Availability of heavy metals in compost-amended soil

Availability of heavy metals in compost-amended soil

blO l SOU (t IC(tlrlO[OG¥ ELSEVIER BioresourceTechnology69 (1999) 1-14 Availability of heavy metals in compost-amended soil Keith R. Baldwin *a, Ja...

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blO l SOU (t IC(tlrlO[OG¥

ELSEVIER

BioresourceTechnology69 (1999) 1-14

Availability of heavy metals in compost-amended soil Keith R. Baldwin *a, James E. Shelton b aDepartment of Horticultural Science, Box 7609, North Carolina State University, Raleigh, NC 27695-7619, USA bDepartment of Soil Science, North Carolina State University, Mountain Horticultural Crops Research and Extension Center, 2016 Fanning Bridge Rd, Fletcher, NC 28732-9216, USA Received 20 January 1998; revised 3 August 1998; accepted 30 September 1998

Abstract

Composted municipal wastes can be applied to cropland to supply nutrients and improve soil physical properties, but farmers are concerned about heavy metal availability. Three municipal composts were applied at 0, 25, 50 and 100 × 106 g ha -~ in 1994 to an unlimed and limed (pH 6.5) Dyke clay (clayey, mixed, mesic Typic Rhodudults), and burley tobacco (Nicotiana tabacum L.) was planted in 1994 and 1995. The composts were municipal solid waste (MSWC), wastewater biosolids (WBC) and co-composted municipal solid waste/wastewater biosolids (COC). Leaf samples were collected three times in each year and analyzed for heavy metal concentration. Soil samples were collected three times in each year, extracted with DTPA and extracts were analyzed for heavy metal concentration. With the exception of Cd in 1994 cured burley leaves, Cd, Ni, and Pb concentrations were generally undetectable for all treatments in both years. When leaf Cu and Zn concentrations in cured leaves from COC and WBC in 1994 were regressed against amounts of Cu and Zn applied with respective compost treatments, mean leaf Cu and Zn were significantly higher in COC (215 mg Cu kg ~ and 738 mg Zn kg -1) than in WBC (173 mg Cu kg -~ and 499 mg Zn kg -~) treatments. Because compost Cu and Zn concentrations in MSWC (53 mg Cu kg -1 and 96 mg Zn kg 01) were much lower than in other composts, cured leaf Cu and Zn in MSWC treatments were not compared with cured leaf Cu and Zn in COC or WBC treatments. DTPA-extractable Zn, Pb, Cd and Cu concentrations increased with increasing soil pH at the 100 × 1 0 6 g ha 1 rates of COC addition in September, 1994. Higher metal composts were associated with higher metal extractability than were lower metal composts: when equal rates of metal addition to soil from different composts were compared, DTPA-extractable Cu and Pb concentrations in September 1994, were significantly higher in COC than in WBC treatments, and DTPA-extractable Cd concentration was significantly lower in MSWC treatments than in COC or WBC treatments. © 1999 Elsevier Science Ltd. All rights reserved. Keywords: Compost; Metals; Biosolids; Sludge; Waste

I. Introduction

1.1. Metal uptake by tobacco Bioavailability o f Cd to tobacco plants (Nicotiana tabacum L.) is a particular c o n c e r n because tobacco is able to absorb fairly high concentrations of Cd with no m a j o r signs of toxicity ( T a n c o g n e et al., 1988). Schroeder and Balassa (1961) c o n d u c t e d a survey of sources of Cd intake by h u m a n s and f o u n d tobacco contained the highest Cd concentration o f all products *Corresponding author. Formerly Graduate Research Assistant, Department of Soil Science, Box 7619, North Carolina State University, Raleigh, NC 27695-7619, USA.

tested. T o b a c c o grown on soils a m e n d e d with sewage sludges can accumulate as m u c h as 4 4 m g k g -~ Cd when the soil contains 1 mg kg 1 Cd ( C h a n e y et al., 1978). King and Hajjar (1990) r e p o r t e d that tobacco grown on soil a m e n d e d with Cd is a significant source o f Cd intake for h u m a n s who smoke and that the potential accumulation of Cd by tobacco grown on sludge-amended soil where Cd levels are elevated is a concern. Recently, Jing and L o g a n (1992) r e p o r t e d on the phytoavailability o f Cd f r o m different sludges where equal a m o u n t s of Cd were applied in each pot. Evidence indicated plant uptake of Cd from sludge with low Cd concentration was less than that from sludge with higher Cd concentration, even if the same total a m o u n t of Cd was applied. C r o p uptake o f Cd

0960-8524/99/$ - - see front matter © 1999 Elsevier Science Ltd. All rights reserved. PII: S0960-85 24(98)00174-6

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K.R. Baldwin, J.E. Shelton/Bioresource Technology 69 (1999) 1-14

increased with increasing sludge Cd concentration. The authors explained these findings in terms of specific Cd binding sites in the sludge: the population of Cd binding sites varied widely in strength of specific Cd adsorption; as sludge Cd concentration increased, the least strongly bound Cd was more phytoavailable. Corey et al. (1987) concluded that specific metal adsorption on sludge surfaces would normally be the controlling factor in metal phytoavailability in soilsludge mixtures; sludges with higher metal concentration cause higher metal uptake by plants when equal amount of metals are applied. King and Hajjar (1990) reported that sludge rate had little effect on concentration of Cr and Pb in tobacco. Concentrations of Cd, Ni, and Zn in tobacco decreased as soil pH increased to 5.8-6.0 but no further reduction was noted at higher pH values. Concentration of Cd and Zn declined markedly with increasing height of leaf on the tobacco stalk. Gutenmann et al. (1983) reported that concentrations of Cd, Ni, and Zn in the leaf laminae from tobacco grown on sludge-amended silt loam soil were higher than those in the control. Lead concentrations were not affected by sludge additions. Soil pH appears to be the most important single soil property that determines Cd availability to plants (CAST, 1980). In heavy metal cation (Zn, Cd, Cu, Ni, Pb, Hg) studies, solubility has been shown to increase with decreasing pH. When sludges were added to soil, Sanders and Adams (1987) found that as soil pH decreased, a threshold pH was reached below which metal solubility was sharply increased. Adams and Sanders (1984) found that the higher the sludge metal concentration, the higher the threshold pH point of decreasing metal solubility. The residual effect of the application of metals to cropland on subsequent crops has been an area of emphasis in trace metals research. Bell et al. (1988) reported elevated concentrations of Zn, Cu, Ni and Cd in tobacco grown on a silt loam 10 y after sludge had been applied to the site. Plant metal concentrations were inversely related to soil pH. In western North Carolina, burley tobacco (Nicotiana tabacum L.) is often grown on steep slopes. Twenty years ago, additions of organic matter, primarily manures, to these soils was a regular management practice which not only provided nutrients to crops but also improved soil physical properties. This is no longer a common practice. Now there is interest in use of composted municipal waste to regularly apply organic matter to burley fields. There remain concerns, however, about the availability of metals contained in composts because tobacco is known to be a metal accumulator. The objective of this experiment was to determine the plant availability of compost metals to a burley tobacco crop.

2. Methods

A field study was conducted in which three composts were applied at four rates at two lime levels and burley tobacco grown for 2yr. The first treatment was a co-composted municipal solid waste and wastewater biosolids compost (COC) produced by an aerobic, in-vessel process. The second treatment was a municipal solid waste compost (MSWC) produced in windrows. The third treatment was a wastewater biosolids compost (WBC) produced from centrifuged, dewatered sewage sludge (18-20% TS) mixed with wood chips and straw in a ratio of 1:5:1 (Huffman et al., 1995). Each material was subsampled, dried at 70°C and ground in a stainless steel Wiley mill to pass a 2 mm sieve. Total N concentration was determined with a Perkin-Elmer PE 2400 CHN Elemental Analyzer. After dry-ashing, other elements were determined by ICP. Chemical analyses of the materials are presented in Table 1. Treatment applications consisted of factorial combinations of three composts, three rates of application (25, 50 and 100 x 106 g dry weight ha-l), and two soil pH levels (5.8 and 6.5). In addition, there were two control plots without compost at each pH. The higher pH was achieved by applying lime at 4000 kg ha 1. All treatments received 224kg N ha 1 and 56 kg P ha -1. The 20 treatments were arranged in randomized complete blocks with four blocks, and plots measured 3.7 x 10.4 m. The treatment materials were distributed by hand and the field was disked to approximately 10 cm. MSWC was insufficient for all treatments so there were only two replications of the 100 x 10 6 g ha -~ treatment and data were treated as missing plot data. In 1994, burley tobacco (Nicotiana tabacum L., cv TN 90) was mechanically transplanted in three rows per plot with 1.23 m between rows and 22 plants per row. Missing and/or dead plants were reset within 7 days. Conventional crop management strategies were employed throughout the growing season (North Carolina Cooperative Extension Service, 1994), and B was foliarly applied (1200 ppm B) to the plants in June. The crop was hand-harvested in September, hung on tobacco sticks, and air-cured in barns. Tobacco leaf samples were collected in June, July, August and September of 1994. Ten most-recentlymatured leaves were stripped from both outside rows in each plot. Leaves obtained in June were rinsed with distilled water before drying; while the remaining leaves were dried without rinsing. Cured leaf samples (composited by weight from all stalk positions) were obtained at time of grading. Leaves were dried at 70°C and ground in a stainless steel Wiley mill to pass a 1 mm sieve. Ground samples were stored at room temperature in acid-washed glass jars.

K.R. BaMwin, J.E. Shelton/Bioresource Technology 69 (1999) 1-14 Table 1 Application rates of COC, MSWC and WBC compost materials and amounts of metals applied to a Dyke soil in 1994 Compost

Trace metal rate

1)

Type

Rate (10ng ha -~)

Zn (kg ha -~)

Cu (kg ha -~)

Cd (kg ha -l)

Ni (kg ha

COC"

25 50 100

18.4 36.9 73.8

5.4 10.8 21.5

0.07 0.15 0.29

1.0 2.0 4.0

5.1 10.2 20.3

MSWCb

25 50 100

2.4 4.8 9.6

1.3 2.6 5.3

0.03 0.05 0.10

0.5 0.9 1.8

0.9 1.7 3.4

WBC c

25 50 100

12.5 25.0 49.9

4.3 8.7 17.3

0.05 0.10 0.21

0.4 0.8 1.6

2.2 4.4 8.8

Pb (kg ha 1)

aC-composted municipal soil waste and wastewater biosolids. bMunicipal soil waste compost. CWastewater biosolids compost.

Dried plant samples were ashed in a muffle furnace at 500°C overnight, brought to volume in distilled water and 6 N HCI and analyzed for elemental content with a Perkin-Elmer Plasma 2000 inductively coupled plasma emission spectrometer (ICP). Nitrogen content was determined with a Perkin-Elmer PE 2400 CHN Elemental Analyzer. In 1995, fertilizer and lime were reapplied to respective plots, but compost materials were not re-applied. Burley tobacco (TN 90) was planted on 30 May after disking to approximately 10 cm and managed conventionally. Blue mold (Peronospora tabacina Adam) required additional sprays of the fungicide dimethomorph (Acrobat ®) in 1995. After harvesting, the leaf was air-cured as previously described. In 1995, 10 leaves were stripped from guard rows in June, July and August. The June samples consisted of most-recently-matured leaves and they were rinsed in distilled water before drying at 70°C. In July and August, 10 leaves were stripped from two stalk positions: most-recently matured leaves and mature leaves from the lower stalk position where leaves had been collected in June. These leaves were not rinsed before drying at 70°C. Cured leaf samples from upper, middle, and lower stalk positions were obtained at time of grading. Dried samples were ground to pass a 1 mm stainless steel sieve and stored in acid-washed glass jars at room temperature. Leaf samples were analyzed as described for 1994. The soil was a Dyke clay (clayey, mixed, mesic Typic Rhodudults) at the Mountain Research Station, Waynesville, North Carolina. A composite soil sample was taken to a depth of 20 cm from the experimental area prior to treatment application. Soil samples were collected from harvest rows in May, July, and September of 1994 and June, July, and September of 1995. A stainless steel soil probe was used to collect a

composite sample of four cores (20 cm length × 2.54 cm diameter) from each plot. Samples were air-dried, ground to pass a 2 m m sieve and stored at room temperature in soil cartons. Samples were extracted with D T P A at pHT.3 (Lindsay and Norvell, 1978). Extracts were analyzed for Zn, Ni, Cu, Cd and Pb on a Perkin-Elmer Plasma 2000 System inductively coupled plasma emission spectrometer (ICP). Comparisons between means were made using a general linear models procedure in the Statistical Analysis System (SAS, 1985). Because the data in the experiment was unbalanced, a least squares means test was used to determine differences among compost treatments. Variation in trace metal concentration within limed and unlimed treatments was large throughout the experiment, and the pH range studied was rather narrow. Consequently, the analysis of variance for each compost treatment was conducted using the General Linear Models (GLM) procedure with p H as a continuous rather than a discrete variable (Ray, 1982). Because individual composts varied in metal concentration, differing amounts of metals were applied with each compost at each application rate as shown in Table 1. Neither leaf metal concentration, nor DTPAextractable soil metal concentration, therefore, could be directly contrasted among composts by rate of compost application. Contrasts could be performed based on rate of metal addition with each compost at each rate. However, regressions of DTPA:extractable metal or leaf metal concentration with rates of addition of metal for each compost did not overlap sufficiently to compare means or slopes among composts. Log transformation of Cu, Zn, Pb and Ni application rates and corresponding tissue or soil concentrations of these metals allowed a direct comparison of COC and WBC treatments. Log transformation of Cd and Ni

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K.R. Baldwin, J.E. Shelton/Bioresource Technology 69 (1999) 1-14

The MSWC was low in N (0.30%) and C (6.4%) content. Almost 75% of the MSWC material was an inorganic 'residue' not subject to mineralization processes. This residue may have been sand that was mixed in with the feedstock materials when compost windrows were turned. The effects of limed and unlimed compost treatments on mean soil pH in September of 1994 and 1995 are shown in Table 3. In both unlimed and limed COC treatments in 1994, soil pH was generally higher in soils receiving 50 and 100 x 106 g ha -1 of COC material than in soils receiving 0 or 25 x 106g ha -1. The same was true for unlimed COC treatments in 1995. Rate of application of material did not result in differences in soil pH in either unlimed MSWC or unlimed WBC treatments in 1994. The enhanced pH from COC is due to the inclusion of CaCO3 with the lime-stabilized sludge feedstock. The Ca concentration of COC was 27.7 g Ca kg -1 compared to 9.4 and 17.2 g Ca kg -1 for MSWC and WBC, respectively. Other researchers have reported this same effect (Chaney and Ryan, 1993; Mazur et al., 1983; Hernando et al., 1989; Smith, 1992).

application rates and corresponding tissue or soil concentrations of these metals allowed a direct comparison of all three composts. Figures presented show all datapoints. Trendlines are presented solely for purposes of illustration.

3. Results and discussion

3.1. Compost characteristics Chemical analyses of the composts are presented in Table 2. Metal concentrations for each material were on the order of those reported by Lisk et al. (1992) for the same types of composts. However, Na and CI concentrations in COC were 6126 and 5117 mgkg -1, respectively. Mean soil conductivity (saturated paste extract) in 100 x 106 g ha -1 COC-amended plots ranged from 2.35 to 3.45 dS m -1 and the conductivity values in the lowest yielding replication was 3.43 dS m -~. Researchers have attributed plant toxicity to compost salinity (Garcia et al., 1992; Chanyasak et al., 1983).

Table 2 Composition of COC, MSWC and WBC composts applied to a Dyke soil in 1994 Compost C (gkg -~)

Al (gkg -1)

Ca (gkg -~)

Fe (gkg -1)

K (gkg -~)

Mg (gkg -1)

N (gkg -~)

P (gkg -~)

S (gkg -~)

COC" MSWC b WB(Y

17.9 36.0 13.7

27.7 9.4 17.2

14.2 34.0 15.8

3.8 2.7 3.5

3,1 2.6 2.2

13.1 3.0 21.2

2.6 0.8 9.6

7.0 0.7 4.3

364.1 64.1 358.9

Cd (mgkg -l) CI (mgkg -~) Cr (mgkg -1) Cu (mgkg -~) Mn (mgkg -~) Na (mgkg -~) Ni (mgkg -~) Pb (mgkg -1) Zn (mgkg -1) COC a MSWC b WBC ~

2.9 1.0 2.1

5117 339 356

58 24 140

215 53 173

370 603 881

6126 449 325

40 18 16

203 34 88

738 96 499

a,b,cSee Table 1 for abbreviations.

Table 3 Comparison of mean soil pH in unlimed and limed 0, 25, 50 and 100 x 106 g ha -1 COC, MSWC and WBC compost treatments at the end of the 1994 and 1995 growing seasons Rate (106g ha -1)

Unlimed

Limed

COC a

MSWC b

WBC ¢

COC

MSWC

WBC

1994 0 25 50 100

5.6ab 5.8ab 6.1b 6.0ab

5.6a 5.7a 5.7a 5.7a

5.6a 5.7a 5.5a 5.6a

5.7a 5.8ab 6.3c 6.2bc

5.7a 6.0b 5.8a 5.7a

5.7a 5.9a 6.0a 5.8a

1995 0 25 50 100

5.6a 5.8a 6.2b 6.1b

5.6a 5.9a 6.0a 5.9a

5.6a 6.1b 5.6a 5.9ab

6.2a 6.2a 6.5a 6.2a

6.2a 6.3a 6.3a 6.2a

6.2a 6.3a 6.1a 6.1a

a,b,cSee Table 1 for abbreviations. Within years within a column means followed by the same letter are not significantly different at P = 0.05.

K.R. Baldwin, J.E. Shelton/Bioresource Technology 69 (1999) 1-14

3.2. Burley yield Yield data from 1994 and 1995 are presented in Table 4. Burley yield in COC treatments was significantly lower than in MSWC, WBC or control treatments in 1994. Transplant wilting, leaf necrosis and subsequent mortality (over 50%) occurred in 100 x 106 g ha -1 treatments. Transplants were reset in this treatment on two different occasions. Lower yields were most likely due to COC salinity (Table 1) but C1 toxicity could have influenced plant performance. Generally, there were no significant yield differences among composts or treatments in 1995. Yields in 1995 were below 1994 levels because of blue mold (Peronospora tabacina Adam) disease.

3.3. Soil analysis The significance of F tests for variables rate (0, 25, 50 and 100 x 106 g ha-l), pH and rate/pH on DTPAextractable soil Zn, Ni, Cu, Cd and Pb concentration in September of 1994 and 1995 are shown in Table 5 for each of the three composts. An inverse relationship was observed between DTPA-extractable Ni concentra-

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tion and pH in MSWC and WBC treatments in September, 1994. No effect of pH was observed on DTPA-extractable Zn, Cu, Cd, Ni or Pb concentration in September, 1995. The response of DTPA-extractable Zn, Cu and Cd concentration to increasing rate of compost addition was generally linear throughout the experiment. No rate effect was observed for DTPAextractable Ni or Pb in 1994 and 1995, respectively. In contrast to Valdares et al. (1983) and King and Hajjar (1990), DTPA-extractable trace metal concentration was not well-correlated with amount of trace metal applied. In COC treatments, DTPA-extractable soil Zn concentration showed a rate/pH interaction in September of 1994 (Fig. 1). Zinc concentration was linearly related to pH in the 100×106gha -1 COC treatment but was not related to pH at other rates, contradicting many reports, including those of MacLean (1974), Friesen et al. (1980) and Gupta et al. (1971). This may have occurred because increasing ionic strength in soils results in decreasing adsorptive preference for divalent over monovalent cations (McBride, 1994). The COC contained 6126mg Na kg -1, and high rates of addition of this compost

Table 4 Yield of burley tobacco in 1994 and 1995 in limed and unlimed COC, MSWC and WBC compost treatments (rates pooled) Compost

1994

COC a MSWC b WBC ~ Control

1995

Limed (kg ha -s)

Unlim e d (kg ha -l )

Limed (kg ha -1)

Unlimed (kg ha - l)

2430a 2852b 2986b 3095b

2340a 3297b 2828c 2848c

2188a 2168a 2231a 2502a

2168a 2103a 2245a 2162a

a.b.c See Table 1 for abbreviations. Within columns data followed by the same letter are not significantly different at P = 0.05.

Table 5 Significance of F tests from analyses of variance of rate, pH and a rate/pH interaction of DTPA-extractable soil trace metals in September of 1994 and 1995 for COC, MSWC and WBC compost treatments Compost

COO

Ag ro nomic variable

Rate(R) pH

R/pH R pH

R/pH R pH R~H

1994

1995

Ni

Zn

Cu

Cd

Pb

Ni

Zn

Cu

Cd

Pb

NS d NS NS NS ** NS NS * NS

** * * * NS NS ** NS NS

** * NS NS NS NS ** NS NS

** * * * NS * ** NS NS

** NS * * NS NS * NS NS

** NS NS NS NS NS ** NS NS

** NS * * NS NS ** NS NS

** NS * * NS NS ** NS NS

* NS * * NS NS * NS NS

NS NS * * NS NS NS NS NS

a.b,c See Table 1 for abbreviations. dNS, * and * * denote no significance, and significance at P = 0.05 and 0.01, respectively.

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K.R. Baldwin, J.E. Shelton/Bioresource Technology 69 (1999) 1-14

1982). Lindsay and Norvell (1978) reported a critical DTPA-extractable Cu value of 0.2 ppm, below which Cu deficiency could be expected for most crops. DTPA-extractable Cu concentration for COC, MSWC and WBC treatments in this experiment ranged from 0.44 to 9.33/~g g-1 (data not shown). In contradiction to reports in the literature (Christensen, 1984; Kuo et al., 1985) and mirroring findings for DTPA-extractable Cu, DTPA-extractable Cd concentration in COC treatments increased as pH increased in September 1994. At higher loading rates, available Zn, Cu, Ca and Mn in solution may have reduced Cd sorption through competition for adsorption sites (Kuo and Baker, 1980; Bittel and Miller, 1974). Considerable Zn, Cu and Ca were added to the soil in COC applications and the Dyke soil contained 870 mg kg-i Mn. Cadmium extractability may also have increased as pH increased because of increases in

resulted in high soil electrical conductivity values. High rates of COC (100 × 106g ha -a) also increased soil pH (data not shown) and soil Zn. Thus, at high application rates of COC, preference for Zn adsorption was decreased and extractable Zn increased as pH increased. Additionally, preference for trace metals on adsorptive surfaces (relative to the prevalent cations in solution, in this case Ca and Na) is decreased at increasing adsorption level; that is, with increasing additions of trace metals to the soil (McBride, 1994). DTPA-extractable Zn concentration was unrelated to pH but linearly related to rate in both WBC and MSWC treatments. DTPA-extractable soil Cu concentration in September, 1994, tended to react similarly to Zn. DTPA-extractable Cu was linearly related to pH in COC-treated soil, contradicting reports in the literature (Cavallaro and McBride, 1980; Dragun and Baker,

10.0 O0 Mg/ha O 25 Mg/ha + 50Me/ha X 100 Mg/ha

9.0

8.0

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X

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6.0 x

t~

X

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4-

s'

5.0

6

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X ° x

4.0

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3.0

X

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+ + + O ..- ..--..- ..- ....-- "n25

2.0 []

1.0

0

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4.5

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5.5

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6.0



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Fig. 1. Effect of pH and rate of COC application (10 6 g ha -1) on 1994 late season/DTPA-extractablesoil Zn concentration.

K.R, BaMwin, J.E. Shelton/BioresourceTechnology69 (1999) 1-14

Cd-CI ion pair formation as COC loading (hence C1 application) increased (Hirsch et al., 1989). However, King (1988) examined the relationship between Cd extractability and soil properties and could not determine strong relationships between extractability and exchangeable Ca and/or pH. DTPA-extractable Pb concentration in September 1994, soil samples taken from COC treatment plots showed a rate/pH interaction in which extractable Pb concentration in 0, 25 and 50× 106g ha -1 treatments did not decrease with increasing pH while at the 100 x 106 g ha 1 rate, DTPA-extractable Pb concentration in COC treatments increased with increasing pH.

3.4. Plant analysis Mean cured leaf Cu concentrations in 1994 and 1995 for differing rates of COC, MSWC and WBC application are shown in Table 6. Generally, leaf Cu concentrations were within the range reported by Collins et al.

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(1961) for flue-cured tobacco (Nicotiana tabacum L.) of 14.9-21.1 mg Cu kg -~. However, mean 1994 cured leaf Cu concentration in the 100× 106gha -~ COC treatment was in the toxicity threshold range ( 2 0 - 3 0 m g k g -1) reported by Robson and Reuter (1981). There was no effect of pH on cured leaf Cu concentration in COC, WBC or MSWC treatments in 1994 (Table 7). A negative correlation between Cu uptake and soil pH has been reported (Tiwari and Kumar, 1982). High leaf Cu concentration at high pH: (l) supported the theory that with high rates of addition of metals, the pH threshold for diminishing metal availability occurs at higher soil pH (Adams and Sanders, 1984); (2) suggested the Jing and Logan (1992) conclusion that "the population of Cd binding sites in sludge varies widely in strength of specific Cd adsorption, and as sludge Cd concentration increases, the least strongly bound Cd is more phytoavailable" can be applied to

Table 6 Mean leaf Cu and Zn concentration of cured burley tobacco leaves in 1994 and 1995 in 0, 25, 50 abd 100 × 106 g ha i COC, MSWC and WBC compost treatments Compost

COC"

MSWC b

WBC c

Rate (106 g ha ~)

0 25 50 100 0 25 50 100 0 25 50 100

1995 Cu

1994 Cu

Composite ~ (mg kg-1)

Lower e (mg kg i)

Middle* (rag kg l)

Upper e (mg kg 1)

8.8a f 12.1b 15.8b 28.7c 7.3ab 5.1b 8.0a 7.8ab 6.9a 7,0a 7,3ab 10,3b

10.2a 13.7ab 15.2b 17.2b 10.9a 12.2a 13.0a 17.9b ll.9a 12.5a 12.4a 21.3a

ll.3a 14.3b 14.6b 16.5b ll.7a 11.2a 14,0a 21.9b ll.5a 15.9b ll.0a 12.6a

14.9a 14.4a 15.6a 24.1b 15.lab 12.9a 15.6ab 20.2b 15.0ab 18.3a 13.4b 16.2ab 1995 Zn

1994 Zn

COC

MSWC

WBC

0 25 50 100 0 25 50 100 0 25 50 100

Composite (mg kg- 1)

Lower (mg kg 1)

Middle (mg kg- 1)

Upper (rag kg -l)

44.0a 50.1b 54.6b 78.6c 38.9a 40.1a 45.2a 61.8b 38.9a 46.la 45.3a 49.8b

38.2a 41.2ab 46.1bc 48.8c 38.9a 40.4a 41.1a 50.0a 40.0a 47.0ab 42.7a 57.7b

40.7a 46.8b 50.5bc 53.1c 41.1a 41.5a 47.0a 49.3a 41.9a 54.6b 44.9ac 52.3bc

42.9a 45.5ab 49.4b 55.8c 42.5a 43.9a 46.0a 50.2a 43.7a 52.7bc 46.4ab 53.9c

a'b'cSee Table 1 for abbreviations. dWeighted composite sample. eStalk position of leaves sampled. %Vithin columns for each compost, means followed by the same letter are not significantly different at P = 0.05.

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K.R. Baldwin, J.E. Shelton/Bioresource Technology 69 (1999) 1-14

c o m p o s t Cu as well: and (3) supported the hypothesis of C o r e y et al. (1987) that sludge chemistry (in this case c o m p o s t chemistry) controls the activity of C u in the soil solution. Leaf Cu concentrations in M S W C and W B C treatments were not related to p H and were relatively low in b o t h cases at low pH. In these cases, adsorptive capacity of c o m p o s t m a y control Cu availability rather than low soil pH. M e a n cured leaf Z n concentrations in 1994 and 1995 for differing rates of C O C , M S W C and W B C application are shown in Table 6. L e a f Zn values at all sampling dates fell within tobacco leaf Z n concentration ranges r e p o r t e d in the literature (Ward, 1941; Miner and Tucker, 1990). Significant r a t e / p H interactions for 1994 cured leaf Z n concentrations in C O C treatments are shown in Fig. 2. At the 100 x 106g ha -~ rate, Z n concentration was linearly related to p H and at the other rates of addition of C O C , leaf Z n concentration was unrelated to pH. L e a f Z n concentrations was unrelated to p H and linearly related to rates in M S W C and W B C treatments in 1994 cured leaf samples. These results contradict reports in the literature that lime application to

cropland r e d u c e d Z n concentration in crop leaf tissues ( P e p p e r et al., 1983; Lee and Craddock, 1969). T h e highest rate of addition of Z n in the experiment (100 × 106g ha -1 C O C ) significantly increased soil p H in both limed and unlimed treatments c o m p a r e d to the control and also resulted in increasing leaf Zn concentration as p H increased. Thus, the A d a m s and Sanders (1984) finding that higher metal concentrations (in applied sludges) resulted in increased metal solubility and hence "increased uptake at higher soil p H values" may be applicable to applied composts, as well. In this experiment, D T P A - e x t r a c t a b l e soil Zn concentration also increased with increasing rate of C O C addition, and at the 100 x 106 g ha -~ rate, extractability increased as p H increased. C u r e d upper, middle and lower leaf Z n concentrations in 1995 were inversely related to p H in the C O C , M S W C , and W B C treatments (data not shown) and positively related to rate in the C O C and W B C treatments (Table 7). U p p e r leaves in C O C and M S W C treatments had significantly higher Z n concentrations than lower leaves (data not shown). This contradicted data presented by King and Hajjar (1990) and F r a n k et al. (1977).

Table 7 Significance of F tests from analyses of variance of rate, pH and rate/pH interaction of burley leaf Cu and Zn concentration of cured leaves in 1994 and 1995 COC, MSWC and WBC treatments Compost

COCa MSWCh WBC~

Agronomic variable

Rate (R) pH R/pH R pH R/pH R pH R/pH

1994 Cu

1995 Cu

Compositea

Loweff

**f NS NS NS NS NS * NS NS

. NS NS * NS NS NS NS NS

1994 Zn

COC MSWC WBC

R pH R/pH R pH R/pH R pH R/pH

.

Middlec .

.

. NS NS ** NS NS NS NS NS

Upper~ . NS NS NS NS NS NS NS NS

1995 Zn

Composite

Lower

Middle

Upper

** NS * ** NS NS * NS NS

** ** NS NS ** NS ** ** NS

** ** ** NS ** NS * ** NS

** * NS ** ** NS * ** NS

,,b.cSee Table 1 for abbreviations. dWeighted composite sample. °Stalk position of leaves sampled. fNS, * and ** denote no significance, and significance at P = 0.05 and 0.01, respectively.

K.R. Baldwin, J.E. Shelton/Bioresource Technology 69 (1999) 1-14

Cured leaf Cd concentrations were inversely related to pH in COC, MSWC and WBC treatments in 1994 (data not shown), but linearly related to rate only in COC treatments (Fig. 3). Reports in the literature have generally reported that soil pH is negatively correlated with plant Cd concentration (Jackson and Alloway, 1990; Adriano et al., 1982). In 1995, there was little detectable Cd in burley tissue at any sampling date. Only 69 out of 87 cured leaf samples contained detectable Cd in 1994. For the purposes of statistical analysis, the 18 samples with Cd concentration below detectable limits were assigned values of 0.4 mgkg -t (50% of the detection limit). Fewer than 15 samples at any other sampling date contained detectable Cd. No Pb was detectable in burley leaf tissue at any sampling date in either 1994 or 1995. Several investigators (Hassett, 1974; Soldatini et al., 1976; Riffaldi et al., 1976; King, 1988) have reported the dominant

9

roles of clay and organic matter content in the soil sorption of Pb. The clay soil in the field plots and the organic matter in the compost treatments effectively adsorbed Pb in the compost and limited Pb uptake. Additionally, Zimdahl and Foster (1976) found that liming the soil did not have a consistent effect on Pb uptake by corn (Zea mays L.) plants. No Ni was detectable in burley leaf tissue at any sampling date in either 1994 or 1995. Organic matter has been shown to adsorb Ni, thereby making it less available to plants (Halstead, 1968; Halstead et al., 1969). Adsorption by compost organic matter probably limited Ni uptake by burley tobacco in this experiment.

3.5. Comparisons among composts Comparisons of leaf Cu concentration were made with log-transformed data. At equal rates of Cu application, leaf Cu concentration was greater in 'higher Cu'

120 oOMg~

X

• 25 M g / h a

110

+ 50 M g / h a X 1O0 M g / h a

I00

90

.,t5 J

~,

?

80

t

X

s

x.t

70

×

i

gl

+

+

X

~

60 --°.

[]

=~=

+.

......

50 0 . ~

L --'''''''~5

O

40

[]

+

~

+

O [2 # 30

O

20

. . . . . 4.5

t 5.0

. . . .

~

. . . . .

5.5

~ 6.0

....

l 6.5

. . . . 7.0

pH Fig. 2. Effect of pH and rate of application (106 g ha -~) on 1994 cured leaf Z n concentration of burley tobacco grown in COC-amended soil.

10

K.R. Baldwin, J.E. Shelton/Bioresource Technology 69 (1999) 1-14

differences in September 1994, DTPA-extractable Cu concentration between COC and WBC treatments (data not shown). Once again, at equal rates of metal application, the compost with the higher metal concentration had more 'plant available' Cu than a lower metal compost. Extractable Cu concentration increased with increasing pH and rate in COC treatments and was unrelated to p H in WBC treatments and this may have contributed to differences in leaf and soil Cu concentration between these treatments. There were significant differences in leaf Zn concentration between COC (737mg Z n k g -t) and WBC (499 mg Zn kg -~) treatments in cured leaves in 1994. Differences in cured leaf Zn concentration in 1994 are shown in Fig. 5. At equal rates of Zn loading, leaf Zn concentration in 'higher Zn' COC treatments was significantly greater than leaf Zn concentration in 'lower Zn' WBC treatments. Reasons for these differences

COC (215 mg C u k g -*) treatments than in 'lower Cu' WBC (173.3 mg Cu kg -1) treatments in cured leaves in 1994 (Fig. 4). This was also the case in September 1994 leaves and in June and September leaves in 1995. This suggested the Corey et al. (1987) conclusion that "sludges with higher metal concentration could cause higher metal uptake by plants when equal amount of metals were applied" could also be applied to composts. However, toxicity effects might also explain the difference in leaf Cu concentration between treatments. Because of high compost salt concentration and/or Cu toxicity, yield in the COC treatments were significantly lower than yields in the WBC treatments (rates pooled). Leaf growth was more vigorous in the WBC treatments, and leaf Cu concentration was, in effect, 'diluted' in those treatments. Comparisons of DTPA-extractable soil Cu were made with log-transformed data and showed significant

4.0

0 0 Mg/ha rn25 Mg/ha + 50 Mg/ha × 100 Mg/ha

3.5

3.0 X []

+ X

2.5 X

E O

2.0

E~

.

o"" " " -

~.

÷xx÷

..,. ~.+

1.5

",.

\

".. \

<>

X "'-. -t-50

1.0 ¢

\

\

0.5

I:11:1 0

0.0

\ \ 25

glx

O+

..... 4.5

5.0

5.5

6.0

6.5

7.0

laH

Fig. 3. Effect of pH and rate of application (10+g ha -~) on cured leaf Cd concentration of burley tobacco grown in COC-amended soil.

K.R. Baldwin, J.E. Shelton/Bioresource Technology 69 (1999) 1-14

are probably similar to those for differences in leaf Cu concentration between COC and WBC composts. The differences in cured leaf Zn concentration may also be partly explained by the interactions of pH and rate in COC treatments in which both leaf Zn and DTPAextractable soil Zn concentration increased with increasing pH at the 100 × 106g ha -1 application rate. However, there was no difference in DTPA-extractable soil Zn concentration between C O C and WBC treatments in 1994. When data was log transformed, there were significant differences in September 1994, DTPA-extractable Cd concentration among compost treatments (data not shown). At equal rates of Cd application, DTPAextractable Cd concentration was significantly higher in 'higher Cd' COC (2.9 mg Cd kg -1) and WBC (2.1 mg

11

Cd kg -1) treatments than in 'lower Cd' MSWC (1.0 mg Cd kg -l) treatments. Log-transformed September 1994 data showed that at equal rates of Pb application, the 'higher Pb' COC (203 nag Pb kg -~) treatments had higher extractable soil Pb concentration than 'lower Pb' WBC (88rag Pb kg -~) treatments (data not shown). When September 1995 data was log transformed (data not shown), 'lower Ni' WBC (16.3 mg Ni kg -~) treatments had higher DTPA-extractable Ni concentration at equal rates of Ni application than 'higher Ni' COC (39.7 mg Ni kg -~) treatments. This contradicted expectations that DTPA-extractable soil Ni would be higher in treatments amended with higher Ni compost. Mulchi et al. (1987) found that lime-stabilized sludge treatments reduced DTPA-extractable soil Ni relative

1.8

X COC

+WBC X

1.6 X

×

eoc 1.4

A

1.2

X

+

.9

x

+

-$ .........

.................

--

..+

0.8

4,

.+- -

.°.°"

:1:

,

+

÷

+

0.6

0.4

.... 0.5

,' ' ' ' ' I .... 0.6

0.7

I . . . . . ., . . . . . . ,. . . . . . ,. . . . . . , 0.8

0.9

1.0

I.I

1.2

~ . . . . . ., . . . 1.3

1.4

1.5

Log Cu Application (kg ha a)

Fig. 4. Effect of rate of application (kg ha -~) of COC and WBC compost Cu on 1994 cured leaf Cu concentrationof burleytobacco.

12

K.R. Baldwin, J.E. Shelton/Bioresource Technology 69 (1999) 1-14

to a control which received no sludge. They attributed the reduction to increased soil pH with sludge treatments.

4. C o n c l u s i o n

Trace metals applied in COC, MSWC and WBC did not accumulate in leaf tissue in sufficient quantities to produce toxicity symptoms in burley tobacco. Burley leaf Pb and Ni concentrations were below detectable limits throughout the experiment. Cadmium concentration was only detectable in cured 1994 leaf samples. Burley leaf Zn and Cu concentrations were linearly related to rate of compost addition, but mean leaf Zn concentration fell within the sufficiency range reported by Miner and Tucker (1990) in all compost treatments.

Leaf Cu was above the sufficiency range reported by Miner and Tucker (1990) in most treatments, but within the normal range for flue-cured tobacco reported by Collins et al. (1961). Cured 1994 leaf Cu in 100 x 10 6 g ha -1 COC treatments was within the toxicity range reported by Robson and Reuter (1981). However, no Cu toxicity symptoms were observed. Taken together, the evidence provided by this experiment indicated that at the same rate of metal application, Zn and Cu in composts are more available from composts containing higher concentrations of these metals than from lower metal composts. Leaf Cu concentration in 1994 and 1995 and leaf Zn concentration in 1994 were generally not related to pH, and the extractability of trace metals generally did not vary with pH (in some cases increased with increasing pH), even at high rates of compost addition.

2.2

xCOC +WBC

X

X x

+

1.9

x

N

X

+

"

. .. .. .....

+ + .. ..... .. . . . .

x

1.6

+

+ X

+

+

1.3

: .... l.O

1.1

I .... 1.2

I .... 1.3

I .... 1.4

, .... 1.5

, .... 1.6

, .... 1.7

, 1.8

1.9

2.0

Log Zn Application (kg h ~ t)

Fig.5.E~ect~frate~fapp~icati~n(kgha-l)~fCOCandWBCc~mp~stZn~n~994cur~d~afZnc~nc~ntrati~n~fbur~eyt~bacc~.

K.R. Baldwin, J.E. Shelton/Bioresource Technology 69 (1999) 1-14

References Adams, T.M., Sanders, J.R., 1984. The effects of pH on release to solution of zinc, copper and nickel from metal-loaded sewage sludges. Environmental Pollution B8, 85-99. Adriano, D.C., Page, A.L, Elseewi, A.A., Chang, A.C., 1982. Cadmium availability to sudan grass grown on soils amended with sewage sludge and fly ash. Journal of Environmental Quality I1, 197-203. Bell, P.F., Adamu, C.A., Mulchi, C.L, Chaney, R.L., 1988. Residual effects of land applied municipal sludge on tobacco: I. effects on heavy metal concentrations in soils and plants. Tobacco Science 32, 33-38. Bittel, J.E., Miller, R.J., 1974. Lead, cadmium and calcium selectivity coefficients of monmorillinite, illite and kaolinite. Journal of Environmental Quality 3, 250-253. CAST (Council for Agricultural Science and Technology), 1980. Effects of sewage sludge on the cadmium and zinc content of crops. Council for Agricultural Science and Technology Report No. 83. Ames, IA. Cavallaro, N., McBride, M.B., 1980. Activities of Cu 2+ and Cd ~÷ ions in soil solutions as affected by pH. Soil Science Society of America Journal 44, 729-732. Chaney, R.L., Ryan, J.A., 1993. Heavy metals and toxic organic pollutants in MSW composts. In: H.A.J. Hoitink, H.M. Keener (Eds), Science and Engineering of Composting: Design, Environmental, Microbiological and Utilization Aspects. Renaissance Publications, Worthington, OH, pp. 451-489. Chaney, R.L., Hundemann, P.T., Palmer, W.T., Small, R.J., White M.C., Decker, A.M., 1978. Plant accumulation of heavy metals and phytotoxicity resulting from utilization of sewage sludge and sludge composts on cropland. In: Proceedings National Conference on Composting Municipal Residues and Sludges. Information Transfer Inc., Rockville, MD, pp. 86-96. Chanyasak, V., Katayama, A., Hirai, M.F., Mori, S., Kubota, H., 1983. Effects of compost maturity on growth of komatsuna Brassica Rapa vat. pervidis in Neubauer's pot: II. growth inhibitory factors and assessment of degree of maturity by org.-C/org.-N ratio of water extract. Soil Science and Plant Nutrition 29, 251-259. Christensen, T.H., 1984. Cadmium soil sorption at low concentrations: I. effect of time, cadmium load, pH, and calcium. Water, Air and Soil Pollution 21, 105-114. Collins, W.K., Jones, G.L., Weybrew, J.A., Matzinger, D.F., 1961. Comparative chemical and physical composition of flue-cured tobacco varieties. Crop Science 1, 407 Corey, R.B., King, LD., Lue-Hing, C., Fanning, D.S., Street, J.J., Walker, J.M., 1987. Effects of sludge properties on accumulation of trace elements by crops. In: A.L. Page (Ed.), Land Application of Sludge. Lewis Publishers, Chelsea, MI, pp. 25-51. Dragun, J., Baker, D.E., 1982. Characterization of copper availability and corn seedling growth by a DTPA soil test. Soil Science Society of America Journal 46, 921-925. Frank, F., Braun, H.E., Holdrinet, M., Stonefield, K.I., 1977. Metal contents and insecticide residues in tobacco soils and cured tobacco leaves collected in southern Ontario. Tobacco Science 21, 74-80. Friesen, K.K., Juo, A.S.R., Miller, M.H., 1980. Liming and limephosphorus-zinc interactions in two Nigerian ultisols. I. interactions in the soil. Soil Science Society of America Journal 44, 1221-1226. Garcia, C., Hernandez, T., Costa, F., Paccual, J.A., 1992. Phytotoxicity due to the agricultural use of urban wastes. Journal of the Science of Food and Agriculture 59, 313-319. Gupta, S.K., Calder, F.W., MacLeod, L.B., 1971. Influence of added

13

limestone and fertilizers upon the micronutrient content of forage tissue and soil. Plant and Soil 35, 249-256. Gutenmann, W.H., Lisk, D.J., Hoffman, D., Adams, J.D., 1983. Selenium in particulates and gaseous fractions of smoke from cigarettes prepared from tobacco grown on fly ash amended soil. Journal of Toxicology and Environmental Health 12, 385-394. Halstead, R.L., 1968. Effect of different amendments on yield and composition of oats grown on a soil derived from serpentine material. Canadian Journal of Soil Science 48, 301-305. Halstead, R.L., Finn, B.J., MacLean, A.J., 1969. Extractability of added lead in soils and its concentration in plants. Canadian Journal of Soil Science 49, 335-342. Hassett, J.J., 1974. Capacity of selected Illinois soils to remove lead from aqueous solution. Communications in Soil Science and Plant Analysis 5, 499-505. Hernando, S., Lobo, M.C., Polo, A., 1989. Effect of the application of a municipal refuse compost on the physical and chemical properties of a soil. Science of the Total Environment 82, 589-596. Hirsch, D., Nir, S., Banin, A., 1989. Prediction of cadmium complexation in solution and adsorption to montmoriUonite. Soil Science Society of America Journal 53, 716-721. Huffman, E.B., Shelton, J.E., Bellamy, J.D., 1995. Pilot-scale testing of the aerated static pile composting process. In: R.K. White (Ed.), Proceedings of a Conference on Composting in the Carolinas. Clemson University, Clemson, SC, pp. 66-76. Jackson, A.P,, Alloway, B.J., 1990. The bioavailability of cadmium to lettuce and cabbage in soils previously treated with sewage sludges. Plant and Soil 132, 179-186. Jing, J., Logan, T.J., 1992. Effects of sewage sludge cadmium concentration on chemical extractability and plant uptake. Journal of Environmental Quality 21, 73-81. King, L.D., 1988. Effect of selected soil properties on cadmium content of tobacco. Journal of Environmental Quality 17, 251-255. King, L.D., Hajjar, L.M., 1990. The residual effect of sewage sludge on heavy metal content of tobacco and peanut. Journal of Environmental Quality 19, 738-748. Kuo, S., Baker, A.S., 1980. Sorption of copper, zinc and cadmium by some acid soils. Soil Science Society of America Journal 44, 969-974. Kuo, S., Jellum, E.J., Baker, A.S., 1985. Effects of soil type, liming, and sludge application on zinc and cadmium availability to swiss chard. Soil Science 139, 122-130. Lee, C.R., Craddock, G.R., 1969. Factors affecting plant growth in high zinc medium. II. influence of soil treatments on growth of soybeans on strongly acid soil containing zinc from peach sprays. Agronomy Journal 61, 565-567. Lindsay, W.L, Norvell, W.A., 1978. Development of a DTPA soil test for zinc, iron, manganese, and copper. Soil Science Society of America Journal 42, 421-428. Lisk, D.J., Gutenmann, W.H., Rutzke, M., Kuntz, H.T., Chu, G., 1992. Survey of toxicants and nutrients in composted waste materials. Archives of Environmental Contamination and Toxicology 22, 190-194. MacLean, A.J., 1974. Effect of soil properties and amendments on the availability of zinc in soils. Canadian Journal of Soil Science 54, 369-378. Mazur, N., Santos, G.De A., Velloso, A.C., 1983. Effect of composted urban waste on the availability of phosphorus in an acid soil. Revista Brasileira de Ciencia do Solo 7, 153-156. McBride, M.B., 1994. Environmental Chemistry of Soils. Oxford University Press, New York, NY, pp. 66-144. Miner, G. and Tucker, M.R., 1990. Plant analysis as an aid in fertilizing tobacco. In: R.L Westerman (Ed.), Soil Testing and Plant Analysis. Soil Science Society of America, Inc., Madison, WI, pp. 645-657. Mulchi, C.L., Bell, P.F., Adamu, C., Chaney, R.L., 1987. Long term

14

K.R. Baldwin, J.E. Shelton/Bioresource Technology 69 (1999) 1-14

availability of metals in sludge amended acid soils. Journal of Plant Nutrition 10, 1149-1161. North Carolina Cooperative Extension Service, 1994. In: 1995 Burley Tobacco Information. AG 376. North Carolina State University, Raleigh, NC. Pepper, I.L., Bezdicek, D.F., Baker, A.S., Sims, J.M., 1983. Silage corn uptake of sludge-applied zinc and cadmium as affected by soil pH. Journal of Environmental Quality 12, 270-275. Ray, A.A. (1982) SAS User's Guide: Statistics. SAS Inst., Cary, NC. Riffaldi, R., Levi-Minzi, R., Soldatini, G.F., 1976. Lead adsorption by soils: II. specific adsorption. Water, Air and Soil Pollution 6, 119-128. Robson, A.D, Reuter, D.J., 1981. Diagnosis of copper deficiency and toxicity. In: J.F. Loneeragan (Ed.), Copper in Soils and Plants. Academic Press, London, pp. 287-312. Sanders, J.R., Adams, T.M., 1987. The effects of pH and soil type on concentration of zinc, copper and nickel extracted by calcium chloride from sewage sludge-treated soils. Environmental Pollution A43, 219-228. SAS, 1985. SAS User's Guide: Statistics. SAS Institute, Cary, NC. Schroeder, H.A., Balassa, J.J., 1961. Abnormal trace metals in man: cadmium. Journal of Chronic Disorders 14, 236-258. Smith, S.R., 1992. Sewage sludge and refuse composts as peat alter-

natives for conditioning impoverished soils: effects on the growth response and mineral status of Petunia grandiflora. Journal of Horticultural Science 67, 703-716. Soldatini, G.F., Riffaldi, R., Levi-Minzi, R., 1976. Lead adsorption by soils. I. adsorption as measured by Langmuir and Freundlich isotherms. Water Air and Soil Pollution 6, 111-118. Tancogne, J., Nguyen Phu Lich, Schiltz, P., Truhaut, R., Claude, J.D., Chouteau, J., 1988. Influence of various growth medium related factors on the absorption of cadmium. CORESTA Information Bulletin 1988 Congress, 9-13 Oct., China. Tiwari, R.C., Kumar, B.M., 1982. A suitable extractant for assessing plant-available copper in different soils. Plant and Soil 68, 131-134. Valdares, J.M.A.S., Gal, M., Mingelgrin, U., Page, A.L., 1983. Some heavy metals in soils treated with sewage sludge, their effects on yield, and their uptake by plants. Journal of Environmental Quality 12, 49-57. Ward, G.M., 1941. Mineral absorption studies with tobacco. The Lighter 11, 16-22. Zimdahl, R.L., Foster, J.M., 1976. The influence of applied phosphorus, manure or lime on uptake of lead from soil. Journal of Environmental Quality 5, 31-34.