Ind J Plant Physiol. (April–June 2016) 21(2):213–218
DOI 10.1007/s40502-016-0214-7
SHORT COMMUNICATION
Municipal sludge: an effective soil supplement for improving plant
growth
B. Dhir1
Received: 24 November 2015 / Accepted: 12 March 2016 / Published online: 28 March 2016
Ó Indian Society for Plant Physiology 2016
Abstract Studies were conducted to evaluate the effect
of municipal sludge amendment in soil on the growth of
crop plants. Tomato (Lycopersicon esculentum) var. Pusa
Hybrid 2 and wheat (Triticum aestivum) var. PBW 343
plants were raised in pots containing soil supplemented
with different proportions (*10, 20, 30 %) of sludge.
Amendment of sludge in soil resulted in enrichment of
nutrients such as phosphorus, nitrogen and potassium.
Increased nutrient availability promoted growth and productivity in plants. The growth and productivity of the
plants raised in sludge supplemented soil was comparable
to those raised in manure and compost supplemented soil.
The growth was significantly higher in all the soil
amendments in comparison to control. The present findings
suggested that municipal sludge can serve as a soil
supplement.
Keywords Growth Lycopersicon Productivity Sludge Triticum
Sludge generated as by-product of wastewater treatment is
treated as a waste and disposed in landfills (both surface
and subsurface). Alternatively it is used in land reclamation, forestry, horticulture, landscaping, energy and
resource recovery (Ahmed et al. 2010). Recently, its usage
in agriculture has been suggested as one of the eco-friendly
option for its disposal (Singh and Agrawal 2010; Rı́os et al.
2012). Sludge components such as organic matter,
macronutrients such as N, P, K, Ca, Na and Mg, trace
& B. Dhir
[email protected]
1
Department of Genetics, University of Delhi South Campus,
New Delhi 110021, India
elements and microorganisms enrich soil and improve its
physico-chemical properties (Rı́os et al. 2012). Organic
amendments such as manure and compost have been
commonly used as supplements for agricultural production
since decades. The interest in the replacement of synthetic
agrochemicals with organic amendments has prompted the
need for eco-friendly alternates. Few researches have been
carried out to explore the possibility of use of sludge as a
soil supplement to enhance the fertility of soils and hence
the agricultural output (Al Zoubi et al. 2008). The present
study was carried out with the objectives, (a) to assess the
utility of sludge as a soil supplement, (b) to compare its
efficacy with other conventional soil amendments, and
(c) assess its effect on plant growth and productivity.
Air-dried sludge generated from treatment of municipal
wastewater (industrial and domestic both) was collected
from Common Effluent treatment Plant (CETP) located at
Mayapuri, New Delhi, India. Soil (clay loam) (collected
from 10 cm surface depth) and sludge was dried, homogenized, passed through a 2-mm sieve and analyzed for
physico-chemical properties (Dhir and Srivastava 2012).
Organic matter (%) and available N, P, K was determined
following the standard methods (Black et al. 1965; Lindsay
and Norvel 1978; Kalra and Maynard 1991). The sludge
was mixed with soil in three proportions representing 10 %
(S1), 20 % (S2) and 33 % (S3). Similarly soil was supplemented with same proportions of vegetal compost (C1, C2,
C3) and cowdung manure (M1, M2, M3). The soil without
any supplement was referred as the control (C). The concentration of the sludge used in the experiment was decided
on the basis of previous studies (Hbaiz et al. 2014). Ten
seeds of tomato var. Pusa Hybrid 2 and wheat (Triticum
aestivum) var. PBW 343 were placed in each pot containing two kilograms of soil-sludge mixtures. Plants harvested after 20 and 60 days of sowing (DAS) were treated
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Ind J Plant Physiol. (April–June 2016) 21(2):213–218
as pre-flowering and flowering stages. The growth parameters such as shoot length were measured in each treatment
consisting of three pot replicates with three plants each.
The leaf chlorophyll content was estimated spectrophotometrically following standard protocol (Arnon
1949). Total soluble protein content was measured
according to Bradford (1976). The amount of total soluble
sugars was estimated by phenol sulphuric acid reagent
method (Dubois et al. 1951). The quantum yield (Y) of
photosynthesis was measured using mini-portable PAM
fluorometer (mini-PAM, Walz, Effeltrich, Germany). The
parameters measured included the efficiency of photosystem II (Fv/Fm), photochemical quenching (qp), non-photochemical (qN) quenching, photochemical efficiency of
PSII (Y), the rate of electron transport (ETR) (Dhir and
Srivastava 2012). The data obtained as mean values from
three independent experiments each with three replicates
was subjected to Duncan’s Multiple Range tests to check
the level of significance differences between control and
treated samples. The mean values of different treatments
were compared using LSD test at 0.05 probability.
Sludge contained high organic carbon, nutrient (N, P, K)
content, water holding capacity, and cation exchange
capacity. Manure and compost also showed high proportions of all these parameters (Table 1). Addition of soil
supplements enhanced nutritional value, water holding
capacity and organic carbon content. The soil enrichment
positively affected the plant growth. The response of plants
to soil amendments varied from species to species and
according to treatment. The morphological parameters such
as shoot length increased in both the plants raised in all soil
amendments (sludge, manure and compost) in comparison
to control, except at flowering stage, where the compost
treated wheat and tomato plants did not show much
difference from controls (Table 2). The chlorophyll content
showed an increase in sludge and manure supplemented
soil at both the growth stages in tomato and wheat plants,
while plants raised in compost supplemented soil showed
varying trend with increases at pre-flowering stage in
tomato and flowering stage in wheat. Total soluble protein
and sugar levels noted an increase in plants raised in soils
amended with manure, sludge and compost in comparison
to control. Total soluble sugars showed a varying trend in
plants under different treatments in comparison to control.
Similar responses of improvement in plant growth after
sludge amendment in soil has been noted in few plant
species including Zea mays, Vigna radiata, Helianthus
annus, Abelmoschus esculentus, Triticum, Vigna, Daucus,
Lactuca, Raphanus, Spinacia (Al Zoubi et al. 2008; Singh
and Agrawal 2010; Roy et al. 2010). Fv/Fm, photochemical
efficiency of chlorophyll-a, showed no significant changes
in any of the treatments with respect to control. Photochemical quenching (qP), non-photochemical quenching
(qN) showed variation within treatments at pre-flowering
and flowering stages in comparison to control. Electron
transport rate (ETR) did not show any significant change in
all the treatments at both the stages in tomato and wheat,
whereas quantum yield of photosystem II [Y(II)] showed
variation at flowering stage (Table 3). Photosystem II
activity was not affected hence inducing no alteration in
photosynthesis. The results are in agreement with earlier
findings in Solanum, Lycopersicon (Dhir and Rajam 2015;
Dhir 2015).
Wheat yield showed increase in soil supplemented with
manure, sludge and compost in comparison to control. The
spike length, number of spikelets per spike, number of
seeds per spike, number of seeds plant-1 and seed weight
was higher in wheat plants raised in treated soils in
Table 1 Physico-chemical characters of sludge, manure, compost and soil
Parameters
Physiochemical characteristics
Sludge
Manure
Compost
Soil
Soil after sludge amendment
10 %
20 %
33 %
pH
EC (dS m-1)
6.8
3.6
7.4
4.2
6.9
3.9
6.5
0.067
6.5
0.01
6.5
0.026
6.7
0.37
TDS (mg l-1)
1769
2345
1878
34
57
89
118
Water holding capacity (%)
114.3
216.4
167.2
40.1
42
45
48
Cation exchange capacity (meq 100-g-1)
46.8
79.6
54.6
16.6
18
21
27
Organic carbon (%)
5.52
15.2
7.6
0.2
0.3
0.7
1.9
Nitrogen (kg ha-1)
289
354
303
56
62
71
81
Phosphorus (kg ha-1)
335
405
356
6.25
45
93
231
Potassium (kg ha-1)
664
711
689
174
191
267
411
The data represent mean values from three independent experiments
123
1345 ± 51c
1350 ± 44c
Total soluble sugars
(lg g-1 fresh wt.)
b
b
2880 ± 22a
2671 ± 23a
Total soluble sugars
(lg g-1 fresh wt.)
a
b
a
2925 ± 31a
5620 ± 48a
976 ± 29
b
42.2 ± 3ab
1104 ± 33b
578 ± 27bc
867 ± 23
35 ± 2b
1223 ± 34c
3388 ± 32a
879 ± 27
35 ± 3a
590 ± 25a
542 ± 19c
607 ± 13
13.3 ± 2a
S3
*, ** Significant difference at p \ 0.05
ab
b
a
2495 ± 33a
5244 ± 38a
924 ± 35
36.6 ± 2a
1204 ± 47a
405 ± 21a
1019 ± 46
33 ± 2b
1238 ± 41b
3233 ± 41a
840 ± 25
32 ± 4a
629 ± 28b
526 ± 21c
605 ± 8
a
13.8 ± 3a
M1
Data followed by different letters in columns are significantly different at p B 0.05
Each value represents mean ± SE
5688 ± 51a
5610 ± 45a
Total soluble protein
(lg g-1 fresh wt.)
987 ± 31
1043 ± 32
Total chlorophyll
(lg g-1 fresh wt.)
b
47.1 ± 3b
Shoot length (cm)
47.1 ± 4b
1186 ± 33b
Total soluble sugars
(lg g-1 fresh wt.)
b
1143 ± 45b
691 ± 21c
Total soluble protein
(lg g-1 fresh wt.)
Wheat
693 ± 23c
1075 ± 44
936 ± 31
30 ± 3ab
28 ± 2ab
Total chlorophyll
(lg g-1 fresh wt.)
Tomato
Shoot length (cm)
Flowering
3310 ± 27a
3221 ± 23a
Total soluble protein
(lg g-1 fresh wt.)
903 ± 31
859 ± 23
b
Total chlorophyll
(lg g-1 fresh wt.)
33 ± 2a
31 ± 4a
Shoot length (cm)
ab
690 ± 26b
660 ± 21b
Total soluble sugars
(lg g-1 fresh wt.)
Wheat
516 ± 23c
478 ± 12b
596 ± 8
a
a
584.1 ± 9
13 ± 2a
S2
13.5 ± 3a
S1
Treatments
Total soluble protein
(lg g-1 fresh wt.)
Total chlorophyll
(lg g-1 fresh wt.)
Shoot length (cm)
Tomato
Pre-flowering
Stage/parameters
a
b
a
2696 ± 28a
5433 ± 36a
956 ± 37
ab
40.7 ± 3ab
1177 ± 43b
410 ± 21a
895 ± 25
35 ± 4b
1223 ± 32b
3433 ± 36a
875 ± 33
34 ± 3a
587 ± 21a
494 ± 12b
614 ± 11
13 ± 2a
M2
Table 2 Various morphological and biochemical parameters measured at different time intervals
a
b
a
2794 ± 23a
5280 ± 42a
936 ± 31
47.7 ± 3b
1154 ± 45b
494 ± 21b
977 ± 37
35 ± 3b
1278 ± 45b
3480 ± 44a
813 ± 23
36 ± 5a
572 ± 24a
446 ± 11a
678 ± 6
a
13.6 ± 2a
M3
a
a
ab
2567 ± 28a
5120 ± 43a
958 ± 29
36.8 ± 2a
1207 ± 48b
511 ± 26b
843 ± 22
24 ± 3a
1190 ± 34ab
3220 ± 33a
802 ± 24
29 ± 3a
564 ± 24a
488 ± 13b
604 ± 9
a
13.9 ± 2a
C1
a
a
a
2667 ± 31a
5280 ± 38a
941 ± 34
a
38.9 ± 3ab
1188 ± 46b
535 ± 12b
840.9 ± 45
24.5 ± 2a
1201 ± 32ab
3301 ± 36a
817 ± 25
31 ± 4a
523 ± 32a
534 ± 25c
604 ± 11
13.5 ± 3a
C2
a
a
a
2365 ± 33a
5244 ± 42a
908 ± 29
33.6 ± 2a
1139 ± 36b
583 ± 56bc
847 ± 35
24 ± 2a
1198 ± 36b
3079 ± 29a
821 ± 19
27.4 ± 3a
528 ± 34a
583 ± 12c
619 ± 8
a
13.8 ± 4a
C3
a
a
2521 ± 28a
5179 ± 34a
908 ± 33a
40 ± 4ab
1216 ± 56a
385 ± 28a
896 ± 46
24 ± 3a
988 ± 33a
3047 ± 28a
815 ± 22a
28 ± 4a
586 ± 42a
423 ± 30a
580 ± 12
12.8 ± 2a
Control
5.80
9.04
7.04*
2.93
6.39*
11.83*
11.53*
1.83
24*
16
18*
3.03
13.39*
15.83*
11.53*
1.23
LSD
(p B 0.05)
Ind J Plant Physiol. (April–June 2016) 21(2):213–218
215
123
123
0.311 ± 0.08ab
0.608 ± 0.1a
0.287 ± 0.06b
0.605 ± 0.1a
qN
Y (II)
0.255 ± 0.05a
0.398 ± 0.06b
0.226 ± 0.05a
0.368 ± 0.04b
qN
Y (II)
0.203 ± 0.05ab
0.576 ± 0.08ab
0.126 ± 0.04b
0.647 ± 0.08a
qN
Y (II)
0.599 ± 0.1ab
0.303 ± 0.06a
0.835 ± 0.9a
49.1 ± 3
a
0.775 ± 0.08a
0.398 ± 0.06b
0.212 ± 0.06a
0.802 ± 0.1a
38 ± 4a
0.702 ± 0.08a
0.655 ± 0.1a
0.263 ± 0.07b
0.910 ± 0.2a
52.17 ± 4
a
0.765 ± 0.1a
0.598 ± 0.05a
0.163 ± 0.06b
0.776 ± 0.08a
47.6 ± 3
a
0.793 ± 0.09a
S3
0.588 ± 0.1ab
0.302 ± 0.05a
0.799 ± 0.2ab
45.8 ± 4
ab
0.773 ± 0.08a
0.486 ± 0.07a
0.284 ± 0.06a
0.753 ± 0.07a
38.33 ± 3a
0.727 ± 0.08a
0.591 ± 0.09a
0.311 ± 0.06ab
0.839 ± 0.1b
47.5 ± 4
a
0.782 ± 0.09a
0.556 ± 0.1a
0.159 ± 0.05b
0.733 ± 0.08a
44.5 ± 6
a
0.780 ± 0.08a
M1
0.502 ± 0.09b
0.264 ± 0.06ab
0.688 ± 0.1b
44.2 ± 3
NS indicates non-significant difference
b
0.765 ± 0.08a
0.513 ± 0.07a
0.241 ± 0.06a
0.794 ± 0.08a
40.7 ± 3a
0.735 ± 0.09a
0.608 ± 0.1a
0.412 ± 0.08a
0.859 ± 0.1b
48.7 ± 3
a
0.786 ± 0.2a
0.583 ± 0.07a
0.234 ± 0.05a
0.776 ± 0.08a
46.7 ± 5
a
0.791 ± 0.09a
M2
Data followed by different letters in columns are significantly different at p B 0.05
0.717 ± 0.1ab
0.849 ± 0.1a
qp
49.2 ± 4
a
51.4 ± 3
a
ETR
Fv/Fm
0.795 ± 0.08a
0.809 ± 0.1a
0.837 ± 0.1a
qp
0.786 ± 0.09a
32.5 ± 4a
34.4 ± 4a
ETR
Wheat
0.632 ± 0.08b
0.604 ± 0.07b
Fv/Fm
Tomato
Flowering
0.839 ± 0.1b
0.820 ± 0.1b
qp
49.7 ± 6
a
48.9 ± 5
a
ETR
Fv/Fm
0.799 ± 0.1a
0.547 ± 0.1a
0.567 ± 0.1a
Y (II)
0.805 ± 0.1a
0.198 ± 0.08b
0.147 ± 0.05b
qN
Wheat
0.715 ± 0.08a
0.773 ± 0.08a
qp
43.2 ± 4
a
0.792 ± 0.08a
S2
45.3 ± 5
a
0.780 ± 0.09a
S1
Treatments
ETR
Fv/Fm
Tomato
Pre-flowering
Stage/parameters
Table 3 Photosynthetic parameters measured at different time intervals
0.613 ± 0.05ab
0.219 ± 0.08ab
0.837 ± 0.09a
42.3 ± 2
b
0.767 ± 0.09a
0.467 ± 0.06a
0.251 ± 0.05a
0.758 ± 0.08a
36.5 ± 5a
0.717 ± 0.09a
0.609 ± 0.2a
0.333 ± 0.0ab
0.828 ± 0.09b
48.6 ± 5
a
0.795 ± 0.1a
0.586 ± 0.06a
0.146 ± 0.07b
0.777 ± 0.09a
46.6 ± 6
a
0.781 ± 0.09a
M3
0.589 ± 0.08ab
0.154 ± 0.05b
0.804 ± 0.1ab
47 ± 4
a
0.767 ± 0.1a
0.499 ± 0.1a
0.21 ± 0.07a
0.845 ± 0.09a
39.7 ± 4a
0.677 ± 0.08a
0.663 ± 0.2a
0.287 ± 0.03b
0.945 ± 0.2a
51 ± 6
a
0.759 ± 0.4a
0.559 ± 0.09a
0.148 ± 0.08b
0.775 ± 0.08a
44.6 ± 5
a
0.756 ± 0.09a
C1
0.519 ± 0.07b
0.293 ± 0.04a
0.698 ± 0.1b
40.8 ± 3
b
0.758 ± 0.09a
0.396 ± 0.05b
0.198 ± 0.05a
0.785 ± 0.09a
34.7 ± 2a
0.628 ± 0.08b
0.584 ± 0.1a
0.435 ± 0.1a
0.807 ± 0.1b
47.6 ± 4
a
0.775 ± 0.5a
0.551 ± 0.06a
0.149 ± 0.09b
0.724 ± 0.09a
43.9 ± 5
a
0.781 ± 0.09a
C2
0.636 ± 0.6a
0.201 ± 0.06ab
0.866 ± 0.2a
50.8 ± 5
a
0.771 ± 0.08a
0.499 ± 0.09a
0.218 ± 0.06a
0.804 ± 0.09a
38.9 ± 4a
0.688 ± 0.08a
0.591 ± 0.1a
0.453 ± 0.07a
0.826 ± 0.1b
47.1 ± 5
a
0.787 ± 0.1a
0.567 ± 0.07a
0.228 ± 0.05a
0.734 ± 0.09a
43.7 ± 2
a
0.786 ± 0.08a
C3
0.615 ± 0.09ab
0.255 ± 0.05ab
0.846 ± 0.2a
47.8 ± 4a
0.771 ± 0.1a
0.464 ± 0.08a
0.217 ± 0.02a
0.757 ± 0.09a
37.2 ± 2a
0.644 ± 0.07b
0.577 ± 0.9a
0.431 ± 0.07a
0.914 ± 0.2a
46.5 ± 4a
0.775 ± 0.1a
0.511 ± 0.04a
0.262 ± 0.02a
0.743 ± 0.08a
41.4 ± 2a
0.707 ± 0.08a
Control
0.06
0.06
0.08
0.56
ns
0.07
0.07
0.08
1.89
0.08
0.06
0.52
0.05
ns
ns
ns
0.09
ns
ns
ns
LSD
(p B 0.05)
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Ind J Plant Physiol. (April–June 2016) 21(2):213–218
5 ± 0.8b
Number of
fruits
plant-1
5 ± 0.6b
4 ± 0.5ab
5 ± 0.7b
16 ± 2ab
2.32 ± 0.4a
0.465 ± 0.6bc
7.3 ± 1bc
11 ± 1a
10.5 ± 2a
1.82 ± 0.5ab
M1
4 ± 0.6ab
18 ± 3a
4.03 ± 0.8b
0.670 ± 0.8b
10 ± 2b
9 ± 0.8ab
10 ± 3a
2.15 ± 0.7ab
M2
Data followed by different letters in columns are significantly different at p B 0.05
16 ± 2ab
Number of
flowers
plant-1
Tomato
15 ± 3ab
3.39 ± 0.5ab
7.5 ± 1c
4.23 ± 0.8b
Seeds weight
(g plant-1)
17 ± 3a
0.678 ± 0.8b
1.58 ± 0.6a
0.847 ± 0.2ab
Seed weight (g
spike-1)
Number of
seeds
spike-1
8 ± 2bc
8 ± 0.6ab
18 ± 4a
10 ± 0.9a
8.5 ± 2ab
1.896 ± 0.2c
S3
12 ± 2ab
9 ± 0.8ab
9.5 ± 1a
8.7 ± 1ab
Spike length
(cm)
Number of
spikelets
spike-1
2.67 ± 0.5a
S2
1.93 ± 0.4b
S1
Treatments
Fresh wt. (g
plant-1)
Wheat
Parameters
Table 4 Yield parameters of tomato and wheat
4 ± 0.5ab
14 ± 3ab
1.88 ± 0.5a
0.376 ± 0.5c
5 ± 1c
8.75 ± 0.5ab
9.2 ± 1ab
0.899 ± 0.4c
M3
4 ± 0.6ab
14 ± 2ab
4.28 ± 0.6b
1.075 ± 0.8a
11 ± 3ab
8 ± 1ab
8 ± 0.9ab
2.5 ± 0.5a
C1
4 ± 0.5ab
16 ± 2ab
3.56 ± 0.7ab
0.890 ± 0.7ab
10 ± 2b
7 ± 0.8ab
7 ± 0.8ab
2.13 ± 0.8ab
C2
4 ± 0.5ab
14 ± 3ab
2.21 ± 0.4a
0.552 ± 0.6bc
9 ± 2bc
6 ± 0.4b
6 ± 0.7b
1.69 ± 0.7b
C3
3 ± 0.4a
12 ± 2b
2 ± 0.4a
0.5 ± 0.5bc
6 ± 1c
6 ± 0.7b
6.5 ± 0.8b
0.98 ± 0.6c
Control
1.53*
3.07*
1.01*
0.87
2.43*
1.56
1.80*
0.45
LSD
(p B 0.05)
Ind J Plant Physiol. (April–June 2016) 21(2):213–218
217
123
218
comparison to control (Table 4). In tomato, number of
flowers plant-1, number of fruits plant-1 increased in
plants raised in soil amended with sludge, compost and
manure in comparison to control (Table 4). It has been
reported that increased nitrogen supply help in increasing
the plant’s yield (Ahmed et al. 2010). Earlier studies
reported that sludge amendment (20 t ha-1) increased the
grain weight (1000 grain) and straw yield in wheat. The
increases noted in grain yield are associated with high
concentrations of nutrient such as N and P (Jamil et al.
2006; Al Zoubi et al. 2008; Tamrabet et al. 2009). Earlier,
fertilization of the soil with 50 % sludge showed significant improvement in agronomic parameters in pepper and
other crop plants (Özyazıcı 2013; Hbaiz et al. 2014).
The present study demonstrated that sludge supplementation @30 % improves soil nutritional quality. The
nutrients as well as organic matter present in sludge
improve soil fertility, which supports plant growth; hence
sludge had good potential as manure and compost for
improving growth of plants. The composition (presence of
toxic contaminants such as microbes, metals) is crucial for
deciding response of the plants. Based on the preliminary
results it can be suggested that sludge could partly substitute for fertilizer if applied in the right amounts to soil.
Further studies for optimization of dose and frequency of
sludge supplementation in soil are required. Therefore
reuse of sludge as soil supplement can prove to be a sustainable approach for its management.
Acknowledgments The financial assistance from University Grants
Commission (UGC) is gratefully acknowledged. The valuable guidance and support of mentor Profesor M.V. Rajam is gratefully
acknowledged.
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