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PJAR_33_4_798_809

 

 

 

Research Article

Effect of Sewage Water Irrigation Frequency on Growth, Yield and Heavy Metals Accumulation of Tomato and Okra

Safina Naz1*, Muhammad Akbar Anjum1, Bushra Siddique2, Syed Atif Hasan Naqvi3*, Sajid Ali1, Hassan Sardar1, Sakeena Tul Ain Haider1, Muhammad Asif Zulfiqar4, Hajra Azeem3, Sibghat Ullah5, Shah Pasand6 and Zehri Khan5

1Department of Horticulture, Bahauddin Zakariya University, Multan, Pakistan; 2Department of Entomology, The Islamia University of Bahawalpur, Pakistan; 3Department of Plant Pathology, Bahauddin Zakariya University, Multan, Pakistan; 4PARC, Research and Training Station, Bahauddin Zakariya University, Multan, Pakistan; 5Pakistan Agricultural Research Council, Horticulture Research Institute, Khuzdar, Pakistan; 6Pakistan Agricultural Research Council, Social Sciences Research Institute, Quetta, Pakistan.

Abstract | The current study was aimed to inspect the efficiency of different sewage water irrigation frequency treatments on growth, yield and heavy metals accumulation of tomato and okra during 2012 and 2013. A statistical randomized complete block design was applied in the field to perform experiments having three replicates while 03 sewage water irrigation frequency treatments i.e., 5, 10 and 15-days interval. The tomato yield, their growth along with the production of the plant biomass were increased considerably with more repetitive (interval of five days) application of the sewage water. While reasonably less repetitive application (interval of fifteen days) of sewage water cause the less production of biomass, yield and growth. Moderately less repetitive applications (interval of ten days) of sewage water showed a significant increase in the addressed attributes of production in okra. The yield, as well as growth aspects of the okra, were reduced noticeably by using the reasonably less repetitive application. Frequent sewage water application resulted in an increased amount of Fe, Cu, Pb, Cr, Ni and Cd in okra pods and tomato fruits than moderately and less repetitive irrigation. The leaves and root of okra and tomato displayed the higher contents of metal when these crops were cultivated with a repetitive application of the sewage water. The final result revealed that the metal concentration high in tomato and okra plant parts with decreasing irrigation intervals of sewage water.


Received | July 20, 2020; Accepted | August 28, 2020; Published | October 09, 2020

*Correspondence | Syed Atif Hasan Naqvi and Safina Naz, Department of Horticulture, Bahauddin Zakariya University, Multan; Department of Plant Pathology, Bahauddin Zakariya University, Multan, Pakistan; Email: atifhasanshah@hotmail.com, safinnaz@bzu.edu.pk

Citation | Naz, S., M.A. Anjum, B. Siddique, S.A.H. Naqvi, S. Ali, H. Sardar, S.T.A. Haider, M.A. Zulfiqar, H. Azeem, S. Ullah, S. Pasand and Z. Khan. 2020. Effect of sewage water irrigation frequency on growth, yield and heavy metals accumulation of tomato and okra. Pakistan Journal of Agricultural Research, 33(4): 798-809.

DOI | http://dx.doi.org/10.17582/journal.pjar/2020/33.4.798.809

Keywords | Irrigation frequency, Sewage water, Growth, Yield, Heavy metals, Vegetables


Introduction

Water is necessary for the physiological activity of crop plants. Too much irrigation at any stage can delay maturity and harvesting and promote vegetative growth, whereas inadequate and less irrigation cause water stress and reduce quality and yield (Yazgan et al., 2008). Proper irrigation time and interval is necessary for production of good quality vegetables. Water shortage at the early stage of growth and development usually results in reduced yield. If the water shortages occur later in the growing season, it may not only adversely affect the quality of vegetables but also reduce the total yield. Large sized fruits and greater yields were obtained when tomato plants were irrigated at 10 days interval compared with other irrigated intervals (Mani et al., 2007). However, Gudugi et al. (2012) recorded a higher number of tomato fruits and greater yield when plants were irrigated at 4 days interval than with 8 days interval. Okra is a warm-season crop and has considerable resistance to drought. Water shortage affects the morphological and physiological processes of the plants, which are associated with growth and development (Moniruzzaman et al., 2007; Yadav and Dhankhar, 1999). Drought stress affects photosynthesis, respiration, nutrient metabolism, and membrane stability index, which ultimately reduces plant growth and productivity of plants (Naveed et al., 2009). Maturity and harvesting of crop were delayed due to the excessive irrigations or shorter irrigation intervals, whereas the yield and quality of crop were also reduced due to insufficient irrigation (Ramalan and Nwokeocha, 2000; Sankar et al., 2008). Greater pod length, pod weight and yield of okra genotypes were recorded under 10 days irrigation interval (Khalil, 2004).

Use of sewage water has positive effects on plant biomass, plant height and yield of tomatoes enriched with vital plants macro and micronutrients (Khan et al., 2011). Similar results have been reported in okra by Khalil (2004) and Rehman (2007). Keeping in view of these facts, the present study was envisaged to determine the effect of frequency of irrigation with sewage water on growth, yield and heavy metals concentration in tomato and okra.

 

Materials and Methods

Six weeks old tomato seedlings were transplanted on both sides of 1 m wide beds with a plant to plant distance of 20 cm on 10th February 2012 (1st year crop) and 10th February 2013 (2nd year crop). By using both margins/border of ridges, okra seeds were sown at 60 cm distance, having PXP distance 20 cm on 5th March 2012 (1st year crop) and 5th March 2013 (2nd year crop). All the cultural practices were carried out according to the requirements of crops and experiments.

The crops were irrigated with sewage water at different intervals/ frequencies. By using these 03 treatments of application (frequencies of sewage water application) via more repetitive application i.e. 5 days interval, moderately less repetitive i.e. 10 days interval and less repititive i.e. 15 days interval, which were replicated thrice in a randomized complete block design (RCBD). The data were collected on different growth and yield parameters and heavy metals accumulation in different parts of these vegetables.

Determination of heavy metals

Pre-treatment and chemicals: The vegetable samples were washed with distilled water to remove any dirt or soil particles and air-dried at room temperature for sixty minutes. After that, sliced the samples into small pieces and incubated in the oven for 72 hours at 70 °C. Crushed the samples into chilled mortar and pestle until the fine powdered is prepared. The prepared fine powder filter through a muslin cloth and preserved in disinfected polythene bags. Required chemicals and heavy metals standards (1ml) viz., Cr Pb, Ni, Cu, Cd, and Fe were graciously achieved from the Merck.

Acid digestion and statistical analysis

Heavy metals were extracted by digesting 500mg dehydrated sample from recommended treatments in 15 mL HNO3 along with 5 ml HClO4 mixture (3:1) by using a hot plate (Velp, Italy) with the temperature at 80ºC until the clear solutions were achieved. The Whatman No. 42 filter paper was used to filter the obtained solution in 25 mL DEPC water (Farooq et al., 2008). These heavy metals contents (Pb, Cu, Ni, Cd, Cr and Fe) were determined in the obtained solution by utilizing the atomic absorption spectrophotometer (Thermo Scientific 3000 series, USA). The data collected were subjected to analysis of variance (ANOVA). Least significant difference test was employed to determine significant differences among the treatment means at 5% level of probability. The data were analyzed using statistical software statistix 8.1.

 

Results and Discussion

Effect of sewage water irrigation frequency on plant growth

Significantly greater height, relative leaf chlorophyll content and leaf area of tomato were recorded when plants were grown with frequent irrigation with the sewage water. Whereas, significantly lower values of these parameters were recorded under less frequent irrigation treatment (Table 1). The mean values for the interaction between various irrigation frequency treatments and years exhibited a statistically significant effect on plant height and leaf area. The taller plants were obtained with the interactive effect of frequent irrigation × year 2012, followed by the interaction of frequent irrigation × year 2013. These two treatments were statistically at par. The combined effect of less frequent irrigation × year 2013 resulted in significantly shorter plants. The combined effect of the frequent × year 2012, the frequent × year 2013 and moderately frequent irrigation × year 2013 resulted in greater leaf area. These three treatment combinations stood statistically at par with each other. Leaf area was significantly lower in the plants grown under less frequent × year 2013 (Table 1).

The maximum plant height and leaf area were produced in okra grown with moderately frequent irrigation treatment, which was followed by frequent irrigation treatment. The minimum values for these parameters were obtained when plants were irrigated with less frequent irrigation treatment. All the treatments were significantly different from each other. Frequent and moderately frequent irrigation treatments were statistically similar with greater relative leaf chlorophyll content. Whereas, significantly lesser content was recorded with less frequent irrigation treatment (Table 1). Significantly higher relative leaf chlorophyll content was recorded when okra plants were grown under the frequent irrigation treatment during the year 2013 and moderately frequent irrigation treatment during the year 2012, which were statistically alike. Whereas relative leaf chlorophyll content was significantly decreased when the plants were grown under less frequent irrigation treatment during year 2013.

Effect of sewage water irrigation frequency on fruiting

The maximum number of tomato fruits, fruit length and fruit diameter were recorded in the plants which received frequent irrigation, while the minimum values for these parameters were recorded with less frequent irrigation with the sewage water. All these three irrigation frequency treatments were statistically different from each other (Table 2). The significantly higher number of tomato fruits was obtained with the interactive effect of frequent irrigation × year 2012, followed by the interaction of frequent irrigation × year 2013. These two treatment combinations were statistically similar. The combined effect of less frequent irrigation × year 2013 and less frequent irrigation × year 2012 produced the minimum number of fruits. These two treatment combinations also behaved statistically alike. However, the combined effect of irrigation frequency treatments and years for fruit length and fruit diameter indicated non-significant differences among the treatment combinations.

Pod number, pod length and diameter in okra were significantly affected by various irrigation frequency treatments with the sewage water. Significantly greater number of pods and pod diameter were recorded with moderately frequent irrigation treatment when compared with frequent and less frequent irrigation treatments. However, latter two treatments were statistically similar. The maximum pod length was observed in the plants under moderately frequent irrigation treatment, followed by in those grown with frequent irrigation treatment. Whereas less frequent irrigation treatment produced the shortest pods. All these three treatments were statistically different from each other.

Effect of sewage water irrigation frequency on yield

Significantly higher fresh and dry weights of fruit and yield per hectare of tomato were recorded with frequent irrigation treatment. The minimum fresh and dry weights of fruit and yield were observed in less frequent irrigation treatment. All these three treatments were statistically different (Table 2).

Moderately frequent irrigation treatment produced the maximum fresh weight per pod of okra, followed by frequent irrigation treatment and it was significantly reduced with less frequent irrigation treatment. However, behavior of all these three treatments was statistically different. Moderately frequent irrigation produced higher dry weight per pod, followed by frequent irrigation treatment and these two treatments were statistically similar. Significantly higher pod yield was achieved in the plants under moderately frequent irrigation treatment. The frequent and less frequent irrigation treatments behaved statistically alike with lower yields (Table 3). Fresh weight per pod was not affected by the interactive effect of irrigation frequency treatments and years. However, greater dry weight of pod was observed with the interactive effect of moderately frequent irrigation treatment × year 2013, moderately frequent irrigation treatment × year 2012, frequent irrigation treatment × year 2013 and frequent irrigation treatment × year 2012. All these four treatment combinations were statistically at par with each other. While the lowest values for a dry weight of pod was observed with the interactive

 

Table 1: Effect of sewage water irrigation frequency on growth of tomato and okra.

Frequency of irrigation water

Tomato

Okra

Year 2012

Year 2013

Mean

Year 2012

Year 2013

Mean

Plant height (cm)

Frequent

90.70a

89.80a

90.25a

85.23a

84.93a

85.08b

Moderately frequent

83.60b

83.23b

83.41b

91.76a

92.13a

91.95a

Less frequent

80.06c

77.16d

78.61c

68.40a

69.36a

68.88c

Mean

84.78a

83.40a

81.80a

82.14a

Relative leaf chlorophyll content

Frequent

63.50a

61.93a

62.71a

62.70b

72.0a

67.55a

Moderately frequent

56.53a

55.86a

56.20b

69.03a

62.03b

65.53a

Less frequent

49.73a

49.96a

49.85c

56.96c

52.50d

54.73b

Mean

56.58a

55.92a

62.90a

62.31a

Leaf area (cm2)

Frequent

24.50a

24.46a

24.48a

198.67a

197.80a

198.23b

Moderately frequent

23.50b

23.86ab

23.68b

204.77a

203.77a

204.27a

Less frequent

21.40c

20.63d

21.01c

185.77a

184.33a

185.03c

Mean

23.13a

22.98a

196.40a

195.29a

Treatment means sharing the different letter(s) in a group are significantly different at p ≥ 0.05

 

Table 2: Effect of sewage water irrigation frequency on fruiting of tomato and okra.

Frequency of irrigation water

Tomato

Okra

Year 2012

Year 2013

Mean

Year 2012

Year 2013

Mean

Number of fruit/pods per plant

Frequent

26.16a

26.03a

26.10a

22.33a

22.50a

22.41b

Moderately frequent

24.26b

23.90b

24.08b

26.33a

25.66a

26.00a

Less frequent

22.53c

22.00c

22.26c

21.66a

21.33a

21.50b

Mean

24.32a

23.97a

23.44a

23.16a

Fruit/pod length (cm)

Frequent

6.87a

6.88a

6.87a

10.06a

10.26a

10.16b

Moderately frequent

5.91a

5.86a

5.89b

12.23a

12.70a

12.46a

Less frequent

5.81a

5.76a

5.79c

9.76a

9.60a

9.68c

Mean

6.20a

6.17a

10.68a

10.85a

Fruit/pod diameter (cm)

Frequent

6.10a

6.23a

6.16a

1.45a

1.44a

1.45b

Moderately frequent

5.80a

5.73a

5.76b

1.56a

1.54a

1.55a

Less frequent

5.36a

5.43a

5.40c

1.40a

1.33a

1.36b

Mean

5.75a

5.80a

1.47a

1.43a

Treatment means sharing the different letter(s) in a group are significantly different at p ≥ 0.05

 

effect less frequent irrigation treatment × year 2013. The highest yield was obtained with the combined effect of moderately frequent irrigation treatment × year 2012, which was statistically different from all other treatment combinations. The treatment combinations, less frequent irrigation treatment × year 2012, less frequent irrigation treatment × year 2013, frequent irrigation treatment × year 2013 and frequent irrigation treatment × year 2012 were statistically at par with each other with significantly lower pod yield.

Effect of sewage water irrigation frequency on biomass production (on fresh and dry weight basis)

Total biomass (fresh and dry) of tomato was significantly affected by different irrigation frequency treatments. Greater values for these parameters were recorded in the plants which were grown with frequent irrigation application. Whereas the minimum fresh and dry biomass was observed with less frequent irrigation treatment. All three irrigation treatments were statistically different from each other. Significantly greater biomass (on fresh weight basis) was recorded with frequent irrigation treatment × year 2012, followed by frequent irrigation treatment × year 2013. These two treatment combinations were statistically alike. Whereas the minimum fresh total biomass was recorded with the interactive effect of less frequent treatments × year 2013, followed by less frequent irrigation treatment × year 2012. These two treatment combinations also behaved statistically alike (Table 4).

Different irrigation frequency treatments affected the total biomass (fresh and dry) of okra. Moderately frequent irrigation treatment resulted in significantly greater total fresh and dry biomass. Whereas, the minimum values for the parameters under study were recorded with less frequent irrigation treatment. These three treatments significantly differed from each other.

Heavy metals contents in tomato fruits and okra pod

Frequent irrigation application with sewage water resulted in greater Pb, Ni and Cr contents in tomato fruits, followed by with moderately frequent irrigation treatment. These two irrigation frequency treatments were statistically at par. Significantly lower contents (Pb, Ni and Cr) were recorded in fruits when plants were grown with less frequent irrigation treatment. This irrigation frequency was statistically similar with moderately frequent irrigation application. Significantly greater Cu content was recorded in fruits when plants were grown with frequent irrigation application compared with moderately or less frequent irrigation application, which was statistically alike with lower Cu contents. Tomato fruits contained significantly greater Cd and Fe contents when the plants were grown with frequent irrigation application. Whereas significantly lower Cd and Fe accumulation in the fruits were recorded with less frequent irrigation application (Table 5).

Significantly higher Pb and Cr contents were noticed in okra pods of the plants grown with frequent irrigation application. Moderately and less frequent irrigation application resulted in lower Pb and Cr contents in okra pods. Okra pods contained higher Ni and Cd contents with frequent irrigation application, followed by moderately frequent irrigation. These two irrigation frequencies were statistically similar. Less frequent irrigation application resulted in lower Ni and Cd contents, which was also statistically at par with moderately frequent irrigation. Frequent irrigation application resulted in greater Cu content in okra pods, followed by those with moderately frequent irrigation application. These two irrigation frequency treatments were statistically alike. While significantly lesser Cu content was detected in pods when less frequent irrigation was applied to okra plants. Significantly greater Fe content was recorded in okra pods with frequent irrigation treatment. Less frequent irrigation application resulted in significantly lower Fe contents in okra pods.

Heavy metals contents in tomato and okra leaves

Among irrigation frequency treatments with sewage water, significantly higher Pb and Fe contents were recorded in leaves when tomato plants were irrigated frequently. Whereas less frequent irrigation resulted in significantly lower Pb and Fe contents. Greater Ni and Cd contents were recorded in leaves of the plants grown with frequent and moderately frequent irrigation treatment. Whereas less frequent irrigation application resulted in the minimum Ni and Cd contents in leaves. Cu and Cr substances were considerably higher in leaves of the plants grown with frequent irrigation application compared with moderately or less frequent irrigation application. The latter two irrigation treatments were statistically similar with lower Cu and Cr contents (Table 6).

Significantly higher heavy metals (Pb, Ni, Cu and Cr) contents were recorded in okra leaves grown with frequent irrigation, followed by moderately frequent irrigation. These two irrigation frequencies were statistically at par. Whereas, less frequent irrigation treatment resulted in a lower value for Pb, Ni, Cu and Cr contents. This treatment was also statistically alike with moderately frequent irrigation treatment. Significantly greater Cd content was recorded with frequent irrigation compared, while moderately and less frequent irrigation treatments were statistically similar with lower Cd contents. Frequent and moderately frequent irrigation applications were statistically similar with greater Fe contents. Whereas significantly lower Fe content was recorded in okra leaves when plants were irrigated with less frequent sewage water.

 

Table 3: Effect of sewage water irrigation frequency on yield of tomato and okra.

Frequency of irrigation water

Tomato

Okra

Year 2012

Year 2013

Mean

Year 2012

Year 2013

Mean

Fresh weight of individual fruit (g)

Frequent

95.46a

95.83a

95.65a

8.96a

9.00a

8.98b

Moderately frequent

92.36a

92.00a

92.18b

9.23a

9.26a

9.25a

Less frequent

88.36a

88.16a

88.26c

8.11a

8.10a

8.10c

Mean

92.06a

92.00a

8.76a

8.78a

Dry weight of individual fruit (g)

Frequent

7.83a

7.90a

7.86a

1.79a

1.80a

1.79a

Moderately frequent

6.80a

6.63a

6.71b

1.84a

1.85a

1.85a

Less frequent

6.16a

6.13a

6.15c

1.62b

1.42c

1.52b

Mean

6.93a

6.88a

1.75a

1.69a

Fruit yield per hectare (tons)

Frequent

48.96a

48.47a

48.71a

10.79c

10.58c

10.69b

Moderately frequent

42.65a

42.10a

42.37b

17.99a

15.60b

16.80a

Less frequent

35.75a

35.45a

33.60c

10.14c

10.29c

10.21b

Mean

41.79a

41.34a

12.97a

12.16a

Treatment means sharing the different letter(s) in a group are significantly different at p ≥ 0.05

 

Table 4: Effect of sewage water irrigation frequency on biomass production (on fresh and dry weight basis) of tomato and okra.

Frequency of irrigation water

Tomato

Okra

Year 2012

Year 2013

Mean

Year 2012

Year 2013

Mean

Total plant biomass on fresh weight basis (g)

Frequent

2885.8a

2877.6a

2881.7a

514.92a

521.39a

518.15b

Moderately frequent

2599.7b

2556.4b

2578.0b

646.93a

637.73a

642.33a

Less frequent

2297.5c

2241.6c

2269.6c

440.27a

443.03a

441.65c

Mean

2594.3a

2558.5a

534.05a

534.46a

Total plant biomass on dry weight basis (g)

Frequent

318.76a

319.14a

318.95a

90.27a

90.91a

90.59b

Moderately frequent

271.39a

264.83a

268.11b

125.71a

123.31a

124.51a

Less frequent

230.35a

224.96a

227.66c

76.42a

72.98a

74.70c

Mean

273.50a

269.64a

97.46a

95.73a

Treatment means sharing the different letter(s) in a group are significantly different at p ≥ 0.05

 

Heavy metals contents in tomato and okra roots

Significantly greater metals contents (Pb, Ni, Cu, Cd and Cr) were recorded in tomato roots grown with frequent irrigation, followed by moderately frequent irrigation treatment. These two treatments were statistically at par. While, less frequent irrigation resulted in lower Pb, Ni, Cu, Cd and Cr contents in roots, which was statistically similar to moderately frequent irrigation. Significantly higher Fe content was recorded in the roots of tomato plants under frequent irrigation treatment, while significantly lower Fe contents were observed with less frequent irrigation application (Table 7).

Significantly higher Pb and Fe contents were recorded in roots of okra plants grown with frequent and moderately frequent irrigation treatments. These two irrigation frequencies were statistically similar. Significantly lower Pb and Fe contents were noticed with less frequent irrigation application. Significantly greater Ni content was recorded in roots when plants were grown with frequent irrigation treatment, significantly lesser Ni content was recorded with less frequent irrigation treatment. Higher Cu, Cd and Cr contents were recorded with frequent irrigation application, which was statistically at par with moderately frequent irrigation application. Lower Cu, Cd and Cr contents were recorded with less frequent irrigation, which was also statistically similar with moderately frequent irrigation application.

Water shortage results in drought stress and poor growth and yields in crop plants. In the present study, significantly greater growth of tomato in terms plant height, relative leaf chlorophyll content and leaf area was recorded with frequent irrigation treatment (5 days interval), followed by moderately frequent (10 days interval) and less frequent irrigation treatment (15 days interval). The interaction between irrigation frequency treatments and years indicated that increased tomato growth (plant height and leaf area) was observed when plants were irrigated frequently during 2012 and 2013, while reduced growth was found with less frequent irrigation interval during both the years. The differences in growth parameters due to various irrigation frequency treatments during the years were possibly due to the availability of more water in frequent irrigation treatment and prevailing weather conditions of the area during the growing season. The current findings are also related with those of Abdel Mouty and Ali (2008), who found increased plant growth of eggplant when irrigated at 10 days irrigation interval than those irrigated with 21 days interval. Kirnak et al. (2001) also found that water shortage reduced plant height, leaf chlorophyll content and vegetative growth of eggplant when grown with different irrigation regimes (100, 80, 60 and 40%). The number of eggplant leaves increased with increasing irrigation frequency (Byari and Al-Rabighi, 1996), being higher at shorter irrigation interval i.e., 6 days.

 

Table 5: Effect of sewage water irrigation frequency on heavy metals contents in tomato fruits and okra pods.

Frequency of irrigation water

Tomato fruits

Okra pods

Year 2012

Year 2013

Mean

Year 2012

Year 2013

Mean

Pb (mg kg-1)

Frequent

8.200a

8.933a

8.566a

3.300a

3.500a

3.400a

Moderately frequent

7.200a

7.400a

7.300ab

2.766a

3.100a

2.933b

Less frequent

5.567a

6.100a

5.833b

2.4333a

2.600a

2.516b

Mean

6.988a

7.477a

2.833a

3.066a

Ni (mg kg-1)

Frequent

12.800a

13.167a

12.983a

8.800a

9.200a

9.000a

Moderately frequent

10.600a

11.13a

10.867ab

8.200a

8.500a

8.350ab

Less frequent

8.700a

9.900a

8.800b

7.400a

7.800a

7.600b

Mean

10.700a

11.067a

8.133a

8.500a

Cu (mg kg-1)

Frequent

9.633a

9.966a

9.800a

10.800a

11.233a

11.017a

Moderately frequent

7.700a

7.666.a

7.683b

9.400a

10.500a

9.950a

Less frequent

6.500a

6.600a

6.550b

8.200a

9.033a

8.617b

Mean

7.944a

8.077a

9.467a

10.256a

Cd (mg kg-1)

Frequent

2.566a

2.700a

2.633a

0.083a

0.333a

0.208a

Moderately frequent

2.166a

2.233a

2.200b

0.053a

0.059a

0.056ab

Less frequent

1.700a

1.800a

1.750c

0.033a

0.040a

0.036b

Mean

2.144a

2.244a

0.056a

0.144a

Fe (mg kg-1)

Frequent

137.00a

139.57a

138.28a

203.93a

210.47a

207.20a

Moderately frequent

116.43a

117.67a

117.05b

143.60a

162.60a

153.10b

Less frequent

80.23a

92.80a

86.52c

128.07a

138.10a

133.08c

Mean

111.22a

116.68a

158.53a

170.39a

Cr (mg kg-1)

Frequent

0.500a

0.603a

0.551a

0.900a

1.333a

1.116a

Moderately frequent

0.333a

0.366a

0.350ab

0.500a

0.633a

0.566b

Less frequent

0.166a

0.233a

0.200b

0.200a

0.366a

0.283b

Mean

0.333a

0.401a

0.533a

0.777a

Treatment means sharing the different letter(s) in a group are significantly different at p ≥ 0.05

 

Table 6: Effect of sewage water irrigation frequency on heavy metals contents in tomato and okra leaves.

Frequency of irrigation water

Tomato fruits

Okra pods

Year 2012

Year 2013

Mean

Year 2012

Year 2013

Mean

Pb (mg kg-1)

Frequent

9.400a

9.966a

9.683a

4.800a

5.300a

5.050a

Moderately frequent

7.800a

7.866a

7.833b

4.033a

4.200a

4.116ab

Less frequent

5.200a

6.133a

5.666c

3.601a

3.600a

3.600b

Mean

7.466

7.988a

4.200a

4.311a

Ni (mg kg-1)

Frequent

16.600a

16.700a

16.650a

10.533a

11.500a

11.017a

Moderately frequent

15.300a

15.633a

15.467a

9.633a

9.700a

9.667ab

Less frequent

13.533a

13.633a

13.583b

8.833a

8.840a

8.833b

Mean

15.144a

15.322a

9.667a

10.011a

Cu (mg kg-1)

Frequent

11.633a

12.267a

11.950a

13.933a

14.667a

14.050a

Moderately frequent

9.767a

9.967a

9.867b

12.433a

12.967a

12.700ab

Less frequent

9.200a

9.300a

9.250b

11.367a

11.267a

11.317b

Mean

10.200a

10.511a

12.578a

12.800a

Cd (mg kg-1)

Frequent

2.866a

3.166a

3.016a

0.800a

0.966a

0.883a

Moderately frequent

2.466a

2.800a

2.633ab

0.433a

0.700a

0.566b

Less frequent

1.866a

2.333a

2.100b

0.300a

0.366a

0.333b

Mean

2.400a

2.766a

0.511a

0.677a

Fe (mg kg-1)

Frequent

249.37a

261.70a

255.53a

259.63a

262.90a

261.27a

Moderately frequent

236.70a

240.20a

238.45b

244.57a

245.43a

245.00a

Less frequent

155.87a

157.13a

156.50c

214.00a

214.63a

214.32b

Mean

213.98a

219.68a

239.40a

240.99a

Cr (mg kg-1)

Frequent

1.600a

1.900a

1.750a

2.200a

2.300a

2.250a

Moderately frequent

1.000a

1.166a

1.083b

1.800a

1.866a

1.833ab

Less frequent

0.701a

0.700a

0.700b

1.500a

1.400a

1.450b

Mean

1.100a

1.255a

1.833a

1.8553a

Treatment means sharing the different letter(s) in a group are significantly different at p ≥ 0.05

 

In the present study, moderately frequent irrigation (10 days interval) gave significantly greater plant height and leaf area of okra than frequent (5 days interval) and less frequent irrigation treatments (15 days interval). This study supports the previous findings of Khalil (2004), who found increased growth rate in terms of plant height and number of leaves per plant when the plants were grown with 10 days’ irrigation interval. Abbas (2007) found that irrigation at every 8 days’ interval gave significantly taller okra plants. The variations in the present and previous results could be due to soil type and environmental differences. The increased growth of summer vegetables by the application of frequent or moderately frequent irrigations with sewage water was possibly due to that this water not only provides moisture but also contains nutrients required for proper growth and development.

In the present study, frequent irrigation application significantly increased the number of fruits per plant, fruit length, fruit diameter, fresh and dry weight of individual fruit and yield per hectare in tomato compared with moderately frequent and less frequent irrigation treatments. The larger size of tomato fruits was probably due to proper supply of water at particular development stage such as reproductive phase, which needs more supply of water and nutrients for the production of an appreciable size of fruits. The yield of tomato significantly increased with increasing the frequency of sewage water (Phene et al., 1986). Gudugi et al. (2012) reported that irrigation interval at 4 days resulted in a higher number of tomato fruits and greater yield than with 8 days interval during 2010-2011, possibly associated with conditions of low humidity and high temperature, which could quickly dry the soil. Less availability of irrigation water negatively affects the hormonal balance, plant growth, development, and nutrients translocation (Salisbury and Ross, 1992). Bafeel and Moftah (2008) concluded that reduced vegetative growth and negative effect on yield and its components in eggplants could be related to drought stress. Similar results were also achieved for tomato by Mahmood (2008).

The present study indicated that the irrigation regimes used have a significant effect on yield and yield components of okra. This difference in yield was possibly due to excessive and low irrigation application to okra crop (Al-Harbi et al., 2008). The decreased yield was also observed in water-stressed okra plants (Sankar et al., 2008). The current findings are connected with the conclusions of Khalil (2004), who found significantly greater pod length, pod weight and yield of okra under 10 days irrigation interval. This difference in the results was due to different soil types and environmental conditions of the growing areas. The increased yield in the present study was also possibly due to the application of sewage water, as this water is enriched with macro and micronutrients and organic matter, which ultimately increased yields of the studied vegetables.

 

Table 7: Effect of sewage water irrigation frequency on heavy metal contents in tomato and okra roots.

Frequency of irrigation water

Tomato fruits

Okra pods

Year 2012

Year 2013

Mean

Year 2012

Year 2013

Mean

Pb (mg kg-1)

Frequent

12.966a

13.200a

13.083a

7.533a

8.100a

7.816a

Moderately frequent

9.500a

11.500a

10.500ab

6.700a

7.200a

6.950a

Less frequent

7.533a

9.600a

8.567b

5.400a

6.300a

5.850b

Mean

10.00a

11.43a

6.544a

7.200a

Ni (mg kg-1)

Frequent

19.633a

23.167a

21.400a

13.500a

13.600a

13.550a

Moderately frequent

17.633a

19.400a

18.517ab

11.700a

12.500a

12.100b

Less frequent

15.700a

17.800a

16.750b

10.067a

10.200a

10.133c

Mean

17.656a

20.122a

11.756a

12.100a

Cu (mg kg-1)

Frequent

16.600a

17.500a

17.050a

16.400 a

15.633a

16.017a

Moderately frequent

14.733a

15.567a

15.150ab

15.300a

15.533a

15.417ab

Less frequent

12.600a

13.700a

13.150b

13.500a

13.967a

13.733b

Mean

14.644a

15.589a

15.067a

15.044a

Cd (mg kg-1)

Frequent

3.800a

4.200a

4.000a

1.333a

1.416a

1.375a

Moderately frequent

3.400a

3.700a

3.550ab

0.700a

1.100a

0.900ab

Less frequent

2.733a

3.200a

2.966b

0.300a

0.6300a

0.466b

Mean

3.311a

3.700a

0.744a

1.050a

Fe (mg kg-1)

Frequent

289.27a

313.63a

301.45a

310.50a

327.53a

311.43a

Moderately frequent

252.47a

266.13a

259.30b

295.33

304.57a

307.53a

Less frequent

172.43a

196.00a

184.22c

271.77a

270.47a

71.12b

Mean

238.06a

258.59a

290.56a

302.83a

Cr (mg kg-1)

Frequent

2.433a

2.700a

2.566a

2.600a

2.933a

2.766a

Moderately frequent

1.800a

2.200a

2.000ab

2.333a

2.533a

2.433ab

Less frequent

1.200a

1.900a

1.550b

1.866a

2.200a

2.033b

Mean

1.811a

2.266a

2.266a

2.555a

Treatment means sharing the different letter(s) in a group are significantly different at p ≥ 0.05

 

Total fresh and dry plant tomato plant biomass was significantly greater with 5 days sewage irrigation frequency, followed by 10 days interval and the minimum was recorded with 15 days irrigation interval. Reduced dry weight of shoot and leaves of tomato results usually due to insufficient soil moisture (Singandhupe et al., 2003). Various plant physiological processes might be hampered due to inadequate availability of soil water. Water stress tends to decrease root growth of the tomato plant, which leads to reduced shoot dry weight because the development of roots and shoots are closely related (Ismail et al., 2008). In another study, total tomato plant biomass was decreased with water stress (Birhanu and Tilahun, 2010).

In the present study, significantly increased fresh and dry total plant biomass were obtained in okra plants grown with moderately frequent irrigation (10 days interval) than frequent (5 days interval) and less frequent irrigation treatment (15 days interval). Reduction in biomass of okra plant due to water stress has already been reported by Sankar et al. (2008).

Significantly greater Pb, Cr, Ni, Fe, Cu and Cd substances were noted in the cultivated tomato fruits and okra pods when plants were irrigated frequently (5 days interval), while less frequent irrigation treatment (15 days interval) resulted in lesser accumulation of these heavy metals. All the fruit and pod samples of tomato and okra plants under all three irrigation frequency treatments exhibited Pb and Cd contents exceeding above the higher approved limits set by Asaolu (1995) and WHO (1996). Ni contents in fruits of tomato plants irrigated with frequent and moderately frequent irrigation treatments were above the maximum permissible limits, and these contents were below the permissible limits when less frequent irrigation was applied. Whereas Cu, Fe and Cr contents in fruits of tomato plants irrigated with all the three irrigation frequency treatments were below the maximum permissible limits. The Ni and Cr contents in okra pods were found below the safer limits when grown with all the three irrigation frequency treatments. The pods contained Cu contents above the permissible limits when sewage water was applied frequently, while moderately and less frequent irrigation treatments resulted in Cu contents below the recommended levels. Frequent and moderately frequent sewage water applications showed higher Fe contents in pods above the permissible limits, while less frequent sewage water application showed lower content in pods lower the safe limits, recognized by Asaolu (1995) and WHO (1996).

Application of sewage water continuously pollutes the soils with heavy metals. Soils act as filters of poisonous compounds, possibly absorbing and retaining heavy metals from sewage water. When soils’ capacity to retain heavy metals, contents is decreased due to loading of these contaminants continuously or soil pH changes, then soils can discharge these toxic metals into water or soil solution and make available for plants uptake. The results of the present study indicated that as the frequency of sewage irrigation application was increased, there was more accumulation of heavy metals in plant parts. It was possibly due to more buildup of heavy metals in soil because of indiscriminate use of sewage water which ultimately contaminated the crop plants grown on those soils. It was observed that as the duration of sewage irrigation interval increased, there was less accumulation of heavy metals in plant parts. It is because the heavy metals contents were increased with frequent irrigation treatment and decreased when grown with moderately and less frequent irrigation applications in the present investigation.

Tomato and okra leaves and roots showed all the heavy metals contents as affected by the frequency of irrigation treatments in order: frequent > moderately frequent > less frequent sewage water application. With the decrease in duration of sewage irrigation application, the metals tended to accumulate in the soil, and their availability in soil solution and uptake resulted in greater metal content in plant parts. Therefore, the frequent irrigation water increased the heavy metals contents in tomato and okra plant parts as compared to moderately frequent irrigation application, while less frequent irrigation application resulted in lower metals contents in plant parts. Thus, the frequent use of sewage water for irrigation has a greater ability to pollute the soil, which in turn results in uptake of metals by crops.

 

Acknowledgement

The data presented in this manuscript is a part of Ph.D. thesis research conducted at the Department of Horticulture, Bahauddin Zakariya University, Multan. The authors are grateful to the Higher Education Commission for financial assistance to conduct the research under the Indigenous PhD Fellowship Program.

 

Novelty Statement

Novelty of the current research highlights the malpractices performed in olericulture by farming community by the frequent use of sewage water application in an increased amount which results in the accumulation of Fe, Cu, Pb, Cr, Ni and Cd in higher amounts in okra and tomato in pods and fruits respectively. Resultantly these commodities are used as food and a serious hazard for human health.

 

Author’s Contribution

The idea was conceived by Safina Naz and Muhammad Akbar Anjum. The experiments were performed by Safina Naz, Sajid Ali, Hassan Sardar and Sakeena Tul Ain Haider. Statistical analysis was performed by Syed Atif Hasan Naqvi and Zehri Khan. The overall management of the article was performed by Muhammad Asif Zulfiqar, Sibghat Ullah, Hajra Azeem and Shah Pasand.

Conflict of interest

The authors have declared no conflict of interest.

 

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