HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (11) Citing Articles via Google Scholar Google Scholar Articles by Nemati, M.R. Articles by Gallichand, J. Search for Related Content PubMed Articles by Nemati, M.R. Articles by Gallichand, J. GeoRef GeoRef Citation Agricola Articles by Nemati, M.R. Articles by Gallichand, J.

DIVISION S-1-SOIL PHYSICS

Stability of Structural Form during Infiltration

Laboratory Measurements on the Effect of De-inking Sludge

Dép. des Sols et de Génie Agroalimentaire, FSAA, Université Laval, QC, Canada G1K 7P4

nematimr{at}inrs-eau.uquebec.ca

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
An adequate understanding of the mechanisms involved in the structural stabilization of soil by different sources of organic matter is needed to help design management strategies aimed at maintaining a stable soil structure. The objective of this study was to identify mechanisms involved in soil structure stabilization by paper sludge application, either by increasing the soil resistance to external stresses (aggregate stability) or by decreasing the magnitude of the external stresses (diminution of the wetting rate). A laboratory study was conducted on three different soil types with application of paper sludge at three rates (8, 16, and 24 dry t ha^-1). The mean weight diameter, bulk density, hydraulic conductivity, and water retention properties were measured before and after a wetting event. The results indicate that most of the changes in physical properties resulting from rapid wetting took place at the soil surface (0–50 mm) and the magnitude of these changes gradually decreased down to a depth of 150 mm. Paper sludge application significantly improved the stability of 1- to 4-mm aggregates to the destructive action of wetting in all three soil types. Paper sludge application increased porosity at potential > -2 kPa, which resulted in higher hydraulic conductivity values (up to 88%) and a smaller increase in soil bulk density (down to 67%) relative to a control following rapid wetting. The wetting rates observed during the wetting event were similar regardless of the treatment, because the increase in the water potential at the wetting front was compensated for by an increase in hydraulic conductivity with increasing rates of sludge application.

Abbreviations: DWR, difference between water retention values before and after wetting event • MWD, mean weight diameter • TDR, time domain reflectometry

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
IN MANY AGRICULTURAL AREAS, there is evidence that inappropriate agricultural land management has resulted in the deterioration of soil quality (Dexter, 1988; Mullins et al., 1990). Better knowledge of the changes in soil properties under different management systems is essential in order to propose appropriate land remediation methods. The stability of the soil pore system is one of the important properties that affect the ability of the soil to store and transmit air, water, and solutes (Gregorich et al., 1993). Several external disruptive mechanisms can influence the soil pore system, including the tillage system, implement traffic, wetting, or even heavy overburden or an excessive wet layer of surface soil (Raney and Edminster, 1961; Canarache, 1991; Ouwerkerk and Soane, 1994). Among these mechanisms, sudden wetting is an important factor that can modify the number, shape, continuity, and size distribution of pores, as well as the strength and stability of the soil (Gregorich et al., 1993). Rapid wetting of a structurally unstable soil results in aggregate disintegration, settling of the soil, filling of the interaggregate pores by microaggregates, reduced porosity, changes in the pore-size distribution, and a decreased infiltration rate (Collis-George and Greene, 1979; Kemper et al., 1988; Or, 1996).

Organic matter plays a fundamental role in the stabilization of soil and the formation of pores (Tisdall and Oades, 1982; Oades, 1984; Bolt et al., 1986). Numerous studies have addressed the beneficial effect of organic amendments on aggregate stability (Tisdall and Oades, 1982; Angers and Carter, 1996; Carter, 1996; Haynes and Beare, 1996) and bulk density (Gupta et al., 1977; Webber, 1978; Weil and Kroontje, 1979; Martens and Frankenberger, 1992).

Soil organic matter can increase the resistance of the pore network to the destructive force of rapid wetting. The stabilizing mechanisms involve: (i) changes in the wettability of individual aggregates (Panabokke and Quirk, 1957; Sullivan, 1990); (ii) increased aggregate cohesion resulting from the adsorption of organic materials onto colloid surfaces (Quirk, 1978; Tisdall and Oades, 1982; Elliott, 1986; Sullivan, 1990; Caron et al., 1992); and (iii) the occlusion of individual aggregate pores sensitive to slaking (Quirk and Williams, 1974; Caron et al., 1996). Since the greatest increase in aggregate stability occurs in the macroaggregate fraction (Tisdall and Oades, 1982; Angers and Carter, 1996; Carter, 1996; Haynes and Beare, 1996), macropores are expected to be more abundant in more stable soils. The superior quality of the pore system, with a higher proportion of elongated transmission pores, produces a more open and homogeneous structure that facilitates water movement and results in higher values of hydraulic conductivity (Pagliai et al., 1995).

Field experiments conducted by Nemati et al. (2000) have shown that the application of de-inking paper sludge increased the stability of the soil pore system during water infiltration by increasing the number of both transmission and storage pores. This change may be the result of increased aggregate stability, but may also be due to a decreased rate of water movement as the initial wetting front progresses through the soil, resulting in a diminution of external stress. A decreased wetting rate would result in greater structural stability (Grant and Dexter, 1990; Caron et al., 1996) that would be followed by a higher infiltration rate into a more stable soil. This decreased rate of wetting may be the result of increased hydrophobicity due to an increase in the production of aliphatic compounds by microbes (Dinel et al., 1991). De-inking sludge also contains a significant amount of clay and wood fibers (Trépanier et al., 1996) that generate microbial by-products which may reduce the wetting rate by clogging some of the transmission pores (Caron et al., 1996). Therefore, the modification of the wetting rate may also play a major role in maintaining soil transmission properties following wetting, in addition to an increased individual aggregate stability.

In well-aggregated soils with a large proportion of macropores, hydraulic conductivity may be initially higher, or it may remain higher in the upper horizons following the passage of the wetting front (Collis-George and Greene, 1979). This could compensate for the lower wettability of these soils and result in wetting rates of equal magnitude at a given depth, resulting in external stresses of similar magnitude in stable and unstable soils. However, little information exists about the influence of changes in aggregate stability, hydraulic conductivity, and wettability on maintenance of structural integrity at the plough depth scale. This study was undertaken to identify the controlling mechanisms responsible for maintaining this integrity, and focused on the reduction of external stresses (wetting rate) as opposed to increased aggregate stability.

	Materials and methods

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Sludge Characteristics
In the pulp and paper industry, the paper de-inking process used to recycle newspaper generates de-inking sludge, a waste by-product that contains mainly paper fibers, clay particles, and residual inks. Trépanier et al. (1996) and Nemati et al. (2000) reported that de-inking sludge produced by Daishowa, Inc., consisted of cellulose (39%), hemicellulose (11%), and lignin (23%). De-inking sludge has a C/N ratio around 300 (rich in carbon and poor in nitrogen) and nitrogen must be added to compensate for the immobilization effect generally associated with sludge application (Trépanier et al., 1996; Nemati et al., 2000). Secondary sludges (C/N 20) are waste by-products, rich in nitrogen and already inoculated with microbes, that decompose cellulose wood-fiber products. Trépanier et al. (1996, 1998) and Nemati et al. (2000) have reported more detailed information on the use of paper sludges, their characteristics and applications, and their potential hazards, which were found to be limited. In this study, a mix composed of 85% de-inking sludge and 15% secondary sludge was used as a sludge amendment. The percentage of total nitrogen in the mixture was adjusted to 1.2% with ammonium nitrate. The secondary de-inking sludge ratio was determined by the average production of both sludges at the mill.

Experimental Setup
Three different soil types were investigated: a Tilly silty clay soil from St. Augustin, a Bedford loamy soil from Ste. Croix, and a L'Atrée sandy loam soil from St. Pierre, Ile d'Orléans. These were chosen because they occupy large areas around a pulp and paper plant in Quebec, Canada, where some of the land is degraded because of intensive cropping. Because of their location and need for organic matter, these areas were therefore very likely to be using this residue. The characteristics of the soils used in this study are summarized in Table 1 .

The wall of each cylinder was perforated before sampling with two vertical rows of seven tapped holes: one row for time domain reflectometry (TDR) probes to monitor water content and the other row for tensiometers to monitor matric potential. Each TDR probe consisted of three 145-mm long stainless steel rods, 2 mm in diameter and spaced 20 mm apart. The tensiometers were 80 mm long and 8 mm in diameter. The holes were made at depths of 25, 50, 75, 100, 150, 200, and 350 mm.

Before starting the incubation experiment, the intact cores were prelabeled as to the treatments (selected at random) they were to receive. The preparation of a seedbed was then simulated by removing the first 150 mm of top soil from each cylinder, air-drying (to a water content of 0.17–0.21 kg kg^-1 for silty clay soil, 0.23–0.27 kg kg^-1 for loamy soil, and 0.13–0.15 kg kg^-1 for the sandy loam soil), and passing it through a 4-mm sieve. During sieving, larger chunks were manually broken down to pass through the sieve. A 50-g sample of sieved 4-mm aggregates was then placed on a nest of sieves (sized 2.0, 1.0, 0.5, 0.25, and 0.1 mm) and vibrated for 2 min at a frequency of 8 cycles s^-1 to determine the initial dry mean weight diameter (MWD_i) at the whole 0- to 150-mm top soil. The weight of soil retained on each sieve was recorded on an oven-dry basis. No correction was made for the presence of sand and gravel in the different size fractions. In this paper, aggregate size distribution therefore refers to both aggregates and primary particles. The initial dry mean weight diameter, before incubation, was computed as follows:

(1)

where w_j is the proportion of the total sample weight occurring in fraction j, and x_j is the mean sieve size for fraction j.

The sieved soil from each cylinder received the predesignated treatment and was mixed manually to obtain a uniform mixture. This induced disturbance and therefore the sludge effect includes the effect due its incorporation into the soil. However, for practical reasons, incorporation is needed with these residues, because bad-odor emission can seriously restrict their use.

The treatments consisted of control (no sludge application), composted de-inked sludge at 24 dry t ha^-1, and sludge at 8, 16, and 24 dry t ha^-1. The amended soils were transferred back to the predesignated cylinders and compacted approximately to their initial bulk density levels. The treatments were replicated three times in a completely randomized block design for each soil, for a total of 45 cylinders (three soil types, five treatments, three replications). The cylinders were then incubated at 25°C because incubation occurs in the field and favors the production of binding agents through microbial decomposition of organic matter residues (Oades, 1984).

The incubation of the sandy loam soil began in August 1995 while the other samples were sealed at their respective field moisture levels and stored at 4°C until incubation. The incubation periods were started sequentially at 2-mo intervals because of the limited capacity of the measuring devices. A 6-mo incubation period was chosen because preliminary laboratory work (H. Zaher, personal communication, 1999) indicated that after 6 mo significant differences in soil structural stability were evident between treatments, and these were representative of the differences observed for a 1- to 12-mo period. During this 6-mo period, water content was maintained constant, at or near the field capacity observed on the site, using a subirrigation device.

After the 6-mo incubation period, three draining cycles were then imposed. The first cycle was designed to measure the initial desorption characteristics. A stress was then imposed through a wetting event (followed by a second draining cycle); the soil was slowly saturated to measure the water desorption curves after the stress application, under identical conditions as for the first measurement, therefore resulting in a third draining cycle.

First Draining Cycle
One block of five treatments underwent measurement. Measurements were performed on three blocks each for the silty clay, loam, and sandy loam sequentially. Samples were saturated by capillary rise, first using a tension table and then through saturation from underneath, raising the water level at a rate of 100 mm d^-1. TDR probes and tensiometers were installed and each cylinder drained to a potential of -50 kPa. The draining was first done by gravity to obtain a potential of at least -10 kPa at each depth. The soil cores were then further drained using a tension table (from the bottom) and an air-blowing system from the top to speed up the draining drying process. The TDR probes were read with a computer-controlled TDR system (Tektronix Metallic TDR Cable Tester, 1502b) and tensions measured with a pressure transducer. These parameters were recorded by a Campbell (Logan, UT) CR10 datalogger using multiplexers (Fig. 1) . The water content and matric potential of the soil profiles were therefore monitored every 10 min for about 10 d.

View larger version (28K): [in this window] [in a new window]   Fig. 1 Structural setup of the experimental stand. A soil under investigation is kept in a PVC sampling cylinder. An array of seven minitensiometers and seven time domain reflectometry (TDR) moisture miniprobes is installed, marking off seven monitored layers of soil

During wetting, readings of the water content and matric potential were recorded at each depth every 2 min. Plots of water content as a function of time were generated, resulting in an exponential inverse curve with two distinct zones. An initial zone, showing a sharp increase in water content, was followed by a zone of slower increase. The wetting rate (/t) was determined by calculating the slope of the linear regression line for the zone with the sharpest increase in water content. After the wetting rate measurements, the effective wetting-front potential (h_f) was calculated using the Green and Ampt approach (Hillel, 1980):

(2)

where K (m s^-1) is the hydraulic conductivity of the transmission-zone, h₀ (m) is the pressure head at the entry surface, h_f (m) is the effective pressure head at the wetting front (wetting-front potential), z_f (m) is the distance from the surface to the wetting front (the depth of the wetted zone), ₀ (m³ m^-3) is the transmission-zone wetness during infiltration, and _i (m³ m^-3) is the initial profile wetness in the wetted zone prior to wetting.

The results of each soil water scan and the soil water matric potential measurements, both in the first drainage and, following the wetting event, in the second drainage, were expressed as a set of numbers: (t_i), P(t_i), t_i, and z_m where (t_i) is the soil volumetric moisture taken at time t_i, P(t_i) is the soil water matric potential taken at time t_i, and z_m is the vertical coordinate at the midpoint of each layer (z_m = 37.5, 62.5, 87.5, 125 mm). With the /t value at each depth, z_m, and the pressure gradient (h/z) between two depths, the hydraulic conductivity values in the first drainage and following the wetting event were estimated using the instantaneous profile method (Watson, 1966).

The hydraulic conductivity functions were obtained for each depth of each cylinder between 0 and -4 kPa, which best fitted exponential regression lines. Hydraulic conductivity values at -0.5, -1.0, -2.0, -3.0, and -4.0 kPa were estimated from the fitted regression lines and statistical analyses performed on these estimated values. Since preliminary work showed that wetting caused no important changes in the soil physical properties of the sandy loam soil, the hydraulic conductivity and wetting rate measurements were performed only on the silty clay and loamy soils.

Third Draining Cycle
After measuring the hydraulic conductivity of each layer, the samples were subjected to another wetting by slowly raising the water level from the bottom to the point of saturation, as for the first draining cycle. The water retention curve of each sample was plotted between 0 and -50 kPa; the final measured mean weight diameter (MWD_f) was determined the same as for MWD_i measurement (Eq. [1]). An attempt was made to measure MWD_i and MWD_f at similar water contents to reduce the effect of water content on the MWD during dry sieving. The water contents at saturation (matric potential = 0) during the first and third draining cycles were used to estimate the total porosity of the soil before and after wetting. Soil bulk density was calculated using the total porosity for each individual layer. Particle density measured using the pycnometer method (Blake and Hartge, 1986) for each soil core in the top 150 mm. The difference between the bulk density values before and after wetting event (bulk density changes) was used to evaluate the compactability of each treated soil against the destructive effect of rapid wetting. Because both (before and after) bulk densities were obtained by slow capillary rise, the amount of trapped air was largely reduced. Trapped air may still be present in the system and have affected some of our measurements, but the fact that the bulk density estimates obtained from the lab were close to those measured in the field (data not shown) suggests that the effect was very small.

The differences between the water retention values measured before (first draining cycle) and after (third draining cycle) the wetting event (DWR) at water potentials of 0, -2.0, -3.5, -6.0, -10.0, and -33.0 kPa were used to evaluate the resistance of the soil pore system to the destructive effect of rapid wetting. The SAS system for Windows (SAS Inst., 1996) was used for the statistical analysis of the results for each depth according to a completely randomized block design. The hydraulic conductivity data were log-transformed before running the statistical analyses, but the data is not presented in logarithm form because we wanted to show the differences between treatments. Both multiple comparison (LSD at P = 0.1) and contrasts (linear and quadratic) were used in this study. For initial and final MWD parameters, the LSD was used to compare all treatments together (compost, control, and 8, 16, and 24 dry t ha^-1) because of their qualitative nature. For other investigated parameters, the comparisons between sludge treatments (control and 8, 16, and 24 dry t ha^-1) were done using linear and quadratic contrasts (only the linear contrasts proved to be significant) between control and each sludge treatment because of their quantitative nature.

	Results and discussion

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Aggregate Size Distribution and Soil Bulk Density
The results indicate that soil structural stability (expressed as MWD) and soil slumping (expressed as bulk density changes) were affected by paper sludge amendment. Statistical analyses of MWD_i showed no significant differences (P 0.1) between the treatments before sludge application (Fig. 2) . This confirmed that the soils on which the treatments were to be applied had the same MWD_i and that any differences found after paper sludge application could be attributed to the treatments themselves. After incubation, the beneficial effect of the sludge amendment on MWD_f was significant at P 0.1 for all three soil types (Fig. 2). Higher sludge application rates resulted in greater MWD_f values for all three soil types.

View larger version (25K): [in this window] [in a new window]   Fig. 2 Variation between initial and final dry mean-weight diameters (MWD) with different rates of sludge application in (A) silty clay soil, (B) loamy soil, and (C) sandy loam soil. Each value of MWD in these figures is the mean MWD for each application rate and therefore represents an average of three replicates. (24-C = composted de-inked sludge at 24 dry t ha-1). The vertical bar represents the least significant difference (LSD) for treatments comparison at P 0.10. Treatments marked by other letters are significantly different

View larger version (30K): [in this window] [in a new window]   Fig. 3 Variation in percentage of size class of aggregates with different rates of sludge application in (A) silty clay soil (B) loamy soil, and (C) sandy loam soil. The * symbol represents a linear contrast significant at P 0.05

View larger version (21K): [in this window] [in a new window]   Fig. 4 Variation in soil bulk density changes at different depths with different rates of sludge application following a wetting event in (A) silty clay soil, (B) loamy soil, and (C) sandy loam soil. Each value in this figure represents the mean of the changes in bulk density for each application rate (i.e., the average of the values from the three replicates). SE = standard error. The , *, ** symbols represent the linear contrasts significant at P 0.10, 0.05, and 0.01, respectively

The results of the aggregate stability and bulk density measurements indicate that paper sludge amendment improved the resistance of amended soils to the effect of rapid wetting, since the seedbeds receiving the highest rates of application were able to maintain the largest MWD and presented the least soil slumping compared to the unamended soils. The beneficial effects of de-inking and secondary sludges might have resulted from increased aggregate stability. Indeed, paper sludge amendments as a source of carbon for microorganisms can also stimulate the production of binding agents (possibly polysaccharides, ill-humified organic materials, and/or lipids) that aggregate soil particles into a more stable soil. Similar results have been reported by Angers et al. (1993). The absence of effect from the compost treatment compared with the de-inking and secondary sludges was probably because readily decomposable organic residues were absent in the compost, since these residues are decomposed during the composting process. The beneficial effects of de-inking and secondary sludges may also be related to a decrease in the wetting rate caused either by the occlusion of pores sensitive to slaking, which may reduce hydraulic conductivity (Quirk and Williams, 1974; Caron et al., 1996), or by the development of hydrophobic properties in the soil due to an increase in the production of aliphatic compounds by microbes (Dinel et al., 1991).

Hydraulic Conductivity and Water Retention Characteristics
Statistical analyses were done on the hydraulic conductivity values at different depths and different water potentials before and during the wetting event. For both soils, the statistical analyses of the results before wetting revealed no significant differences between treatments. However, the statistical analyses of the results during the wetting event showed significant differences between treatments in the first layer (depth of 0–38 mm) in both soils. In this layer, hydraulic conductivity was significantly lower (P 0.1) in the control than in the amended soil for a water potential between -0.5 and -2.0 kPa in the silty clay soil (Fig. 5) and between -0.5 and -3.0 kPa in the loamy soil. No significant effect of paper sludge amendment was detected on the hydraulic conductivity at other depths (between 38 and 125 mm) or water potentials. The maximum difference in hydraulic conductivity between the control and the amended soil was found in the first layer of soil (0–38 mm), but this difference decreased between the 38- and 125-mm depths. The extent of these differences in hydraulic conductivity depended on water potential: the higher the potential (-0.5 kPa), the greater the differences. At -3.0 kPa in the silty clay soil and at -4.0 kPa in the loamy soil, differences in hydraulic conductivity between the control and amended soil were not significant.

View larger version (29K): [in this window] [in a new window]   Fig. 5 Variation in the observed hydraulic conductivity values at a depth of 0–38 mm at different water potentials with different rates of sludge application in a silty clay soil, estimated during the second draining cycle

The statistical analyses of the water retention values for water potentials between 0 and -33 kPa showed no significant differences between treatments before or after the wetting event (statistics not shown). In the silty clay soil, at water potentials between 0 and -2.0 kPa, the control had significantly higher DWR values than the amended soil (Fig. 6) . No significant effect of paper sludge application was detected on DWR values at other water potentials or in other soil types, regardless of a general decrease in the DWR value with increasing rates of sludge application. The results of DWR measurements for each independent layer showed generally the same trends as those described on Fig. 6 for both the silty clay and loamy soil. These trends were more pronounced at the surface layer and become insignificant at larger depths. No significant effect of compost on hydraulic conductivity or DWR values was detected in either soil type.

View larger version (44K): [in this window] [in a new window]   Fig. 6 Variation in DWR (difference between water retention values before and after wetting event) at different water potentials with different rates of sludge application in (A) silty clay soil and (B) loamy soil. Each value in this figure represents the mean DWR value at each application rate (i.e., the average of the values from three replicates and five depths). The , ** symbols represent linear contrasts significant at P 0.10 and 0.01, respectively

Wetting Rate and Water Potential at the Wetting Front
The results of the analyses of the effect of paper sludge on wetting rates (Fig. 7) show that paper sludge application did not significantly lower wetting rates in either the silty clay soil or loamy soil (Table 2) . A significant decrease (P = 0.0001) in the wetting rate was observed with increasing depth in both soils (Table 2 and Fig. 7). The maximum rate of water uptake was observed at the 0- to 50-mm depth and the wetting rate gradually decreased down to a depth of 150 mm. These results were in agreement with those found for bulk density, which showed smaller bulk density changes with increasing soil depth. Below the depth of 150 mm, the wetting rate was negligible (<10^-5 kg kg^-1 s^-1). Wetting rate measurements showed that the quantity of applied water (50 mm during 1 h) could infiltrate down to a maximum depth of 150 to 170 mm. Therefore, the lowest soil depths were not affected by the wetting rate. No significant interaction between sludge application and depth (treat x depth insignificant) was observed for the wetting rate (Table 2). Also no significant effect of compost on the wetting rate was detected in either soil type.

View larger version (23K): [in this window] [in a new window]   Fig. 7 Variation in the wetting rate at different depths and for different rates of sludge application during the wetting event for (A) silty clay soil and (B) loamy soil. Each value in this figure represents the mean wetting rate by application rate (i.e., the average of the values from three replicates)

View larger version (31K): [in this window] [in a new window]   Fig. 8 Variation in potential at the wetting front during the wetting event with different rates of sludge application in two soil types. Each value in this figure represents the mean potential at the wetting front for each application rate (i.e., the average of the values from three replicates)

	Conclusions

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
When submitted to sudden wetting, de-inking paper sludge application up to 24 dry t ha^-1 can improve the resistance of the amended soil to the destructive action of rapid wetting. The beneficial effects increased linearly with the sludge application rate, a result of increased aggregate stability. The wetting rate remained constant between treatments because the observed increase in the water potential at the wetting front was compensated for by an increase in hydraulic conductivity following wetting in the treatments with the sludge amendment.

The soil physical property measurements showed that the paper sludge improved the stability of large aggregates, mainly in the 1- to 4-mm size class, resulting in higher porosity retaining water at potentials > -2 kPa. Measurements also showed a hydraulic conductivity higher in the amended soils than in the control after a wetting event. Finally, composting these residues prior to their application does not appear to be advantageous for improving or maintaining soil physical properties.Musy Soutter 1991; SAS Institute 1996

	ACKNOWLEDGMENTS

 
The authors are grateful to Daishowa, Inc., and the Natural Sciences and Engineering Research Council of Canada for their financial support. Special thanks are extended to Luc Trépanier, Farzaneh Shishehgarha, Gilles Grenier, and Robert Kawa for their field and laboratory assistance. Financial support from the Iranian Ministry of Agriculture is gratefully acknowledged by M.R. Nemati.

Received for publication April 8, 1999.

	REFERENCES

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 

• Angers D.A., Bissonnette N., Legere A., Samson N. Microbial and biochemical changes in a soil under barley production. Can. J. Soil Sci. 1993;73:39-50.
• Angers D.A., Carter M.R. Aggregation and organic matter storage in cool, humid agricultural soils. In: Carter M.R., Stewart B.A., eds. Structure and organic matter storage in agricultural soils. Boca Raton, FL: Lewis Publ, 1996:193-211.
• Blake G.R., Hartge K.H. Particle density. In: Klute A., ed. Methods of soil analysis. Part 1. Madison, WI: ASA and SSSA, 1986:377-382 Agron. Monogr. 9..
• Bolt, G.H., M.F. De Boodt, M.H.B. Hayes, M.B. McBride, and E.B.A. Destrooper. 1986. Interactions at the soil colloid–soil solution interface. p. 410–463. Kluwer Academic, Boston.
• Canarache A. Factors and indices regarding excessive compactness of agricultural soils. Soil Tillage Res. 1991;19:145-164.
• Caron J., Espindola C.R., Angers D.A. Soil structural stability during rapid wetting: Influence of land use on some aggregate properties. Soil Sci. Soc. Am. J. 1996;60:901-908.[Abstract/Free Full Text]
• Caron J., Kay B.D., Stone J.A. Improvement of structural stability of a clay loam with drying. Soil Sci. Soc. Am. J. 1992;56:1583-1590.[Abstract/Free Full Text]
• Carter M.R. Analysis of soil organic matter storage in agroecosystems. In: Carter M.R., Stewart B.A., eds. Structure and organic matter storage in agricultural soils. Boca Raton, FL: Lewis Publ, 1996:3-11.
• Collis-George N., Greene R.S.B. The effect of aggregate size on the infiltration behavior of a slaking soil and its relevance to ponded irrigation. Aust. J. Soil Res. 1979;17:65-73.
• Dexter A.R. Advances in characterization of soil structure. Soil Tillage Res. 1988;11:199-238.
• Dinel H., Lévesque M., Mehuys G.R. Effects of long-chain aliphatic compounds on the aggregate stability of a lacustrine silty clay. Soil Sci. 1991;151:228-239.
• Elliott E.T. Aggregate structure and carbon, nitrogen, and phosphorus in native and cultivated soils. Soil Sci. Soc. Am. J. 1986;50:627-633.
• Grant C.D., Dexter A.R. Air entrapment and differential swelling as factors in the mellowing of moulded soil during rapid wetting. Aust. J. Soil Res. 1990;28:361-369.
• Gregorich E.G., Reynolds W.D., Culley J.L.B., McGovern M.A., Curnoe W.E. Changes in soil physical properties with depth in a conventionally tilled soil after no-tillage. Soil Tillage Res. 1993;26:289-299.
• Gupta S.C., Dowdy R.H., Larson W.E. Hydraulic and thermal properties of a sandy soil as influenced by incorporation of sewage sludge. Soil Sci. Soc. Am. Proc. 1977;41:601-605.
• Haynes R.J., Beare M.H. Aggregation and organic matter storage in meso-thermal, humid soils. In: Carter M.R., Stewart B.A., eds. Structure and organic matter storage in agricultural soils. Boca Raton, FL: Lewis Publ, 1996:213-262.
• Hillel, D. 1980. Applications of soil physics. p. 13–16. Academic Press, New York.
• Kemper W.D., Trout T.J., Humpherys A.S., Bullock M.S. Mechanisms by which surge irrigation reduces furrow infiltration rates in silty loam soil. Trans. ASAE 1988;31:821-829.
• Martens D.A., Frankenberger W.T. Modification of infiltration rates in an organic-amended irrigated soil. Agron. J. 1992;84:707-717.[Abstract/Free Full Text]
• Mullins C.E., Macleod D.A., Northcote K.H., Tisdall J.M., Young I.M. Hardsetting soils: Behavior, occurrence, and management. Adv. Soil Sci. 1990;11:37-108.
• Musy, A., and M. Soutter. 1991. Physique du sol. p. 113–115. Presses Polytechniques et Universitaires Romandes.
• Nemati M.R., Caron J., Gallichand J. Using paper de-inking sludge to maintain soil structural form: Field measurements. Soil Sci. Soc. Am. J. 2000;64:275-285.[Abstract/Free Full Text]
• Oades J.M. Soil organic matter and structural stability: Mechanisms and implication for management. Plant Soil. 1984;76:319-337.
• Or D. Wetting-induced soil structural changes: The theory of liquid phase sintering. Water Resour. Res. 1996;32:3041-3049.
• Ouwerkerk V.C., Soane B.D. Conclusions and recommendations for further research on soil compaction in crop production. In: Soane B.D., Ouwerkerk V.C., eds. Soil compaction in crop production. New York: Elsevier Publ, 1994:627-642.
• Pagliai M., Raglione M., Panini T., Maletta M., La Marca M. The structure of two alluvial soils in Italy after 10 years of conventional and minimum tillage. Soil Tillage Res. 1995;34:209-223.
• Panabokke C.R., Quirk J.P. Effect of initial water content on stability of soil aggregates in water. Soil Sci. 1957;83:185-195.
• Quirk J.P. Some physico-chemical aspects of soil structural stability. A review. In: Emerson W.W., et al. , ed. Modification of soil structure. London: Wiley & Sons, 1978:3-16.
• Quirk, J.P., and G.B. Williams. 1974. The disposition of organic materials in relation to stable aggregation. p. 165–173. In A.D. Voronin, et al. (ed.) Trans. Int. Congr. Soil Sci., 10th. 1974. Inst. Pochvovedeniya y Agrokhimii, Moscow.
• Raney W.A., Edminster T.W. Approaches to soil compaction research. Trans. ASAE 1961;4:246-248.
• SAS Institute. The SAS system for Windows. Cary, NC: SAS Inst, 1996 Release 6.12..
• Sullivan L.A. Soil organic matter, air encapsulation and water-stable aggregation. J. Soil Sci. 1990;41:529-534.
• Tisdall J.M., Oades J.M. Organic matter and water stable aggregate in soils. J. Soil Sci. 1982;33:141-163.
• Trépanier L., Gallichand J., Caron J., Thériault G. Environmental effects of de-inking sludge application on soil and soil water quality. Trans. ASAE 1998;41:1279-1287.
• Trépanier, L., G. Thériault, J. Caron, J. Gallichand, S. Yelle, and C.J. Beauchamp. 1996. Impact of de-inking sludge amendment on agricultural soil quality. p. 529–537. In Proc. of the TAPPI Environ. Conf. Tappi Press.
• Watson K.K. An instantaneous profile method for determining the hydraulic conductivity of unsaturated porous materials. Water Resour. Res. 1966;2:709-715.
• Webber L.R. Incorporation of nonsegregated, noncomposted solid waste and soil physical properties. J. Environ. Qual. 1978;7:397-400.[Abstract/Free Full Text]
• Weil R.R., Kroontje W. Physical condition of a Davidson clay loam after five years of heavy poultry manure applications. J. Environ. Qual. 1979;8:387-392.[Abstract/Free Full Text]

This article has been cited by other articles:

				G. W. Price and R. P. Voroney Papermill Biosolids Effect on Soil Physical and Chemical Properties J. Environ. Qual., November 1, 2007; 36(6): 1704 - 1714. [Abstract] [Full Text] [PDF]

				F.-l. Zheng, S. D. Merrill, C.-h. Huang, D. L. Tanaka, F. Darboux, M. A. Liebig, and A. D. Halvorson Runoff, Soil Erosion, and Erodibility of Conservation Reserve Program Land under Crop and Hay Production Soil Sci. Soc. Am. J., July 1, 2004; 68(4): 1332 - 1341. [Abstract] [Full Text] [PDF]

				M. R. Nemati, O. Banton, J. Caron, and L. Delaporte Contamination by Slaked Fragments with Sorbed Compounds in a Structured Soil Soil Sci. Soc. Am. J., May 1, 2003; 67(3): 694 - 702. [Abstract] [Full Text] [PDF]

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (11) Citing Articles via Google Scholar Google Scholar Articles by Nemati, M.R. Articles by Gallichand, J. Search for Related Content PubMed Articles by Nemati, M.R. Articles by Gallichand, J. GeoRef GeoRef Citation Agricola Articles by Nemati, M.R. Articles by Gallichand, J.