ 12.1a 172.3 ˘ 0.6ab 10,279.0 ˘ 1095.1a
C-TR#02 25.0 ˘ 1.0ab 27.0 ˘ 0.0ab 18.8 ˘ 1.5a 183.7 ˘ 1.5a 175.3 ˘ 1.5ab 14,444.7 ˘ 1815.2b
C-TR#03 26.0 ˘ 1.0b 28.0 ˘ 0.9b 20.2 ˘ 1.6a 184.0 ˘ 7.5a 176.0 ˘ 5.0ab 15,511.3 ˘ 893.6b
C-TR#04 26.3 ˘ 0.6b 27.5 ˘ 0.7ab 19.5 ˘ 0.8a 187.0 ˘ 6.1a 178.7 ˘ 3.1b 14,921.0 ˘ 829.5b
C-TR#05 24.7 ˘ 1.2ab 28.8 ˘ 0.3b 19.7 ˘ 0.3a 168.3 ˘ 7.6a 163.7 ˘ 9.9a 19,241.0 ˘ 1324.8c
F 5.292 4.535 1.314 3.402 3.738 19.767
p 0.015 0.024 0.330 0.053 0.041 0.000
Second experiment
C-TR#01 19.3 ˘ 0.0a 26.4 ˘ 0.8a 15.9 ˘ 0.8a 102.0 ˘ 11.5b 96.7 ˘ 8.6b 9,867.6 ˘ 774.9a
C-TR#02 20.0 ˘ 1.7a 26.2 ˘ 1.1a 15.5 ˘ 0.1a 94.0 ˘ 2.6ab 86.7 ˘ 5.5ab 11,558.6 ˘ 1932.7ab
C-TR#03 20.7 ˘ 1.2a 26.6 ˘ 2.2a 16.3 ˘ 1.8a 92.7 ˘ 8.6ab 86.0 ˘ 7.0ab 12,901.9 ˘ 1956.9ab
C-TR#04 19.7 ˘ 1.5a 25.5 ˘ 0.9a 15.3 ˘ 0.8a 81.3 ˘ 5.0a 75.7 ˘ 3.8a 13,529.1 ˘ 850.7ab
C-TR#05 20.3 ˘ 1.2a 25.9 ˘ 0.7a 15.1 ˘ 1.2a 76.0 ˘ 3.5a 72.7 ˘ 4.0a 16,392.3 ˘ 3227.2b
F 0.368 0.342 0.764 6.482 7.494 4.580
p 0.826 0.884 0.572 0.008 0.005 0.023
Different letters indicate significant differences by Turkey’s honestly significant difference test at p < 0.05.
4. Conclusions
In this study, the responses of vegetables irrigated with water of different salinity levels were
investigated under greenhouse conditions. The analysis results of crop growth components and
yields of lettuce and Chinese cabbage demonstrated that the factors that were more significantly
affected by saline irrigation water were crop yields rather than crop components such as number
of leaves, leaf length, and leaf width. In particular, compared to the first experiment, there were
more significant differences in yields of lettuce and Chinese cabbage among treatments in the second
experiment where saline irrigation water was continually supplied without the change of soil after the
first experiment. This result led to the conclusion that the continuous application of saline irrigation
Water 2016, 8, 127 8 of 9
water resulted in noticeable changes in crop yields in relation to the negative effect of saline irrigation
water. Furthermore, it was found that the use of saline irrigation water under greenhouse conditions
stimulated Na+ accumulation in both soil and crops.
Acknowledgments: This work was supported by the Korea Institute of Planning and Evaluation for Technology
in Food, Agriculture, Forestry and Fisheries (IPET) through the Agri-Bio industry Technology Development
Program, funded by the Ministry of Agriculture, Food and Rural Affairs (MAFRA) (grant number 114060-3).
Author Contributions: Hakkwan Kim and Hanseok Jeong designed the experiment, performed the experiment
work and statistical analysis, produced the tables, and wrote the paper. Jihye Jeon and Seungjon Bae performed
the experimental work, data collection, and chemical analyses. Hakkwan Kim, Hanseok Jeong, Jihye Jeon, and
Seungjong Bae all read and made improvements to the manuscript.
Conflicts of Interest: The authors declare no conflict of interest.
References
1. Yazgan, S.; Ayas, S.; Demirtas, C.; Büyükcangaz, H.; Candogan, B.N. Deficit irrigation effects on lettuce
(Lactuca sativa var. Olenka) yield in unheated greenhouse condition. J. Food Agric. Environ. 2008, 6, 357–361.
2. FAO. Good Agricultural Practices for Greenhouse Vegetable Crops; FAO Plant Production and Protection Paper
217; Food and Agriculture Organization of the United Nations: Rome, Italy, 2013.
3. MAFRA. Agriculture, Food, and Rural Affairs Statistics Yearbook; Ministry of Agriculture, Food and Rural
Affairs: Sejong, Korea, 2015.
4. Lee, S.B.; Hong, C.O.; Oh, J.G.; Gutierrez, J.; Kim, P.J. Effect of irrigation water salinization on salt
accumulation of plastic film house soil around Sumjin river estuary. Korean J. Environ. Agric. 2008, 27,
349–355.
5. De Pascale, S.; Orsini, F.; Pardossi, A. Irrigation water quality for greenhouse horticulture. In Good Agricultural
Practices for Greenhouse Vegetable Crops; FAO Plant Production and Protection Paper 217; Food and Agriculture
Organization of the United Nations: Rome, Italy, 2013; pp. 169–204.
6. Plaut, Z.; Edelstein, M.; Ben-Hur, M. Overcoming salinity barriers to crop production using traditional
methods. Crit. Rev. Plant Sci. 2013, 32, 250–291. [CrossRef]
7. Kim, H.; Fonseca, J.M.; Choi, J.; Kubota, C.; Kwon, D.Y. Salt in irrigation water affects the nutritional and
visual properties of romaine lettuce (Lactuca sativa L.). J. Agric. Food Chem. 2008, 56, 3772–3776. [CrossRef]
[PubMed]
8. Beltran, J.M. Irrigation with saline water: Benefits and environmental impact. Agric. Water Manag. 1999, 40,
183–194. [CrossRef]
9. Ould Ahmed, B.A.; Yamamoto, T.; Inoue, M. Response of drip irrigated sorghum varieties growing in dune
sand to salinity levels in irrigation water. J. Appl. Sci. 2007, 7, 1061–1066.
10. Feizi, M.; Hajabbasi, M.A.; Mostafazadeh-fard, B. Saline irrigation water management strategies for better
yield of safflower (Carthamus tinctorius L.) in an arid region. Aust. J. Crop Sci. 2010, 4, 408–414.
11. Shannon, M.C.; Grieve, C.M. Tolerance of vegetable crops to salinity. Sci. Hortic. 1998, 78, 5–38. [CrossRef]
12. Rameshwaran, P.; Tepe, A.; Yazar, A.; Ragab, R. The effect of saline irrigation water on the yield of pepper:
Experimental and modelling study. Irrig. Drain. 2015, 64, 41–49. [CrossRef]
13. Andriolo, J.L.; da Luz, G.L.; Witter, M.H.; Godori, R.S.; Barros, G.T.; Bortolotto, O.C. Growth and yield of
lettuce plants under salinity. Hortic. Braz. 2005, 23, 931–934. [CrossRef]
14. Ünlükara, A.; Cemek, B.; Karaman, S.; Erşahin, S. Response of lettuce (Lactuca sativa var. Crispa) to salinity
of irrigation water. New Zeal. J. Crop Hortic. Sci. 2008, 36, 263–271.
15. Reina-Sanchez, A.; Romero-Aranda, R.; Cuartero, J. Plant water uptake and water use efficiency of
greenhouse tomato cultivars irrigated with saline water. Agric. Water Manag. 2005, 78, 54–66. [CrossRef]
16. Lee, M.K.; van Iersel, M.W. Sodium chloride effects on growth, morphology, and physiology of
chrysanthemum. HortScience 2008, 43, 1888–1891.
17. Feigin, E.; Pressman, E.; Imas, O.; Miltau, O. Combined effects of KNO3 and salinity on yield and chemical
composition of lettce and chiness cabbage. Irrig. Sci. 1991, 12, 223–230. [CrossRef]
18. Garrido, Y.; Tudela, J.A.; Marín, A.; Mestre, T.; Martínez, V.; Gil, M.I. Physiological, phytochemical and
structural changes of multi-leaf lettuce caused by salt stress. J. Sci. Food Agric. 2014, 94, 1592–1599. [CrossRef]
[PubMed]
Water 2016, 8, 127 9 of 9
19. Lee, J.S.; Oh, K.S.; Sohn, S.M. Effects of NaCl salinity at tillerling stage on mineral contents, growth and yield
of rice. Korean J. Int. Agri. 1993, 5, 167–174.
20. Lee, C.K.; Yang, Y.H.; Shin, J.C.; Lee, B.W.; Kim, C.K. Growth and yield of rice as affected by saline water
treatment at different growth stages. Korean J. Crop Sci. 2002, 47, 402–408.
21. Choi, S.; Kim, H.; Ahn, Y.; Jang, J.; Oh, J. Salinity effects on growth and yield components of rice. Korean J.
Limnol. 2004, 37, 248–254.
22. Wu, L.; Guo, X.; Harivandi, A. Salt tolerance and salt accumulation of landscape plants irrigated by sprinkler
and drip irrigation systems. J. Plant Nutr. 2001, 24, 1473–1490. [CrossRef]
23. Katerji, N.; van Hoorn, J.W.; Hamdy, A.; Mastrorilli, M. Salinity effect on crop development and yield,
analysis of salt tolerance according to several classification methods. Agric. Water Manag. 2003, 62, 37–66.
[CrossRef]
24. Zarzo, D.; Campos, E.; Terrero, P. Spanish experience in desalination for agriculture. Desalination Water Treat.
2013, 51, 53–66. [CrossRef]
25. Mass, E.V.; Grattan, S.R. Crop yields as affected by salinity. In Agricultural Drainage; Skaggs, R.W.,
van Schilfgaarde, J., Eds.; American Society of Agronomy, Crop Science Society of America, Soil Science
Society of America: Madison, WI, USA, 1999; pp. 55–108.
26. APHA. Standard Methods for the Examination of Water and Wastewater; American Public Health Association:
Washington, DC, USA, 1995.
27. Chapman, H.D.; Pratt, P.F. Methods of Analysis for Soils, Plants and Waters; University of California: Riverside,
CA, USA, 1961.
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