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EFFECTS OF PELLETIZED SEWAGE SLUDGE ON SOIL PROPERTIES OF A CRACKING CLAY FROM EASTERN AUSTRALIA
Waste Management & Research (1996) 14, 571–580
EFFECTS OF PELLETIZED SEWAGE SLUDGE ON SOIL PROPERTIES OF A CRACKING CLAY FROM EASTERN AUSTRALIA N. R. Hulugalle Co-operative Research Centre for Sustainable Cotton Production, New South Wales Department of Agriculture, Australian Cotton Research Institute, PMB, Myall Vale Mail Run, Narrabri, NSW 2390, Australia (Received 1 March 1995, accepted in revised form 22 September 1995) The effects of applying varying rates (0–250 g kg−1) of pelletized mixtures of sewage sludge and other waste materials (peat and cotton “gin trash”) on the soil physical and chemical properties of a cracking clay from Eastern Australia was investigated in a laboratory study. Soil properties measured were pH, electrical conductivity, nitrate-N, organic C, exchangeable cations, aggregate density, dispersion and geometric mean diameter aggregates formed after soil had been puddled and dried. In comparison with untreated soil, application of the pellets increased soil acidity, electrical conductivity, nitrate-N and organic C, and decreased exchangeable Ca and Na. Partial substitution of sewage sludge and peat with cotton “gin trash” reduced the intensity of the above changes in soil properties. Changes in soil physical properties were limited to a small decrease in soil density. Addition of pelletized sewage sludge/waste material mixtures to a cracking clay had significant short-term effects on soil chemical properties but limited effects on soil physical properties. 1996 ISWA
Key Words—Pelletized sewage sludge, peat, cotton “gin trash”, soil properties, cracking clay.
1. Introduction Use of waste materials as soil amendments and fertilizers has been practised by human society for many thousands of years. Some common examples are the application of farmyard manure and sewage to crops as fertilizers (Bezdicek et al. 1984; Awad et al. 1989). More recently, with rapid increases in the size of major urban centres and consequent increases in the volume and rate of production of waste materials such as sewage sludge (World Commission on Environment and Development 1987), a strong interest has developed in their application to commercial agricultural and forest lands (Bezdicek et al. 1984; Awad et al. 1989; Jayawardane et al. 1992). The potential benefits from sewage sludge applications to farm and forestry land are thought to be due to improvements in soil physical, chemical and biological properties (Epstein et al. 1976; Bezdicek et al. 1984; Metzger & Yaron 1987; Awad et al. 1989; Jayawardane et al. 1992; Lerch et al. 1992; Martens & Franckenberger 1992; Bevacqua & Mellano 1994). The disadvantages of sewage sludge application include eutrophication of waterways due to erosion and runoff, contamination of soil with heavy metals, organo-chlorines and organo-phosphates, and high costs involved with transporting sludge from urban centres to rural areas (Bezdicek et al. 1984; Awad et al. 1989; Jayawardane et al. 1992; 0734–242X/96/060571+10 $25.00/0
1996 ISWA
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TABLE 1 Properties of experimental soil Property
Value
Clay (%) Silt (%) Sand (%) Size distribution of air-dried aggregates: >4 mm (%) 2–4 mm (%) 1–2 mm (%) <1 mm (%) CaCO3 (%) Plastic limit (%) Aggregate density (mg m−3) Nitrate-nitrogen (mg kg−1) pH (1:5 soil:water) Electrical conductivity (1:5 soil:water) dSm−1) Organic C (%) Exchangeable Ca [cmol (+) kg−1] Exchangeable Mg [cmol (+) kg−1] Exchangeable K [cmol (+) kg−1] Exchangeable Na [cmol (+) kg−1] Total CEC [cmol (+) kg−1]
60 18 22 31 42 22 5 0.1 21 1.3 65 8.3 0.15 0.75 28 16 2 2 48
CEC, cation exchange capacity.
Bevacqua & Mellano 1994). The latter disadvantage can be overcome to a large extent by removing [90% of water from sewage sludge and pelletizing the residues, frequently in combination with composted vegetable materials, peat or agricultural waste materials such as cotton “gin trash” (detritus of plant materials left after cotton seed and lint have been removed by ginning) (K. Luscombe, pers. comm.). Published information on the effects of applying the abovementioned pelletized waste materials to agricultural land is, however, sparse. The objective of the present study, therefore, was to quantify the effects of mixing commercially available pelletized combinations of sewage sludge and other waste materials with a cracking clay soil, typical of many irrigated soils in the semi-arid zone of Eastern Australia, on the latter’s physical and chemical properties. 2. Materials and methods Soil was sampled in December 1992 from the surface 0.2 m of a cotton field at the Australian Cotton Research Institute (annual rainfall 616 mm) in Northern New South Wales, Australia, which had been sown with an irrigated cotton (Gossypium hirsutum)–wheat (Triticum aestivum) rotation for the previous 10 years, and taken to the laboratory. The soil was a self-mulching, cracking clay and classified as a fine, thermic, montmorillonitic, Typic Pullustert (Soil Survey Staff 1987). Soil properties in the surface 0.2 m are summarized in Table 1. Land preparation prior to planting cotton (in October) consisted of disc and chisel ploughing to a depth of 0.2 m followed by ridging, whereas that prior to sowing of wheat (in May) was notillage. All residues from the previous crop were incorporated during the tillage operations.
Effects of pelletized sewage sludge on soil properties
573
The field soil was air-dried in a drying room for 4 months, ground and passed through a sieve with 2-mm apertures. One kilogramme of soil (on an oven-dried basis) was then transferred to a 2.5 l plastic bag. Sixty-six such bags were made up. Water was added to each bag resulting in a soil water content of 0.40 kg kg−1. Two types of pelletized sewage sludge1/waste material mixtures (1:1 sewage sludge:peat and 2:2:1 sewage sludge:peat:cotton “gin trash”) which had been previously dried at 105°C were then added to each bag at rates of 10, 25, 50, 100 and 250 g kg−1 of oven-dried soil and mixed with the soil. Chemical properties of 1:1 sewage sludge:peat pellets are summarized in Table 2. A control treatment to which no pellets were added was also included in the trial. The bags were then closed and fastened with a rubber band to minimize evaporative losses of water. The soil+pellet mixtures were incubated for 8 months in a store room where mean minimum and maximum air temperatures were 14°C and 22°C, respectively. The experimental design used was a randomized complete block with six replications (Federer 1955). TABLE 2 Chemical properties of 1:1 sewage sludge:peat pellets (expressed on an oven-dried basis) Chemical property pH (1:5 soil:water) Electrical conductivity (1:5 soil:water) (dS m−1) Nitrate-nitrogen (mg kg−1) P (%) Ca (%) Mg (%) K (%) Na (%) As (mg kg−1) Cd (mg kg−1) Cr (mg kg−1) Cu (mg kg−1) Hg (mg kg−1) Ni (mg kg−1) Pb (mg kg−1) Se (mg kg−1) Zn (mg kg−1)
Value 5.7 1.8 5 1.8 1.5 0.4 0.1 0.1 9 1 50 306 <2 33 60 13 408
After incubation, the soils were dried in a forced-draft oven at 30°C for 72h, and the following analyses were conducted after passing through a sieve with 2-mm diameter apertures. pH and electrical conductivity were determined in a 1:5 soil:water suspension, water soluable nitrate-N was determined by automated colorimetry after extraction in a 1:5 soil:water suspension, exchangeable Ca, Mg, K and Na were determined after extraction with alcoholic 1M NH4Cl at a pH of 8.5 (Rayment & Higginson 1992), and dispersion was determined in irrigation water according to the method of Schipitalo & Protz (1988). Dispersion index was expressed as:
1
Dewatered cake from St. Mary’s sludge treatment plant, near Sydney, Australia.
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Dispersion index (%)= Mass of soil particles<2lm released into the suspension due to immersion in water ×100 Mass of soil particles <2lm released into suspension after complete dispersion of sample
Soil reactivity, a measure of the self-mulching ability of the soil, was determined by puddling and oven-drying at 40°C for 72h, 400 mg of air-dried soil which had been passed through a sieve with aperture diameters of 2 mm. The size distribution of the aggregates formed (determined by dry-sieving on a mechnical shaker at 1440 vibrations min−1 for 5 min) was expressed as the geometric mean diameter of the soil aggregates (Klute 1986). Total soil organic carbon was determined by the wet oxidation method of Walkley and Black on soil which had been passed through a sieve with aperture diameters of 0.5 mm. Soil density was determined on oven-dried soil aggregates (1–4 mm diameter) using the kerosene saturation method of McIntyre & Stirk (1954). Effects of pellet application rates (0–250 g kg−1) were determined by analysing data according to a one-way analysis of variance (Federer 1955). Effects of cotton “gin trash” and interactions between cotton “gin trash” and pellet application rate were analysed according to a randomised complete block design where the control (0 g kg−1) treatment had been deleted from the analysis (Federer 1955). 3. Results and discussion Increasing pellet application rate significantly decreased soil pH (P<0.001), exchangeable Ca (P<0.05), exchangeable Na (P<0.001), Ca/Mg (P<0.01) and exchangeable sodium percentage (ESP) (P<0.001); and significantly increased electrical conductivity (P<0.001), nitrate-N (P<0.001) and organic C (P<0.001) (Figs 1–3). Exchangeable Mg and K, and soil physical properties monitored in this study were not affected significantly by pellet application rate. The decreases in soil pH, exchangeable Ca and Na, and increases in electrical conductivity may be due to mixing an acidic substance of high electrical conductivity (pellets) with a alkaline substance of low electrical conductivity (soil). A possible mechanism for these changes is suggested in Fig. 4. A preferential substitution by H of Ca and Na is also suggested in Fig. 2. The increases in organic C and nitrate-N are presumably due to the addition of pellets at an increasing rate to the soil. Figures 1–3 also show that where application rates in excess of 50 g kg−1 were used, changes in nitrate-N, pH, electrical conductivity, exchangeable Ca and Na, ESP and Ca/Mg occurred at a diminishing rate (i.e. the “law of diminishing returns” appears to be operating). The application rate of 50 g kg−1 equivalent to a field application rate of 58 t ha−1 where bulk density in the surface 0.1 m is 1.15 Mg m−3 at the plastic limit (Hulugalle, unpub. data, 1992) is lower than the maximum permitted sludge application rates in New South Wales which are 67 t ha−1 for dewatered sludge (20% solids) and 267 t ha−1 for wet sludge (5% solids) (Awad et al. 1989). Transport and application costs of pelletized sludge mixtures may, therefore, be lower than those associated with applying wet or dewatered sludge. Addition of cotton “gin trash” to the pellets significantly increased pH (P<0.001) and ESP (P<0.05), and decreased electrical conductivity (P<0.01), nitrate-N (P<0.001) and soil density (P<0.05) (Table 3). In addition, significant interactions between pellet type and pellet application rate occurred with respect to pH (P<0.01), electrical conductivity (P<0.05) and nitrate–N (P<0.001). Reducing the amounts of sewage sludge and peat, and substituting cotton “gin trash”
Effects of pelletized sewage sludge on soil properties
575
± S.E.
7.5
6.5
Ln 100 × electrical conductivity
pH
8.5
0
100
200
4.2 ± S.E.
3.7
3.2
300
0
Application rate (g kg–1)
100
200
300
Application rate (g kg–1)
0.95 Organic carbon (%)
Nitrate-nitrogen (mg kg–1)
300
± S.E.
200
100
100
0
200
0.75
0.65
300
± S.E.
0.85
0
–1
200
300
21 Geometric mean diameter (mm)
Aggregate density (mg m–3)
1.4
± S.E.
1.3
1.2
1.1
100
–1 Application rate (g kg )
Application rate (g kg )
0
100
200
Application rate (g kg–1)
300
± S.E.
18
15
0
100
200
300
Application rate (g kg–1)
Fig. 1. Effect of pellet application rate on soil pH, electrical conductivity, nitrate-N, organic C, aggregate density and geometric mean diameter of soil aggregates after puddling and drying.
576
N. R. Hulugalle 30 Exchangeable Ca [cmol (+) kg–1]
Exchangeable Mg [cmol (+) kg–1]
24
± S.E.
20
16
12
0
100
200
± S.E.
28
26
24
300
0
100
Application rate (g kg–1)
200
300
Application rate (g kg–1)
Exchangeable Na [cmol (+) kg–1]
Exchangeable K [cmol (+) kg–1]
1.9
± S.E.
1.8
1.7 0
100
200
1.4
± S.E.
1.2
1.0
300
0
100
–1
200
300
Application rate (g kg–1)
Application rate (g kg )
± S.E.
1.50
1.25
0
100
200
300
–1 Application rate (g kg )
3.5 Dispersion index (%)
Ca/Mg
1.75
Exchangeable sodium percentage (%)
Fig. 2. Effect of pellet application rate on exchangeable cations.
3.0 ± S.E.
2.5
2.0
0
100
200
300
–1 Application rate (g kg )
2.8 ± S.E.
2.4
2.0
0
100
200
300
–1 Application rate (g kg )
Fig. 3. Effect of pellet application rate on Ca/Mg, exchangeable sodium percentage and dispersion index.
Effects of pelletized sewage sludge on soil properties
Acidic pellets
Hydrogen ions released into soil solution
577
Substitution of exchangeable Ca, Mg K and Na with H ions
pH decreases Basic cations released into soil solution
Electrical conductivity increases Fig. 4. Suggested explanation for observed increases in electrical conductivity, and decreases in pH and exchangeable cations.
in the pellets appears to reduce the intensity of the changes in soil properties brought about by adding 1:1 sewage sludge:peat pellets to the soil. With respect to nitrate-N, this may be due to nitrogen mineralization in alkaline conditions being greatly increased by combining sewage sludge and peat (Diez et al., 1992). Reduction of either component can, therefore, reduce the efficiency of this process. Substitution of sludge and peat with materials of high C:N ratios, such as cotton “gin trash” (Ghidey & Alberts 1993), may also result in enhanced denitrification with the microbial populations utilizing the latter as a substrate (Russell 1973). The wet soil in the sealed bags is likely to have resulted in anaerobiosis, and may have further facilitated denitrification (Russell 1973). In comparison with pellets of 1:1 sewage sludge: peat, therefore, adding pellets of 2:2:1 sewage sludge:peat:cotton “gin trash” decreased nitrate-N levels in soil, presumably due to a greater rate of denitrification. The lower soil density where pellets with cotton “gin trash” were used may be due to incorporation of low-density plant materials into soil aggregates by microbial activity (Russell 1973; Doran et al. 1994). In summary, therefore, addition of pelletized sewage sludge/waste material mixtures to a cracking clay had significant effects on soil chemical properties and very limited effects on soil physical properties monitored in this study. The negligible effects of the pellets on soil physical properties such as dispersion is surprising in view of the contrary statements in the literature (Bezdicek et al. 1984; Metzger & Yaron 1987; Jayawardane et al. 1992; Martens & Franckenberger 1992). The fact that the test soil was taken from a field which had been in a rotation system for the preceding 10 years, where all crop residues were retained in situ, and which had experienced no tillage for the preceding cropping phase may have contributed to these results (Bezdicek et al. 1984; Doran et al. 1994) 4. Conclusions In comparison with untreated control soil, application of pelletized sewage sludge/waste material (peat and cotton “gin trash”) mixtures resulted in a cracking clay which was more acidic and saline, had higher nitrate-N, and lower exchangeable Ca and Na. Partial substitution of sewage sludge and peat with cotton “gin trash” reduced the
2.5 2.7 2.9 2.9 2.4 2.7
P1
P< n.s. n.s.
+.. 0.05 0.11
0.33 0.46 0.61 0.84 0.94 0.59
±.. 0.42 0.93
15.7 16.9 17.5 17.3 20.4 17.5
P2
P< n.s. n.s.
26.3 26.7 26.0 25.0 23.7 25.6
P1
±.. 0.29 0.64
26.5 27.5 25.2 24.2 25.8 25.9
P2
Exch. Ca [cmol(+)kg−1]
(3.489) (3.818) (4.109) (4.435) (4.548) (4.080)
P2
±.. 9.5 21.1
104 181 277 335 404 261
P2
P< n.s. n.s.
1.7 1.7 1.9 1.9 1.7 1.8
P1
±.. 0.04 0.09
1.8 1.8 1.8 1.7 1.9 1.8
P2
Exch. K [cmol(+)kg−1]
P< 0.001 0.001
93 132 208 241 191 173
P1
Nitrate-N (mg kg−1)
±.. 0.022 0.049
0.75 0.75 0.73 0.79 1.02 0.81
P2
P< n.s. n.s.
1.5 1.3 1.2 1.1 1.0 1.2
P1
±.. 0.03 0.06
1.4 1.3 1.1 1.0 1.0 1.2
P2
Exch. Na [cmol(+)kg−1]
P< n.s. n.s.
0.72 0.67 0.84 0.85 0.89 0.80
P1
Organic C (%)
P< n.s. n.s.
1.7 1.7 1.5 1.5 1.4 1.6
P1
Ca/Mg
P< 0.05 n.s.
1.27 1.22 1.20 1.24 1.26 1.24
P1
±.. 0.03 0.07
1.7 1.6 1.5 1.4 1.3 1.5
P2
±.. 0.009 0.030
1.30 1.22 1.31 1.27 1.27 1.27
P2
Soil density (mg m−3)
P< 0.05 n.s.
3.2 2.9 2.6 2.5 2.4 2.7
P1
ESP
P< n.s. n.s.
18.1 19.5 19.5 18.7 19.4 19.1
P1
P2
±.. 0.06 0.15
3.0 2.8 2.5 2.3 2.0 2.5
P2
±.. 0.81 1.80
17.2 19.0 17.1 18.3 16.4 17.6
GMD (mm)
∗ Values in parantheses are loge transformed values of 100×electrical conductivity of a 1:5 soil:water suspension. P1, 2:2:1 sewage sludge:peat:cotton “gin trash”; P2, 1:1 sewage sludge:peat; Ec, electrical conductivity; n.s., not significant, ESP, exchangeable sodium percentage; GMD, geometric mean diameter of soil aggregates formed after puddling and drying air-dried soil.
15.8 15.9 17.5 17.5 17.4 16.8
P1
Ec∗
P< ±.. 0.01 (0.0223) 0.05 (0.0500)
(3.545) (3.804) (4.052) (4.283) (4.249) (3.987)
P1
Exch. Mg [cmol(+)kg−1]
0.35 0.45 0.58 0.73 0.70 0.54
2.6 3.0 3.0 2.7 2.3 2.8
P2
Dispersion index (%)
±.. 0.04 0.08
P< 0.001 0.01
P2 7.8 7.5 7.2 7.0 6.6 7.2
pH
7.9 7.6 7.4 7.1 7.2 7.4
P1
P< Pellet type n.s. Rate x pellet n.s. type
10 25 50 100 250 Mean
Application rate (g kg−1)
Pellet type Rate x pellet type
10 25 50 100 250 Mean
Application rate (g kg−1)
TABLE 3 Effect of pellet type on soil properties
578 N. R. Hulugalle
Effects of pelletized sewage sludge on soil properties
579
intensity of the above changes in soil properties. Changes in soil physical properties were limited to a small decrease in soil density. The insensitivity of the other soil physical properties to the experimental treatments were presumably due to the management history of the test soil. The changes in heavy metal, organo-chlorine and organo-phosphate concentrations were not quantified in this study, and hence, no conclusions can be drawn with respect to their accumulation in cracking clays.
Acknowledgements Mr. K. Luscombe of Luscombe Contracting Pty. Ltd. is thanked for providing gratis samples of the pelletized sewage sludge/waste material mixtures. The technical assistance of Mrs. J. Lindsay, Miss J. Renaud and Mr. P. Entwistle is gratefully appreciated. Analyses of nitrate-N, organic C and exchangeable cations were performed by the Analytical Services Unit of the New South Wales Department of Agriculture at Rydalmere, near Syndey.
References Awad, A. S., Ross, A. D. & Lawrie, R. A. (1989) Guidelines for the Use of Sewage Sludge on Agricultural Land. Sydney, Australia: New South Wales Department of Agriculture & Fisheries, 23pp. Bevaqua, R. F. & Mellano, V. J. (1994) Cumulative effects of sludge compost on crop yields and soil properties. Communications in Soil Science and Plant Analysis 25, 395–406. Bezdicek, D. F., Power, J. F., Keeney, D. R. & Wright, M. J. (eds) (1984) Organic Farming: Current Technology and its Role in a Sustainable Agriculture. Madison, WI, U.S.A.: ASA/ CSSA/SSSA, 192pp. Diez, J. A., Polo, A. & Guerrero, F. (1992) Effect of sewage sludge on nitrogen availability in peat. Biology and Fertility of Soils 13, 248–251. Doran, J. W., Coleman, D. F., Bezdicek, D. F. & Stewart, B. A. (eds) (1994) Defining Soil Quality for a Sustainable Environment. Madison, WI, U.S.A.: SSSA, 244pp. Epstein, E., Taylor, J. M. & Chaney, R. L. (1976) Effects of sewage sludge and sludge compost applied to soil on some soil physical and chemical properties. Journal of Environmental Quality 5, 422–426. Federer, W. T. (1995) Experimental Design: Theory and Application. New York, NY, U.S.A.: Macmillan, 544pp. Ghidey, F. & Alberts, E.E. (1993) Residue type and placement effects on decomposition: Field study and model evaluation. Transactions of the American Society of Agricultural Engineers 36, 1611–1617. Jayawardane, N. S., Blackwell, J., Muirhead, W. A. & Kirchof, G. (1992) Slotting – a new deep tillage technique for improving crop productivity on sodic, acid and other degraded soils and for land treatment of urban and rural waste. Commonwealth and Scientific and Industrial Research Organization Water Resources Series 5, 22pp. Klute, A. (ed) (1986) Methods of Soil Analysis, Part 1: Physical and Mineralogical Methods. Madison, WI, U.S.A.: ASA, 1188pp. Lerch, R. N., Barbarick, K. A., Sommers, L. E. & Westfall, D. G. (1992) Sewage sludge proteins as labile carbon and nitrogen sources. Soil Science Society of America Journal 56, 1470–1476. Martens, D. A. & Frankenberger, W. T., Jr (1992) Modification of infiltration rates in an organicamended irrigation soil. Agronomy Journal 84, 707–717. McIntyre, D. S. & Stirk, G. B. (1954) A method for determination of apparent density of soil aggregates. Australian Journal of Agricultural Research 5, 291–296. Metzger, L & Yaron, B. (1987) Influence of sludge organic matter on soil physical properties. Advances in Soil Science 7, 141–161. Page, A. L., Miller, R. H., and Keeney, D. R., (eds.), (1982) Methods of Soil Analysis, Part 2: Chemical and Microbiological Properties, 1159pp. Madison, WI, USA: ASA.
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Rayment, G. E. & Higginson, F. R. (1992) Australian Laboratory Handbook of Soil and Water Chemical Methods. Melbourne and Sydney, Australia:Inkata, 330pp. Russell, E. W. (1973) Soil Conditions and Plant Growth, 10th Edition. London, U.K.: Longman, 849pp. Schipitalo, M. J. and Protz, R. (1988) Factors influencing the dispersibility of clay in worm casts. Soil Science Society of America Journal 52, 764–769. Soil Survey Staff (1987) Keys to soil taxonomy. SMSS Technical Monograph No. 6. Ithaca, NY, U.S.A. Cornell University, 280pp. World Commission on Environment and Development (1987) Our Common Future (“The Brundtland Report”). Oxford, U.K.: Oxford University Press, 400pp.
EFFECTS OF PELLETIZED SEWAGE SLUDGE ON SOIL PROPERTIES OF A CRACKING CLAY FROM EASTERN AUSTRALIA N. R. Hulugalle Co-operative Research Centre for Sustainable Cotton Production, New South Wales Department of Agriculture, Australian Cotton Research Institute, PMB, Myall Vale Mail Run, Narrabri, NSW 2390, Australia (Received 1 March 1995, accepted in revised form 22 September 1995) The effects of applying varying rates (0–250 g kg−1) of pelletized mixtures of sewage sludge and other waste materials (peat and cotton “gin trash”) on the soil physical and chemical properties of a cracking clay from Eastern Australia was investigated in a laboratory study. Soil properties measured were pH, electrical conductivity, nitrate-N, organic C, exchangeable cations, aggregate density, dispersion and geometric mean diameter aggregates formed after soil had been puddled and dried. In comparison with untreated soil, application of the pellets increased soil acidity, electrical conductivity, nitrate-N and organic C, and decreased exchangeable Ca and Na. Partial substitution of sewage sludge and peat with cotton “gin trash” reduced the intensity of the above changes in soil properties. Changes in soil physical properties were limited to a small decrease in soil density. Addition of pelletized sewage sludge/waste material mixtures to a cracking clay had significant short-term effects on soil chemical properties but limited effects on soil physical properties. 1996 ISWA
Key Words—Pelletized sewage sludge, peat, cotton “gin trash”, soil properties, cracking clay.
1. Introduction Use of waste materials as soil amendments and fertilizers has been practised by human society for many thousands of years. Some common examples are the application of farmyard manure and sewage to crops as fertilizers (Bezdicek et al. 1984; Awad et al. 1989). More recently, with rapid increases in the size of major urban centres and consequent increases in the volume and rate of production of waste materials such as sewage sludge (World Commission on Environment and Development 1987), a strong interest has developed in their application to commercial agricultural and forest lands (Bezdicek et al. 1984; Awad et al. 1989; Jayawardane et al. 1992). The potential benefits from sewage sludge applications to farm and forestry land are thought to be due to improvements in soil physical, chemical and biological properties (Epstein et al. 1976; Bezdicek et al. 1984; Metzger & Yaron 1987; Awad et al. 1989; Jayawardane et al. 1992; Lerch et al. 1992; Martens & Franckenberger 1992; Bevacqua & Mellano 1994). The disadvantages of sewage sludge application include eutrophication of waterways due to erosion and runoff, contamination of soil with heavy metals, organo-chlorines and organo-phosphates, and high costs involved with transporting sludge from urban centres to rural areas (Bezdicek et al. 1984; Awad et al. 1989; Jayawardane et al. 1992; 0734–242X/96/060571+10 $25.00/0
1996 ISWA
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TABLE 1 Properties of experimental soil Property
Value
Clay (%) Silt (%) Sand (%) Size distribution of air-dried aggregates: >4 mm (%) 2–4 mm (%) 1–2 mm (%) <1 mm (%) CaCO3 (%) Plastic limit (%) Aggregate density (mg m−3) Nitrate-nitrogen (mg kg−1) pH (1:5 soil:water) Electrical conductivity (1:5 soil:water) dSm−1) Organic C (%) Exchangeable Ca [cmol (+) kg−1] Exchangeable Mg [cmol (+) kg−1] Exchangeable K [cmol (+) kg−1] Exchangeable Na [cmol (+) kg−1] Total CEC [cmol (+) kg−1]
60 18 22 31 42 22 5 0.1 21 1.3 65 8.3 0.15 0.75 28 16 2 2 48
CEC, cation exchange capacity.
Bevacqua & Mellano 1994). The latter disadvantage can be overcome to a large extent by removing [90% of water from sewage sludge and pelletizing the residues, frequently in combination with composted vegetable materials, peat or agricultural waste materials such as cotton “gin trash” (detritus of plant materials left after cotton seed and lint have been removed by ginning) (K. Luscombe, pers. comm.). Published information on the effects of applying the abovementioned pelletized waste materials to agricultural land is, however, sparse. The objective of the present study, therefore, was to quantify the effects of mixing commercially available pelletized combinations of sewage sludge and other waste materials with a cracking clay soil, typical of many irrigated soils in the semi-arid zone of Eastern Australia, on the latter’s physical and chemical properties. 2. Materials and methods Soil was sampled in December 1992 from the surface 0.2 m of a cotton field at the Australian Cotton Research Institute (annual rainfall 616 mm) in Northern New South Wales, Australia, which had been sown with an irrigated cotton (Gossypium hirsutum)–wheat (Triticum aestivum) rotation for the previous 10 years, and taken to the laboratory. The soil was a self-mulching, cracking clay and classified as a fine, thermic, montmorillonitic, Typic Pullustert (Soil Survey Staff 1987). Soil properties in the surface 0.2 m are summarized in Table 1. Land preparation prior to planting cotton (in October) consisted of disc and chisel ploughing to a depth of 0.2 m followed by ridging, whereas that prior to sowing of wheat (in May) was notillage. All residues from the previous crop were incorporated during the tillage operations.
Effects of pelletized sewage sludge on soil properties
573
The field soil was air-dried in a drying room for 4 months, ground and passed through a sieve with 2-mm apertures. One kilogramme of soil (on an oven-dried basis) was then transferred to a 2.5 l plastic bag. Sixty-six such bags were made up. Water was added to each bag resulting in a soil water content of 0.40 kg kg−1. Two types of pelletized sewage sludge1/waste material mixtures (1:1 sewage sludge:peat and 2:2:1 sewage sludge:peat:cotton “gin trash”) which had been previously dried at 105°C were then added to each bag at rates of 10, 25, 50, 100 and 250 g kg−1 of oven-dried soil and mixed with the soil. Chemical properties of 1:1 sewage sludge:peat pellets are summarized in Table 2. A control treatment to which no pellets were added was also included in the trial. The bags were then closed and fastened with a rubber band to minimize evaporative losses of water. The soil+pellet mixtures were incubated for 8 months in a store room where mean minimum and maximum air temperatures were 14°C and 22°C, respectively. The experimental design used was a randomized complete block with six replications (Federer 1955). TABLE 2 Chemical properties of 1:1 sewage sludge:peat pellets (expressed on an oven-dried basis) Chemical property pH (1:5 soil:water) Electrical conductivity (1:5 soil:water) (dS m−1) Nitrate-nitrogen (mg kg−1) P (%) Ca (%) Mg (%) K (%) Na (%) As (mg kg−1) Cd (mg kg−1) Cr (mg kg−1) Cu (mg kg−1) Hg (mg kg−1) Ni (mg kg−1) Pb (mg kg−1) Se (mg kg−1) Zn (mg kg−1)
Value 5.7 1.8 5 1.8 1.5 0.4 0.1 0.1 9 1 50 306 <2 33 60 13 408
After incubation, the soils were dried in a forced-draft oven at 30°C for 72h, and the following analyses were conducted after passing through a sieve with 2-mm diameter apertures. pH and electrical conductivity were determined in a 1:5 soil:water suspension, water soluable nitrate-N was determined by automated colorimetry after extraction in a 1:5 soil:water suspension, exchangeable Ca, Mg, K and Na were determined after extraction with alcoholic 1M NH4Cl at a pH of 8.5 (Rayment & Higginson 1992), and dispersion was determined in irrigation water according to the method of Schipitalo & Protz (1988). Dispersion index was expressed as:
1
Dewatered cake from St. Mary’s sludge treatment plant, near Sydney, Australia.
574
N. R. Hulugalle
Dispersion index (%)= Mass of soil particles<2lm released into the suspension due to immersion in water ×100 Mass of soil particles <2lm released into suspension after complete dispersion of sample
Soil reactivity, a measure of the self-mulching ability of the soil, was determined by puddling and oven-drying at 40°C for 72h, 400 mg of air-dried soil which had been passed through a sieve with aperture diameters of 2 mm. The size distribution of the aggregates formed (determined by dry-sieving on a mechnical shaker at 1440 vibrations min−1 for 5 min) was expressed as the geometric mean diameter of the soil aggregates (Klute 1986). Total soil organic carbon was determined by the wet oxidation method of Walkley and Black on soil which had been passed through a sieve with aperture diameters of 0.5 mm. Soil density was determined on oven-dried soil aggregates (1–4 mm diameter) using the kerosene saturation method of McIntyre & Stirk (1954). Effects of pellet application rates (0–250 g kg−1) were determined by analysing data according to a one-way analysis of variance (Federer 1955). Effects of cotton “gin trash” and interactions between cotton “gin trash” and pellet application rate were analysed according to a randomised complete block design where the control (0 g kg−1) treatment had been deleted from the analysis (Federer 1955). 3. Results and discussion Increasing pellet application rate significantly decreased soil pH (P<0.001), exchangeable Ca (P<0.05), exchangeable Na (P<0.001), Ca/Mg (P<0.01) and exchangeable sodium percentage (ESP) (P<0.001); and significantly increased electrical conductivity (P<0.001), nitrate-N (P<0.001) and organic C (P<0.001) (Figs 1–3). Exchangeable Mg and K, and soil physical properties monitored in this study were not affected significantly by pellet application rate. The decreases in soil pH, exchangeable Ca and Na, and increases in electrical conductivity may be due to mixing an acidic substance of high electrical conductivity (pellets) with a alkaline substance of low electrical conductivity (soil). A possible mechanism for these changes is suggested in Fig. 4. A preferential substitution by H of Ca and Na is also suggested in Fig. 2. The increases in organic C and nitrate-N are presumably due to the addition of pellets at an increasing rate to the soil. Figures 1–3 also show that where application rates in excess of 50 g kg−1 were used, changes in nitrate-N, pH, electrical conductivity, exchangeable Ca and Na, ESP and Ca/Mg occurred at a diminishing rate (i.e. the “law of diminishing returns” appears to be operating). The application rate of 50 g kg−1 equivalent to a field application rate of 58 t ha−1 where bulk density in the surface 0.1 m is 1.15 Mg m−3 at the plastic limit (Hulugalle, unpub. data, 1992) is lower than the maximum permitted sludge application rates in New South Wales which are 67 t ha−1 for dewatered sludge (20% solids) and 267 t ha−1 for wet sludge (5% solids) (Awad et al. 1989). Transport and application costs of pelletized sludge mixtures may, therefore, be lower than those associated with applying wet or dewatered sludge. Addition of cotton “gin trash” to the pellets significantly increased pH (P<0.001) and ESP (P<0.05), and decreased electrical conductivity (P<0.01), nitrate-N (P<0.001) and soil density (P<0.05) (Table 3). In addition, significant interactions between pellet type and pellet application rate occurred with respect to pH (P<0.01), electrical conductivity (P<0.05) and nitrate–N (P<0.001). Reducing the amounts of sewage sludge and peat, and substituting cotton “gin trash”
Effects of pelletized sewage sludge on soil properties
575
± S.E.
7.5
6.5
Ln 100 × electrical conductivity
pH
8.5
0
100
200
4.2 ± S.E.
3.7
3.2
300
0
Application rate (g kg–1)
100
200
300
Application rate (g kg–1)
0.95 Organic carbon (%)
Nitrate-nitrogen (mg kg–1)
300
± S.E.
200
100
100
0
200
0.75
0.65
300
± S.E.
0.85
0
–1
200
300
21 Geometric mean diameter (mm)
Aggregate density (mg m–3)
1.4
± S.E.
1.3
1.2
1.1
100
–1 Application rate (g kg )
Application rate (g kg )
0
100
200
Application rate (g kg–1)
300
± S.E.
18
15
0
100
200
300
Application rate (g kg–1)
Fig. 1. Effect of pellet application rate on soil pH, electrical conductivity, nitrate-N, organic C, aggregate density and geometric mean diameter of soil aggregates after puddling and drying.
576
N. R. Hulugalle 30 Exchangeable Ca [cmol (+) kg–1]
Exchangeable Mg [cmol (+) kg–1]
24
± S.E.
20
16
12
0
100
200
± S.E.
28
26
24
300
0
100
Application rate (g kg–1)
200
300
Application rate (g kg–1)
Exchangeable Na [cmol (+) kg–1]
Exchangeable K [cmol (+) kg–1]
1.9
± S.E.
1.8
1.7 0
100
200
1.4
± S.E.
1.2
1.0
300
0
100
–1
200
300
Application rate (g kg–1)
Application rate (g kg )
± S.E.
1.50
1.25
0
100
200
300
–1 Application rate (g kg )
3.5 Dispersion index (%)
Ca/Mg
1.75
Exchangeable sodium percentage (%)
Fig. 2. Effect of pellet application rate on exchangeable cations.
3.0 ± S.E.
2.5
2.0
0
100
200
300
–1 Application rate (g kg )
2.8 ± S.E.
2.4
2.0
0
100
200
300
–1 Application rate (g kg )
Fig. 3. Effect of pellet application rate on Ca/Mg, exchangeable sodium percentage and dispersion index.
Effects of pelletized sewage sludge on soil properties
Acidic pellets
Hydrogen ions released into soil solution
577
Substitution of exchangeable Ca, Mg K and Na with H ions
pH decreases Basic cations released into soil solution
Electrical conductivity increases Fig. 4. Suggested explanation for observed increases in electrical conductivity, and decreases in pH and exchangeable cations.
in the pellets appears to reduce the intensity of the changes in soil properties brought about by adding 1:1 sewage sludge:peat pellets to the soil. With respect to nitrate-N, this may be due to nitrogen mineralization in alkaline conditions being greatly increased by combining sewage sludge and peat (Diez et al., 1992). Reduction of either component can, therefore, reduce the efficiency of this process. Substitution of sludge and peat with materials of high C:N ratios, such as cotton “gin trash” (Ghidey & Alberts 1993), may also result in enhanced denitrification with the microbial populations utilizing the latter as a substrate (Russell 1973). The wet soil in the sealed bags is likely to have resulted in anaerobiosis, and may have further facilitated denitrification (Russell 1973). In comparison with pellets of 1:1 sewage sludge: peat, therefore, adding pellets of 2:2:1 sewage sludge:peat:cotton “gin trash” decreased nitrate-N levels in soil, presumably due to a greater rate of denitrification. The lower soil density where pellets with cotton “gin trash” were used may be due to incorporation of low-density plant materials into soil aggregates by microbial activity (Russell 1973; Doran et al. 1994). In summary, therefore, addition of pelletized sewage sludge/waste material mixtures to a cracking clay had significant effects on soil chemical properties and very limited effects on soil physical properties monitored in this study. The negligible effects of the pellets on soil physical properties such as dispersion is surprising in view of the contrary statements in the literature (Bezdicek et al. 1984; Metzger & Yaron 1987; Jayawardane et al. 1992; Martens & Franckenberger 1992). The fact that the test soil was taken from a field which had been in a rotation system for the preceding 10 years, where all crop residues were retained in situ, and which had experienced no tillage for the preceding cropping phase may have contributed to these results (Bezdicek et al. 1984; Doran et al. 1994) 4. Conclusions In comparison with untreated control soil, application of pelletized sewage sludge/waste material (peat and cotton “gin trash”) mixtures resulted in a cracking clay which was more acidic and saline, had higher nitrate-N, and lower exchangeable Ca and Na. Partial substitution of sewage sludge and peat with cotton “gin trash” reduced the
2.5 2.7 2.9 2.9 2.4 2.7
P1
P< n.s. n.s.
+.. 0.05 0.11
0.33 0.46 0.61 0.84 0.94 0.59
±.. 0.42 0.93
15.7 16.9 17.5 17.3 20.4 17.5
P2
P< n.s. n.s.
26.3 26.7 26.0 25.0 23.7 25.6
P1
±.. 0.29 0.64
26.5 27.5 25.2 24.2 25.8 25.9
P2
Exch. Ca [cmol(+)kg−1]
(3.489) (3.818) (4.109) (4.435) (4.548) (4.080)
P2
±.. 9.5 21.1
104 181 277 335 404 261
P2
P< n.s. n.s.
1.7 1.7 1.9 1.9 1.7 1.8
P1
±.. 0.04 0.09
1.8 1.8 1.8 1.7 1.9 1.8
P2
Exch. K [cmol(+)kg−1]
P< 0.001 0.001
93 132 208 241 191 173
P1
Nitrate-N (mg kg−1)
±.. 0.022 0.049
0.75 0.75 0.73 0.79 1.02 0.81
P2
P< n.s. n.s.
1.5 1.3 1.2 1.1 1.0 1.2
P1
±.. 0.03 0.06
1.4 1.3 1.1 1.0 1.0 1.2
P2
Exch. Na [cmol(+)kg−1]
P< n.s. n.s.
0.72 0.67 0.84 0.85 0.89 0.80
P1
Organic C (%)
P< n.s. n.s.
1.7 1.7 1.5 1.5 1.4 1.6
P1
Ca/Mg
P< 0.05 n.s.
1.27 1.22 1.20 1.24 1.26 1.24
P1
±.. 0.03 0.07
1.7 1.6 1.5 1.4 1.3 1.5
P2
±.. 0.009 0.030
1.30 1.22 1.31 1.27 1.27 1.27
P2
Soil density (mg m−3)
P< 0.05 n.s.
3.2 2.9 2.6 2.5 2.4 2.7
P1
ESP
P< n.s. n.s.
18.1 19.5 19.5 18.7 19.4 19.1
P1
P2
±.. 0.06 0.15
3.0 2.8 2.5 2.3 2.0 2.5
P2
±.. 0.81 1.80
17.2 19.0 17.1 18.3 16.4 17.6
GMD (mm)
∗ Values in parantheses are loge transformed values of 100×electrical conductivity of a 1:5 soil:water suspension. P1, 2:2:1 sewage sludge:peat:cotton “gin trash”; P2, 1:1 sewage sludge:peat; Ec, electrical conductivity; n.s., not significant, ESP, exchangeable sodium percentage; GMD, geometric mean diameter of soil aggregates formed after puddling and drying air-dried soil.
15.8 15.9 17.5 17.5 17.4 16.8
P1
Ec∗
P< ±.. 0.01 (0.0223) 0.05 (0.0500)
(3.545) (3.804) (4.052) (4.283) (4.249) (3.987)
P1
Exch. Mg [cmol(+)kg−1]
0.35 0.45 0.58 0.73 0.70 0.54
2.6 3.0 3.0 2.7 2.3 2.8
P2
Dispersion index (%)
±.. 0.04 0.08
P< 0.001 0.01
P2 7.8 7.5 7.2 7.0 6.6 7.2
pH
7.9 7.6 7.4 7.1 7.2 7.4
P1
P< Pellet type n.s. Rate x pellet n.s. type
10 25 50 100 250 Mean
Application rate (g kg−1)
Pellet type Rate x pellet type
10 25 50 100 250 Mean
Application rate (g kg−1)
TABLE 3 Effect of pellet type on soil properties
578 N. R. Hulugalle
Effects of pelletized sewage sludge on soil properties
579
intensity of the above changes in soil properties. Changes in soil physical properties were limited to a small decrease in soil density. The insensitivity of the other soil physical properties to the experimental treatments were presumably due to the management history of the test soil. The changes in heavy metal, organo-chlorine and organo-phosphate concentrations were not quantified in this study, and hence, no conclusions can be drawn with respect to their accumulation in cracking clays.
Acknowledgements Mr. K. Luscombe of Luscombe Contracting Pty. Ltd. is thanked for providing gratis samples of the pelletized sewage sludge/waste material mixtures. The technical assistance of Mrs. J. Lindsay, Miss J. Renaud and Mr. P. Entwistle is gratefully appreciated. Analyses of nitrate-N, organic C and exchangeable cations were performed by the Analytical Services Unit of the New South Wales Department of Agriculture at Rydalmere, near Syndey.
References Awad, A. S., Ross, A. D. & Lawrie, R. A. (1989) Guidelines for the Use of Sewage Sludge on Agricultural Land. Sydney, Australia: New South Wales Department of Agriculture & Fisheries, 23pp. Bevaqua, R. F. & Mellano, V. J. (1994) Cumulative effects of sludge compost on crop yields and soil properties. Communications in Soil Science and Plant Analysis 25, 395–406. Bezdicek, D. F., Power, J. F., Keeney, D. R. & Wright, M. J. (eds) (1984) Organic Farming: Current Technology and its Role in a Sustainable Agriculture. Madison, WI, U.S.A.: ASA/ CSSA/SSSA, 192pp. Diez, J. A., Polo, A. & Guerrero, F. (1992) Effect of sewage sludge on nitrogen availability in peat. Biology and Fertility of Soils 13, 248–251. Doran, J. W., Coleman, D. F., Bezdicek, D. F. & Stewart, B. A. (eds) (1994) Defining Soil Quality for a Sustainable Environment. Madison, WI, U.S.A.: SSSA, 244pp. Epstein, E., Taylor, J. M. & Chaney, R. L. (1976) Effects of sewage sludge and sludge compost applied to soil on some soil physical and chemical properties. Journal of Environmental Quality 5, 422–426. Federer, W. T. (1995) Experimental Design: Theory and Application. New York, NY, U.S.A.: Macmillan, 544pp. Ghidey, F. & Alberts, E.E. (1993) Residue type and placement effects on decomposition: Field study and model evaluation. Transactions of the American Society of Agricultural Engineers 36, 1611–1617. Jayawardane, N. S., Blackwell, J., Muirhead, W. A. & Kirchof, G. (1992) Slotting – a new deep tillage technique for improving crop productivity on sodic, acid and other degraded soils and for land treatment of urban and rural waste. Commonwealth and Scientific and Industrial Research Organization Water Resources Series 5, 22pp. Klute, A. (ed) (1986) Methods of Soil Analysis, Part 1: Physical and Mineralogical Methods. Madison, WI, U.S.A.: ASA, 1188pp. Lerch, R. N., Barbarick, K. A., Sommers, L. E. & Westfall, D. G. (1992) Sewage sludge proteins as labile carbon and nitrogen sources. Soil Science Society of America Journal 56, 1470–1476. Martens, D. A. & Frankenberger, W. T., Jr (1992) Modification of infiltration rates in an organicamended irrigation soil. Agronomy Journal 84, 707–717. McIntyre, D. S. & Stirk, G. B. (1954) A method for determination of apparent density of soil aggregates. Australian Journal of Agricultural Research 5, 291–296. Metzger, L & Yaron, B. (1987) Influence of sludge organic matter on soil physical properties. Advances in Soil Science 7, 141–161. Page, A. L., Miller, R. H., and Keeney, D. R., (eds.), (1982) Methods of Soil Analysis, Part 2: Chemical and Microbiological Properties, 1159pp. Madison, WI, USA: ASA.
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Rayment, G. E. & Higginson, F. R. (1992) Australian Laboratory Handbook of Soil and Water Chemical Methods. Melbourne and Sydney, Australia:Inkata, 330pp. Russell, E. W. (1973) Soil Conditions and Plant Growth, 10th Edition. London, U.K.: Longman, 849pp. Schipitalo, M. J. and Protz, R. (1988) Factors influencing the dispersibility of clay in worm casts. Soil Science Society of America Journal 52, 764–769. Soil Survey Staff (1987) Keys to soil taxonomy. SMSS Technical Monograph No. 6. Ithaca, NY, U.S.A. Cornell University, 280pp. World Commission on Environment and Development (1987) Our Common Future (“The Brundtland Report”). Oxford, U.K.: Oxford University Press, 400pp.