Surface%20Seal%20Reduction%20Using%20Anionic%20Polyacrylamide%20(PAM)

1
Surface Seal Reduction Using Anionic
Polyacrylamide (PAM)
Soil, Environmental Atmospheric Sciences

• Sang Soo Lee
• MS Candidate
• Advisor Dr. C.J. Gantzer

University of Missouri
2
Overview

• Introduction
• Objectives
• Methods Materials
• Expected Results

3
Definition of Surface Sealing

• The deposition by water, orientation and/or
  packing of a thin layer of fine soil particles on
  the immediate surface of the soil, greatly
  reducing its water permeability.

4
Definition of Surface Sealing

• A seal is a nonuniform layer situated at the soil
  surface.
• It results from compaction and rearrangement of
  the soil particles in the disturbed upper zone
  due to the raindrop impact, and from fine soil
  particles percolating in-depth during
  infiltration.

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Rationale

• Rainfall-induced soil surface sealing can reduce
  infiltration rate by 10 to 100 times compared to
  an unsealed soil.
• (McIntyre, 1958)

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Rationale
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PAM - Sealing Soil Erosion
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Rationale

• Rainfall-induced soil surface sealing can have
  severe detrimental agricultural effects.
• By reducing infiltration, rainfall recharge is
  usually reduced, lowering the potential available
  water needed for plant growth and development.

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Rationale

• Rainfall-induced soil surface sealing can have
  detrimental hydrological, and environmental
  effects.
• By reducing infiltration, surface runoff
  increases. This is usually accompanied with
  accelerated erosion and nonpoint source pollution
  transported to streams reducing water quality.

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The History of PAM
1948 Research started to find a synthetic soil
conditioner 1951 Krilium manufactured Too costly
for widespread use.
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What is PAM?

• Depiction of an individual acrylamide monomer as
  found in a polyacrylamide molecule.
• cf R. Sojka USDA-ARS

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Polyacrylamide (PAM)
PAM increases soil cohesion enhances the
aggregates by binding particles together
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Calcium and Anionic Polyacylamide Monomer Effect
on the diffuse Double Layer

• Ca in the water shrinks the diffuse electrical
  double layer surrounding soil particles (having a
  net negative charge) and bridge the anionic
  surfaces of soil particles and PAM molecules,
  enhancing flocculation of individual soil
  particles. (cf Wallace and Wallace, 1996)

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PAM Use

• PAM formulations for use in irrigated agriculture
  are water soluble anionic polymers with typical
  molecular weights of 12 to 15 Mg mole-1 and gt1.5
  x 106 monomer units/molecule). ( Lentz et al.
  2000)
• Anionic PAM, used in soil systems, are reported
  to have low toxicity to macrofauna, edaphic
  microorganisms, or crop species (Barvenik, 1994
  Kay-Shoemake et al., 1998).

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Why is PAM of Interest?

• Results from research with PAM show
• Effective erosion control
• Sustained water infiltration rates
• Reduce soil surface sealing

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PAM Enhances Flocculation
Effect of PAM on turbidity after PAM
application vs. Control (no PAM).
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• Illustration of the effectiveness of PAM for
  furrow irrigation. cf Bob Sojka - USDA-ARS

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Objective

• Apply the theory for predicting Saturated
  Hydraulic Conductivity (Ksat) of sealed soils
  presented in Rainfall-Induced Soil Surface
  Sealing A Critical Review of Observations,
  Conceptual Models, and Solutions by Assouline,
  (2004. Vadose Zone Journal 357059).
• Using this theory, evaluate and document the
  benefits of PAM by studying changes in soil
  properties using x-ray CT and standard laboratory
  measurements.

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Materials and Methods

• Ksat
• CT (X-ray Computer Tomography)
• Theory of Assoulines (2004)
• Experiment Design
• Soil Samples Preparation

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Saturated Hydraulic Conductivity Ksat Darcy's law

• The proportionality factor in Darcy's law as
  applied to the viscous flow of water in soil,
  i.e., the flux of water per unit gradient of
  hydraulic potential.

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Darcy's law

• Flow of water through saturated porous media.The
  law is
• K Q L / (H A T)
• where,
• Q is the volume of water mm3,
• A is the area of the bed, mm2
• L is sample thickness mm,
• H is the head of water on top of the sample, mm
  and
• K is the Hydraulic Conductivity and is dependent
  on the nature of the soil. mm hr-1

cf Brady
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• Measurement of Ksat

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Measurement of Ksat
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Measurement of Ksat
25
Ultra-High X-ray Computed Tomography (CT)

• High-resolution X-ray computed tomography (CT) is
  a new technology well suited to a range of soil
  investigations. It is a quick and nondestructive
  method to produce images that correspond closely
  to serial sections through an soil core.

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Ultra-High X-ray Computed Tomography (CT)

• Visualization of CT data typically profits from
  the ability to view oriented sections through the
  three-dimensional volume represented by the data,
  and from the capability to selectively extract
  and measure features of interest.

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CT (X-ray Computed Tomography)

• X-ray CT of soil surface seals formed from
  raindrop impact is being used to create 3-D
  volume rendered images to characterize the
  surface seal.

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• CT data collection systems

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CT (X-ray Computer Tomography)
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An Example of a 2-D Scan of a Intact Soil Core

• A slice of a 76mm by 5mm thick intact Mexico
  series soil core collected from a no-tillage
  plot. After Gantzer and Anderson, 2002.

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An Example of a 3-D Scan of a Intact Soil Core

• A volume rendering of a 76mm by 5mm thick intact
  Mexico series soil core collected from a
  no-tillage plot. cf Gantzer and Anderson, 2002.

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A 2-D Scan of an Intact Soil Core of a Soil
Surface Seal

• CT scan of a 40 mm dia. Mexico soil surface seal
  cf Gantzer, 2005

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A 3-D Scan Surface Plot of Density of an Intact
Soil Core of a Soil Surface Seal

• CT scan of a 40 mm dia. Mexico soil surface seal
  cf Gantzer, 2005

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Theory of Flow Through Seal

• The seal bulk density, (?c), is the highest at
  the surface and decreases exponentially with
  depth, (h), to that of the undisturbed soil.

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Theory of Flow Through Seal

• ?c(h) ? ??0exp(-?h) h-Z 1
• where
• ?c is the bulk density
• h is the depth
• Z is the depth taken positive upward,
• ??0 is the maximum change in bulk density at the
  soil surface (h0), and
• ? is a characteristic parameter of the soil
  rainfall interaction.
• Mualem and Assouline (1989).

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Theory of Flow Through Seal

• Ruth (1997) suggested that a sigmoidal function
  would be better for describing the density
  profile since, once the maximum compaction at the
  surface has been attained, further drop impact
  would likely induce increased compaction at
  increasing depth.
• ?c(h) ? ??0/(1avhv)(1-1/v) 2
• where
• a and v are constants related to the
  soil-rainfall system.

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Theory of Flow Through Seal

• The exponential model of Mualem and Assouline
  (1989) can be extended to include the case where
  maximum compaction extends in-depth. The
  mathematical expression of this
• ?c(h) ? ??0exp(-ßhn) 3
• Where
• ß and n are constants related to the
  soil-rainfall system.
• It is flexible enough to fit both the exponential
  (Eq.1) and sigmoidal models (Eq.2).

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Theory of Flow Through Seal

• The modeled distribution with depth of the bulk
  density within the seal layer according to a)
  exponential (Eq.1) and b) sigmoidal models
  models compared with the experimental data of a
  sandy silt (Roth, 1997) and b) a silt loam soil.
  cf Assouline, 2004.

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Theory of Flow Through Seal
Fitted parameters from Eqs. 1 2 3 for the
sandy silt and the silt loam soils density data
of Roth (1997).
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Theory of Flow Through Seal

• Water retention a) and hydraulic conductivity b)
  simulated with model 3 of at different depths
  within the seal layer for the Atwood soil. After
  S. Assouline 2004.

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Theory of Flow Through Seal

• Distribution with depth and time of the ?c
  simulated by the model 3 for the Sharon sandy
  loam.

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Theory of Flow Through Seal

• Distribution with depth and time of the Ksat of
  the seal simulated by model 3 of for a Sharon
  sandy loam.

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Theory of Flow Through Seal

• The goal of my work is to apply the theory for
  predicting Ksat of sealed soils
• Use this theory, to evaluate and document the
  benefits of PAM by studying changes in soil
  properties using x-ray CT and standard laboratory
  measurements.

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Experiment Design

• Sets of six repacked Mexico silt loam 150 mm i.d
  soil cores soil cores, equilibrated to -3.5 kPa
  water potential will be used to produce surface
  seals for scanned using a ultra-high CT scanner
  located at the University of Texas-Austin.
• Twelve soil cores (diameter 6 inchs, depth 6
  inchs) scans were taken in each core at 10-mm
  spacings.

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Soil

• MEXICO SERIES
• The Mexico series consists of very deep, somewhat
  poorly drained, very slowly permeable soils
  formed in loess or loess and pedisediment. These
  soils are on uplands and have slopes of 1-5.
• TAXONOMIC CLASS Fine, smectitic, mesic Aeric
  Vertic Epiaqualfs

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Soil
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Soil

• Mexico soils from Bradford Research Farm in Boone
  County, Missouri will be studied.
• Mexico soils are sensitive to surface sealing,
  and highly erodible (Revised Universal Soil Loss
  Equation soil erodibility is 0.43, among the
  highest in the county).

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Soil

• Disturbed soils will be collected and air-dried.
• Soils will be sieved to pass a 4-mm sieve.
• Soil will be packed into soil cylinders to an
  average ?b of 1.3 Mg m-3.

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Experiment Design

• Twelve soil cores will be subjected to simulated
  rainfall at 55 mm/hr using the rainfall
  simulator of Regmi and Thompson, (2000).
• Samples will be subjected to 0-, 7.5-, 15-, 30-,
  and 60-min of rainfall after which seal will be
  collected for scanning.
• Replicate samples treated in the same fashion
  will be evaluated for measurement of Ksat.

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Rainfall Simulation

• A paired set eight 150 mm i.d soil sample for
  seal formation prior to and after rainfall
  application.

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Seal Sampling
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Expected Results

• To confirm the precision of the new theory of
  water flow through soil surface seal.
• To determine the usefulness of ultra-high
  resolution x-ray computer tomography in measuring
  surface seals.

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Expected Results

• To evaluate various rates of surface-applied PAM
  on surface sealing, water infiltration, and soil
  erosion.
• To explain why PAM solutions reduce soil surface
  sealing.

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Questions
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