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Published online 1 November 2007
Published in J Environ Qual 36:1704-1714 (2007)
DOI: 10.2134/jeq2007.0043
© 2007 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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TECHNICAL REPORTS

Waste Management

Papermill Biosolids Effect on Soil Physical and Chemical Properties

G. W. Price* and R. P. Voroney

Dep. of Land Resource Science, Univ. of Guelph, Guelph, Ontario, Canada N1G 2W1

* Corresponding author: (gprice{at}uoguelph.ca).

Received for publication January 24, 2007.

   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 Materials and Methods
 Results
 Discussion
 Conclusions
 REFERENCES
 
Papermill biosolids (PB) can provide multiple benefits to the soil system. The purpose of this study was to quantify the effects of a high C/N ratio (C/N = 100) de-inked PB on soil physical and chemical properties, including soil bulk density, infiltration rates, wet aggregate stability, total soil carbon, and heavy metal concentrations. Four rates of PB (0, 50, 100, and 150 Mg ha–1) were applied annually, for up to 3 yr, on four agricultural soils in Ontario, Canada. Decreases in soil bulk density between 0.27 and 0.35 g cm–3, relative to the nonamended treatment, were observed in soils receiving PB treatments over 3 yr. Total soil carbon increased within 1 yr on PB-amended soils planted to soybeans but not on soils planted to corn. Hydraulic conductivities (Kfs) were greater in all soils receiving PB amendments relative to the nonamended treatment throughout the study. Other properties measured, such as pH and electrical conductivity, were relatively unchanged after 2 yr of PB applications. While some increases in heavy metal accumulation occurred, there were no clear trends observed at any of the sites related to PB rates. The results of this study provide support to the idea that annual applications of PB can add significantly to the stability of soil structure.

Abbreviations: PB, papermill biosolids • EC, electrical conductivity • DM, dry mass • GSM, gravimetric soil moisture • MOE, Ministry of the Environment • OMAF, Ontario Ministry of Agriculture and Food


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
Materials and Methods
 Results
 Discussion
 Conclusions
 REFERENCES
 
ORGANIC by-products, such as animal manures and crop residues, have been used on agricultural soils as fertilizers and conditioners for centuries (Tisdale et al., 1985; Russell, 1988; Norrie and Fierro, 1998). In fact, the earliest scientific agricultural experiments conducted were designed to prove the valuable nature of these organic by-products on both the soil and crop growth (Russell, 1988). Organic amendments are used to improve soil physical and chemical properties, including bulk density, infiltration, nutrient availability, and soil carbon pools (Stratton and Rechcigl, 1998; Reynolds et al., 2003).

Increasing consumer demand for manufactured paper products has led to a growth in papermill biosolids (PB) generation. Consumption of paper and paper-board products in Canada is estimated at 8.1 million Mg annually (Ince et al., 2001). Only half of the paper material consumed is recovered through recycling programs (NRC, 2003; MillWatch, 2004). Increasingly, rising costs of disposal, i.e., higher land-fill tipping fees, high cost to benefit ratio of municipal recycling programs, have forced all levels of government to examine alternative ways of managing waste (EPIC, 2005).

Papermill biosolids are composed of cellulose, hemi-cellulose, lignins, clays, and, in the case of de-inked PB, chemical residuals from industrial processes (Norrie and Fierro, 1998; Nemati et al., 2000a). In Ontario, Canada, most PB are land-filled with the remaining quantities either incinerated, stockpiled, or land-applied. Currently, PB can be land-applied at 30 fresh Mg ha–1, as a soil conditioner, but is strictly regulated by the Ministry of the Environment (MOE) and the Ontario Ministry of Agriculture and Food (OMAF). Public safety concerns and a lack of longer term research on the effects of amending agricultural soils with PB have limited widespread adoption of this practice.

A growing body of research on the use of PB as a soil conditioner in agriculture and as a growth medium in horticultural research has shown benefits to plant growth and soil health (Simard, 2000; National Council of the Paper Industry for Air and Stream Improvement, 2003; Chong and Purvis, 2004). Some studies have reported increased crop yields from agricultural experiments examining a variety of PB amendments (Phillips et al., 1997; Simard, 2000; Curnoe et al., 2006). However, immobilization of soil nitrogen after applications of PB have also been reported to reduce crop yields (Aitken et al., 1998; Vagstad et al., 2001). In particular, using primary or de-inked PB, with high C/N ratios (>100), have been reported to cause yield reductions across a variety of crops if additional nitrogen fertilizer was not applied (Dolar et al., 1972; Norrie and Gosselin, 1996; Tripepi et al., 1996).

Benefits to soil structure and soil chemical properties have been found in soils amended with PB (Fierro et al., 1999; Zibilske et al., 2000; Chow et al., 2003). In addition, increased enzymatic and microbial activity, suggestive of a highly available carbon pool, has been observed after PB applications (Zibilske, 1987; Lalande et al., 2003; Charest et al., 2004). Increases in soil aggregate stability and plant-available water have been measured following several years of PB applications (Zibilske et al., 2000; Newman et al., 2005).

Not many field studies have examined the effect of applying multiple PB applications on soil physical and chemical properties. The aim of this study was to quantify the effect of applying increasing rates of a high C/N ratio de-inked PB on four agricultural soils on soil physical and chemical properties. We measured soil bulk density, infiltration rates, wet aggregate stability, and soil moisture content over 3 yr. In addition, we also measured changes in total soil carbon and nitrogen, electrical conductivity (EC), pH, and heavy metal concentrations after 2 yr of PB applications. This was part of a larger study aimed at developing management guidelines for amending agricultural soils with PB in Ontario, Canada.


   Materials and Methods
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
 Discussion
 Conclusions
 REFERENCES
 
Papermill Biosolids Characteristics and Composition
Fresh de-inked PB was obtained from Atlantic Packaging Ltd., Toronto, Ontario, a paper and packaging company that has recycling facilities to process manufactured corrugated containers, newspapers, magazines, and office paper waste. Fresh PB delivered to each site was sampled following a modified methodology for testing compost piles (CCREF, 2001). Four 1-L samples were manually composited using a shovel, at three pile locations, i.e., top, middle, bottom, after removing approximately 1 m of the pile surface layer. This was replicated three times for each pile location at all the sites during the study period. A total of 27 composited PB samples were collected throughout the study. One 25-g subsample was collected from each composite sample and sent to the Laboratory Services, University of Guelph, for chemical analysis during each year of the study (Table 1 ).


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  		Table 1. Chemical properties of Atlantic Packaging Ltd. papermill biosolids (means ± SEM) used throughout the study{dagger}.

 
Field Experiment
Study Location
The study was established at four sites spanning a soil textural gradient in southwestern Ontario, Canada. The field study was conducted between 1999 and 2002. The field sites were three University of Guelph Research Stations, at Elora (43°39' N, 80°35' W) representing a silty loam soil, near Cambridge (43°21' N, 80°18' W) representing a coarse sandy loam soil, at Vineland (43°11' N, 79°24' W) representing a loam soil, and at a private farm near Campden (43°13' N, 79°43' W) representing a clay loam soil. The chemical characteristics of the soils before the start of this study are given in Table 2 . The site at Elora was previously planted in continuous corn (Zea mays L.) and the site at Cambridge was previously under a corn–soybean (Glycine max L.)–wheat (Triticum aestivum L.) rotation. The Elora and Cambridge Research Stations were used throughout the whole study period. Field studies were conducted at the Vineland Horticultural Research Station from 1999 to 2000 and on the private farm in Campden, Ontario from 2000 to 2001. The field at Vineland was converted from a peach (Prunus persica) orchard in 1997 and maintained with a barley (Hordeum vulgare L.) cover crop until 1999 and Campden was planted to a corn–soybean rotation before the experiment.


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  		Table 2. Initial soil chemical characteristics (0 to 30 cm) measured at the research sites before PB applications (means ± SEM).

 
Experimental Setup
The field study was divided into two experiments, one examining corn and the other soybeans grown on soils receiving annual spring applications of PB. Plots measuring 3 x 12 m were established at each site and treatments were arranged in a randomized complete block design (RCBD) with four replicates. Four rates of fresh PB (0, 50, 100, and 150 Mg ha–1) were applied by hand before planting each spring, from 1999 to 2001, and immediately incorporated to a 15-cm depth. In 2002, PB was not applied and all the plots were sown to corn. A control treatment receiving no PB and no nitrogen fertilizer was established for each crop.

In the spring, ten soil cores (0 to 30 cm) for each treatment were collected and composited to determine the pre-plant 2 mol L–1 KCl-extractable NO3–N and NH4–N concentrations (Maynard and Kalra, 1993) and extractable P and K using 0.5 mol L–1 NaHCO3 (Schoenau and Karamanos, 1993). Phosphorus and K (0–20–20) were broadcast by hand, before planting, as required based on the Ontario Ministry of Agriculture and Food's (OMAF) recommendations for corn and soybeans (OMAF, 1996). Nitrogen fertilizer rates were calculated based on the pre-plant 2 mol L–1 KCl-extractable NO3–N content of the soils (0 to 30 cm) collected for each treatment and the OMAF recommended rate of nitrogen fertilizer for corn and soybeans. A supplemental nitrogen fertilizer treatment was applied on PB-amended plots to meet the biological demand to decay the material. Plots planted to corn received 1 kg N Mg–1 PB and plots planted to soybean received 0.5 kg N Mg–1 PB. The soybeans were expected to compensate for the reduction in plant-available nitrogen, resulting from the PB, through increased N fixation. Therefore, only a half rate of the supplemental nitrogen fertilizer treatment was applied on the plots planted to soybeans. Nitrogen fertilizer was applied as NH4NO3 (34-0-0) and split with half broadcast by hand at planting and the remaining half side-dressed by hand at the fifth leaf stage (V2 stage) of corn growth.

The corn hybrid Northrup King N17-C5 was planted in 1999 and DeKalb C35–50 from 2000 to 2002. The planting density of corn was approximately 74000 plants ha–1, with an inter-row spacing of 0.75 m. Corn was planted in May 1999, June to July 2000, May to June 2001, and May 2002. Corn grain was harvested by hand from the two center rows (total area = 7.5 m2) at maturity between October and early November and dried at 65°C to 150 g kg–1 moisture basis. The soybean hybrid OAC Bayfield was planted in 1999 and DeKalb Round-Up Ready from 2000 to 2001. A seeding rate of 100 kg ha–1 was used with an inter-row spacing of 0.18 m. Soybean was planted in May 1999, June to July 2000, and May to June 2001. Soybeans were harvested by hand from the center of each plot (total area = 17.5 m2) at maturity between October and early November. Harvested soybean pods were dried to 140 g kg–1 moisture basis. Throughout the study, all aspects of crop management, including weed and insect control, followed were based on provincial crop recommendations (OMAF, 1996).

Soil Physical Parameter Measurements
Bulk Density
Approximately 2 wk after the soybean harvest (October-November), every year from 1999 to 2001, two soil cores (10-cm diameter and 28-cm height) were collected from each treatment for soil bulk density analysis. Soil bulk density was determined following methods described by Culley (1993). Intact soil cores were placed in sealable plastic bags and stored at 4°C until analyzed. Soil cores were oven dried at 105°C until a constant weight was achieved.

Surface Water Infiltration
Infiltration measurements were conducted between 1999 and 2001. Two samples per treatment were taken in the fall of each year from plots planted to corn. A constant head pressure infiltrometer method (Reynolds and Elrick, 1990) was used to provide in situ estimates of field saturated hydraulic conductivity (Kfs) and matric flux potential ({Phi}m). A Guelph permeameter with the ring attachment was used to obtain measurements of rate of water infiltration from the selected treatment plots (Reynolds and Elrick, 1985). A stainless steel ring with a diameter of 0.1 m was inserted 0.05 m into the soil. Surface water infiltration measurements were taken on the highest rate of PB treatment, 150 Mg ha–1, and nonamended treatments. An applied hydraulic head of 0.10 m was established on all three soils measured. Water flow was measured at regularly timed intervals until a quasi-steady flow rate was achieved. Flow rate was deemed to be quasi-steady when the rate of change in the water level of the reservoir was constant for 10 min. The values for Kfs and {Phi}m were calculated using a soil texture–dependent parameter, {alpha}*, value of 12 m–1.

Water-Stable Aggregate Soil Analyses
At the end of the first year of PB applications, the fall of 1999, a composite consisting of two soil samples (0 to 15 cm) was collected from each treatment planted to corn for analysis. A 10-g soil (field moist) sample was used to separate soil aggregates by wet sieving following the procedures given by Angers and Mehuys (1993). Wet aggregate stability was measured on particles in the 1- to 2-mm size class. A modified wet-sieving apparatus was used to quantify water-stable aggregates in the PB-treated soils (Kemper and Rosenau, 1986). Soil aggregates were oven-dried at 105°C. In the third year of PB applications, fall of 2001, soil samples were collected again for analysis but only from the nonamended treatment and the 150 Mg ha–1 PB treatment planted to corn. Analysis was conducted on particles in the 1- to 2-mm and 2- to 4-mm size distribution classes.

Gravimetric Moisture Content (GSM)
Soil cores (0 to 30 cm) from treatments planted to corn were collected every year, from 1999 to 2002, at pre-plant, fifth leaf stage of corn growth, tasseling-silking stage of corn growth, and post-harvest. Ten soil cores from each treatment were composited and a 10-g sample was used for gravimetric soil moisture content (GSM) determination. Samples were weighed fresh and then oven-dried at 105°C until a constant weight was achieved.

Soil Chemical Parameter Measurements
Total Carbon and Nitrogen
Total soil carbon measurements were taken at the end of the first year of PB application, the fall of 1999, from all treatments planted to soybeans. Ten soil cores (0 to 30 cm) were composited from each treatment and analyzed for total soil C. In the fall of 2000, total soil carbon and nitrogen measurements were taken from all treatments planted to corn. All soil samples were air-dried and ground before analysis. Total soil C was determined by dry combustion using a LECO SC-444 (LECO Corp., St. Joseph, MI). Total soil nitrogen was determined by dry combustion using a LECO FP-428 nitrogen determinator (LECO Corp, St. Joseph, MI). Total soil carbon and nitrogen were expressed on an area basis (Mg ha–1), based on a 30-cm soil depth, and using the bulk density values measured in each PB treatment.

pH and Electrical Conductivity
After the corn harvest in the second year of the study, in 2000, ten soil cores (0 to 30 cm) were composited from all treatments and analyzed for pH and EC. Soil pH was measured in 0.01 mol L–1 CaCl2 using a 2:1 ratio of soil to water (Hendershot et al., 1993) and EC (dS m–1) was measured following the method outlined by Rhoades (1982).

Heavy Metal Concentrations
Before amending soils with PB, in the spring of 1999, ten soil cores (0 to 30-cm) from each treatment planted to corn were collected and composited for analysis of heavy metal concentrations at three of the study sites (Elora, Cambridge, and Vineland). In the spring of 2000, ten soil cores, collected from the treatments planted to corn, were composited and analyzed to determine baseline soil heavy metal concentrations at Campden. After corn harvesting in the second year of the study, in 2000, ten soil cores, collected from each treatment planted to corn, were composited and analyzed for heavy metal concentrations. Heavy metal concentrations were determined using a nitric/hydrochloric acid digestion method and analyzed by either atomic absorption spectrum (Hg, As, Se) or inductively coupled plasma (Cd, Co, Cr, Cu, Pb, Mo, Ni, Zn) (Soon and Abboud, 1993).

All the soil chemical analyses described in this section were conducted at Laboratory Services, University of Guelph (Guelph, Ontario, Canada).

Statistical Analysis
Data were analyzed following a method described in Chong et al. (1991). Soil bulk density, wet aggregate stability, EC, total soil carbon, total soil nitrogen, pH, soil heavy metal concentrations, and GSM were regressed in response to increasing PB rates. The model represents a series of lines and curves radiating from a common intercept. Both linear and quadratic relationships were tested. Where two or more lines or curves were not significantly different (P > 0.05), a common regression was fitted. Repeated measures analysis was also conducted on time series data, including soil bulk density and infiltration. An analysis of variance (ANOVA) using the PROC GLM procedure in SAS was used to examine treatment effects on hydraulic conductivity and water-stable aggregates. All treatment effects were considered to be significant at P < 0.05. Statistical analysis was performed using the SAS program version 9.1 (SAS Institute, 2003).


   Results
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and Methods
 Results
Discussion
 Conclusions
 REFERENCES
 
Bulk Density
A decrease in soil bulk density due to increasing rates of PB was significant (P < 0.05) at all the sites (Fig. 1 and 2 ). At Elora, a significant decrease (P < 0.001) in soil bulk density with PB rates was observed in both 1999 and 2000. Repeated measures analysis revealed significant differences across the 3 yr (P < 0.001) but they were independent of PB rates. At Cambridge, the linear relationships for 1999 and 2000 were regressed into a single line. The decline in bulk density with PB rates in these 2 yr was highly significant (P < 0.001). In 2001, a significant (P = 0.03) decrease in bulk density with increasing PB rates also occurred. A significant difference between the years was observed (P = 0.0024), as well as a significant year x PB effect (P = 0.018). After 2 yr of PB applications at Campden, a significant decrease (P = 0.003) in soil bulk density was observed with PB rates in 2001. At the end of 1999, after 1 yr of PB applications at Vineland, soil bulk density decreased significantly (P = 0.04) with PB rates.


Figure 1
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  		Fig. 1. Bulk density (1999 to 2001) in response to increasing rates of papermill biosolids (PB) at Elora and Cambridge on plots planted to soybeans. When no significant differences were observed between the sampling periods (P > 0.05), a common line was fitted. NS, dotted line, indicates that the slope was not significant (P > 0.05).

 

Figure 2
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  		Fig. 2. Regressions of soil bulk density measured at Campden (2001) and Vineland (1999) in response to increasing rates of papermill biosolids (PB) on plots planted to soybeans. Linear relationships were considered to be significant at P < 0.05.

 
Surface Water Infiltration
At most of the study sites, greater Kfs (m s–1) values were observed in the PB treatment (150 Mg ha–1) than the nonamended treatment (Fig. 3 ). At Elora, the PB-treated plots had higher (P < 0.05) hydraulic conductivities in each year than the nonamended treatment. Repeated measures analysis indicated that the differences in mean hydraulic conductivities across the years were dependent on the PB treatment (P = 0.005). At Cambridge, the PB treatment did not influence hydraulic conductivity (P > 0.05) after 1 yr of application relative to the nonamended treatment. However, hydraulic conductivities in the PB treatment were higher (P < 0.05) than the nonamended treatment in each of the two subsequent years. Analysis across the years revealed a significant effect of year and an interaction effect of Yr x PB (P = 0.004). This suggests that the increases in mean hydraulic conductivity, with the PB treatment, were based on a cumulative effect of the applications. At Vineland, the PB treatment had higher (P < 0.05) hydraulic conductivity than the nonamended treatment in each of the 2 yr measured. Repeated measures analysis indicated significant differences in mean hydraulic conductivities across the years. In 2000, hydraulic conductivities were greater in both the PB and nonamended treatments than the previous year. At Campden, hydraulic conductivities were greater in the PB-treated plots, in both years, than the nonamended plots. No differences were observed across the years.


Figure 3
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  		Fig. 3. Infiltration rates, Kfs, (m s–1) on four agricultural soils planted to corn and receiving a nonamended and 150 Mg PB ha–1 treatment during the study period (1999 to 2001). Bars indicate least squares standard error and treatments with different letters within each year were significantly different at P < 0.05. Please note differences in scale.

 
Water-Stable Aggregates
Papermill biosolids treatments did not affect (P > 0.05) wet aggregate stability, in the 1- to 2-mm size classes, of the soils planted to corn after 1 yr of applications at Elora, Cambridge, or Vineland (Fig. 4 ). In 2001, the number of water-stable aggregates in the 150 Mg ha–1 PB treatment, in the 2- to 4-mm and 1- to 2-mm size classes, were greater (P < 0.05) than in the nonamended treatment at all sites (Fig. 5 ). At Elora and Cambridge, a greater number of water-stable aggregates in the 2- to 4-mm size class were observed than in the 1- to 2-mm size class on plots receiving PB.


Figure 4
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  		Fig. 4. Regressions of water-stable aggregates (1–2 mm) in response to papermill biosolids (PB) rates after 1 yr (1999) on plots planted to corn at Elora, Cambridge, and Vineland. NS, dotted lines, indicates that the slopes of the regressions were not significant (P > 0.05).

 

Figure 5
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  		Fig. 5. Water-stable aggregates (1–2 mm and 2–4 mm), after 3 yr of PB applications, from the nonamended and 150 Mg ha–1 PB treatments on plots planted to corn at Elora, Cambridge, and Campden. Bars indicate least squares standard error and treatments with different letters within each year were significantly different at P < 0.05.

 
Gravimetric Soil Moisture (GSM)
At all the sites, GSM increased as rates of PB treatments increased (Table 3 ). At Elora, GSM increased over all the sample periods between 1999 and 2001. In 2002, residual effects were observed within each sampling period but the slope decreased from pre-plant to post-harvest. At Cambridge, increases in GSM over PB treatments were observed through most sampling periods. A decline in the GSM slope in 2002 during the growing season was also observed at Cambridge. Gravimetric soil moisture also increased at Campden and Vineland in response to PB treatments.


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  		Table 3. Regressions of gravimetric soil moisture content, measured during the growing season, in response to increasing rates of PB on four agricultural soils planted to corn.

 
Soil Chemical Parameters
Total Carbon and Nitrogen
On plots planted to soybeans, increases in total soil C resulted after 1 yr of PB applications (Fig. 6 ). Total C increased, relative to the control soil by 29 Mg ha–1 at Cambridge and 42 Mg ha–1 at Vineland, at the highest PB rate. Linear increases with PB rates were significant at Cambridge (P = 0.01) and Vineland (P < 0.001) but not at Elora.


Figure 6
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  		Fig. 6. Total soil carbon (0 to 30 cm) after 1 yr (1999) with increasing PB rates on plots planted to soybeans at Elora, Cambridge, and Vineland. NS, dotted line, indicates that the regression was not significant (P > 0.05).

 
On plots planted to corn, total soil C was not significantly different (P > 0.05) between the nonamended and the PB treatments at any of the sites (Table 4 ).


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  		Table 4. Total soil carbon and nitrogen in response to increasing rates of PB (0, 50, 100, 150 Mg ha–1) after 2 yr of applications on four agricultural soils planted to corn.

 
Total soil N decreased at Elora with increasing PB rates but no differences were observed at the other sites at the end of 2 yr of PB applications (Table 4).

pH and Electrical Conductivity
Electrical conductivity and pH were mostly unaffected by PB treatments after 2 yr on plots planted to corn (Table 5 ). At Cambridge, EC increased with PB rates. No differences were observed for EC at any of the other sites. An increase in pH with PB was observed at Vineland but not at the three other sites.


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  		Table 5. Electrical conductivity (dS m–1) and pH in response to 2 yr of PB applications on soils planted to corn at four study sites.

 
Heavy Metal Concentrations
The response in soil heavy metal concentrations, after 2 yr, to increasing rates of PB varied between the sites (Table 6 ). At Elora, concentrations of As and Cr declined over increasing rates of PB. However, Pb concentrations increased with PB input by up to 1.5 mg kg–1, at the highest rate of PB amendment. No significant differences were observed in any of the other heavy metals at Elora with increasing PB inputs. At Cambridge, Cr and Se concentrations were reduced as PB inputs increased whereas concentrations of Cu increased. No responses to PB amendments were observed in the other heavy metals. At Vineland, no significant changes in heavy metal concentrations occurred with increasing PB inputs. At Campden, after 1 yr of PB application, an increase in Co concentrations with PB inputs was measured.


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  		Table 6. Heavy metal concentrations{dagger} in response to increasing rates of papermill biosolids after 2 yr of applications on four agricultural soils planted to corn.

 

   Discussion
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and Methods
 Results
 Discussion
Conclusions
 REFERENCES
 
Crop residues provide benefits to agricultural soils ranging from increased infiltration rates, reduced erosion, and higher soil carbon pools (Tisdale et al., 1985). Similarly, organic residues from various industries, such as pulp and paper, enhance soil carbon and plant-available water levels (Nemati et al., 2000a; De Neve et al., 2003; Newman et al., 2005). The results of our study further demonstrate the potential of PB to enhance soil physical characteristics of field soils.

The impact of PB applications on soil bulk density was observed within the first year at all of the sites. The trend of decreasing soil bulk density with increasing rates of PB is consistent with results from a number of studies (Wei et al., 1985; Nemati et al., 2000b; Foley and Cooperband, 2002). Foley and Cooperband (2002) tested lower C/N ratio (<44:1) PB amendments over 2 yr and observed decreases in bulk density, particularly with the higher C/N ratio amendments. Furthermore, Brauer and Aitken (2006), after 1 yr of PB addition (C/N = 30; PB rates = 0, 22, 44, and 88 Mg ha–1), reported significant reductions in bulk density with increasing PB rates. In our study, the effect of further additions of PB on bulk density was smaller by the third year of PB applications at Elora and Cambridge. Fierro et al. (2000) examined the decomposition of a high C/N ratio PB (>200), applied at 105 dry Mg ha–1 to an abandoned mining sandpit, over 27 mo. They reported a one third reduction in the total PB mass after 3 mo, with more than half the total PB mass lost after 16 mo. This suggests that after an initial highly active decomposition period, the effects of the PB on soil physical properties may be reduced. In two studies, annual contributions of PB were needed to maintain positive effects on plant-available water and wet aggregate stability (Nemati et al., 2000b; Foley and Cooperband, 2002).

The observed increase in hydraulic conductivity on PB-amended soils in our study is consistent with previous studies (Wei et al., 1985; Nemati et al., 2000b; Chow et al., 2003). Increasing the organic matter content of soils is important toward both maintaining stability of the soil aggregates which in turn stabilizes the pore network. Amending soils with PB has been shown to reduce the ability of surface runoff to cause damage to the soil structure (Chow et al., 2003). In a laboratory study, Nemati et al. (2000a) found that applying a high C/N ratio PB (>200) improved the resistance of soils to rapid wetting. In a subsequent field study, Nemati et al. (2000b) reported increases in Kfs with higher rates of PB after 2 yr of applications. In our study, the high rate of PB (150 Mg ha–1) increased hydraulic conductivity, at most sites, after 1 yr of application relative to the nonamended treatment. Hydraulic conductivity values, in the PB-amended soil, were also greater than the nonamended treatment in each subsequent year. After the second year of application, hydraulic conductivities in the PB treatment were relatively unchanged at most of the sites. Nemati et al. (2000b) also observed a reduced effect on hydraulic conductivity after the second year of adding PB. They attributed this reduced effect to clogging of the soil pores with kaolinite clay or fibers from the decomposing PB. It is also likely that kaolinite clays associated with the de-inked PB may be buffering the residues from decomposition (Fierro et al., 2000).

Nemati et al. (2000a) found that PB amendments, up to 24 dry Mg ha–1 (C/N > 200), increased soil aggregate sizes in three different soils in a 6-mo incubation experiment. They conjectured that macro-aggregate changes from the PB amendments stabilized the soil pore system resulting in greater resistance to rapid wetting events and greater hydraulic conductivities relative to the control soils. A trend toward greater water-stable aggregates in the 1- to 2-mm size class was evident, but not significant, in the first year of our study. By the third year of our study, water-stable aggregates in the PB treatment were between two and three times higher than the nonamended treatment. Zibilske et al. (2000) only observed increases in wet aggregate stability after 3 and 5-years of annual PB applications. Nemati et al. (2000b) reported increases in wet aggregate stability on PB-amended soils which were short-lived (8 to 12 months). The positive effects on wet aggregate stability from previous PB applications are likely to be maintained when considering the slower decomposition rate of higher C/N ratio PB.

Greater soil moisture retention can have an impact on microbial activity (van Veen et al., 1985), reduced irrigation water requirement (Foley and Cooperband (2002), and greater plant-available water for crop growth (Nemati et al., 2000b). In our study, GSM increased between 10 and 20 g of water kg–1 of soil with each 50 Mg PB ha–1 increment, relative to the nonamended soil. Foley and Cooperband (2002) observed greater amounts of plant-available water at field capacity, by almost one and a half times in the higher C/N ratio PB treatments, after 2 yr of PB applications. However, they did report a decline in water retention as the material decomposed. Other studies have also shown increased water retention, after 1 yr, on soils receiving PB amendments (Wei et al., 1985; Nemati et al., 2000a; Chow et al., 2003). Zibilske et al. (2000) have suggested that some of the increases in plant-available water observed in their study were related to the particle sizes of the PB creating larger soil pore spaces; therefore, the amount of plant-available water would be a transient and not a permanent change to the soil system. The variability in GSM during the growing season in our study would also suggest that the gains in GSM are a temporary function of the larger particles mixed into the soil matrix.

Linear increases in total soil C occurred at two of our study sites after 1 yr of PB applications on plots planted to soybean. After 4 yr, Newman et al. (2005) reported up to 3.3 times more total carbon in a PB-amended soil above the initial baseline soil (C/N = 12 to 34). Papermill biosolids rate-dependent linear increases in soil C on agricultural soils have also been reported by other researchers (Foley and Cooperband, 2002; Brauer and Aitken, 2006). Despite 2 yr of PB applications on plots planted to corn, total soil C was not significantly different at any of our study sites. Foley and Cooperband (2002) reported total C increases in PB treatments (C/N = 12 to 44) up to two to five times greater than the nonamended soil over 2 yr with potatoes and snapbean. However, they observed a decline in total C back to soil baseline levels in the year following PB applications. Zibilske et al. (2000) reported net increases in soil C of 15 and 60 g kg–1 in soils planted to corn and amended with 90 and 225 dry Mg PB ha–1, respectively. Substantial increases in soil C were not obtained in Zibilske et al.'s (2000) study until the fifth year of PB application. The highest rate used in Zibilske et al.'s (2000) study, 225 dry Mg PB ha–1, was over three times higher than the highest PB treatment in our study (150 fresh Mg PB ha–1 or ~66 dry Mg PB ha–1). Availability of nitrogen and greater rate of decomposition of the soybean versus corn residues might also account for the differences in total C observed between the two experiments in our study.

Total nitrogen in our study was also relatively unchanged after 2 yr of PB amendments planted to corn. In a study conducted by Fierro et al. (1999), a one-time PB amendment of 105 dry Mg PB ha–1 was combined with two rates of nitrogen fertilizer (315 and 945 kg N ha–1). They observed a decline in total soil nitrogen concentration of the whole soil in all treatments after 2 yr but reported overall higher amounts of soil nitrogen in the presence of the PB. In addition, the PB in our study would only contribute about 0.73 kg N Mg–1 PB which would not be sufficient to meet microbial demands for decomposition, even if it were all available.

The heavy metal concentrations in our study were below the typical background soil concentrations in Ontario (Ministry of the Environment, 1996) and were lower than amounts found in sewage sludges or animal manures (Charest and Beauchamp, 2002). No clear trends in heavy metal accumulation related to PB applications were evident from our study. Differences in heavy metal concentrations in our study may be a result of characteristics related to the soil textures. Madejón et al. (2001) reported increases, relative to nonamended soils, in concentrations of Fe, Pb, Mn, Zn, and Cu on two sandy soils receiving 50 Mg PB ha–1 (C/N = 84). However, concentrations declined in both soils over the incubation period and were typically <20 mg kg–1. It is possible that the higher Cu concentrations at Cambridge are linked to the soil texture and the lower exchange capacity of the sandy loam soil compared to the other soils in our study (Jones and Belling, 1967). The concentration of Cu in the PB used in our study was considerably lower than those found in other organic by-products, such as sewage sludges, mineral fertilizers, and manures (Beauchamp et al., 2002). The results of our study suggest that, in the short term, accumulation of heavy metals in the soil is small, even with PB rates up to 150 Mg ha–1.

The EC values ranged from 0.16 to 0.35 dS m–1 across the sites in our study but were generally not affected by the PB treatments. In agriculture, an EC > 4 dS m–1 is considered a threshold leading to potential crop or root damage (Jacobs and Timmer, 2005). In a greenhouse study conducted by Tripepi et al. (1996), very high EC values, ranging from 4 to 6 dS m–1, were recorded in soils amended with composted and raw PB mixtures. However, the cottonwood plants in the PB-amended soils had improved growth. In a 3-yr study in Spain, 40 Mg ha–1 yr–1 of a primary PB applied to an orange orchard resulted in no significant changes in EC values compared to a control (Madejón et al., 2003). Similarly, the pH of the soils in our study remained relatively unchanged after 2 yr of PB applications, with the exception of Vineland which had a pH increase of 0.4 at the highest PB treatment rate (150 Mg ha–1). In a laboratory study, Madejón et al. (2001) observed a trend toward increasing pH on soils amended with 50 Mg ha–1 of a primary PB (C/N = 84). Studies testing the use of raw PB as container nursery growth media have also reported increases in pH (Chong and Purvis, 2004). The lack of pH increases at most of our sites is likely the result of a larger buffering capacity of the soils relative to the amount of PB added. Despite these results, moderate increases in pH resulting from PB applications could aid in reducing availability of some heavy metals (Madejón et al., 2001).


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This study demonstrated that up to 3 yr of PB applications improved soil bulk density, wet aggregate stability, and surface water infiltration on four agricultural soils. Total soil C also increased in some of the soils studied. Heavy metal concentrations in the soil were not significantly altered despite multiple applications of increasing rates of the de-inking PB. This study showed that annual applications of a high C/N ratio PB on agricultural soils can provide multiple benefits to soil physical and chemical properties.


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