CONTAMINATION OF SOIL WITH HARD COAL ASH AS MODIFIER OF PHYSICOCHEMICAL AND BIOLOGICAL PROPERTIES OF SOIL

Jan Kucharski, Ewa Jastrzębska, Jadwiga Wyszkowska
Department of Microbiology, University of Warmia and Mazury in Olsztyn, Poland

ABSTRACT

A vegetation experiment (88 days) studied the effect of soil contamination with fly ash produced in hard coal combustion (0.0; 33.3; 66.6; 99.9 g·kg^-1 of soil) on the physicochemical properties of soil, the yield of oat (Borowiak) and maize (Reduta), selected soil bacteria count and the activity of soil enzymes: dehydrogenases, urease, alkaline and acid phosphatases. Oat was grown as the main crop and maize – as the successive crop. Two doses of nitrogen fertilisation were applied: 75 and 150 mg N·kg^-1 of soil. Physicochemical, biochemical and microbiological analyses were conducted twice – after oat and maize harvest. A study of the ash-contaminated soil revealed an increase in the soil content of C, N, K, Mg, P, Ca, Na, Cu and Ni, the soil alkalisation, disturbed microbiological balance and reduced activity of dehydrogenases, urease and acidic phosphatase.

Key words: fly ash, soil contamination, yields, physicochemical properties, microorganisms count, soil enzymes.

INTRODUCTION

Ash-slag mixtures and fly-ashes are produced in power plants, thermal-electric power stations, heat generating plants and individual households from hard coal used as fuel. According to the data provided by the Central Statistical Office [6], 12.7 m tonnes of this kind of waste was produced in Poland in 2003. Currently, 261.6 m tonnes of ash is stored at plant dumpsites and other sites intended for this purpose.

Ash from hard coal is sometimes used in building construction [12]. Its alkaline character and a high concentration of mineral substances (which are indispensable to plants) have resulted in attempts at using it as fertiliser, both in itself [9] and in connection with sludge [31] or peat [26]. Ash has also been used to enhance the physicochemical properties of soil [10].

Unfortunately, apart from necessary nutrients, combustion ashes contain elevated concentrations of heavy metals [24], which, once in the soil, can adversely affect its biological properties and, if taken up by plants, can be excessively accumulated in their tissues [23].

Ash may either have a positive or negative effect on plant growth and yielding. This effect is determined primarily by the chemical composition and the ash dose applied. In a study by Kalra et al. [11] ash (5-12 t·ha^-1·year^-1) modified the soil physicochemical properties and decreased the wheat yield. On the other hand, Khan and Khan [13] in their studies into the effect of increasing concentrations of ash in the soil (from 10 to 100% of the volume) on the growth of tomatoes, observed a positive effect of ash on plants (higher yields of plants and fruits, greater content of chlorophyll and carotenoids) even at soil contamination with ash of 50% of its volume. Only greater ash doses decreased the yield. According to these authors, ash increased soil porosity and pH and enriched the soil with the elements such as P, K, Ca, Mg, Mn, Cu, Zn and P, necessary for plant growth and development. On the other hand, overdosed ash may lead to an increased accumulation of heavy metals in the soil and plants which can have a negative effect on the growth and development of both the plants and the soil microorganisms.

Based on the previous results, the effect of soil fertilisation with ash has been quite well explored although the effect of this contaminant on the soil microorganisms is not well covered in literature. These microorganisms are an important element of the soil environment as they participate in the degradation of organic matter and make the nutrients available to other soil organisms, favour the formation of soil aggregates and immobilise heavy metals [3]. Pati and Sahu [21] observed a slight stimulation of the activity of dehydrogenases, protease and amylase at low soil contamination with ash (2.5%) and a decrease in the activity of the enzymes examined at higher soil contamination (from 5 to 50%).

A great amount of elements (C, K, Ca, Mg, Cu, Zn, Cd, Cr and Ni) get into the soil as a result of the ash used at high doses and may probably change the chemical as well as physicochemical soil properties, which, in turn, may determine the biological and biochemical soil properties, irrespective of the crop. Therefore, this study aimed at determining the effect of combustion ashes on physicochemical properties of soil, enzymatic activity and microorganisms count.

MATERIAL AND METHODS

A pot experiment was carried out in a greenhouse, in four replications. The pot soil taken showed the following characteristics: Eutric Cambisols from the humus horizon (0-20 cm) with pH_KCl – 6.65, base saturation (BS) – 87.38% and cation exchange capacity (CEC) – 73.40 mmol(+)·kg^-1. The ash from hard coal (pH_KCl – 12.2) was obtained from the OZOS thermal-electric power station in Olsztyn. The chemical composition of ash is given in Table 1.

The experiment included the following factors: a) dose of ash hard coal (g·kg^-1 of soil) – 0.0; 33.3; 66.6; 99.9; b) level of N fertilisation in urea – 75 or 150 mg N·kg^-1 of soil; crop – ‘Borowiak’ oat and ‘Reduta’ maize.

Each soil sample (3.2 kg) was mixed with the appropriate amount of ash as well as macro- and microelements and then placed in a polyethylene pot. In all the objects, the same level of mineral fertilization was applied (calculated as a pure element in mg·kg^-1 of soil): – P – 100 (KH₂PO₄), K – 150 (KH₂PO₄+KCl) and Mg – 50 (MgSO₄·7H₂O), Zn – 5 (ZnCl₂), Cu – 5 (CuSO₄·5H₂O), Mn – 5 (MnCl₂·5H₂O), Mo – 5 (Na₂MoO₄·2H₂O) and B – 0.33 (H₃BO₃).

Fifteen oat plants were grown in each pot as the main crop, whereas 5 maize plants were grown in each pot as a successive crop. Throughout the experiment 60% of the soil water capillary capacity was maintained with distilled water.

The experiment took 88 days; 43 days of oat growing (plants were harvested during the panicle emergence) and 45 days of maize vegetation. On the harvest day the plant yield was determined and soil sampled. The soil samples were stored in polyethylene bags at 4°C until the laboratory analyses were conducted (7 days). The microbiological analyses of the soil included a determination of the bacteria count in selective medium using the plate method in three reps. The counts of oligotrophic bacteria (Olig), spore-forming oligotrophic bacteria (Olig_p), copiotrophic bacteria (Cop), spore-forming copiotrophic bacteria (Cop_p), ammonifying bacteria (Am), nitrogen immobilising bacteria (Im), cellulolytic bacteria (Cel), Azotobacter spp. (Az), actinomycetes (Act) and fungi (Fun) were determined with methods reported by Kucharski and Wyszkowska [15] and the counts of Arthrobacter spp. (Art) and Pseudomonas spp. (Ps) according to Mulder and Antheumisse methods [18]. Microorganisms were incubated at 28°C and the number of the colonies grown was counted with a bacterial colony counter.

Biochemical analysis involved the activity of soil enzymes: dehydrogenases (Deh) with TTC substrate, according to the Öhlinger method [19], urease (Ure) determined with Alef and Nannipieri [1], acid phosphatase (Pac) and alkaline phosphatase (Pal) with methods developed by Alef et al. [2]. Based on the enzymatic activity of the soil and the organic carbon content, the potential biochemical index of soil fertility (M_w) was calculated from Kucharski’s formula [14]:

M_w = (Ure/10 + Deh + Pac + Pal)·%C_org

The soil reaction (pH) was determined potentiometrically in a 1 mol·dm^-3 KCl aqueous solution, hydrolytic acidity (Hh) and the total content of alkaline exchange cations (S) were measured using the Kappen method and the organic carbon C_org, soil cation exchange capacity (cec) and base saturation (BS) – with the Tiurin method [17].

The contents of particular elements in soil samples after the maize harvest and in ash included:

• available forms of P and K – with the Egner-Riehm method – the soil was extracted with an aqueous solution of 0.02 mol dm^-3 (CH₃CHOHCOO)₂Ca·5H₂O, (soil to extractor ratio – 1:50); phosphorus content was determined spectrophotometrically, potassium – with the AAS (atomic absorption spectrometry) method [15]; Mg – with the method of atomic emission spectrometry after extracting the soil with a 0.0125 M solution of CaCl₂·6H₂O (soil to calcium chloride ratio – 1:10) [15]; Zn with the AAS method after extracting the soil with 1M HCl (soil to extractor ratio – 1:10) [22];

• the total content of N – with the Kjeldahl method [15], Ca, K and Mg – with the method of atomic emission spectrometry, P – with the vanadium-molybdenum method after mineralization in sulphuric acid, Na, Zn, Cd, Cr, Cu, Fe, Ni, Pb, Mn, As – with the AAS method after mineralization in aqua regia or in a mixture of acids (nitric and perchloric acids, 4:1 v/v), Hg – with the AAS method [20].

The results were verified with ANOVA variance analysis and Duncan’s test. Pearson’s simple correlation coefficients between the doses of ash and urea, the plant yield and the soil microorganisms count, the enzymatic activity of the soil and contents of respective elements were also calculated. Statistical analysis was accomplished with STATISTICA^® [28].

RESULTS AND DISCUSSION

Physicochemical properties of hard coal ashes depend on their origin and the composition of coal used for combustion. Ashes are usually alkaline [24,31] and contain high concentrations of Mg, Ca, Na and heavy metals: Al, Si, Cr, Cd and B [24]. In this study, the contamination with ash resulted in an increase in the content of C, N, K, Mg, P, Ca, Na, Cu and Ni (Table 2) in the soil, which modified the physicochemical soil properties and affected its biological activity.

Regardless of the nitrogen fertilization dose and the crop, increasing doses of hard coal ash resulted in an increase in the soil pH, the total content of alkaline exchange cations, soil cation exchange capacity and the base saturation and a decrease in the hydrolytic acidity (Table 3). The results are similar to those reported by Meller [16].

The physicochemical properties of the soil were also modified by a diverse level of urea fertilization and by the cultivation of the successive crop. Both, a higher dose of nitrogen fertilization (150 mg N) and the cultivation of maize increased soil acidity.

The oat and maize response to soil contamination with ash was negative and manifested by a reduced yield, both in the soil fertilized with the lower and the higher dose of urea, although according to expectations, the average yield was higher in the soil fertilized with higher doses of nitrogen (Fig. 1). The results obtained confirm the findings of other authors [12,30] who observed a decreased biomass of plants grown on ash-contaminated soil, as well as retarded germination and development, a decreased content of chlorophyll and proteins in plants and an increased concentration of heavy metals.

The count and activity of soil bacteria depend on a number of factors; the climate, type and physicochemical properties of the soil [4], the composition of species [27] and toxic substances, including heavy metals whose presence in the soil is usually a result of human activity [25].

In this study, the hard carbon ash modified the soil bacteria count, and its effect depended on the dose, the plant species grown and the group of bacteria under study (Table 4). Contamination of the soil with ash stimulated the count of oligotrophic and copiotrophic bacteria as well and spore-forming oligotrophic and copiotrophic bacteria, amonifying bacteria, nitrogen-immobilising bacteria, Pseudomonas spp. and actinomycetes. The ash doses applied (33.3; 66.6; 99.9 g·kg^-1 of soil) increased the count of oligotrophic bacteria by 1.6, 2.6 and 4.6-times, respectively, of spore-forming oligotrophic bacteria by 1.1, 4.6 and 5.3-times, respectively, and Pseudomonas spp. – by 2.0, 2.2 and 3.3-times, respectively. Pati and Sahu [21] also observed intensive respiration of fly-ash contaminated soil, which reflected an increased activity of soil bacteria.

Fungi and bacteria of Azotobacter spp. as well as Arthrobacter spp. also showed a negative reaction to ash. Schutter and Fuhrmann [27] found the dose of 505 Mg·ha^-1 of ash to modify the species composition of soil bacteria slightly. The highest count among the ash-contaminated soil bacteria was found for Arthrobacter genus, ranging from 25 to 42% of all the aerobic heterotrophic bacteria isolated from the soil. Among those bacteria, the count of Arthrobacter photophormiceae was lower and that of Arthrobacter ilicis was higher in the ash contaminated soil.

The count of cellulolytic bacteria in the soil where oat was grown was low. However, a tendency for the bacteria count to decrease with increasing ash doses was found. A much more positive effect on cellulolytic bacteria was exerted by maize, where ash stimulated the bacterial development. A higher activity of cellulolytic bacteria in ash-contaminated soil (120 Mg·ha^-1 of soil) was observed also by Meller [16].

Similarly to the results obtained by Schutter and Fuhrmann [27], the oat and maize significantly affected the soil bacteria. At the beginning of the experiment, when oat was cultivated, the oligotrophic, spore-forming oligotrophic, copiotrophic, spore-forming copiotrophic, ammonifying, nitrogen-immobilising, cellulolytic bacteria counts as well as the count of fungi and Azotobacter spp. were higher than in the soil under the successive crop (maize), whereas as for the other microorganisms under study, the count was lower. An increase in soil fertilisation dose from 75 to 150 mg N·kg^-1 resulted in an increase in the count of copiotrophic, spore-forming copiotrophic, ammonifying bacteria, actinomycetes and bacteria of Pseudomonas spp.

Not only the bacteria count, but also biochemical soil properties are extremely sensitive to the factors which disturb the biological balance of soil [8,29]. The activity of soil enzymes, among other factors, affects soil fertility. Therefore, many authors [7,15,29] use enzymatic activity to determine the biochemical soil fertility index, whose value reflects the changes in the environment. Contaminating the soil with ash reduced the activity of dehydrogenases, urease and acid phosphatase as well as the value of the potential biochemical index of soil fertility (Table 5). Alkaline phosphatase activity was least affected by ash. This is not surprising as the soil pH was optimal for alkaline phosphatase activity, as determined by Dick et al. [5].

The urea fertilization and the cultivation of the successive crop significantly affected the activity of soil enzymes and the value of the potential biochemical index of soil fertility. A higher average activity of dehydrogenases, alkaline and acid phosphatases was observed in the soil under maize. However, an increase in nitrogen fertilisation to 150 mg N positively affected only the average activity of alkaline phosphatase. This does not change the fact that the ash produced in the process of combustion of hard coal deteriorates the enzymatic activity of soil, which was observed by Pati and Sahu [21] investigating the activity of dehydrogenases, protease and amylase.

Of all the factors under study, the dose of ash and the cultivation of crops had the most powerful effect on the soil bacteria count, the soil enzymatic activity and the content of elements in the soil, which was confirmed by the highest number of significant correlation coefficients. On the other hand, the weakest effect was exerted by the dose of urea (Table 6). It should be stressed the high values of coefficients of the correlation between nitrogen content in soil and the ash dose and between the ash dose and plant yield and the activity of soil dehydrogenases and the value of the potential biochemical index of soil fertility.

CONCLUSIONS

1. The contamination of the soil with hard coal ash increased the soil content of C, N, K, Mg, P, Ca, Na, Cu and Ni and alkalized the soil.

2. Hard coal ash increased the count of oligotrophic and copiotrophic bacteria as well and spore-forming oligotrophic and copiotrophic bacteria, amonifying bacteria, nitrogen-immobilising bacteria, Pseudomonas spp. and actinomycetes, but decreased the number of fungi and Azotobacter spp. and Arthrobacter spp.

3. Activity of dehydrogenases, urease and acid phosphatase as well as the value of the potential biochemical index of soil fertility and yields of oat and maize were negatively correlated with the level of soil contamination with ash.

4. Fertilizing the soil with higher dose of nitrogen (150 mg N·kg^-1) enhanced the count of copiotrophic bacteria, spore-forming copiotrophic bacteria, amonifying bacteria, actinomycetes, Pseudomonas spp. and the activity of alkaline phosphatase.

5. A higher activity of dehydrogenases, alkaline and acid phosphatases was observed in the soil under maize than oat.

REFERENCES

1. Alef K., Nannipieri P., 1998. Urease activity. [In:] Methods in Applied Soil Microbiology and Biochemistry, Alef K., Nannipieri P. (eds.), Academic Press, Harcourt Brace & Company, Publishers, London, 316-320.

2. Alef K., Nannipieri P., Trasar-Cepeda C., 1998. Phosphatase activity. [In:] Methods in Applied Soil Microbiology and Biochemistry. Eds. K. Alef, P. Nannipieri). Academic Press, Harcourt Brace & Company, Publishers, London, 335-344.

3. Bi Y.L., Li X.L., Christie P., Hu Z.Q., Wong M.H., 2003. Growth and nutrient uptake of arbuscular mycorrhizal maize in different depths of soil overlying coal fly ash. Chemosphere 50, 863-869.

4. Dšbek-Szreniawska M., Wyczółkowski A., Józefaciuk B., Księżopolska A., Szymona J., Stawiński J., 1996. Relation between soil structure, number of selected groups of soil microorganisms, organic matter content and cultivation system. Int. Agroph. 10(1), 31-35.

5. Dick W.A., Cheng L., Wang P., 2000. Soil acid and alkaline phosphatase activity as pH adjustment indicators. Soil Biol. Biochem. 32, 1915-1919.

6. Dmochowska H., 2004. Rocznik Statystyczny Rzeczypospolitej Polskiej [Statistical Yearbook of the Republic of Poland]. Warszawa [in Polish].

7. Dumontet S., Mazzatura A., Casucci C., Perucci P., 2001. Effectiveness of microbial index in discriminating interactive effects and crop rotations in a Vertic Ustorthens. Biol. Fertil. Soils. 34 (6), 411-416.

8. Ekenler M., Tabatabai M.A., 2004. Arylamidase and amidohydrolases in soils as affected by liming and tillage systems. Soil Tillage Res. 77, 157-168.

9. Gregorczyk K., 2001. Concentration of some heavy metals in both oat varieties growing in the soil at different content of fly-ash. Folia Univ. Agric. Stetin., Agricultura 88, 49-56.

10. Kalra N., Jain M.C., Joshi H.C., Choudhary R., Harit R.C., Vatsa B.K., Sharma S.K., Kumar V., 1998. Fly ash as soil conditioner and fertilizer. Bioresource Technol. 64, 163-167.

11. Kalra N., Jain M.C., Joshi H.C., Choudhary R., Kumar S., Pathak H., Sharma S.K., Kumar V., Kumar R., Harit R.C., Khan S.A., Hussain M.Z., 2003. Soil properties and crop productivity as influenced by fly ash incorporation in soil. Environ. Monit. Assess. 87 (1), 93-109.

12. Kalra N., Joshi H. C., Chudhary A., Choudhary R., Sharma S.K., 1997. Impact of fly ash incorporation in soil on germination of crops. Bioresource Technol. 61, 39-41

13. Khan M.R., Khan M., 1996. The effect of fly ash on plant growth and yield of tomato. Environ. Pollut. 92 (2), 105-111.

14. Kucharski J., 1997. Relacje między aktywnosciš enzymów a żyznosciš gleby [Relationships between enzymatic activity and soil fertility]. [W:] Drobnoustroje w srodowisku – występowanie, aktywnosc i znaczenie, pod red. W. Barabasza, AR Kraków [in Polish].

15. Kucharski J., Wyszkowska J., 2000. Response of soil microorganisms and buckwheat plants to cytokinines. Rostlinna Vyroba 46 (11), 527-532.

16. Meller E., 1999. Changes in the properties of sandy soil fertilized with different doses of ashes from “Dolna Odra” power station. Fol. Univ. Agric. Stetin., Agricultura 78, 189-202.

17. Mocek A., Drzymała S., Maszner P., 1997. Geneza, analiza i klasyfikacja gleb [Origin, analysis and soil classification]. Wyd. AR w Poznaniu [in Polish].

18. Mulder E.G. Antheumisse J., 1963. Morphologie, physiologie et ecologie des Arthrobacter. Ann. de Institut Pasteur 105, 46-74.

19. Öhlinger R., 1996. Dehydrogenase activity with the substrate TTC [In:] Methods in Soil Biology. Eds. F. Schinner R. Öhlinger, E. Kandeler, R. Margesin. Springer Verlag Berlin Heidelberg.

20. Ostrowska A., Gawliński S., Szczubiałka Z., 1991. Metody analizy i oceny własciwosci gleb i roslin [Methods of analysis and evaluation of soil and plant properties]. Katalog IOS [in Polish].

21. Pati S.S., Sahu S.K., 2004. CO₂ evolution and enzyme activities (dehydrogenase, protease and amylase) of fly ash amended soil in presence and absence of earthworms (Drawida willsi Michaelsen) under laboratory conditions. Geoderma 118, 289-301.

22. Polska Norma PN-92 R- 04016, 1992. Analiza chemiczno-rolnicza gleby. Oznaczanie zawartosci przyswajalnego cynku w glebach mineralnych [Chemical and agricultural analysis of soil. Determination of the content of available zinc in mineral soils]. Polski Komitet Normalizacji Miar i Jakosci [in Polish].

23. Rai U.N., Pandey K., Sinha S., Singh R., Saxena R., Gupta D.K., 2004. Revegetating fly ash landfills with Prosopis juliflora L.: impact of different amendments and Rhizobium inoculation. Environ. Int. 30, 293-300.

24. Rai U.N., Tripathi R.D., Singh N., Kumar A., Ali M.B., Pal A., Singh S.N., 2000. Amelioration of fly ash by selected nitrogen fixing blue green algae. Environ Contam. Toxicol. 64, 294-301.

25. Renella G., Chaudri A.M., Brookes P.C., 2002. Fresh addition of heavy metals does not model long-term effects on microbial biomass and activity. Soil Biol. Biochem. 34, 121-124.

26. Rogalski M., Kapela A., Kardyńska S., Wieczorek A., Kryszak J., 1998. Badania nad poczštkowym wzrostem i rozwojem niektórych gatunków traw rosnšcych na popiołach z elektrowni Dolna Odra [Studies on the initial growth and development of some grass cultivars grown in ashes originating from the Dolna Odra power station]. Archiv. Envirnon. Protection. 24 (3), 123-128 [in Polish].

27. Schutter M.E., Fuhrmann J.J., 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.

28. StatSoft, Inc., 2001. STATISTICA (data analysis software system), version 6, www.statsoft.com

29. Trasar-Cepeda C., Leiros C., Gill-Sotres F., Seoane S., 1998. Towards a biochemical quality index for soils: An expression relating several biological and biochemical properties. Biol. Fertil. Soils 26, 100-106.

30. Tripathi R.D., Vajpayee P., Singh N., Rai U.N., Kumar A., Ali M.B., Kumar B., Yunus M., 2004. Efficacy of various amendments for amelioration of fly-ash toxicity: growth performance and metal composition of Cassia siamea Lamk. Chemosphere 54 (11), 1581-1588.

31. Veeresh H., Tripathy S., Choudhury D., Ghosh B.C., Hart B.R., Powell M.A., 2003. Changes in physical and chemical properties of three soil types in India as a result of amendment with fly ash and sewage sludge. Environ. Geol. 43, 513-520.

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