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Soil Science Society of America Journal 67:630-636 (2003)
© 2003 Soil Science Society of America

DIVISION S-6—SOIL & WATER MANAGEMENT & CONSERVATION

Infiltration and Erosion in Soils Treated with Dry PAM and Gypsum

Jian Yua, T. Leib, I. Shainberg*,c, A. I. Mamedovc and G. J. Levyc

a Institute of Water Resources, Huhhot, Inner Mongolia, P.R. China
b Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Yangling, Shanxi Province, 712100 P.R. China
c Inst. of Soil, Water, and Environmental Sci., Agricultural Research Organization (ARO), The Volcani Center, P.O. Box 6, Bet Dagan 50-250, Israel

* Corresponding author (ishain{at}agri.gov.il)


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSIONS
 CONCLUSIONS
 REFERENCES
 
Seals formed at the soil surface during rainstorms reduce rain infiltration and cause runoff and erosion. Surface application of anionic polyacrylamide (PAM) in solution has been found to be very effective in decreasing seal formation, runoff, and erosion. The objective of this study was to investigate the effect of surface application of granular PAM (10 and 20 kg ha-1) and gypsum (2 and 4 Mg ha-1) on the infiltration rate (IR) and soil erosion from a silty loam (Calcic Haploxeralf) and sandy clay (Typic Chromoxerert) during simulated distilled water rainstorms. Mixing dry PAM with the upper 5 mm of the soil surface reduced slightly the IRs, and reduced significantly soil erosion from the two soils. Spreading gypsum at the soil surface doubled the final IR compared with that of control and reduced erosion slightly. Spreading dry PAM mixed with gypsum was very effective in increasing the rain IR and reducing erosion. Mixture of 20 kg ha-1 PAM and 4 Mg ha-1 gypsum increased the final IR of the two soils by four times and reduced erosion to 30% that of the control. Gypsum added to the erosion benefits of PAM by increasing infiltration and decreasing runoff. However, mixing gypsum with dry PAM decreased the beneficial effect of PAM in reducing erosion in the silty loam soil. The mechanisms responsible for the specific effects of PAM (mixed with soil and gypsum) on rain infiltration and soil losses are discussed.

Abbreviations: ESP, exchangeable sodium percentage • IR, infiltration rate • PAM, polyacrylamide • PG, phosphogypsum


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSIONS
 CONCLUSIONS
 REFERENCES
 
SURFACE RUNOFF and erosion are responsible for extensive losses of topsoil and agricultural productivity throughout the world. One of the major mechanisms causing this is low IR caused by surface seal formation when soil is exposed to the beating action of raindrops. Seal formation is the result of two complementary mechanisms (Agassi et al., 1981): (i) physical disintegration of surface soil aggregates and (ii) physicochemical dispersion of soil clays, which then migrate into the soil with the infiltrating water, clog the pores beneath the surface, and form a layer of low permeability termed the "washed in" zone (McIntyre, 1958). The first mechanism is mechanical in nature and is determined by the wetting rate of the surface aggregates (Loch, 1994; Levy et al., 1997), the raindrop kinetic energy (Mamedov et al., 2000), and soil aggregates stability (Loch, 1994). The second one depends on the electrolyte concentration of the applied water and the exchangeable sodium percentage (ESP) of the soils (Agassi et al., 1981).

Recent studies have examined the use of soil amendments to decrease runoff and erosion from soils susceptible to sealing (Agassi and Ben-Hur, 1992; Flanagan et al., 1997a,b; Miller, 1987; Shainberg et al., 1990; Shainberg and Levy, 1994). Miller (1987) found that spreading gypsum at the soil surface significantly increased infiltration and decreased runoff and erosion under rainfall conditions for three typical soils from southeast USA. Gypsum dissolution maintained high concentration of electrolytes in the soil solution at the soil surface during rainstorm, thus preventing chemical dispersion of the clay particles and the formation of low infiltration seal (Keren and Shainberg, 1981; Shainberg et al., 1990). Phosphogypsum (PG) was more effective than mined gypsum in decreasing seal formation because of its higher rate of dissolution (Keren and Shainberg, 1981).

Polyacrylamide dissolved in irrigation water (10 mg kg-1) has been extensively used to prevent erosion and increase infiltration in furrow irrigation (Lentz et al., 1992; Lentz and Sojka, 2000). Polyacrylamide with high molecular weight (12–15 x 106 Da) and moderate anionic charge density (18–20% hydrolysis) was found to be most effective in preventing erosion and increasing water infiltration (Lentz et al., 1992; Green et al., 2000). Similarly, PAM in concentrations of 5, 10, and 20 mg L-1 was found to be effective in controlling runoff and erosion from loamy loess and a grumusol during sprinkler irrigation (Levy et al., 1992; Flanagan et al., 1997a,b). Soil losses in all the PAM treatments were significantly lower than those in the control treatment (Levy et al., 1992). It was concluded that PAM in irrigation water in concentrations <20 mg L-1 is effective in decreasing runoff and erosion. However, dilute PAM solutions applied in sprinkler irrigation were less effective in preventing erosion compared with PAM in furrow irrigation.

In the case of natural rainstorms, PAM must be added to the soil surface before the rainy season. Polyacrylamide may be added as a dry granular PAM or the dry PAM is dissolved in water in concentration of up to 1000 mg L-1 and the concentrated solution is sprayed at the soil surface (Shainberg et al., 1990). Treatment of the soil surface with 10 to 20 kg ha-1 of anionic PAM dissolved in water increased the final IR of a silty loam and a sandy clay by an order of magnitude and reduced runoff severalfold (Shainberg et al., 1990). Spreading PG at soil surfaces in addition to PAM application before distilled water rain increased the beneficial effect of PAM on IR (Shainberg et al., 1990). It was suggested that when the concentration of electrolytes in the soil solution exceeds the flocculation value of the clay, the cementing action of PAM polymers was more effective (Shainberg et al., 1990).

In most PAM applications to the soil surface, PAM dissolved in irrigation water was applied. This practice is not possible in rain-fed agriculture because water for dry PAM dissolution is not available. To apply 10 to 20 kg ha-1 PAM, the volume of PAM solution to be sprayed is 10 to 20 m3 ha-1 because solutions of >1000 g m-3 are too viscous to be practical. Also, because PAM is not readily soluble, it is difficult to dissolve PAM in water to the 1-kg-m-3 concentration. Thus, labor and water needed for PAM dissolution and spraying makes PAM application in dryland farming uneconomical.

The general objective of this study was to investigate the effect of incorporating dry granular PAM (at the rates of 10 and 20 kg ha-1) with soil material or with gypsum, on infiltration and erosion from soils. Since spreading uniformly a small amount of PAM (10–20 kg ha-1) in the field is impossible, the PAM granules must be mixed with a cheap and readily available material. One option was to mix the PAM granules with the local soil. Another option was to mix the PAM with gypsum (2 and 4 Mg ha-1). Hence, the two specific objectives of the study were to investigate the effects of (i) mixing dry PAM at the rates of 10 and 20 kg ha-1 with the upper 5 mm of the soil surface, and (ii) mixing of dry PAM with gypsum and spreading the mixture on the soil surface, on sealing, runoff, and erosion in two crusting soils.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSIONS
 CONCLUSIONS
 REFERENCES
 
Soils
Two arable soils from Israel were chosen for this study: a silty loam-loess (Calcic Haploxeralf) from the northern Negev, and sandy clay (Chromic Haploxerert) from the Pleshet Plains. Samples of the soils were taken from the cultivated layer (0–250 mm) and were analyzed using standard analytical methods (Klute, 1986; Page et al., 1982). Selected physical and chemical properties of the soils are given in Table 1. The dominant exchangeable cation in the soils was Ca, and ESP was low. Smectite was the dominant clay mineral (60%), with illite and kaolinite also present (Banin and Amiel, 1970). Organic matter content in the soils was low.


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  		Table 1. Physical and chemical properties of the soils (0–250 mm).

 
Rain Simulation Studies
The experiments were performed with a drip-type rainfall simulator. The simulator consisted of a 750- by 600- by 80-mm closed chamber in which rainfall of a known constant drop size was generated through a set of hypodermic needles ({approx}1000) arranged at a spacing of 20 by 20 mm and pointed downward. Average droplet diameter was 2.97 x 10-2 mm. A drop fall of 2.2 m was used to obtain drops with an impact velocity of 5.64 m s-1 and a kinetic energy of 15.9 kJ m-3 (Epema and Riezebos, 1983). Rain intensity was maintained at 36 mm h-1 using a peristaltic pump.

Air-dried soils, crushed to pass through a 4.0-mm sieve, were packed in trays 200 by 400 mm, 40 mm deep, over a 10-mm thick layer of coarse sand. The bulk density of the soils in the trays was maintained at 1.32 (±0.02) g cm-3 and 1.17 (±0.01) g cm-3 for the silty loam and sandy clay, respectively. These bulk densities were maintained by weighing the same amount of soil, in 200-g portions, into the trays and smoothing the soil surface after each soil addition. These bulk densities were easily achieved because they are similar to the natural bulk densities in the cultivated fields. The trays were saturated from below with tap water (electrical conductivity of 0.9 dS m-1 and sodium adsorption ratio of 2.5) and were placed under the rain simulator at a slope of 15% (enabling the collection of most of the detached materials in the runoff flow) and exposed to 72 mm of deionized water (electrical conductivity of 0.04 dS m-1) rain (simulating the chemistry of natural rain). During each storm, water infiltrating through the soils was collected, in 4-min intervals, in graduated cylinders placed underneath a special outlet at the bottom of the tray, and water volume was recorded as a function of time. Runoff water was collected in buckets continuously throughout the event, and its volume at the end of the event was determined. Thereafter, runoff water was mixed, three samples were taken in beakers, dried, and total amount of soil removed by runoff during the entire event was calculated. Splash from the soil trays was not measured. Three replicates were performed concurrently (under the same rainfall simulator) for each treatment.

Treatments
Negative PAM (A110, Cytec, Inc., North Andover, MA) with a high molecular weight (12 x 106 Da) and 15% hydrolysis was used in this study. In the experiments where dry granular PAM was mixed with gypsum, mined gypsum (95% CaSO4, and particle size < 2 mm) was used. Eight treatments were studied: (i) control (no addition of PAM and gypsum), (ii) dry granules of PAM at the rate equivalent to 20 kg ha-1 were mixed with the upper 5 mm of the soil (2 g of PAM mixed with 6.5 kg of the soil), (iii and iv) two rates of gypsum equivalent to 2 and 4 Mg ha-1 were spread at the soil surface, and (v–viii) four mixtures of PAM and gypsum, (PAM 10 and 20 kg ha-1, gypsum 2 and 4 Mg ha-1) were spread at the soil surface. In the PAM and soil mixture, 520 g of the above mixture was spread at the soil surface in the 800-cm2 trays.

Data Analysis
Infiltration data obtained from the rainfall simulator were analyzed with the nonlinear equation proposed by Morin and Benyamini (1977):

[1]
where It is the instantaneous IR (mm h-1); Ii is the initial IR (mm h-1); If is the final IR (mm h-1); {gamma} is the soil coefficient related to surface aggregate stability (mm-1); t is the time (h) from the beginning of the storm; and p is the rain intensity (mm h-1).

A nonlinear regression program used the measured It, If, and p values to calculate the other two parameters of the equation (Ii and {gamma}) that gave the best coefficient of determination (R2 > 0.9) between the paired calculated and the measured It values.

Final IR, runoff, and soil loss values data were subjected to an analysis of variance and results for each soil is presented in Table 2. Significance of difference values, among treatments for the infiltration, runoff, and erosion parameters studied, were determined using Tukey's procedure for multiple range test at the 0.05 significance level (Steel and Torrie, 1981).


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  		Table 2. Analysis of variance of treatments for each soil.

 

   RESULTS AND DISCUSSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSIONS
CONCLUSIONS
 REFERENCES
 
Infiltration Rate and Runoff
The effects of PAM, gypsum, and the mixtures of PAM and gypsum on the IR curves of the silty loam are presented in Fig. 1 . The steep drop of the IR and the low value of the final IR of the control (3.9 mm h-1) indicate that the silty loam was susceptible to seal formation. The impact of raindrops combined with the absence of electrolytes in the rainwater was enough to form a seal in <40 mm rain (Fig. 1). A soil which contains 22% clay, 36% silt, and <1% organic matter is known to have an unstable structure and to be susceptible to sealing (Ben-Hur et al., 1985; Mamedov et al., 2001).



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  		Fig. 1. Effects of amendments on the infiltration rate of the silty loam. Bars indicate ±2 standard deviations. G2 and G4 indicate 2 and 4 Mg ha-1 gypsum, respectively; PAM 10 and PAM 20 indicate 10 and 20 kg ha-1 polyacrylamide, respectively.

 
Spreading gypsum at the soil surface resulted in a more moderate drop in the IR and higher final IR values compared with the control treatment (Fig. 1, Table 3). Applying 2 and 4 Mg ha-1 (200 and 400 g m–2, respectively) gypsum increased the final IR of the silty loam by 50 and 100%, respectively. Gypsum at the soil surface dissolves during the rainstorm and releases electrolytes into the soil solution. Thus, clay dispersion was reduced and seal formation was decreased (Keren et al., 1983). The lower values of IR in the 2-Mg-ha-1 treatment, compared with the 4-Mg-ha-1 treatment (Table 3), were probably due to nonavailability of gypsum over the entire surface (Keren et al., 1983). The IR curves of the gypsum treatment in this study were comparable with the curves obtained with PG (e.g., Shainberg et al., 1990), suggesting that gypsum with particle size < 2mm was as effective as PG in maintaining high IR values (Keren et al., 1983).


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  		Table 3. Effect of treatments on final infiltration rate (FIR) and runoff.

 
Mixing granular PAM (20 kg ha-1 or 2 g m-2) with the upper-5-mm layer of the soil surface before exposing the soil to distilled water rain resulted in IR values that were similar to those of the control treatment (Fig. 1). Effect of PAM mixed with the upper layer of the soil was not beneficial with respect to maintaining infiltration and reducing runoff. It could be explained by its dissolution in the soil solution. Anionic polymers are good flocculent and only a few segments of the polymer chain (which consist of 100 000 to 200 000 monomers) are adsorbed on the soil particles, while the long chains are present in the form of long loops and tails in the solution (Barvenik, 1994; Ben-Hur and Keren, 1997). Thus, an anionic PAM has a relatively long grappling distance that facilitates the formation of interparticle bridges and flocculation (Ben-Hur and Keren, 1997). In addition to surface seal formation and compaction by the drop impact, the tails of the long chains could block the conducting pores of the soil and reduce the hydraulic conductivity of the soil surface layer (Malik and Letey, 1992; Letey, 1996). The long chains, which cement soil particles together, may also reduce soil erosion (see later).

Spreading dry PAM mixed with gypsum on the soil surface increased the IR of the silty loam remarkably (Fig. 1). These treatments increased the final IR of the silty loam by up to four times compared with the control (Fig. 1, Table 3). Similarly, runoff from the 72-mm rainstorm dropped from 55.75 mm in the control to 19.85 mm in the mixture of 20 kg ha-1 PAM and 4 Mg ha-1 gypsum (Table 3). Dry PAM mixed with dry gypsum spread on the soil surface was found to be as effective as PAM in solution sprayed at the soil surface (Shainberg et al., 1990). The high efficacy of the dry PAM plus gypsum mixture in maintaining high IR, compared with mixing just PAM with the soil is explained by gypsum dissolution. When rainwater comes in contact with the dry PAM plus gypsum mixture, gypsum dissolves and increases the electrolyte concentration in the soil solution. With increase in electrolyte concentration in the soil solution, the repulsion forces between the negative sites on the anionic polymer diminishes and the dissolved polymer exists as coiled and short chains whose effect on the polymer's solution viscosity diminishes (Barvenik, 1994). Therefore, the short polymer chains are apparently ineffective in clogging the conducting pores, and effective in stabilizing the surface aggregates and preventing seal formation.

In the PAM treatment of 10 kg ha-1, the beneficial effect of gypsum on IR was similar in the two gypsum treatments (Fig. 1). In the PAM treatment of 20 kg ha-1, the effect of gypsum quantity was pronounced and the IR curve of the 4 Mg ha-1 treatment was above that of the 2 Mg ha-1 treatment. This interaction suggests that the higher amount of PAM application needs a higher amount of gypsum to achieve the best infiltration result.

The effect of PAM plus gypsum treatments on the IR of the sandy clay as a function of cumulative rain is presented in Fig. 2 . The following should be noted: (i) The sandy clay is less susceptible to sealing than the silty loam. The final IR of the sandy clay was higher than that of the silty loam (Table 3) and its IR curve dropped more slowly with rainfall depth (Fig. 1 and 2). The higher percentage of clay, which acted as a cementing material, stabilized the aggregates, reduced aggregate breakdown and seal formation at the soil surface, and maintained higher IR values (Ben-Hur et al., 1985). (ii) Similar to their effects on the IR of the silty loam, PAM mixed with the surface soil layer did not prevent seal formation, reduced the soil's hydraulic conductivity, and therefore its IR (Fig. 2). Thus, the IR curve of the PAM treatment was similar to or lower than that of the control (Fig. 2). Clogging of the soil pores by the PAM-stretched chains account for the low IR. (iii) Polyacrylamide mixed with gypsum was very effective in increasing the IR of the sandy clay (Fig. 2). The effect of the PAM plus gypsum treatments in the sandy clay was quite similar to those in the silty loam (Fig. 1, 2). In both soils, gypsum plus PAM treatments increased the final IR of the soils by a factor of four.



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  		Fig. 2. Effects of amendments on the infiltration rate of the sandy clay. Bars indicate ±2 standard deviations. G2 and G4 indicate 2 and 4 Mg ha-1 gypsum, respectively; PAM 10 and PAM 20 indicate 10 and 20 kg ha-1 polyacrylamide, respectively.

 
The effect of amendments on the final IR and runoff from the two soils is summarized in Table 3. The silty loam was slightly more susceptible to sealing and the final IR of the silty loam was lower (3.9 mm h-1) compared with 6.0 mm h-1 for the sandy clay. Similarly, the amount of runoff in the silty loam was slightly higher (Table 3). The soil with 22% clay and high silt content was more susceptible to sealing than the soils with 40% clay (Ben-Hur et al., 1985). The effect of amendments in the two soils seems to be similar (Table 3). In both soils, PAM mixed with the soils decreased the IR insignificantly and PAM plus gypsum treatments increased the final IR and decreased runoff significantly. Spreading dry granular PAM, mixed with gypsum on the soil surface was as effective as spraying PAM solution on the soil surface of gypsum treated soils.

Soil Loss
Soil losses from 72-mm rainstorms for the silty loam and sandy clay are presented in Fig. 3 and 4 , respectively. In both soils, the largest amounts of soil losses were observed in the control, and these amounts were similar ({approx}130 g tray-1 72 mm-1 rain). Gypsum treatments reduced soil losses in the two soils by {approx}50% of that in the control. Gypsum treatments were effective in reducing erosion due to runoff reduction and enhanced deposition of the entrained particles (Warrington et al., 1990)



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  		Fig. 3. Soil losses from the silty loam as a function of gypsum and polyacrylamide (PAM) treatments. G2 and G4 indicate 2 and 4 Mg ha-1 gypsum, respectively; PAM 10 and PAM 20 indicate 10 and 20 kg ha-1 polyacrylamide, respectively. Columns labeled by the same letter do not differ significantly at the 0.05 level.

 


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  		Fig. 4. Soil losses from the sandy clay as a function of gypsum and polyacrylamide (PAM) treatments. G2 and G4 indicate 2 and 4 Mg ha-1 gypsum, respectively; PAM 10 and PAM 20 indicate 10 and 20 kg ha-1 polyacrylamide, respectively. Columns labeled by the same letter do not differ significantly at the 0.05 level.

 
The effect of PAM mixed with the soil on soil loss was unexpected. The PAM treatment was the most effective in preventing soil loss (Fig. 3, 4). In this treatment, soil losses were only 15 and 30% of soil loss in the control for the silty loam and sandy clay, respectively, in spite of the low IR and the resultant high runoff (Table 3). The long chains of PAM polymers in the soil surface exposed to distilled water rain explain both, the low IR and the low soil loss. The chain length of the PAM polymer in dilute solutions may reach 0.1 to 0.2 mm (Barvenik, 1994). The polymer is then adsorbed on the external surfaces of the aggregates (Ben-Hur and Keren, 1997) and binds soil particles far apart together, thereby increasing their resistance to splash by raindrop impact and detachment by runoff (Smith et al., 1990). These stretched chains also block the conducting pores between the soil particles, and the IR is low. In high electrolyte concentration (i.e., in the dry polymer plus gypsum treatments), the polymer chains are shorter and less efficient in binding together soil particles that are far apart. Thus, in the presence of electrolytes, the efficiency of the polymers in decreasing soil losses was reduced. It is concluded that salt concentration has two effects: (i) in the very low range of salt concentration, increase in salt concentration reduces the length of the polymers and reduces its binding efficiency and its contribution to the cohesiveness of the soil surface; (ii) as the concentration of electrolytes increases, the effect of electrolytes on polymer's length is small and the polymers are more effective in stabilizing aggregates and the stable and big aggregates are less erodible (Levy and Ben-Hur, 1998).

Comparing the effect of amendments on runoff and soil losses (Table 3 and Fig. 3, 4, respectively) it seems that relative to control, gypsum was as effective in reducing runoff as in reducing soil loss in both soils. Conversely, the PAM plus gypsum treatments were more effective in reducing runoff than in reducing soil erosion (Table 3 and Fig. 3, 4, respectively). For both soils, the differences in the values of soil loss between gypsum and gypsum plus PAM treatments were in general not significant (Fig. 3, 4). However, the PAM plus gypsum treatments were more effective in reducing soil loss in the sandy clay than in the silty loam (Fig. 3, 4, respectively). It is concluded that the PAM plus gypsum treatment was more effective in preventing seal formation than in preventing soil detachment. Stabilization of aggregates at the soil surface by the PAM plus gypsum treatment prevents seal formation, but is less effective in preventing particle detachment. Particle detachment decreases when cohesion forces between particles increase. Because of the presence of gypsum, PAM chains were shorter and evidently less effective in enhancing interparticle bonding, thus enabling more soil detachment. Comparing the results of current study with previously published data (Levin et al., 1991), which were conducted on same soil types and in similar experimental condition with PAM solution and PG, it should be noted that spreading dry PAM mixed with gypsum was as effective as spraying PAM solutions on gypsum-treated soils.

The above discussion of the effect of the amendments on IR, runoff, and soil loss is supported by the pictures of the silty loam surfaces treated with the control, PAM mixed with gypsum, and PAM mixed with the soil (Fig. 5a,b,c , respectively). The soils were exposed to 72 mm of rain and air-dried. The smooth surface and the absence of aggregates in the control treatment (Fig. 5a) is a clear indication that surface aggregates were disintegrated by wetting and drop impact and of the presence of a seal. The strength of the seal prevented craters to be formed by the impact of raindrops, and the soil surface is smooth.



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  		Fig. 5. The surface of the silty loam: (a) control, (b) polyacrylamide (PAM; 20 kg ha-1) mixed with gypsum (4 Ma ha-1), and (c) PAM mixed with the soil surface. Note the 2-cm scale.

 
Spreading PAM plus gypsum on the soil surface resulted in a soil surface that was not smooth, showing numerous aggregates that had not been destroyed, separated by smooth sealed layers among them (Fig. 5b). Evidently, PAM plus gypsum stabilized the aggregates but had only a slight effect on the cohesion between the particles at the soil surface. The presence of electrolytes prevented the stretching of the polymers and the long range bridging between soil particles. Thus, soil erosion was determined by the level of runoff rather than by particle detachment. Runoff was determined by the ratio in area between the aggregated zones with high permeability and the smooth sealed regions of low permeability (Levy et al., 1988).

The PAM mixed with the soil treatment showed nonsmooth surface (Fig. 5c), which was distinctly different from the nonsmooth surface of the PAM plus gypsum treatment (Fig. 5b). There were hardly any aggregates, yet craters formed by raindrop impact were noted, suggesting that the strength of the soil surface was low. The PAM chains which linked the soil particles reduced soil hydraulic conductivity and thus the IR, while at the same time prevented particle detachment.


   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSIONS
 CONCLUSIONS
REFERENCES
 
The effect of dry granular PAM mixed with soil or gypsum on IR and erosion of soils exposed to distilled water rain was studied. The amendments had similar effects on a silty loam (loess soil) and sandy clay (vertisol). Spreading gypsum at the soil surface increased the IR and reduced runoff and erosion. Spreading dry PAM mixed with gypsum was very effective in increasing the IRs of the two soils and in reducing runoff and soil losses. Mixing dry PAM with soil was not effective in increasing IR and reducing runoff. However, this treatment was very effective in reducing soil losses. In dilute solutions, PAM chains adsorbed on the external surfaces of a soil particle are 0.1 to 0.2 mm in length, and therefore block the water-conducting pores while binding the particles together into a cohesive surface. The observed low IR is therefore due to a reduction in soil hydraulic conductivity rather than seal formation.

Mixing dry PAM with soil was most effective in preventing erosion, because it increased interparticle bonding due to the long polymer chains. Polyacrylamide mixed with gypsum also reduced erosion, but the mechanism was different. The high electrolyte concentration due to the presence of gypsum flocculated the clay particles, coiled the PAM chains, enhanced aggregation, and decreased seal formation. The combination of seals with high IR and stable aggregates reduced erosion. Our results suggest that soil and water conservation in dryland farming in soils susceptible to sealing and erosion can be improved by spreading dry PAM mixed with gypsum on the soil surface.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSIONS
 CONCLUSIONS
 REFERENCES
 
Joint contribution of the Institute of Soil, Water, and Environmental Sci, ARO, Bet Dagan, Israel (607/2002 series) and China Agric. Univ., Beijing, P.R. China.

Received for publication February 12, 2002.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSIONS
 CONCLUSIONS
 REFERENCES
 




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Z. Tang, T. Lei, J. Yu, I. Shainberg, A. I. Mamedov, M. Ben-Hur, and G. J. Levy
Runoff and Interrill Erosion in Sodic Soils Treated with Dry PAM and Phosphogypsum
Soil Sci. Soc. Am. J., February 27, 2006; 70(2): 679 - 690.
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G. K. Ganjegunte, G. F. Vance, and L. A. King
Soil Chemical Changes Resulting from Irrigation with Water Co-Produced with Coalbed Natural Gas
J. Environ. Qual., November 7, 2005; 34(6): 2217 - 2227.
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H. Blanco-Canqui, C. J. Gantzer, S. H. Anderson, and A. L. Thompson
Soil Berms as an Alternative to Steel Plate Borders for Runoff Plots
Soil Sci. Soc. Am. J., September 1, 2004; 68(5): 1689 - 1694.
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