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Chemical Movement in Layered Soils:

User's Manual

CGed Science
Library

JAN S0 1990
universityy of florid

D.L. Nofziger and A.G. Hornsby

,COMPUTER SERIES

Software in Soil Science

Florid Coopewamtil Exton Srvid / Intitut of Food iad Agricultuara Sdln /I Univwniy of Florida / John T. Woe. Dean

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User s Man.uia.l

by

D.L. Nofziger and A.G. Hornsby

Department of Agronomy
Oklahoma State University

and

Soil Science Department
University of Florida

Copyright 1987, University of Florida

1

UNIVERSITY OF FLI, LRARIES

ACKNOWLEDGEMENT S

This software is based on the model published by D.L. Nofziger and A.G.
Hornsby (1986) entitled "A Microcomputer-Based Management Tool for Chemical
Movement in Soil" (Applied Agricultural Research 1:50-56). That model is an
expansion of the procedure presented by P.S.C. Rao, J.M. Davidson, and L.C.
Hammond, 1976, in "Estimation of Nonreactive and Reactive Solute Front
Locations in Soils" (EPA-600/9-76-015, July, 1976).

The authors wish to express appreciation to Dr. P.S.C. Rao for his helpful
suggestions during the development of the software and review of the software.

DISCLAIMER

The University of Florida (UF), Institute of Food and Agricultural Sciences
(IFAS), and Florida Cooperative Extension Service (FCES) shall have no
liability or responsibility to cooperator or any other person or entity with
respect to any liability, loss, or damage caused or alleged to be caused
directly or indirectly by programs released by IFAS for sale or cooperative
use including but not limited to any interruption of service, loss of
business, or anticipatory profits or consequential damages resulting from use
or operation. And, in no event, shall FCES be liable for loss of profits,
indirect, special, or consequential damages arising out of any breach of the
agreement or obligations of this contract.

CONDITION OF RELEASE OR SALE

All computer software distributed by IFAS or FCES are on an 'AS IS' basis
without warranty. Distribution or resale without written permission of the
department of origin is not permitted.

Ch1-iemical Movement in Layered Soils :
mUser s Manual.

by

D.L. Nofziger and A.G. Hornsbyl

TABLE OF CONTENTS

Introduction . . . . . . . . . . . . . . . 5
Hardware and Software Requirements . . . . . . . . . . 6
Getting Started . . .. . . . . . . . . . . . 7
Operating Conventions . . . . . . . . . . . . . 9
Software Examples
-Introductory Information . . . . . . .. . . . 10
-Main Menu .. . . . . . . . . . . . . . . 12
-Calculate Chemical Movement in Soil . . . . . . . . 14
-Enter, Modify, or Print Soil Data File . . . . . . . 23
-Enter, Modify, or Print Chemical Data File . . . . . . 26
-Enter, Modify, or Print Rainfall Data File . . . . . . 28
-Enter, Modify, or Print Evapotranspiration Data File . . . . 30
-Select Default Files and Options . . . . . . . . . 13
-Import ASCII Data Files . . . . . . . . . . . 32
Description and Assumptions of Model . . . . . . . . . 36
References . . . . . . . . . . . . . . . . 40
Appendix:Use of the Full-Screen Editor . . . . . . . . . 41
Index . . . . . . . . . . . . . . . . . 44

1. Professor, Department of Agronomy, Oklahoma State University and Professor,
Soil Science Department, IFAS, University of Florida, Gainesville,
respectively.

INTRODUCTION

This manual describes the use of an interactive microcomputer model, CMLS,
which was written to serve as a management tool and a decision aid in the
application of organic chemicals to soils. The model estimates the location of
the peak concentration of non-polar organic chemicals as they move through a
soil in response to downward movement of water. The model also estimates the
relative amount of each chemical still remaining in the soil at any time. The
results may be displayed in graphical as well as in tabular forms.

The software is based on a model described by Nofziger and Hornsby (1986).
This model is an expansion of a simpler model (CMIS) of Nofziger and Hornsby
(1985) for organic chemical movement in a uniform (homogeneous) soil. CMLS
differs from CMIS in six ways: (1) This model can deal with soils with up to
20 layers or horizons. Thus, soil properties need not be assumed uniform over
all depths. (2) This model enables the user to enter partition coefficients
for each horizon in the soil. (3) This model enables the user to specify the
degradation half-life of the chemical of interest for each horizon in the
soil, rather than using one value for all depths. (4) This model enables the
user to simulate movement of the chemical for up to 15 years. (5) This
software includes graphical displays for the relative amount of the chemical
remaining in the soil as a function of time as well as tabular displays of the
time required for the selected chemicals to move to user-specified depths in
the soil profile. (6) The data management part of this program is greatly
enhanced.

This manual describes the required software and hardware for using this model,
procedures for using the software, and operating conventions. It then
illustrates the use of the software. Finally, the theoretical framework of the
model and assumptions inherent in it are presented.

HARDWARE AND SOFTWARE REQUIREMENTS

This software requires an IBM2 PC, XT, or AT or a compatible computer with at
least 512K bytes of random access memory and two floppy disks or one floppy
disk and a fixe-- disk. A color/graphics or enhanced graphics board and a
compatible monitor are essential to fully utilize this software. A printer is
useful but is not essential. If an 8087 or 80287 math coprocessor is present,
it will dramatically speed up computations.

The operating system must be PC-DOS or MS-DOS 2.0 or a later version. The
GRAPHICS.COM file from your DOS diskette must be executed to obtain copies of
the graphics on a printer by pressing the and keys.

2. IBM is a registered trademark of International Business Machines, Inc.
2. IBM is a registered trademark of International Business Machines, Inc.

GETTING STARTED

Files on Distribution Diskette: This software is distributed on a single
floppy disk. It consists of the following 5 files:

This is the executable program file.

This data file contains the soil data needed in the
simulation.

This data file contains the chemical data required in the
model.

This file contains a sample of effective rainfall data for
1985.

This file contains daily evapotranspiration data for 1985.

Making a Working Copy: The first step is to make a working copy of the
software on the distribution diskette. If the software will be used on a
floppy disk system, you will need to format a floppy diskette and copy the
software. The FORMAT command of DOS may be used to format the working disk.
The following steps can be used to make a working copy on a floppy diskette:

1. Place the DOS diskette in default drive A.

2. Place a new diskette in drive B.

3. Format the new diskette using the command FORMAT B:/S.

4. Copy the GRAPHICS.COM file from your DOS diskette to the new diskette
using the command COPY A:GRAPHICS.COM B:.

5. Copy the ANSI.SYS file from the DOS diskette to the new diskette using
the command COPY A:ANSI.SYS B:.

6. Remove the DOS diskette from drive A and replace it with the CMLS
distribution diskette. Copy the entire contents of the distribution
diskette to the working diskette using the command COPY A:*.* B:.

7. Create a CONFIG.SYS file containing at least the entry DEVICE=ANSI.SYS
on one line and store this file on the boot-up disk. When the system
boots up, this file will cause the system to load the ANSI device driver
into memory.

8. Create an AUTOEXEC.BAT file with the entry GRAPHICS on one line. When
the system boots up, it will execute this file automatically. This will
execute the GRAPHICS.COM program so screen dumps of graphics can be
obtained using the - keys.

9. Place the distribution diskette in a safe place.

If the software will be used on a fixed disk, you will likely want to make a
new subdirectory for this application. The files should then be copied to the
fixed disk. The distribution diskette should then be stored in a safe place.
You will also need to make sure that the CONFIG.SYS file used on boot-up
contains the line DEVICE=ANSI.SYS and that the AUTOEXEC.BAT file contains the
GRAPHICS command on one line.

Program Execution: To execute CMLS, place the working diskette in the default
disk drive. Then enter CMLS to execute the program.

NOTE: As you increase the size of your data files, the program and data may
not all fit on one diskette. It may be most convenient to place the disk with
all the data files in the default disk drive. The program can then be executed
from another drive.

OPERATING CONVENTIONS

The following conventions are used throughout this software:

1. Program Interruption: The user can interrupt the program and return to
the previous menu or data-entry screen by pressing the key. The
key can also be used to skip over introductory material presented
at the beginning of the program.

2. Keyboard Inputs: Single-character entries such as menu selections and
responses to yes/no questions are made by pressing only the desired key.
The key is not required. All other inputs require use of the
key.

3. Default Values: This software makes use of default values to reduce the
amount of typing required. Default values are displayed in square
brackets when inputs are requested. If the default value is the desired
entry, the user need only press the key rather than retype the
entry. If another value is desired, however, that value must be entered.
The value selected becomes the default value for that parameter until it
is changed or until the program is terminated.

4. File Names: File names may be any legal MS-DOS or PC-DOS file
identifier, including the disk drive and path. File extensions are not
needed. Meaningful file extensions for different types of files will be
assigned by the software.

5. Using the Parameter Editor: To enable the user to easily modify
parameters in screens such as those shown in option A, an editor is
included in the software. When the information initially appears on the
screen, values will be present for all parameters. These values will be
default values the first time the option is used. If the option is used
repeatedly, the previous entries will be present. The user may then use
the cursor keys to move up or down on the screen in order to make the
desired changes. The and keys will move the
cursor up or down one line, respectively. The and keys
will move the cursor to the top line. The and keys will
move the cursor to the bottom line. When all the changes on a particular
screen have been made, the key should be pressed to continue
execution of the option. The key may be pressed at any time to
abort the option and return to the previous screen. Brief help messages
may be obtained by pressing the key.

INTRODnUCTO0RW INFORMArTI N

CHEMICAL MOVEMENT IN LAYERED SOILS
Version 4.0
by
D. L. Nofziger and A. G. Hornsby
Department of Agronomy
Oklahoma State University
and
Soil Science Department
Institute of Food and Agricultural Sciences
University of Florida
Copyright 1987
by
University of Florida
Institute of Food and Agricultural Sciences
This program has been written to illustrate the influence of soil
properties, chemical properties, rooting depth, precipitation,
and evapotranspiration upon the movement and persistence of
organic chemicals (pesticides) in well-drained soils.

Figure 1. Purpose of the program.

Figure 1 is the first screen of the program. It describes the purpose of the
software. Figures 2 and 3 list the required inputs and possible outputs for
the model.

The program requires the following inputs:
Soil (for each horizon):
1. Depth of Bottom of Horizon
2. Percent Organic Carbon
3. Bulk Density
4. Water Content at matric potential of -0.01 MPa (-0.1 bar)
5. Water Content at matric potential of -1.5 MPa (-15 bars)
6. Water Content at saturation
Chemical:
1. Partition Coefficient Normalized for Organic Carbon Content
2. Degradation Half-Life
Maximum Rooting Depth of Plant
Application Depth of Chemical
Daily Effective Precipitation Records
Daily Evapotranspiration Records
Soil, chemical, and climatic data can be stored in data files
for repeated use.

Figure 2. Required inputs for the model.

Outputs from the program include:
Graphs:
1. Precipitation and depth of movement of each chemical
as functions of time.
2. Relative amount and depth of movement of each chemical
as functions of time.
Tables:
1. Precipitation, depth of movement of selected chemical,
and relative amount of chemical remaining in soil as
a function of time since application of chemical.
2. Time required for chemicals to move to specified
depth in soil and the relative mass of the chemical
in the profile at that time.
(Tables may be output to screen, printer, or disk.)

Figure 3. Output options for the model.

MAIN MENU

CHEMICAL MOVEMENT IN LAYERED SOILS
by
D. L. Nofziger and A. G. Hornsby
Version 4.0
Copyright 1987
OPTIONS :
A. Calculate Chemical Movement in Soil
B. Enter, Modify, or Print Soil Data File
C. Enter, Modify, or Print Chemical Data File
D. Enter, Modify, or Print Rainfall Data File
E. Enter, Modify, or Print Evapotranspiration Data File
F. Display File Directory
G. Select Default Files and Options
I. Import ASCII Data Files
Q. Quit. Terminate Program and Return to DOS
Desired Option 7 a

Figure 4. Main menu of the program.

Figure 4 contains the main menu of this program. Options
entering the letter corresponding to the option desired.
option A was selected. A brief description of each option is
use of each option is illustrated on the following pages.

are selected by
In this example
given below. The

Calculate Chemical Movement in Soil
This option is used to simulate the movement of chemicals
in soil. The user must define the system to be modeled and
select various types of outputs.

Enter, Modify, or Print Soil Data File
The required data for each soil must be stored in a data
file. These data are then used to estimate the movement of
the chemical. This option permits the user to enter new
information into the file, modify existing information, or
display information from the file on the screen or
printer.

Enter, Modify, or Print Chemical Data File
Required information for each chemical may be stored in a
file for repeated use in simulations. This option enables
the user to enter, modify, or display the chemical data.

Enter, Modify, or Print Rainfall Data File
The estimation of chemical movement using this software
requires daily records of the amount of rainfall or
irrigation water entering the soil. This option permits
the user to enter, modify, and display these data for the
site and time period of interest.

Enter, Modify, or Print Evapotranspiration Data File
This requires daily records of water lost from the soil by
evapotranspiration, or the sum of the amounts lost by
evaporation from the soil surface and that lost by
transpiration through the growing plant. This option
enables the user to enter, modify, and display these data.

Display File Directory
This option simply displays the file directory for the
default disk drive.

Select Default Files and Options
This option permits the user to specify the soil and
chemical files to be used in the program. It also enables
the user to specify whether partition coefficients and
half-life values will be entered for each soil horizon and
whether the user wants to select graphics limits manually.

Import ASCII Data Files
This option permits the user to read soil, chemical,
effective rainfall, and evapotranspiration files stored as
ASCII text. The files are converted and stored in the
forms used in this model. This is especially useful for
chemical, rainfall, and evapotranspiration files created
and used in CMIS (Nofziger and Hornsby, 1985).

Quit. Terminate Program and Return to DOS
This option is used to end the program and return control
to the disk operating system.

CALCULATE CHEMICAL MOVEMENT IN SOIL

This option is the most commonly used option in this model. It is used to
define the application of interest. After the definition is completed, the
simulation is carried out. The user is then given various options for
displaying the results. Figure 5 illustrates the screen image used to define
the overall system. Entries in the figure are described below.

Define Problem
English or metric units of length, (E,M) :E
Name of chemical#1 :DIURON
Organic carbon partition coefficient, (ml/g OC):383
Degradation half-life, days :328
Application date, (month/day/year) :1/1/85
Application depth, (in) :0.00
Name of chemical#2 : TEMIK
Organic carbon partitio coe ficient, (ml/g OC):12
Degradation half-life, 4ays :28
Application date (mon h /day/year) 5/1/85
Application depth, (in :0.00
Soil identifier :S27-8-(1-6)
Rooting depth, (in) :10.00
Infiltration or rainfall file name :LOCAL85.R
Evapotranspiration file name :LOCAL85.ET
Date to end simulation,(month/day/year) :12/31/85
Use cursor keys to position cursor. Then make desired changes.
Press when finished entering all information.
Press for help. Press to abort this option.

Figure 5. Defining the soil and chemical system of interest.

English or metric

units of length
This entry is the character E or M to specify the
preferred units of length to be used in the displayed
results. If metric units are selected, rainfall and
evapotranspiration are displayed in millimeters, and
application depth, rooting depth, depth of chemical, and
depths of soil horizons are shown in meters. If English
units are specified, the parameters listed above will be
displayed in inches. The organic carbon partition
coefficient is entered as ml/g of organic carbon
regardless of the conventions chosen for other parameters.

Names of chemical#1 and chemical#2
This model permits the user to select up to two chemicals
to be simulated and displayed at one time. These entries
can be either common names or trade names of the
chemicals. When a name is entered, the computer searches
the default chemical file for that name. If a match is
found, the partition coefficient and half-life values for
the chemical are displayed below the name. If the name is
not found, a message to that effect is displayed. The user

may then enter another name or the correct partition
coefficient and half-life for the new chemical. If only
one chemical is desired, the word "NONE" may be inserted
for the second chemical.

Organic carbon partition coefficient, KOC
Some of the chemical in the soil is dissolved in the soil
water and some is adsorbed on the soil solids. This
partitioning of the chemical between soil and water is
represented in this model by the linear relationship CS =
KdCW where CS and CW represent the concentration of the
chemical in the soil and water phases, respectively, and
Kd is the partition coefficient for the chemical in the
soil. The organic carbon partition coefficient, KOC, is
the partition coefficient, Kd, normalized with respect to
the organic carbon content of the soil. The units are ml/g
of organic carbon. In most instances this value will be
read from the chemical file as explained above, so this
entry will not need to be modified by the user.

NOTE: Organic carbon partition coefficients and half-lives
entered here are not stored in the chemical file, but are
stored in the random access memory of the computer.
Permanent changes to the chemical data file can only be
made using option C.

Degradation half-life
This is the degradation half-life in days for the chemical
selected. This value is also stored in the chemical file
and will not need to be modified in most cases. If the
manual entry of half-lives for each horizon is enabled,
another screen (illustrated on the following page) will
appear for entering partition coefficients or half-lives
for each horizon.

Application date This entry represents the date on which the chemical was
applied to the soil. It is specified in numeric form, as
indicated.

Application depth This is the depth of application of the chemical in the
system of units chosen.

Soil identifier This is a unique identifier for the soil to be used in the
simulation. This identifier must match with a soil
identifier in the default soil file. The properties of
that soil are then used.

Rooting depth This is the depth of roots 'for the plant growing on this
soil. It determines the maximum depth to which- ater may

be lost by evapotranspiration. The number must be entered
in the units shown on the screen. This model does not
allow changes in rooting depth with time.

Infiltration or rainfall file name
This entry is the file identifier for the file containing
the daily infiltration or effective rainfall amounts for
the period of time being simulated.

Evapotranspiration

file name
This entry
the daily
time being

is the file identifier for the file
evapotranspiration amounts for the
simulated.

containing
period of

Date to end simulation
This date determines the maximum time for
simulation is to be carried out. It is entered
form as shown.

which the
in numeric

After the user has made the desired entries in Figure 5 and pressed the
key, the computer determines if the manual entry of partition coefficient, Kd,
and half-life for each soil horizon (option G) is enabled. If so, a screen
such as that illustrated in Figure 6 is shown for each chemical specified. The
user may then use the parameter editor to enter a partition coefficient or
half-life for each horizon. If the user has disabled this manual-entry option,
the KOC value shown in Figure 5 is combined with the organic carbon content of
each horizon to determine the Kd for the horizon. If the manual-entry option
is disabled, the half-life value shown in Figure 5 is used for all horizons.

PROPERTIES OF DIURON FOR EACH HORIZON
Horizon Maximum Depth (in) Kd Half-Life
of Horizon (ml/g soil) days)
1 4.00 2.107 200
2 8.00 1.609 300
3 21.00 0.345 400
4 42.00 0.230 500
5 48.00 0.153 500
6 80.00 0.077 500
Fl-Help; F2-Entering Columns; F5-Copy Value Above;
Fl0-End Editing; Esc-Abort;
Figure 6. Entering the partition coefficient and half-life for each
horizon.

After the soil and chemical systems of interest have been defined, the
computer calculates the depth of movement of each chemical in the soil profile
and the relative amount of the material applied to the soil which is still
present for each day of the simulation period. These data are then used for
the outputs selected in Figure 7.

Select Outputs Desired
Graph rainfall & depth vs time
for DIURON :Y
for TEMIK :Y
Graph of depth & relative amount vs time
for DIURON :Y
for TEMIK :Y
Table of depth & relative amount vs time
for DIURON :Y
for TEMIK :Y
Table of t avel times to depths below :Y
Depth 1 (in) :10.00
Depth 2 in) :20.00
Depth 3 (in) :30.00
Depth 4 (in) :40.00
Output device or file :SCREEN
Use cursor keys to position cursor. Then make desired changes.
Press when finished entering all information.
Press for help. Press to abort this option.

Figure 7. Selecting graphical and tabular outputs of interest.
The outputs available include:

1. Graphs of daily rainfall as a function of time and of calculated depth
of the chemical as a function of time. These are illustrated in Figure
8. The shaded region in the graph of the depth of the chemical as a
function of time represents soil depths below the maximum depth defined
for this soil. Predictions in this shaded region must be viewed with
caution since the soil properties for this region are not known but are
assumed to be the properties of the deepest horizon specified.

2. Graphs of the relative amount of the chemical remaining in the profile
as a function of time and of the calculated depth of the chemical as a
function of time. These are illustrated in Figure 9. NOTE: The relative
amounts (y-axis) are shown on a log scale rather than a linear scale.

3. Tables of the depth of chemical movement and of the relative amount of
the chemical remaining in the profile as functions of time. These values
are displayed only for those dates on which rainfall occurred. These are
illustrated in Table 1.

4. Table of the times required for the chemical to reach four depths in the
profile selected by the user. This table also includes the relative
amount of the chemical in the profile at the time the chemical reaches
the specified depth. This table is illustrated in Table 2.

The entries in Figure 7 permit the user to select desired outputs by entering
'Y' or 'N'. Copies of graphs can be obtained by pressing the and
keys. The "Output device or file" option in Figure 7 determines
whether the selected tables will be displayed on the screen, displayed on a
printer, or stored in an ASCII text file. These are selected by entering the
words SCREEN, PRINTER, or a valid file identifier.

3.0

1.5

0.

150-
An

0 100 200 300 40
LAPSED TIME, s JaVs

. . . . . . *
..................

. . . . . . . . . . . .. . ,. . *. .
. # 0 "5 5
. . . .. .. . . . . .. . . . .
.i i l l l i .t . . . . . .I S
pl ll i t il l ll l55l l5~St*SS t l t 55.

JOU ,I ----t----- i ----------
Rainfall and Depth of Cheical as Functions of Time.,
Figure 8. Daily rainfall and depth of chemical movement as
time since simulation began.

TEa function of

a function of

11lI

Simulation
BelIns
1/ 1/1985
Fnds
12/31/1985

Soil
TAUARES FS
S27-8-(I-6)

Root Depth

Chemical

-

i

I111.1

I II I I

R
E
L

A .01
H
0
0

D
K
P
t
II 159

I
A
Anfl

B

LAPSED TIME,Jays

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

. . . . . . . . * * * * . .
* * * * * *s . . .* . .
. . . . . . . . . . . . . . . . . .
,* * * * * * * . . . . . . * e .
* * * * * * * * * * * e ase * * * e .

Simulation
Begins
I/ 1/1985
Ends
12/31/1985

Soil
TAVARES BS
S27-8-(1-)

Root Depth

Chemical
. IRON

*I*I**

Relative Amount and Depth of Chemical as Functions of TiNe.
Figure 9. Relative amount of chemical remaining in the profile and depth of
chemical movement as a function of time. Note that the relative
amount is shown on a log scale.

m

'I

= :1

-

I

Table 1. Simulated Depth and Relative Amount of Diuron in a Tavares Fine
Sand.
Chemical Movement in Layered Soils
Soil Name : TAVARES FS Identifier : S27-8-(1-6)
Horizon Depth Organic Carbon Bulk density Volumetric Water Content, (%) at
(In) (%4 ( cc) -0.1 bars -15 bars Saturation
1 4.00 0.55 42 6.5 1.3 47.4
2 8.00 0.42 1.40 7.2 1.5 48.1
3 21.00 0.09 1.50 5.2 0.8 44.4
4 42.00 0.06 1.56 5.4 0.7 42.2
5 48.00 0.04 1.56 6.1 0.8 42.2
6 80.00 0.02 1.58 11.9 1.0 41.5

Name of chemical
Organic carbon partition coefficient, (ml/g
Degradation half-life, (days)
Application depth, (in)
Application date, (onth/day/year)
Ending date, (month/day/year)
Rooting depth, in)
Infiltration or rainfall file name
Evapotranspiration file name

:DIURON
OC):383
:200
:0.00
:1/7 /85
:12/31/85
:10.00
:LOCAL85.R
:LOCAL85.ET

Horizon Maximum Depth (in) Kd (ml/g soil) Half-Life (days)
of Horizon ---------------DIURON ------
1 4.00 2.107 200
2 8.00 1.609 300
3 21.00 0.345 400
4 42.00 0.230 500
5 48.00 0.153 500
6 80.00 0.077 500

Total Rainfall:
Total Evapotranspiration:
Potential Evapotranspiration:

Rainfall
in
0.33
0.68
0.28
1.48
0.23
0.20
0.70
0.12
2.00
0.40
0.44
2.27
0.10
0.57
0.17
0.70
2.33
2.97
0.43
1.63
0.83
0.83
0.33
1.53
0.50
0.28

67.3
24.4
56.7

Solute Depth
in
0.1
0.3
0.4
0.9
1.0
1.0
1.3
1.3
1.9
2.0
2.1
2.9
2.9
3.0
3.0
3.2
3.9
5.1
5.2
5.9
6.2
6.4
6.4
7.0
7.0
7.0

inches
inches
inches
Relative Amount
1.00
0.99
0.94
0.93
0.93
0.91
0.91
0.90
0.90
0.88
0.86
0.86
0.85
0.83
0.82
0.82
0.80
0.80
0.78
0.78
0.78
0.77
0.77
0.76
0.76
0.75

Elapsed Time
days
2
19
20
22
26
27
29
32
36
43
44
47
53
58
59
64
65
74
75
76
79
82
85
89
92

Date
1- 2-1985
1- 3-1985
1-20-1985
1-21-1985
1-23-1985
1-27-1985
1-28-1985
1-30-1985
2- 2-1985
2- 6-1985
2-13-1985
2-14-1985
2-17-1985
2-23-1985
2-28-1985
3- 1-1985
3- 6-1985
3- 7-1985
3-16-1985
3-17-1985
3-18-1985
3-21-1985
3-24-1985
3-27-1985
3-31-1985
4- 3-1985

Table 1. Continued.
Date Rainfall
in
4- 8-1985 1.07
4- 9-1985 2.56
4-10-1985 0.16
Chemical Movement Below
4-15-1985 2.56
4-16-1985 0.25
4-19-1985 0.61
4-23-1985 1.50
5- 4-1985 0.26
5-14-1985 0.60
5-17-1985 1.35
5-24-1985 2.43
6- 5-1985 0.39
6- 7-1985 2.05
6- 8-1985 1.67
6-22-1985 1.03
6-29-1985 0.41
7- 1-1985 0.33
7-20-1985 0.43
7-21-1985 0.26
7-24-1985 0.13
7-26-1985 0.25
7-27-1985 0.35
7-31-1985 0.40
8- 2-1985 1.32
8- 3-1985 1.32
8- 4-1985 1.72
8- 5-1985 0.10
8- 7-1985 0.18
8- 8-1985 1.68
8-13-1985 0.17
8-14-1985 0.10
8-31-1985 0.17
9- 2-1985 0.12
9- 3-1985 0.15
9- 5-1985 0.29
9-13-1985 1.95
9-20-1985 0.14
9-22-1985 0.38
10- 9-1985 0.35
10-10-1985 0.38
10-11-1985 0.33
10-12-1985 0.12
10-13-1985 0.11
10-14-1985 0.55
10-15-1985 0.17
10-18-1985 0.17
11- 5-1985 0.10
11-16-1985 0.24
11-20-1985 0.14
11-21-1985 2.17
11-25-1985 2.30
11-28-1985 0.49
11-29-1985 0.36
12- 4-1985 0.38
12- 7-1.985 0.22
12-12-1985 2.04
12-14-1985 0.41
12-15-1985 0.11
12-17-1985 0.70
12-18-1985 0.68
12-19-1985 0.19
12-29-1985 1.39

Solute Depth
in
7.3
9.4
9.4
Root Zone
13.0
13.3
13.5
15.2
15.2
15.3
16.8
20.1
20.1
23.7
27.2
28.5
28.5
28.5
28.5
28.5
28.5
28.5
28.5
28.5
30.7
33.6
37.4
37.4
37.4
41.1
41.1
41.1
41.1
41.1
41.1
41.1
45.6
45.6
45.6
45.6
45.8
46.4
46.5
46.5
48.0
48.2
48.2
48.2
48.2
48.2
55.2
63.6
64.7
65.9
65.9
65.9
72.5
74.0
74.3
76.2
78.6
79.0
82.6

Relative Amount
0.74
0.74
0.74
0.73
0.73
0.73
0.72
0.71
0.70
0.69
0.69
0.67
0.67
0.67
0.66
0.65
0.65
0.63
0.63
0.63
0.63
0.62
0.62
0.62
0.62
0.62
0.62
0.61
0.61
0.61
0.61
0.59
0.59
0.59
0.59
0.58
0.58
0.58
0.56
0.56
0.56
0.56
0.56
0.56
0.56
0.56
0.54
0.53
0.53
0.53
0.53
0.53
0.53
0.52
0.52
0.52
0.51
0.51
0.51
0.51
0.51
0.50

Elapsed Time
days
98
99
104
105
108
112
123
133
136
143
155
157
158
172
179
181
200
201
204
206
207
211
213
214
215
216
218
219
224
225
242
244
245
247
255
262
264
281
282
283
284
285
286
287
290
308
319
323
324
328
331
332
337
340
345
347
348
350
351
352
362

Table 2. Travel Times for Chemicals to Move to Selected Depths and Relative
Amounts of the Chemical Remaining in the Soil at Those Times.

------------------------------------------------------------------
Chemical DIURON TEMIK
Partition Coefficient, KQc, (ml/g OC) 383 12
Application date, kmont day year) 11 85 5/1/85
Ending date, (month/day/year) 12/31/85 12/31/85
Application depth, (in) 0.00 0.00
Rooting depth, (in) 10.00 10.00

Time (days) to 10.00 in
Relative Amount Remaining
Time (days) to 20.00 in
Relative Amount Remaining
Time (days) to 30.00 in
Relative Amount Remaining

104
0.7333
143
0.6854
213
0.6192

16
0.3833
23
0.3261
23
0.3261

Time (days) to 40.00 in 219 23
Relative Amount Remaining 0.6141 0.3261

Soil Name : TAVARES FS Identifier : S27-8-(1-6)
Horizon Depth Organic arbon Bulk Density Volumetric Water Content, (%) at
t(In) Z /cC) -0.1 bars -15 bars Saturation
1 4.00 0.55 42 6.5 1.3 47.4
2 8.00 0.42 1.40 7.2 1.5 48.1
3 21.00 0.09 1.50 5.2 0.8 44.4
4 42.00 0.06 1.56 5.4 0.7 42.2
5 48.00 0.04 1.56 6.1 0.8 42.2
6 80.00 0.02 1.58 11.9 1.0 41.5

Maximum Depth (in)
of Horizon
4.00
8.00
21.00
42.00
48.00
80.00
Maximum Depth (in)
of Horizon
4.00
8.00
21.00
42.00
48.00
80.00

Kd (ml/g soil) Half-Life (days)
---------------DIURON-------------
2.107 200
1.609 300
0.345 400
0.230 500
0.153 500
0.077 500
Kd (ml/g soil) Half-Life (days)
----- --- TEMIK---------------
0.066 10
0.050 20
0.011 30
0.007 30
0.005 30
0.002 30

Horizon
1
2
3
4
5
6
Horizon
1
2
3
4
5
6

ENTER, MODIFY. OR PRINT SOIL DATA FILE

This option is used to enter the required soil parameters into a file, to
modify data entered previously, and to print the contents of the file on the
screen or a printer. This simulation model requires the following parameters
for each soil:

Soil name

Soil identifier

This is a descriptive name of the soil. The name
displayed along with all simulated results. It may be
to 20 characters in length.

This is the sequence of characters which will be used
the simulation option to select this soil. Therefore,
must be different for each soil. It may be up to
characters in length, but shorter identifiers
recommended.

Depth of the bottom of each horizon
The distance from the soil surface to the bottom of each
horizon is required to define the soil-horizon limits so
the soil properties of that horizon are used for the
proper depths. If the model predicts that a chemical will
move below the depth of the deepest characterized horizon,
the soil properties are assumed to be those of the deepest
horizon.

Percent organic carbon of each horizon
This value is used to obtain the partition coefficient for
the soil horizon of interest from the normalized partition
coefficient for the chemical. If the organic carbon
content of the soil horizon is not known it can be
estimated by multiplying the organic matter content of the
horizon by 0.4.

Bulk density of each horizon
This is the mass of dry soil per unit volume of soil.
Since most agricultural data bases represent bulk density
in g/cm3, these units are used here for both English and
metric units. Unit weight (lb/ft3) may be converted to
g/cm3 by multiplying by 0.016.

Soil water content

at a matric potential of -0.01 MPa (-0.1 bars)
This is the volumetric water content (expressed as a
percent) at the matric potential specified. This value is
used as an estimate of "field capacity" for the soil. It
is required for each horizon in the profile. Note: The
water content at a matric potential of -0.033 MPa (-0.33
bars) may be entered in lieu of the water content ate -0.01

MPa if the user deems this a
the "field capacity" of the
will indicate that the value
content at -0.01 MPa.

Soil water content

Soil water content

more appropriate estimate of
soil. However, the program
entered represents the water

at a matric potential of -1.5 MPa (-15 bars)
This is the volumetric water content (expressed as a
percent) at the matric potential specified. This value is
used as an estimate of "permanent wilting point" for the
soil. It is required for each horizon in the profile.

at saturation
This is the volumetric water content (expressed as a
percent) when all the pores of the soil are filled with
water.

Figure 10 illustrates the first screen requiring user input after selecting
this option. Here, the user specifies the units of length to be used, the soil
file name to be used, and whether the edit function or an output function is
desired. In this case the edit option was selected.

Distances or lengths can be expressed in the following units:
E. English inches
M. Metric meters and millimeters
Enter or for desired units [Default is E] : E

Enter Name of File to be Used [Default is SOIL.S]:FLORIDA
OPTIONS:
E. Enter or edit data
P. Display data on printer
S. Display data on screen
F. Convert data to a text file
Desired Option: E

Figure 10.

Selecting units, soil file, and edit option.

Figure 11 illustrates the use of the full-screen editor for entering soil
data. Each line on the screen represents a particular horizon. In this case,
several columns of data exist to the right of the edge of the screen. The user
may use the cursor keys to move around on the screen. The contents of the
screen are shifted horizontally to enable the user to enter or edit any
parameter for each horizon. The cursor and function keys used in this editor
are described in the Appendix.

Record Horizon No.

ORANGEBURG FSL
ARREDONDO FINE SAND
GAINESVILLE SAND
CHAIRS FINE SAND
TROUP FINE SAND
FUQUAY FINE SAND
MYAKKA FINE SAND
LAKELAND FINE SAND
BLANTON FINE SAND
TAVARES FINE SAND
TAVARES FINE SAND
TAVARES FINE SAND
TAVARES FINE SAND
TAVARES FINE SAND
TAVARES FINE SAND
TAVARES FINE SAND
LAUDERHILL MUCK
SPARR FINE SAND

S37-8-AVE
S1-66-AVE
S1-73-AVE
S37-20-AVE
S37-5-AVE
S37-25-AVE
S49-10-AVE
S61-29-AVE
S16-14-AVE
S27-8-AVE
S27-8-( 1-6
S27-8-(1-6
S27-8-(1-6
S27-8-(1-6
S27-8-(1-6
S27-8-(1-6)
S50-27-AVE
S1-66-AVE

-HELP;
-Abort

-Entering Rows;
-Delete Record;
-Save Data;

-Insert Record;
-Copy Above Field;
-End Editing;

Figure 11. Entering or editing soil data with the full-screen editor.

Several points should be made about the manner in which soil data are entered.

1. Soil horizons are numbered sequentially from the surface.

2. All horizons for a specific soil have the same soil name and the same
soil identifier. If the name and identifier are entered for horizon 1,
the key can be used to copy these values to the new horizons.

3. The depths of the horizons must increase as the horizon index increases.

A particular soil file may contain up to 1000 horizons or approximately 150
soils. If more soils are needed they must be stored in additional files.

Soil Name

Soil Identifier

ENTER MODIFY, OR PRINT CHEMICAL DATA
FILE

This option is used to enter chemical data into a data file or to modify or
print those data. The model requires the following information for each
chemical:

Common Name

This is the common name for the chemical. It may be used
for selecting the chemical to be used in the simulation.

Partition coefficient
This is the organic carbon partition coefficient or the
linear sorption coefficient normalized with respect to
organic carbon content (KOC). It must be entered with
units of ml/gram of organic carbon. This value is combined
in the model with the fractional organic carbon content OC
(gram organic carbon/gram soil) to determine the linear
sorption coefficient for the soil (Kd) by means of the
equation

Kd KOC*OC

Half-life

Trade names

Upon
used
only

The half-life is the length of time (days) required for
one-half of the present concentration to be degraded.

Up to four trade names for each chemical may be entered.
These trade names may also be used to select the chemical
of interest when simulating chemical movement.

entering this option
(Figure 12). Since,
the key was

the user is asked to specify the chemical file to be
in this example, the user wanted the default file,
pressed. The user then chose the Edit option.

Enter Name of File to be Used [Default is CHEM.CHM]:
OPTIONS:
E. Enter or edit data
P. Display data on printer
S. Display data on screen
F. Convert data to a text file
Desired Option: E

Figure 12. Selecting the chemical file and the edit option.

Chemical data can be edited and entered using the full-screen editor as shown
in Figure 13. In this case each line represents a single chemical. The fields
for the four trade names are off to the right of the screen shown in this
figure. See the Appendix for details on use of the editor.

Each chemical file can store data for up to 200 chemicals. If more chemicals
are needed additional files may be used.

Record
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
-HELP;
-Abort

Commc
ALDIC
FENAM
OXAMY
CAPTA
PENTA
DIURC
PICLO
BROMW
TERBA
TRIDI
HALOX
LINUR
DICA
ATRA2
SIMAZ
PARAT
METHYL
MALAT

on Name Partition Coeff.
(ml/g OC)
:ARB 12
1IPHOS 171
L 99
iN 33
LCHLOROPHENOL 14290
)N 383
)RAM 26
)CIL 72
LCIL 46
IPHANE 5600
CYFOPMETHYL 75
RON 863
(BA 2
1INE 163
ZINE 138
HION 10650
TL PARATHION 5102
LHION 1797

-Entering Rows; -
-Delete Record; -
-Save Data;

Half-Life
(days)
28
10
6
3
48
328
138
106
50
28
1
75
14
48
75
35
4
1

Insert Record;
Copy Above Field;
-Ehd Editing;

Figure 13. Entering or editing chemical data using the full-screen
editor.

ENTER, MODIFY, AND PRINT RAINFALL DATA
FILE

This option is used to enter, edit, or display daily effective rainfall
records. Effective rainfall is used here to mean the amount of water entering
the soil. The source of the water may be either irrigation or rainfall. Water
known to run off the soil surface should not be included.

Rainfall may be entered either in English units of inches or in metric units
of millimeters. This selection is made as shown in Figure 14. The figure also
illustrates that the user chose to edit file LOCAL85 on disk drive B:.

Distances or lengths can be expressed in the following units:
E. English inches
M. Metric meters and millimeters
Enter or for desired units [Default is E] : E

Enter Name of File to be Used : b:local85
OPTIONS:
E. Enter or edit data
P. Display data on printer
S. Display data on screen
F. Convert data to a text file
Desired Option: e

Figure 14. Selecting units, rainfall file, and edit option.

Figure 15 illustrates the editing screen for rainfall data. This option also
uses the full-screen editor. The editor provides the date automatically so the
user only needs to enter the effective rainfall amounts on the proper dates.
Other days may be left containing only decimal points.

Rainfall files may contain up to 15 years of data. This software cannot be
used for simulations exceeding 15 years in a single pass. However, by noting
the depth of chemical movement at the end of a simulation, a subsequent
simulation can be run by specifying this depth as the application depth.

Effe tive Rainfall
(in)
0.33
0.68

6.28

-HELP;
-Abort

-Entering Rows;
-Delete Record;
-Save Data;

-Insert Record;
-Copy Above Field;
-Ehd Editing;

Figure 15.

Entering or editing rainfall data with the full-screen editor.

Date
1- 1-1985
1- 2-1985
1- 3-1985
1- 4-1985
1- 5-1985
1- 6-1985
1- 8-1985
1- 9-1985
1-10-1985
1-11-1985
1-12-1985
1-13-1985
1-14-1985
1-15-1985
1-16-1985
1-17-1985
1-18-1985
1-19-1985
1-20-1985

ENTER, MODIFY, AND PRINT
EVAPOTRANSP IRATION DATA FILE

This option is used to enter daily evapotranspiration amounts for the site of
interest. Evapotranspiration is the total amount of water lost by evaporation
from the soil surface and transpiration through the plant. User interaction
with the computer for this option is identical to that for the rainfall files
illustrated above. Evapotranspiration files are limited to 15 years of data,
as are rainfall files.

SELECT DEFAULT FILES AND OPTIONS

This option, illustrated in Figure 16, is used to select the soil and chemical
files to be used in option A. It may be needed if several soil or chemical
files are used or if the files to be used are on a disk drive other than the
default disk drive. The third entry is used to specify whether the user will
be entering partition coefficients, Kd, and half-life values for each horizon.
The fourth entry permits the user to select the limits for graphs to be
displayed.

Configuration Option
Name of Chemical Data File :CHEM.CHM
Name of Soil Data File :SOIL.S
Manually enter Kd and half-life values (Y,N) :Y
Manually select graph limits (Y,N) :N

Use cursor keys to position cursor. Then make desired changes.
Press when finished entering all information.
Press for help. Press to abort this option.
Figure 16. Selecting default files and options.

IMPORT ASCII DATA FILES

Some data required in this model may already exist in computer-readable form.
In these cases, it may be advantageous to create ASCII files of the data and
to import the data into this software. This option reads selected ASCII files
and creates binary files used in this software.

The menu shown in Figure 17 is used to select the type of file to be imported.
In each case, the system asks for the name of the ASCII file and the units
used if relevant. The system then reads the file into random access memory.
The user is then prompted for the name of the output file. At this point the
data are displayed in the full-screen editor. The user may inspect or edit the
data. The data will be written to the output file if the user presses the
or keys as is done for normal editing.

IMPORT ASCII DATA FILES
OPTIONS :
S. Soil Data File
C. Chemical Data File
R. Rainfall Data File
E. Evapotranspiration Data File
Q. Quit. Return to Main Menu.
Desired Option ?

Figure 17. Menu for importing data files.

A description of the required form of the input data is given below.

Soil Data File

For each soil, the following sequence of parameters must
be stored in the ASCII file. Each parameter must be on a
separate line.

1. Soil name

2. Soil identifier

3. Number of horizons

4. For each horizon

a. Depth of bottom of horizon, (inches or meters)

b. Organic Carbon Content, (%)

c. Bulk Density, (g/cm3)

d. Water content at -0.1 bar, (% by volume)

e. Water content at -15 bars, (% by volume)

f. Water content at saturation, (% by volume)

NOTES:

1. All the parameters for horizon 1 are given before
those for horizon 2, etc.

2. This format is not the same as that used for soil
files in CMIS (Nofziger and Hornsby, 1985) since
this model requires more data for each horizon.

Chemical Data File

The following sequence of parameters must be stored in the
ASCII file for each chemical. Each parameter must be on a
separate line.

1. Common name

2. Trade name #1

3. Trade name #2

4. Trade name #3

5. Trade name #4

6. Partition coefficient, KOC, (ml/g OC)

7. Degradation half-life, (days)

NOTES:

1. A space character may be placed on a
one or more trade names.

Rainfall Data File

line instead of

2. This file structure is identical to that used in
CMIS (Nofziger and Hornsby, 1985).

The following values must be stored in the ASCII file for
each rainfall event. Each parameter must be on a separate
line.

1. Month (as a number from 1 to 12)

2. Day

3. Year

4. Effective Rainfall, (inches or millimeters)

NOTE:

This file structure is identical to that used in
CMIS (Nofziger and Hornsby, 1985).

Evapotranspiration Data File
The following values must be stored in the ASCII file for
each day. Each parameter must be on a separate line.

1. Month (as a number from 1 to 12)

2. Day

3. Year

4. Evapotranspiration, (inches or millimeters)

NOTES:

1. If an evapotranspiration file does not contain data
for a certain day, the value present for the
previous day is used in the simulation model.

2. This file structure is identical to that used in
CMIS (Nofziger and Hornsby, 1985).

DESCRIPTION AND ASSUMPTIONS OF MODEL

This model estimates the depth of the peak concentration of a non-polar
organic chemical as a function of time after application. It also calculates
the relative amount of the chemical in the soil profile as a function of time.
The model has been described by Nofziger and Hornsby (1986). Details of the
computational scheme are presented there. An overview of the model and its
assumptions are included here for your information.

MODEL DESCRIPTION: The basis for predicting the location of the chemical in
this model is the work of Rao, Davidson, and Hammond (1980). The model assumes
that chemicals move only in the liquid phase in response to soil water
movement. The change in depth of the chemical depends upon the quantity of
water moving past the chemical, properties of the chemical, and selected
properties of the soil. If dC represents the depth of the peak concentration
of the chemical and q represents the amount of water passing that depth, the
change in depth of the chemical, AdC, is given by

AdC q/R 9FC

if q > 0 and AdC 0 otherwise. Here eFC is the volumetric water content at
"field capacity" and R is the retardation factor for the chemical. Assuming a
linear and reversible equilibrium adsorption model, the retardation factor is
given by

R = 1 + (pKd)leFc

where p is the soil bulk density and Kd is the linear sorption coefficient or
the partition coefficient for the chemical in this soil.

In general, the partition coefficient, Kd, depends upon the chemical and soil
properties. However, Hamaker and Thompson (1972) and Karickhoff (1981, 1984)
have shown that the partition coefficient for a particular organic chemical in
a soil, divided by the organic carbon content of that soil, is essentially
constant for a wide range of soils. That is

Kd = KOC'OC

where KOC is the partition coefficient normalized for organic carbon content
and OC is the organic carbon content of the soil. This relationship enables
one to determine the Kd value for any soil if the organic carbon content is
known for that soil and the KOC of the chemical is known. This equation is
used in this model for obtaining partition coefficients for different soils
and for different horizons within a given soil. However, if the user has
specific Kd values for the soil and chemical of interest, these values can be
entered for each horizon by choosing the manual entry option for Kd and half-
life (option G in the main menu).

Estimating the depth of the chemical involves estimating q for each day and
calculating the depth of the chemical on that day from the depth on the
preceding day and the change in depth for that day. The process is then
repeated for each day in the time period of interest.

Estimating the amount of water passing the depth of the chemical: In this
model, the amount of water passing the depth of the chemical is equal to the
amount of water entering the soil on that day minus the amount of water stored
in the soil profile above the depth of the chemical. The amount of water
stored above the depth of the chemical depends upon the wetness of the soil at
the beginning of the day and the capacity of the soil to store water. For each
day the following steps are carried out:

1. The water content above the maximum rooting depth of the crop is
adjusted for evapotranspiration. The amount of water removed from each
horizon in the root zone is assumed to be proportional to the relative
amount of water available for plant growth in that horizon. The water
content in each horizon may not decrease below the "permanent wilting
point" of that horizon.

2. The water content in the rooting zone is adjusted for infiltration.
Using the water content after adjusting for evapotranspiration as the
initial water content, the soil is recharged to "field capacity" until
the water supply is exhausted or the entire root zone is recharged. If
the chemical depth is less than the root-zone depth, the quantity of
water passing the chemical depth is noted while calculating the
recharge. If the chemical depth exceeds the root-zone depth, the
quantity of water passing the chemical depth is equal to the amount of
water leaving the root zone, since the soil below the root zone is
assumed to be at "field capacity" at all times.

Determining the new depth of the chemical: If the amount of water passing the
depth of the chemical is less than or equal to zero, the change in depth is
zero so the depth is equal to that of the preceding day. If the amount of
water is greater than zero, the chemical was moved by the infiltrating water.
The equation above for AdC forms the basis for calculating this change in
depth, but it must be applied carefully since R and 8FC change with each
horizon. Computational details for this calculation are given in Nofziger and
Hornsby(1986).

Determining the relative amount of the chemical in the profile: The relative
amount of chemical remaining in the soil profile j days after application, M-,
is calculated by means of the equation

Mj = Mj-.exp[-ln(2)/half-life]

where Mj-1 is the relative amount remaining on the preceding day, and half-
life is the degradation half-life of the chemical. At the time of application,

j-0, and MO = 1. If the half-life of the chemical changes with soil depth, the
half-life value used in the equation is that value for the horizon containing
the peak concentration of chemical. That is, the degradation of the chemical
is calculated as if the entire mass of chemical were located in the horizon
containing the maximum concentration of the chemical.

MODEL ASSUMPTIONS: Some assumptions have been made in the development of this
model. Here is a list of those assumptions and a brief statement of their
significance.

1. Chemicals move only in the liquid phase in response to soil-water
movement. The model ignores vapor movement. If the chemical volatilizes
readily, some of the chemical will be lost to the atmosphere. Thus,
estimates of the amount of chemical in the profile from this model will
likely exceed the-actual amount present.

2. The chemical pulse is considered to be of infinitely small thickness and
is actually taken as a point. Chemical pulses moving in soil tend to
become dispersed. This dispersion depends upon several factors,
especially the rate of water movement and the pore-size distribution.
Since these factors are not available a priori and they are not readily
computed, representation of dispersion in the model is not practical. As
a result, the model predicts the location of the peak of the chemical
pulse. Some chemical will also be present at greater and at lesser
depths.

3. The adsorption process can be described by a linear, reversible,
equilibrium model. If sorption is described by a nonlinear isotherm, the
partition coefficient decreases with increasing concentration of the
chemical. Thus, the depth to which the chemical will be leached will
depend upon the concentration. This aspect is probably not significant
for the range of concentrations of interest in agricultural
applications. If adsorption equilibrium is not instantaneous, the
chemical will be transported to depths greater than those predicted
here. If sorption is irreversible, the depth of the chemical will be
less.

4. All water residing in the soil pore space participates in the transport
process. Water present in the soil profile is completely displaced ahead
of water entering at the soil surface. If this assumption is not valid
and a portion of the water is bypassed by the infiltrating water, this
model would tend to underestimate the depth of the peak concentration of
chemical.

5. Water entering the soil redistributes instantaneously to "field
capacity". This assumption is approached for coarse textured soils. If
the water redistributes more slowly, as in the case of fine textured
soils, the depths predicted in this model for a particular day will be

somewhat overestimated or may be associated with a time a few days later
than the time specified.

6. Evapotranspiration removes water from each soil horizon in the root zone
in proportion to the amount of water available in that layer. No
provision is made for nonuniform root densities nor for root density
changes with time. This assumption will have little effect on calculated
changes in the depth of the chemical for depths greater than the maximum
rooting depth. It may tend to overestimate the depth of movement for
depths within the root zone, however.

7. Upward movement of soil water does not occur in the soil profile. Water
lost from the root zone by evapotranspiration is not replaced by water
from below. This assumption implies that the chemical does not move
upward in the soil during long periods without infiltration. As a result
of this assumption, the chemical depth predicted may slightly exceed the
real depth.

8. The half-life for biological degradation of the chemical is invariant
over time. Degradation-rate coefficients are dependent upon a variety of
environmental factors, so seasonal changes in degradation rates can be
expected. These variations are ignored in this model, since insufficient
data are available to formulate mathematical relationships describing
these effects.

REFERENCES

1. Hamaker, J.W., and J.M. Thompson. 1972. Adsorption. In Goring, C.A.I.,
and J.W. Hamaker. (ed.) Organic Chemicals in the Environment. Marcel
Dekker Inc., NY. pp. 49-143.

2. Karickhoff, S.W. 1981. Semi-empirical estimation of sorption of
hydrophobic pollutants on natural sediments and soils. Chemosphere
10:833-846.

3. Karickhoff, S.W. 1984. Organic pollutant sorption in aquatic systems. J.
Hydr. Eng. 110:707-735.

4. Nofziger, D.L., and A.G. Hornsby. 1985. Chemical movement in soil: IBM
PC user's guide. IFAS, University of Florida. Circular 654.

5. Nofziger, D.L., and A.G. Hornsby. 1986. A microcomputer-based management
tool for chemical movement in soil. Applied Agricultural Research
1:50-56.

6. Rao, P.S.C., J.M. Davidson, and L.C. Hammond. 1976. Estimation of
nonreactive and reactive solute front locations in soils. In Proc.
Hazardous Wastes Research Symp., EPA-600/9-76-015, Tucson, Ariz. pp.
235-241.

APPENDIX:

USE OF THE FULL-SCREEN EDITOR

Full-Screen Data Editor: Data may be entered and edited using a full-screen
editor as illustrated in Figures 11, 13, and 15. It is convenient to think of
each file as a two-dimensional table. The rows in the file are called
"records" and the columns are called "fields". The editor is designed to
permit the user to enter or edit data for any record or field. The user simply
moves the cursor to the record and field of interest and makes the desired
entry. Values entered are compared with the range of values permitted in that
field. If the value is out of range, a message is displayed and the user must
change the value before moving on. The software uses the cursor control keys
and the function keys to carry out the many diverse functions of the editor.
The following pages list various keys and their functions.

This key is used to move the cursor to the right within
the present field. If the cursor is located at the end of
a field, this key will move the cursor to the beginning of
the next field.

This key is used to move the cursor to the left within the
present field. If the cursor is located at the beginning
of a field, this key will move the cursor to the beginning
of the preceding field.

This key is used to move the cursor up one record.

This key is used to move the cursor down one record.

This key is used to move the cursor left one field.

This key is used to move the cursor right one field.

This key moves the cursor to the first record in the file.
The field is unchanged.

This key moves the cursor to the last record in the file.
The field is unchanged.

This key is used to move the cursor up 20 records (one
screen). The field is unchanged.

This key is used to move the cursor down 20 records (one
screen). The field is unchanged.

This key displays help information for the field being
entered.

Data may be entered by rows or by columns. This key is
used to select the preferred method of entry. The choice
determines the field to which the cursor moves after the
key is pressed.

This key is used to insert a new record into the file
providing that the new file size will not exceed the
maximum size allowed. The new record is inserted just
above the record containing the cursor at the time the key
is pressed. All records below this one are moved down to
make room for the new record. The new record is filled
with decimal points to indicate that no data have been
entered into this record.

This key is used to delete the record in which the cursor
is located. The number of the record to be deleted is
displayed at the bottom of the screen and the user is
asked to confirm that it should be deleted. After deleting
a record the number of records in the file is decreased by
one. Data in records below the one deleted are moved up.

Depressing this key causes the value in the field above
the cursor (i.e. the previous record) to be copied to the
field containing the cursor. This is useful when several
consecutive records in a file contain the same information
(e.g. soil name and identifier for all horizons of one
soil).

This key is used to write data stored .in random access
memory in a disk file. After saving these data, the user
may continue using the editor. Users should get in the
habit of saving data to disk regularly (approximately
every ten minutes) as a precaution against power failures
and other system problems.

This key saves the data on disk just as does key F9.
However, after saving the data, control returns to the
main menu.

This key is used to end data entry or editing of a
particular field. Characters to the right of the cursor
are dropped. If there are no characters to the left of the
cursor, the key does nothing. If the system is set
for entering by row (see above), the cursor is moved
right one field. If the system is entering by columns, the
cursor moves down one record.

This key is used to delete the character to the immediate
left of the cursor.

This key is used to delete the character at the cursor
location.

Pressing the key aborts the present option. Nothing
is written to disk, so the disk file remains as it was the
last time data were saved.

Decimal point If a user enters only a decimal point in a field, the
system considers this as 'no data'.

IMPORTANT: The user must exit from the editor using if the data entered
into random access memory are to be written on a disk file. Aborting by means
of the key does not save any of the contents of memory in a disk file.

Incdex

A
abort 9
assumptions 38
C
chemical parameters 7, 26
cursor keys 9, 41, 42, 43
D
data files
importing 32
default files 31
default values 9
E
Esc 43
escape key 9, 43
evapotranspiration 7, 13,
16, 30
F
file
chemical 31
soil 31
file names 9
file output 17
files
importing 32
file size
chemical 27
evapotranspiration 30
rainfall 28
soil 25
full-screen editor 41
special keys 41, 42,
43
function keys 9, 41, 42,
43
G
graphics
printer 6, 7
graph limits 31
graphs 17
H
half-life 15 26
for each Aorizon 15,
16, 31

hardware 6
help messages 9, 41
I
infiltration 28
L
linear sorption
coefficient 26
M
missing data 43
model assumptions 38
model description 5, 36
0
operating system 6
output device 17
IP
partition coefficient 15,
26
for each horizon 16
organic carbon 15, 26
printer 17
R
rainfall 7, 28
rooting depth 15
S
screen attributes 7
software
execution 8
soil parameters 7 23
special keys 41, 42, 43
T
tables 17
theory 36
U
units 14

44

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