Bull Environ Contam Toxicol (2014) 92:160–164 DOI 10.1007/s00128-013-1182-5
Fly Ash Addition Affects Microbial Biomass and Carbon Mineralization in Agricultural Soils A. K. Nayak • Anjani Kumar • R. Raja • K. S. Rao • Sangita Mohanty • Mohammad Shahid Rahul Tripathy • B. B. Panda • P. Bhattacharyya
•
Received: 14 August 2013 / Accepted: 16 December 2013 / Published online: 22 December 2013 Ó Springer Science+Business Media New York 2013
Abstract The microbial biomass carbon (MBC) and carbon mineralization of fly ash (FA) amended soil at (0 %, 1.25 %, 2.5 %, 5 %, 10 % and 20 % FA; v/v) was investigated under laboratory conditions for 120 days at 60 % soil water-holding capacity and 25 ± 1°C temperature. The results demonstrated that soil respiration and microbial activities were not suppressed up to 2.5 % FA amendment and these activities decreased significantly at 10 % and 20 % FA treatment with respect to control. Application of 10 % and 20 % FA treated soils showed a decreasing trend of soil MBC with time; and the decrease was significant throughout the period of incubation. The study concluded
A. K. Nayak (&) A. Kumar R. Raja K. S. Rao S. Mohanty M. Shahid R. Tripathy B. B. Panda P. Bhattacharyya Crop Production Division, Central Rice Research Institute, Cuttack 753 006, Orissa, India e-mail: [email protected] A. Kumar e-mail: [email protected] R. Raja e-mail: [email protected] K. S. Rao e-mail: [email protected] S. Mohanty e-mail: [email protected] M. Shahid e-mail: [email protected] R. Tripathy e-mail: [email protected] B. B. Panda e-mail: [email protected] P. Bhattacharyya e-mail: [email protected]
123
that application of FA up to 2.5 % can thus be safely used without affecting the soil biological activity and thereby improve nutrient cycling in agricultural soils. Keywords Fly ash Cultivated soil Microbial biomass carbon Soil respiration
Fly ash, an inorganic by-product of coal combustion, emitted at coal-fired power generating stations has been reported to be a repository of nutrients which helps in reclamation of alkaline and saline soils and also improves soil properties for plant growth (Kesh et al. 2003). However, a number of environmental impacts have been identified that can result from the use of FA as a soil amendment and most of these impacts are associated with trace elements present in FA such as B, Se, Mo, As, Cd, and Ni (Page et al. 1979). Application of acidic FA up to 100 t ha-1 in an agricultural soil had no measurable impact on soil heterotrophic microbial activity as determined by cumulative CO2–C production but application of FA at levels of 400 and 700 t ha-1 inhibited CO2–C production (Arthur et al. 1984). To study microbial activities in soil, carbon mineralisation is a reliable method, which assesses the changes in carbon mineralization rate and has also been used as a criterion for assessing pollutant toxicity (Torstenssen and Stenstorm 1986). During microbial mediated biodegradation of carbonaceous compounds, the altered rate of CO2 evolution from soil indicates changes in ecosystem-level process, specifically carbon cycling. However, this effect on carbon cycling may have ramifications on the mineralization of other plant-essential elements, such as P, N, S, and K contained in the soil. Microbial biomass carbon is the fraction of soil organic matter that is sensitive to management practices and pollution (Powlson
Bull Environ Contam Toxicol (2014) 92:160–164
1994) and considered as an important attribute of soil quality (Doran and Parkin 1994). The soil MBC is used as a predictor of pollutant degradation capacity (Voos and Groffman 1997) and is commonly used to characterize the microbiological status of soil (Nannipieri et al. 1990). MBC is very sensitive to management practices such as nutrient application (Nayak et al. 2012), pesticide application (Kumar et al. 2012) and field management (Perrott et al. 1992). To consider FA as a soil amendment, especially in agricultural soils, its potential impacts on soil microbiological processes need to be evaluated as part of an effort to maintain soil fertility and crop productivity. Our aim in this paper is to study the effect of FA application on soil MBC and Cmin.
Materials and Methods Soil samples were collected in polythene bags from the surface layer (0–15 cm) from Central Rice Research Institute, Cuttack, India (85°550 E, 20°250 N; elevation 24 m above mean sea level). Mean annual maximum and minimum temperatures of the area are 39.2 and 22.5°C, respectively, and the mean annual temperature is 27.7°C. The area receives an annual precipitation of about 1,500 mm year-1. It qualifies for the hyperthermic temperature class as the difference between mean summer soil temperature and mean winter soil temperature is more than 5°C. The soil of the farm area has been developed from the deltaic sediments of Mahanadi River in recent times. The detail of the experimental soil and FA used in this experiment is given in Table 1. The soil sample was processed and sieved using a 2 mm sieve; 100 g of processed soil sample was taken in each Schott bottles (500 mL), and a calculated quantity of water was added to bring the soil samples to 60 % of maximum water holding capacity. They were then acclimatized at 25(± 1)°C in the dark for 1 week. FA was collected from the FA-dykes of Aarati Steel Plant, Athagarh, Odisha India. The FA was stabilized at 52°C for 24 h to kill off pathogens and dried at room temperature for 1 week. After the stabilization period, they were ground to pass through a 4 mm sieve to obtain homogeneous samples before mixing with the soil. Calculated amounts of FA @ 0.5 %, 1.25 %, 2.5 %, 5 %, 10 % and 20 %, which corresponds to 10, 25, 50, 100, 200 and 400 t ha-1, were applied to 100 g soil in individual Schott bottles. Eight sets of each FA treated soil, along with control were maintained under similar conditions and replicated thrice. The treated soils in Schott bottles were incubated at 60 % water-holding capacity and 25°C temperature. Each bottle contained 0.1 N NaOH in a vial to trap evolved CO2. The vials were removed
161 Table 1 Physico-chemical properties and heavy metal content of the soil and FA used Parameters
Fly ash
Soil
2.0–0.02 mm
35.5
52.5
0.02–0.002 mm
53.8
20.2
\0.002 mm
10.7
26.7
Particle size (%)
Bulk density (mg m-3)
0.99
1.43
pH (1:2 H20)
7.6
6.8
Electrical conductivity (dSm-1) Total N (%)
0.4 Traces
0.4 0.07
Total P (%)
0.05
0.04
Total K (%)
0.2
0.13
Total S (%)
0.8
0.04
CEC (cmol (P?)/kg)
6.3
14.9
Organic carbon (g kg-1)
4.2
7.1
Fe
112
41.5
Cu
4.5
1.25
Mn
75.3
4.01
Zn
5.00
0.82
Cd
0.43
0.03
Pb
2.44
0.67
Cr
0.79
0.11
DTPA extractable metals (mg kg-1)
periodically at 0 (2 h after application), 7, 15, 30, 45, 60, 90 and 120 days of incubation for estimation of Cmin. The CO2–C evolved from soil was measured by back titrating the unspent alkali in the vial with standard HCl for estimating potential carbon mineralization (Zibilski 1994). Three subsamples, 10 g each, were taken from the Schott bottle for estimation of MBC. One subsample of soil was fumigated using ethanol-free chloroform (25 mL) placed in a vacuum desiccators (Joergensen 1996). The chloroform was allowed to boil under reduced pressure for 2 min followed by incubation at 25°C for 24 h. The second subsample of soil was kept under similar conditions in the desiccator without chloroform (unfumigated). The third subsample of soil was kept in an oven for estimation of the moisture content. The fumigated and unfumigated soils were extracted separately with 40 mL of 0.5 (M) K2SO4 for 30 min in an oscillating shaker at 200 rpm. An aliquot of the filtered extract (8 mL) was refluxed with 0.4 (N) K2Cr2O7 (2 mL) for 30 min, and the residual dichromate was measured by back titration with 0.04 (N) ferrous ammonium sulfate using ferroin indicator (Vance et al. 1987) to estimate the extracted carbon. MBC was calculated by subtracting the extracted carbon in unfumigated samples from that measured in fumigated samples, and dividing it by a Kc value (extraction efficiency of microbial biomass carbon) of 0.45 (Vance et al. 1987).
123
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Bull Environ Contam Toxicol (2014) 92:160–164
Soil and fly ash samples were air dried and homogenized by grinding in a stainless steel grinder and then passed through a 2 mm sieve to analyze heavy metals. Phyto available heavy metals of fly ash and soil was determined following DTPA extraction technique (Lindsay and Norvell 1978) and the metals were determined using atomic absorption spectrophotometer (Varian SpectrAA55B). A SAS statistical package was used for one-way ANOVA analysis to compare the means of the different treatments. When significant F values were detected, the differences between individual means were tested (p B 0.05) using the least significant difference (LSD) test. Duncan’s multiple range tests was used to perform the significance differences between the treatment means.
Results and Discussion An important bio-indicator of soil quality is potential microbial activity (Gregorich et al. 1994) which is efficiently measured by carbon mineralization (Gray 1990). It is an important parameter for assessing the side effects of stress like pesticide and FA (Sommerville 1987; Alef 1995) and depends not only on the intensity of the stress but also on the period of exposure of the microbes to the stress. The Cmin values recorded under the present experimentation are shown in Table 2. CO2 evolution in soils treated with 0.5 %–5 % FA, initially increased for 7 days, and then decreased up to 120 days. However, a decreasing trend of CO2 evolution was observed in soils treated with 10 %–20 % FA. Cmin in soils treated with 10 %–20 % FA was significantly lower compared to control throughout the incubation period except on day 0. Whereas, beyond 7 days of incubation period, Cmin in 0.5 %–2.5 % FA treated soils remained statistically at par with control, except at some days of incubation where the treatments showed increasing or decreasing events, which later on was at par with control.
This indicates that the FA application at 0.5 %–2.5 % is not high enough to suppress soil microbial activities. Arthur et al. (1984) reported that unweathered, acidic FA applications up to 100 t ha-1 in soil had no measurable impact on soil heterotrophic microbial activity as determined by cumulative CO2–C production, but application of FA at levels of 400 and 700 t ha-1 inhibited CO2–C production. Pati and Sahu (2004) found little or no inhibition of CO2 up to 2.5 % FA amendment but further addition of FA, significantly decreased CO2 evolution and MBC. On the other hand, significant stimulation of CO2 evolution and microbial activities were observed up to 5 % FA amendment when the soils contained earthworms. This may be due to increased microbial activity induced by substrates that are produced by the earthworms. Surridge et al. (2009) has reported that FA addition has a liming effect on the soil leading to increased mobility of calcium and hydroxide ions, ultimately causing an increase in bacterial species richness. However, FA also has a high content of toxic heavy metals (Page et al. 1979) which can hinder normal microbial metabolic processes, when added in the soil at higher concentrations. Several short-term laboratory incubation studies reported that addition of FA at higher rates to different soils inhibited microbial respiration, enzyme activity and soil nitrogen cycling processes such as nitrification and N mineralization (Cerevelli et al. 1986; Wong and Wong 1986; Pichtel 1990; Pichtel and Hayes 1990; Garau et al. 1991). MBC is the fraction of soil organic matter that is sensitive to management practices and pollution (Powlson 1994) and it is a good indicator of soil health since it regulates nutrient cycling and acts as a highly labile source of plant available nutrients (Jenkinson and Ladd 1981). MBC in 0.5 %–5 % FA treated soils increased significantly up to 30 days, thereafter decreased progressively with time (Table 3). Application of 10 % and 20 % FA treated soils showed a decreasing trend of soil MBC with time; and the decrease was significant throughout the period of
Table 2 Carbon mineralization following application of FA Treatment
Control
Carbon mineralization (mg CO2–C kg-1 soil) at different days (d) of incubation 0 day
7 days
15 days
30 days
45 days
60 days
90 days
120 days
106.92BCb
293.85Ba
120.78Ab
69.59ABc
52.16Ad
46.71Be
30.72ABf
5.28BCg
10 T (0.5 %)
113.68ABb
326Aa
104.56Bb
68.42ABc
55.23Ad
46.03Bd
34.37Ae
4.03CDf
25 T (1.25 %)
116.72ABb
331.08Aa
121.48Ab
65.51Bc
50.40ABd
53.07Ad
25.39BCe
5.76BCf
50 T (2.5 %)
128.6Ab
339.81Aa
113.07ABb
72.91Ac
45.16Bd
46.32Bd
28.39Be
11.28Af
100 T (5.0 %)
106.92BCb
193.6Ca
73.72Cc
65.46Bc
30.73Cde
35.47Cd
26.88BCe
3.752Df
200 T (10 %)
96.76Ca
76.38Db
34.66Dc
31.35Cc
21.08Dd
21.55Dd
23.04Cd
13.76Ae
400 T (20 %)
94.64Ca
67.88Db
27.16Dc
34.36Cc
14.32Ee
17.96Ee
22.21Cd
7.52Bf
Means with the same upper case letter are not significantly different in a column on the same day; means with the same lower case letter are not significantly different in a row in same treatment
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Bull Environ Contam Toxicol (2014) 92:160–164
163
Table 3 Microbial biomass carbon in soil following application of FA Treatment
Microbial biomass carbon (mg kg-1) in soil at different days of incubation 0 days
7 days
15 days
30 days
45 days
60 days
90 days
120 days
Control
168.05Ac
181.52Bb
197.91Da
184.52Cb
181.52Cb
173.92BCc
168.05Bc
167.96ABc
10 T (0.5 %)
173.92Ae
197.91Ac
229.12Ab
248.95Aa
221.55Ab
184.52ABd
181.52Ad
172.53Ae
25 T (1.25 %)
172.53Ad
184.52ABc
220.58ABb
238.64Aa
209.06Ab
184.52ABc
173.92ABd
168.05ABd
50 T (2.5 %)
167.96Abe
181.52BCd
213.23BCb
237.61Aa
208.78ABb
193.79Ac
167.96Be
165.76Abe
100 T (5.0 %)
161.28Bd
173.92Cc
206.47CDa
213.23Ba
197.91BCb
168.05Ccd
147.99Ce
151.41Be
200 T (10 %)
144.67Ca
132.90Db
116.98Ec
110.13Dc
99.93Dd
86.17De
80.00De
75.10Ce
400 T (20 %)
143.11Ca
129.21Db
115.73Eb
99.87Dc
92.60Dc
80.66Dd
74.67Dd
71.69Cd
Means with the same upper case letter are not significantly different in a column in same day; means with the same lower case letter are not significantly different in a row in same treatment
incubation. MBC was significantly higher in 0.5 %–2.5 % FA treated soils as compared to control up to 60 days except initial period (0 days). However, the soil MBC was significantly lower throughout the period of incubation in 10 %–20 % FA treatment as compare to control. Rippon and Wood (1975) confirmed increased microbial population with FA addition to the release of nutrients from FA with time. However, FA also has a high content of toxic heavy metals (Page et al. 1979) which can hinder normal microbial metabolic processes when added in the soil at higher concentrations. Saffigna et al. (1989) and Wong and Wong (1986) reported that dehydrogenase activity and microbial biomass in soil was highest at 10 % FA amendment, since FA amendment at moderate levels provides nutrients to the micro-organisms for carrying out various metabolic activities without any adverse effect. According to Rumpel et al. (1998), when FA was added at higher levels ([ than 10 %), a decline in microbial activity was observed, this could have been due to a decrease in substrate availability associated with accumulation of persistent lignite-derived organic carbon compounds. Schutter and Fuhrmann (2001) indicated that FA amendment may be a benefit more to fungi and gram-negative bacteria than other components of the soil microbial community.
Conclusion Soil heterotrophic microbial populations, as measured by microbial biomass carbon and carbon mineralization is minimally affected by low (upto 2.5 %) levels of FA amendment. But, at high levels of amendment (10 % or 20 %), soil microbial activity is adversely affected. However, laboratory results and field results may differ a lot, as in the field condition many factors could mask or, reduce the potential toxicity of FA. Therefore, before arriving at a general conclusion for the effect of FA on microbial
biomass and carbon mineralization activities of soil microbial populations, further detail studies under field condition would be a more realistic approach. Acknowledgments Financial support provided by the Department of Science and Technology, Government of India via the project ‘‘Confidence building and facilitation of large scale use of fly ash as an ameliorant and nutrient source for enhancing rice productivity and soil health’’ for this study is greatly appreciated.
References Alef K (1995) Estimation of soil respiration. In: Alef K, Nannipieri P (eds) Methods in applied soil microbiology and biochemistry. Academic Press, London Arthur MA, Zwick TC, Tolle DA, Voris PV (1984) Effects of fly ash on microbial CO2 evolution from an agricultural soil. Water Air Soil Pollut 22:209–216 Cerevelli S, Petruzzelli G, Perna A, Menicagli R (1986) Soil nitrogen and fly ash utilization: a laboratory investigation. Agrochemica 30:27–33 Doran JW, Parkin TB (1994) Defining and assessing soil quality. In: Doran JW, Coleman DC, Bezdicek DF, Stewart BA (eds) Defining soil quality for sustainable environment. Special Pub. 35. Soil Science Society of America, Madison Garau MA, Dalmau JL, Felipo MT (1991) Nitrogen mineralization in soil amended with sewage sludge and fly ash. Biol Fertil Soils 12:199–201 Gray TRG (1990) Methods for studying the microbial ecology of soil. In: Grigorovia R, Norris JR (eds) Methods in microbiology, vol 22. Academic Press, London, pp 309–342 Gregorich EG, Carter MR, Angers DA, Monreal CM, Ellert BH (1994) Towards a minimum data set to assess soil organic matter quality in agricultural soils. Can J Soil Sci 74:367–385 Jenkinson DS, Ladd JN (1981) Microbial biomass in soil: measurement and turnover. In: Paul EA, Ladd JN (eds) Soil Biochemistry. Decker, New York, pp 415–471 Joergensen RG (1996) The fumigation–extraction method to estimate soil microbial biomass: calibration of the kEC value. Soil Biol Biochem 28:25–31 Kesh S, Kalra N, Sharma SK, Chaudhary A (2003) Fly ash incorporation effects on soil characteristics, growth and yield of wheat. Asia Pacific J Environ Dev 4:53–69 Kumar A, Nayak AK, Shukla AK, Panda BB, Raja R, Shahid M, Tripathi R, Mohanty S, Rath PC (2012) Microbial biomass and
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164 carbon mineralization in agricultural soils as affected by pesticide addition. Bull Environ Contam Toxicol 88:538–542 Lindsay WL, Norvell WA (1978) Development of DTPA soil test for Zn, Fe, Mn and Cu. Soil Sci Soc Am J 42:421–428 Nannipieri P, Grego S, Ceccanti B (1990) Ecological significance of the biological activity in soil. Soil Biol Biochem 6:293–355 Nayak AK, Gangwar B, Shukla AK, Sonali PM, Kumar A, Raja R, Kumar A, Kumar V, Rai PK, Mohan U (2012) Long-term effect of different integrated nutrient management on soil organic carbon and its fractions and sustainability of rice–wheat system in Indo Gangetic Plains of India. Field Crop Res 127:129–139 Page AL, Elseewi AA, Straughan IR (1979) Physical and Chemical properties of fly ash from coal-fired power plants with special reference to environmental impacts. Residue Rev 71:83–120 Pati SS, Sahu SK (2004) CO2 evolution and enzyme activities (dehydrogenase, protease and amylase) of fly ash amended soil in the presence and absence of earthworms (Drawid awillsi Michaelsen) under laboratory conditions. Geoderma 118: 289–301 Perrott KW, Sarathchandra SU, Dow BW (1992) Seasonal and fertilizer effects on the organic cycle and microbial biomass in a hill country soil under pasture. Austr J Soil Res 30:383–394 Pichtel JR (1990) Microbial respiration in fly ash/sewage sludge amended soils. Environ Pollut 63:225–237 Pichtel JR, Hayes JM (1990) Influence of fly ash on soil microbial activity and populations. J Environ Qual 19:593–597 Powlson DS (1994) The soil microbial biomass: before, beyond and back. In: Dighton J, Giller KE, Ritz K (eds) Beyond the biomass. Wiley, Chichester Rippon JE, Wood MJ (1975) Microbiological aspects of pulverized fuel ash. In: Chadwick MJ, Goodman GT (eds) The ecology of resource degradation and renewal. John Wiley and Sons, New York, pp 331–349
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Bull Environ Contam Toxicol (2014) 92:160–164 Rumpel C, Knicker H, Kogel-Knaber I, Skjiemstad JO, Huuetti RF (1998) Types and chemical composition of organic matter in reforested lignite-rich mine soils. Geoderma 86:123–142 Saffigna PG, Powlson DS, Brookes PC, Thomas GA (1989) Influence of sorghum residues and tillage on soil organic matter and soil microbial biomass in an Australian vertisol. Soil Biol Biochem 21:759–765 Schutter FE, Fuhrmann JJ (2001) Soil microbial community responses to fly ash amendment as revealed by analyses of whole soils and bacterial isolates. Soil Biol Biochem 33:1947–1958 Sommerville L (1987) Perspective on side effect testing. In: Sommerville L, Greaves MP (eds) Pesticide effects in soil microflora. Taylor and Francis, London Surridge AKJ, Merwe A, Kruger R (2009) Preliminary microbial studies on the impact of plant sand South African fly ash on amelioration of crude oil polluted soils. In World of Coal Ash (WOCA) Conference, May 4–7 Torstenssen L, Stenstorm J (1986) Basic respiration rate as a tool for prediction of pesticide persistence in soil. Toxic Assess 1:57–72 Vance ED, Brookes PC, Jenkinson DS (1987) An extraction method for measuring soil microbial biomass. Soil Biol Biochem 19:703–707 Voos G, Groffman PM (1997) Relationship between microbial biomass and dissipation of 2, 4-D and Dicamba in soil. Biol Fertil Soils 24:106–110 Wong MH, Wong JWC (1986) Effects of fly ash on soil microbial activity. Environ Pollut Asses 40:127–144 Zibilski LM (1994) Carbon mineralization. In: Bingham JM, Mickelson SH (eds) ‘Methods of soil analysis’, Part 2. Microbiological and biochemical properties SSSA, Book Series No. 5.ASA, SSSA, Madison
Fly Ash Addition Affects Microbial Biomass and Carbon Mineralization in Agricultural Soils A. K. Nayak • Anjani Kumar • R. Raja • K. S. Rao • Sangita Mohanty • Mohammad Shahid Rahul Tripathy • B. B. Panda • P. Bhattacharyya
•
Received: 14 August 2013 / Accepted: 16 December 2013 / Published online: 22 December 2013 Ó Springer Science+Business Media New York 2013
Abstract The microbial biomass carbon (MBC) and carbon mineralization of fly ash (FA) amended soil at (0 %, 1.25 %, 2.5 %, 5 %, 10 % and 20 % FA; v/v) was investigated under laboratory conditions for 120 days at 60 % soil water-holding capacity and 25 ± 1°C temperature. The results demonstrated that soil respiration and microbial activities were not suppressed up to 2.5 % FA amendment and these activities decreased significantly at 10 % and 20 % FA treatment with respect to control. Application of 10 % and 20 % FA treated soils showed a decreasing trend of soil MBC with time; and the decrease was significant throughout the period of incubation. The study concluded
A. K. Nayak (&) A. Kumar R. Raja K. S. Rao S. Mohanty M. Shahid R. Tripathy B. B. Panda P. Bhattacharyya Crop Production Division, Central Rice Research Institute, Cuttack 753 006, Orissa, India e-mail: [email protected] A. Kumar e-mail: [email protected] R. Raja e-mail: [email protected] K. S. Rao e-mail: [email protected] S. Mohanty e-mail: [email protected] M. Shahid e-mail: [email protected] R. Tripathy e-mail: [email protected] B. B. Panda e-mail: [email protected] P. Bhattacharyya e-mail: [email protected]
123
that application of FA up to 2.5 % can thus be safely used without affecting the soil biological activity and thereby improve nutrient cycling in agricultural soils. Keywords Fly ash Cultivated soil Microbial biomass carbon Soil respiration
Fly ash, an inorganic by-product of coal combustion, emitted at coal-fired power generating stations has been reported to be a repository of nutrients which helps in reclamation of alkaline and saline soils and also improves soil properties for plant growth (Kesh et al. 2003). However, a number of environmental impacts have been identified that can result from the use of FA as a soil amendment and most of these impacts are associated with trace elements present in FA such as B, Se, Mo, As, Cd, and Ni (Page et al. 1979). Application of acidic FA up to 100 t ha-1 in an agricultural soil had no measurable impact on soil heterotrophic microbial activity as determined by cumulative CO2–C production but application of FA at levels of 400 and 700 t ha-1 inhibited CO2–C production (Arthur et al. 1984). To study microbial activities in soil, carbon mineralisation is a reliable method, which assesses the changes in carbon mineralization rate and has also been used as a criterion for assessing pollutant toxicity (Torstenssen and Stenstorm 1986). During microbial mediated biodegradation of carbonaceous compounds, the altered rate of CO2 evolution from soil indicates changes in ecosystem-level process, specifically carbon cycling. However, this effect on carbon cycling may have ramifications on the mineralization of other plant-essential elements, such as P, N, S, and K contained in the soil. Microbial biomass carbon is the fraction of soil organic matter that is sensitive to management practices and pollution (Powlson
Bull Environ Contam Toxicol (2014) 92:160–164
1994) and considered as an important attribute of soil quality (Doran and Parkin 1994). The soil MBC is used as a predictor of pollutant degradation capacity (Voos and Groffman 1997) and is commonly used to characterize the microbiological status of soil (Nannipieri et al. 1990). MBC is very sensitive to management practices such as nutrient application (Nayak et al. 2012), pesticide application (Kumar et al. 2012) and field management (Perrott et al. 1992). To consider FA as a soil amendment, especially in agricultural soils, its potential impacts on soil microbiological processes need to be evaluated as part of an effort to maintain soil fertility and crop productivity. Our aim in this paper is to study the effect of FA application on soil MBC and Cmin.
Materials and Methods Soil samples were collected in polythene bags from the surface layer (0–15 cm) from Central Rice Research Institute, Cuttack, India (85°550 E, 20°250 N; elevation 24 m above mean sea level). Mean annual maximum and minimum temperatures of the area are 39.2 and 22.5°C, respectively, and the mean annual temperature is 27.7°C. The area receives an annual precipitation of about 1,500 mm year-1. It qualifies for the hyperthermic temperature class as the difference between mean summer soil temperature and mean winter soil temperature is more than 5°C. The soil of the farm area has been developed from the deltaic sediments of Mahanadi River in recent times. The detail of the experimental soil and FA used in this experiment is given in Table 1. The soil sample was processed and sieved using a 2 mm sieve; 100 g of processed soil sample was taken in each Schott bottles (500 mL), and a calculated quantity of water was added to bring the soil samples to 60 % of maximum water holding capacity. They were then acclimatized at 25(± 1)°C in the dark for 1 week. FA was collected from the FA-dykes of Aarati Steel Plant, Athagarh, Odisha India. The FA was stabilized at 52°C for 24 h to kill off pathogens and dried at room temperature for 1 week. After the stabilization period, they were ground to pass through a 4 mm sieve to obtain homogeneous samples before mixing with the soil. Calculated amounts of FA @ 0.5 %, 1.25 %, 2.5 %, 5 %, 10 % and 20 %, which corresponds to 10, 25, 50, 100, 200 and 400 t ha-1, were applied to 100 g soil in individual Schott bottles. Eight sets of each FA treated soil, along with control were maintained under similar conditions and replicated thrice. The treated soils in Schott bottles were incubated at 60 % water-holding capacity and 25°C temperature. Each bottle contained 0.1 N NaOH in a vial to trap evolved CO2. The vials were removed
161 Table 1 Physico-chemical properties and heavy metal content of the soil and FA used Parameters
Fly ash
Soil
2.0–0.02 mm
35.5
52.5
0.02–0.002 mm
53.8
20.2
\0.002 mm
10.7
26.7
Particle size (%)
Bulk density (mg m-3)
0.99
1.43
pH (1:2 H20)
7.6
6.8
Electrical conductivity (dSm-1) Total N (%)
0.4 Traces
0.4 0.07
Total P (%)
0.05
0.04
Total K (%)
0.2
0.13
Total S (%)
0.8
0.04
CEC (cmol (P?)/kg)
6.3
14.9
Organic carbon (g kg-1)
4.2
7.1
Fe
112
41.5
Cu
4.5
1.25
Mn
75.3
4.01
Zn
5.00
0.82
Cd
0.43
0.03
Pb
2.44
0.67
Cr
0.79
0.11
DTPA extractable metals (mg kg-1)
periodically at 0 (2 h after application), 7, 15, 30, 45, 60, 90 and 120 days of incubation for estimation of Cmin. The CO2–C evolved from soil was measured by back titrating the unspent alkali in the vial with standard HCl for estimating potential carbon mineralization (Zibilski 1994). Three subsamples, 10 g each, were taken from the Schott bottle for estimation of MBC. One subsample of soil was fumigated using ethanol-free chloroform (25 mL) placed in a vacuum desiccators (Joergensen 1996). The chloroform was allowed to boil under reduced pressure for 2 min followed by incubation at 25°C for 24 h. The second subsample of soil was kept under similar conditions in the desiccator without chloroform (unfumigated). The third subsample of soil was kept in an oven for estimation of the moisture content. The fumigated and unfumigated soils were extracted separately with 40 mL of 0.5 (M) K2SO4 for 30 min in an oscillating shaker at 200 rpm. An aliquot of the filtered extract (8 mL) was refluxed with 0.4 (N) K2Cr2O7 (2 mL) for 30 min, and the residual dichromate was measured by back titration with 0.04 (N) ferrous ammonium sulfate using ferroin indicator (Vance et al. 1987) to estimate the extracted carbon. MBC was calculated by subtracting the extracted carbon in unfumigated samples from that measured in fumigated samples, and dividing it by a Kc value (extraction efficiency of microbial biomass carbon) of 0.45 (Vance et al. 1987).
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Soil and fly ash samples were air dried and homogenized by grinding in a stainless steel grinder and then passed through a 2 mm sieve to analyze heavy metals. Phyto available heavy metals of fly ash and soil was determined following DTPA extraction technique (Lindsay and Norvell 1978) and the metals were determined using atomic absorption spectrophotometer (Varian SpectrAA55B). A SAS statistical package was used for one-way ANOVA analysis to compare the means of the different treatments. When significant F values were detected, the differences between individual means were tested (p B 0.05) using the least significant difference (LSD) test. Duncan’s multiple range tests was used to perform the significance differences between the treatment means.
Results and Discussion An important bio-indicator of soil quality is potential microbial activity (Gregorich et al. 1994) which is efficiently measured by carbon mineralization (Gray 1990). It is an important parameter for assessing the side effects of stress like pesticide and FA (Sommerville 1987; Alef 1995) and depends not only on the intensity of the stress but also on the period of exposure of the microbes to the stress. The Cmin values recorded under the present experimentation are shown in Table 2. CO2 evolution in soils treated with 0.5 %–5 % FA, initially increased for 7 days, and then decreased up to 120 days. However, a decreasing trend of CO2 evolution was observed in soils treated with 10 %–20 % FA. Cmin in soils treated with 10 %–20 % FA was significantly lower compared to control throughout the incubation period except on day 0. Whereas, beyond 7 days of incubation period, Cmin in 0.5 %–2.5 % FA treated soils remained statistically at par with control, except at some days of incubation where the treatments showed increasing or decreasing events, which later on was at par with control.
This indicates that the FA application at 0.5 %–2.5 % is not high enough to suppress soil microbial activities. Arthur et al. (1984) reported that unweathered, acidic FA applications up to 100 t ha-1 in soil had no measurable impact on soil heterotrophic microbial activity as determined by cumulative CO2–C production, but application of FA at levels of 400 and 700 t ha-1 inhibited CO2–C production. Pati and Sahu (2004) found little or no inhibition of CO2 up to 2.5 % FA amendment but further addition of FA, significantly decreased CO2 evolution and MBC. On the other hand, significant stimulation of CO2 evolution and microbial activities were observed up to 5 % FA amendment when the soils contained earthworms. This may be due to increased microbial activity induced by substrates that are produced by the earthworms. Surridge et al. (2009) has reported that FA addition has a liming effect on the soil leading to increased mobility of calcium and hydroxide ions, ultimately causing an increase in bacterial species richness. However, FA also has a high content of toxic heavy metals (Page et al. 1979) which can hinder normal microbial metabolic processes, when added in the soil at higher concentrations. Several short-term laboratory incubation studies reported that addition of FA at higher rates to different soils inhibited microbial respiration, enzyme activity and soil nitrogen cycling processes such as nitrification and N mineralization (Cerevelli et al. 1986; Wong and Wong 1986; Pichtel 1990; Pichtel and Hayes 1990; Garau et al. 1991). MBC is the fraction of soil organic matter that is sensitive to management practices and pollution (Powlson 1994) and it is a good indicator of soil health since it regulates nutrient cycling and acts as a highly labile source of plant available nutrients (Jenkinson and Ladd 1981). MBC in 0.5 %–5 % FA treated soils increased significantly up to 30 days, thereafter decreased progressively with time (Table 3). Application of 10 % and 20 % FA treated soils showed a decreasing trend of soil MBC with time; and the decrease was significant throughout the period of
Table 2 Carbon mineralization following application of FA Treatment
Control
Carbon mineralization (mg CO2–C kg-1 soil) at different days (d) of incubation 0 day
7 days
15 days
30 days
45 days
60 days
90 days
120 days
106.92BCb
293.85Ba
120.78Ab
69.59ABc
52.16Ad
46.71Be
30.72ABf
5.28BCg
10 T (0.5 %)
113.68ABb
326Aa
104.56Bb
68.42ABc
55.23Ad
46.03Bd
34.37Ae
4.03CDf
25 T (1.25 %)
116.72ABb
331.08Aa
121.48Ab
65.51Bc
50.40ABd
53.07Ad
25.39BCe
5.76BCf
50 T (2.5 %)
128.6Ab
339.81Aa
113.07ABb
72.91Ac
45.16Bd
46.32Bd
28.39Be
11.28Af
100 T (5.0 %)
106.92BCb
193.6Ca
73.72Cc
65.46Bc
30.73Cde
35.47Cd
26.88BCe
3.752Df
200 T (10 %)
96.76Ca
76.38Db
34.66Dc
31.35Cc
21.08Dd
21.55Dd
23.04Cd
13.76Ae
400 T (20 %)
94.64Ca
67.88Db
27.16Dc
34.36Cc
14.32Ee
17.96Ee
22.21Cd
7.52Bf
Means with the same upper case letter are not significantly different in a column on the same day; means with the same lower case letter are not significantly different in a row in same treatment
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Table 3 Microbial biomass carbon in soil following application of FA Treatment
Microbial biomass carbon (mg kg-1) in soil at different days of incubation 0 days
7 days
15 days
30 days
45 days
60 days
90 days
120 days
Control
168.05Ac
181.52Bb
197.91Da
184.52Cb
181.52Cb
173.92BCc
168.05Bc
167.96ABc
10 T (0.5 %)
173.92Ae
197.91Ac
229.12Ab
248.95Aa
221.55Ab
184.52ABd
181.52Ad
172.53Ae
25 T (1.25 %)
172.53Ad
184.52ABc
220.58ABb
238.64Aa
209.06Ab
184.52ABc
173.92ABd
168.05ABd
50 T (2.5 %)
167.96Abe
181.52BCd
213.23BCb
237.61Aa
208.78ABb
193.79Ac
167.96Be
165.76Abe
100 T (5.0 %)
161.28Bd
173.92Cc
206.47CDa
213.23Ba
197.91BCb
168.05Ccd
147.99Ce
151.41Be
200 T (10 %)
144.67Ca
132.90Db
116.98Ec
110.13Dc
99.93Dd
86.17De
80.00De
75.10Ce
400 T (20 %)
143.11Ca
129.21Db
115.73Eb
99.87Dc
92.60Dc
80.66Dd
74.67Dd
71.69Cd
Means with the same upper case letter are not significantly different in a column in same day; means with the same lower case letter are not significantly different in a row in same treatment
incubation. MBC was significantly higher in 0.5 %–2.5 % FA treated soils as compared to control up to 60 days except initial period (0 days). However, the soil MBC was significantly lower throughout the period of incubation in 10 %–20 % FA treatment as compare to control. Rippon and Wood (1975) confirmed increased microbial population with FA addition to the release of nutrients from FA with time. However, FA also has a high content of toxic heavy metals (Page et al. 1979) which can hinder normal microbial metabolic processes when added in the soil at higher concentrations. Saffigna et al. (1989) and Wong and Wong (1986) reported that dehydrogenase activity and microbial biomass in soil was highest at 10 % FA amendment, since FA amendment at moderate levels provides nutrients to the micro-organisms for carrying out various metabolic activities without any adverse effect. According to Rumpel et al. (1998), when FA was added at higher levels ([ than 10 %), a decline in microbial activity was observed, this could have been due to a decrease in substrate availability associated with accumulation of persistent lignite-derived organic carbon compounds. Schutter and Fuhrmann (2001) indicated that FA amendment may be a benefit more to fungi and gram-negative bacteria than other components of the soil microbial community.
Conclusion Soil heterotrophic microbial populations, as measured by microbial biomass carbon and carbon mineralization is minimally affected by low (upto 2.5 %) levels of FA amendment. But, at high levels of amendment (10 % or 20 %), soil microbial activity is adversely affected. However, laboratory results and field results may differ a lot, as in the field condition many factors could mask or, reduce the potential toxicity of FA. Therefore, before arriving at a general conclusion for the effect of FA on microbial
biomass and carbon mineralization activities of soil microbial populations, further detail studies under field condition would be a more realistic approach. Acknowledgments Financial support provided by the Department of Science and Technology, Government of India via the project ‘‘Confidence building and facilitation of large scale use of fly ash as an ameliorant and nutrient source for enhancing rice productivity and soil health’’ for this study is greatly appreciated.
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