ET-Based Irrigation Scheduling Tool
for Kansas Summer Annual Crops
Gary A. Clark,
Danny H. Rogers, and Steven Briggeman
KanSched Audio Help Files
Introduction TOP OF PAGE
KanSched is a program that is designed to help monitor the root zone soil profile water balance and schedule irrigation events on a field using evapotranspiration (ET) data. The program can also be used to monitor the soil profile water content of non-irrigated fields. ET-based irrigation scheduling is a tool that can help you determine when and how much irrigation water to apply. The basic process involves using data on crop water use (crop evapotranspiration or ETc), rainfall, and soil water storage to assess when an irrigation event is needed and how much water could be applied.
This program was developed as part of the Mobile Irrigation Lab, which is supported by a partnership between K-State Research and Extension, the Kansas Water Office with State Water Plan Funds, Kansas Water Resources Research Institute, and the Kansas Corn Commission.
General Overview TOP OF PAGE
Irrigation scheduling that uses evapotranspiration (ET) information is much like checkbook accounting procedures where the valued commodities are tracked. In this case, soil water, rather than money, is the valued commodity and the debit is crop water use while credits are rainfall and irrigation. One notable difference is that the water balance can be too high as well as deficient. ETc, short for crop evapotranspiration, is the amount of water that a crop withdraws from the soil water reserve. Deposits to the soil water reserve are rainfall and applied irrigation. The major goal of the accounting procedure is to help the irrigation manager keep the amount of water in reserve above a minimum soil water balance level to prevent water stress to the growing crop. The upper limit to the account is the amount of water that can be physically stored in the root zone area of the soil profile. Deposits of water, once the upper limit is exceeded, result in the water being lost as either deep percolation or surface runoff.
Irrigation scheduling can help minimize deep percolation losses, although even the most rigorously followed schedule cannot prevent all losses since large rainfall events can exceed soil water storage capacity by themselves. The benefits of irrigation scheduling generally translate into increased net returns through several possible avenues. Irrigation scheduling may also reduce irrigation labor and equipment operation pumping cost, and may also result in improved yields due to less water stress or less loss of fertilizer due to leaching.
One of the major obstacles to adoption of on-farm irrigation scheduling has been the time management problem of gathering, processing, and implementing scheduling on a daily irrigation cycle period. Computer technology presents the opportunity for information gathering, transferring, and processing to be done much more easily, efficiently, and sometimes automatically. Scheduling software, communication, and control technology exists that can provide management recommendations which could then be remotely implemented. This manual will help to step you through the KanSched program, input windows, and help screens.
The Start Screen TOP OF PAGE
Each time you
start KanSched, you’ll begin with the screen pictured in Figure
1. From this point, you have several options to choose from depending
on how you want to use the program. The following sections will describe
each of these options in detail and how you can use them to your advantage
when using KanSched.
Figure 1 – The start screen of KanSched
Menu Bar TOP
At the top of each window in KanSched is the menu bar. The start screen’s menu bar has three main menus: File, Information, and Demo. The File menu simply offers an Exit option for quitting KanSched; although, you can always exit KanSched by clicking the button at the top right corner of the KanSched window. The Information menu provides two choices: Contact Information and Credits and Version Information. The Contact Information and Credits option gives you the names and phone numbers of individuals who can assist you with any KanSched related questions you might have. The Version Information option displays the version number of the KanSched program you are running. The Demo menu allows you to use a demo field that is fully functional with all field and weather information pre-entered, making it easy to quickly become acquainted with the functions of KanSched.
Start a new field TOP OF PAGE
To initialize a new field,
click the green button labeled “Start a new field”. A new
window will appear displaying the input boxes for the initial field information
and soil information (Figure 2). The input screen will be discussed in
detail later on in this manual.
Figure 2 - The input data screen of KanSched
ET TOP OF PAGE
quickly enter daily reference ET data for a group of fields that are in
the same region, click the green button labeled “Quick ET Update.”
The Quick ET feature makes the daily process of updating your fields’
reference ET values quick and easy. When you click on the Quick ET Update
button, you’ll see the window in Figure 3. Select the desired ET
Field Group (the process of creating an ET Field group will be discussed
later in the manual) from the list. When a group is selected, the fields
within the group will be listed in the “Fields in this group”
list. On the right side of the window you’ll see the input boxes
for the daily reference ET values. Simply enter the required reference
ET values and all of the fields in that ET field group will be automatically
updated. Be sure to click the green “Save Group ET Data” button
to save the reference ET info that you just entered.
Figure 3 – The Quick ET update screen
ET Field Groups TOP OF PAGE
Fields that you enter in KanSched can be grouped together according to their source of reference ET data, making it quick and easy to make one daily ET entry for the entire group. By clicking the “View ET Field Groups” button, you can view each group you created, along with the fields they contain. A sample of the ET Field Groups screen is shown in Figure 4. As you can see, there are two field groups, East Group and West Group. The East Group contains one field, called Demo Field. The West Group also contains just one field, called Demo Field #2. If any fields existed that were not associated with a field group, they would be listed in the “Individual Fields” section.
Also available from
the Field Groups screen are the options found just below the list of field
groups: Create a new group, Rename this group, and Delete this group.
These options will be discussed in detail later in this manual.
Figure 4 – The ET Field Groups screen
an Existing Field TOP OF PAGE
Sometimes while using KanSched,
you will want to delete a field. This option is available throughout the
software, as well as on the Start screen. Clicking the “Delete an
existing field” button will display the window shown in Figure 5.
The deletion process is described below the list of fields. When you’re
finished, simply click the Done button or close the window. Remember,
once a field is deleted, it cannot be recovered!
Figure 5 – The ‘Delete a Field’ screen
Information Into KanSched
TOP OF PAGE
Before KanSched can begin tracking the field’s soil water content and crop water usage, you need to provide it with information about the soil type, growing season, and crop for each field. The following sections will guide you through the input entering process required to begin using KanSched. This section starts with the main Input screen, the first screen you see when starting a new field or opening a previously created field.
The Input Screen TOP OF PAGE
The Input screen (Figure 2) requires some information that characterizes the soil type, growing season, and crop type for a field. All of the inputs on this screen must be entered before KanSched can track your field’s soil water content and crop water usage. If some of these values are unknown to you, simply click the question mark button in the lower right corner of the screen. After pushing this button, the help options will be enabled and you will see three horizontal blue bars appear behind the sections that have a help section. To get help with any of those sections, simply click on the question mark button associated with each section. Help screens are available for soil characteristics, crop growth characteristics, and crop coefficients.
The following section will describe each input required:
or ID: TOP
Soil Available Water
Holding Capacity and Soil Permanent Wilting Point:
TOP OF PAGE
Figure 6 – The Soil Help Screen
Date: TOP OF PAGE
KanSched needs to know the emergence date of the crop in order to start tracking water usage. The emergence date is simply the date your crop emerges from the ground after planting.
Date to Start the Water Budget: TOP OF PAGE
The water budget start date is the date that KanSched will actually start tracking the soil water content. This date must be after the emergence date.
Root Depth on the Start Date: TOP OF PAGE
KanSched tracks root growth throughout the season. In order to do this, it must know the root depth on the date it starts the water budget. This can be determined by going out to the field on the start day and dig around the crop to measure the root depth. As an early season guess, use 6 inches.
Maximum Managed Root Zone: TOP OF PAGE
Entering a maximum managed root zone lets KanSched calculate the maximum depth of the soil profile that your crop can draw water from. While the actual root depth may be deeper, this value is the managed depth for the crop’s roots. Normally, managed root zone depth is 3 to 4 feet unless the root-depth is limited by restrictive soils.
Date the Crop Canopy Cover Exceeds 10% of the field area,
The above dates are required by KanSched in order to monitor the growth
stages of the crop and to create a crop coefficient curve. If you need
assistance with calculating these values, simply enable the help options
and click the question mark button in this section. The Date Help screen,
shown in Figure 7, will automatically calculate these dates. Select the
crop type, enter the season length and emergence date, then press the
Calculate Values button. The calculated values are displayed at the bottom
of the screen. Click the “Use these values on the input page”
button to automatically enter these values on the input screen; however,
they can be adjusted later if needed.
Figure 7 – The Crop Date Help Screen
The Maximum Crop Coefficient, and
The Final Crop Coefficient: TOP OF PAGE
To determine how much water
the crop is using, KanSched uses crop coefficients. The crop coefficient
changes over the season; starting very small, increasing as the crop grows,
peaking at the beginning of reproduction, then declining as the plant’s
water usage stops with maturation. To gain assistance with calculating
these values, enable the help options and click the associated question
mark button. The Crop Coefficient Help screen is shown in Figure 8. Select
your crop type from the dropdown list. If necessary, select your reference
ET system if it isn’t a grass based reference. Because crop coefficients
are adjusted according to different reference ET bases (grass or alfalfa),
you need to determine and then select the appropriate reference ET system.
This information should be available from your automated weather station
or reference ET information source.
Figure 8 – The Crop Coefficient Help Screen
Allowed Deficit (MAD): TOP OF PAGE
The Management Allowed is the percentage of the available water in the soil that will be removed by the crop before you decide to irrigate. The MAD value will vary across different crops and according to how risk adverse you are as a producer. For high value crops, the MAD may be 40 percent or less. For lower value crops, the MAD may be 60 percent. A MAD of 50 percent is reasonable for most row crops.
Before KanSched starts tracking your soil water content, it must have
an initial value to start with. The initial soil water availability is
the percentage of available water to the crop on the budget start date
entered earlier. A value of zero (0%) is associated with the permanent
wilting point water content while a value of 100% represents a full profile
at the field capacity level. KanSched defaults to 100%, but this value
usually needs to be changed to reflect your initial soil water value.
Budget Screen TOP OF PAGE
The Budget screen (Figure 9)
consists of rows of input for each day. These inputs include reference
ET, rainfall, and gross irrigation. When these inputs are entered into
KanSched, it can track the soil water that is available to your crop.
The following sections describe the individual inputs needed and the program’s
Figure 9 – The Budget Sheet
ET TOP OF PAGE
The reference ET values can be obtained from on-site measurements or from an automated weather station in your county or region. This value needs to be entered for each day of the season as KanSched tracks the water content. However, you can also enter the ET values from several days at one time. The reference ET can also be updated using the Quick ET button from the start screen.
Crop ET TOP OF PAGE
After the daily reference ET value is entered, KanSched will calculate and display the crop ET. This value is the amount of water (in inches) your crop used during each of the listed days. KanSched uses the crop coefficient values and the reference ET values to calculate the crop ET value.
Rain TOP OF PAGE
Whenever the crop receives rainfall, enter the value for the appropriate day in KanSched. This value will then be used to calculate your soil’s current water content. Rainfall is entered as a previous day value, as reference ET. So, if it rains on May 29th, enter that rainfall amount in the ‘Rain’ input cell for May 30th.
Gross Irrigation TOP OF PAGE
Input gross irrigation amounts into KanSched every time you irrigate your crop. You will notice that this is a gross irrigation amount. At the top of the budget sheet (Figure 9) is an input box labeled Irrigation System Efficiency. By default, a value of 100% is entered, meaning that KanSched uses the exact value entered into the Gross Irrigation box. If you know the efficiency of your irrigation system, you can enter it in the box at the top of the budget sheet. Then, each Gross Irrigation value will be recalculated to a Net Irrigation value (e.g. if you set the irrigation system efficiency at 80% and you enter 1.0 inch in the gross irrigation box, KanSched will use the Net Irrigation amount of 0.8 inches). Most sprinkler systems will have system efficiency values that range from 80% to 90%. If you are unsure, try 85%.
Measured Soil Water Availability TOP OF PAGE
KanSched gives you the option of entering your own value for the Soil Water Availability. KanSched tends to be a conservative estimate of soil water. Therefore, if KanSched is indicating that the soil is drier than it actually is, you can simply enter a new value for the soil water availability, automatically recalibrating KanSched to the accurate field-based values.
Calculated Soil Water Availability TOP OF PAGE
KanSched’s calculation of the available water in the soil is displayed in the Calculated Soil Water Availability column. This value can be defined as the percent of water that is available for the crop to use from the available water profile. When this value drops below your MAD value, the Calculating Soil Water Availability numbers turn red, alerting you to the current situation. A value of zero (0%) represents PWP while 100% represents field capacity.
Available Soil Water Content Above PWP TOP OF PAGE
Another way that KanSched interprets the soil’s current water content is in the Available Soil Water Content Above PWP column. This figure gives you an estimate of approximately how much water is in the soil that your crop can use before it enters the permanent wilting point (e.g. if the Available Soil Water Content Above PWP value is 1.5 inches, this means that 1.5 inches of water is available in the soil for the crop to use). Keep in mind that when the water content reaches the MAD value, crop stress is beginning to occur.
Root Zone Water Deficit TOP OF PAGE
How much water will it take to fill the soil profile to full capacity? The Root Zone Water Deficit value answers that question by displaying how much water (in inches) the managed root zone soil profile needs before the water would be lost either to runoff or deep percolation.
Effective Rain TOP OF PAGE
How does KanSched handle rainfall events on a soil that is already at field capacity? Basically, when the soil profile is at field capacity, any water that is applied to the field will either run off or be lost in the soil through deep percolation. KanSched keeps track of the soil’s current profile status and will ignore any rainfall or irrigation events that occur on the soil when it has reached field capacity. This ensures that the program won’t credit the soil with more water than it can hold when it receives many rainfall events (or one large rainfall event) in a short period of time.
The summary screen (Figure 10) gives you a snapshot of the current total
season amounts for your crop. You can get total reference ET, crop ET,
rainfall, effective rainfall, gross irrigation amounts, and net irrigation
amounts. A periodic check-up on this screen will let you know your current
water-use statistics at a glance. As shown in Figure 10, even though actual
rainfall was recorded as 2.00 inches, the field soil profile must have
been wet and only 0.04 inches was effective.
Figure 10 – The Summary Sheet
Water Chart TOP OF PAGE
One of KanSched’s most useful features is the Soil Water Chart, shown in Figure 11. This chart shows a visual representation of the field soil water content as it changes throughout the season. In addition, each rainfall and irrigation event are displayed at the bottom of the chart. The horizontal axis of the chart is labeled with the dates of the crop season, while the vertical axis is in units of inches of water contained within the defined soil profile. Before fully utilizing the Soil Water Chart, one must understand how to read the chart. The following section describes each component of the Soil Water Chart.
The Soil Water Chart has the ability to get detailed information about any point on the chart. Using your mouse, position the cursor arrow and click on any line or column in the chart to get information about that point. This is an easy way to see how much rain or irrigation you received on a particular day, without having to scroll through the budget page to find the information.
Figure 11 – Soil Water Management Chart
Storage at Field Capacity-
TOP OF PAGE
The dark blue line that forms the upper boundary of the chart is called the Soil Water Storage at Field Capacity line. This line represents the total amount of water that your soil can hold before runoff or deep percolation occurs. This line also represents a water availability value of 100%. This value is determined using the soil characteristics from the input screen and the depth of the root zone, as are the PWP and MAD values described next.
Soil Water Storage at PWP- TOP OF PAGE
The dark red line that forms the lower boundary of the chart is called the Soil Water Storage at PWP line. This line represents the moisture content of the soil where plants are unable to pull the water from the soil, causing them to wilt and die. This line also represents a water availability value of 0%.
Soil Water Storage at MAD-
TOP OF PAGE
TOP OF PAGE
Gross Irrigation- TOP OF PAGE
Each irrigation event is represented by a dark blue column on the date the irrigation was received. The height of the column reflects the amount of the irrigation event.
Using ET Groups with KanSched TOP OF PAGE
Often times, you will be managing many fields within KanSched that all require the same daily reference ET value. If all of your fields are within the same general area where you get your daily reference ET value, you can place all of your fields into one ET Group. Managing multiple fields in KanSched is an easy task with the use of ET Groups. Initially, every new field is identified as an Individial Field, meaning each field’s reference ET values are unique to that field alone. Basically, once you create an ET Group and add your fields to the group, each field’s daily reference ET values can be automatically updated by entering the value just once. The following section will describe how to create an ET Group, place your fields within the group, and update the daily reference ET for the group.
Creating an ET Group TOP OF PAGE
You can create an ET Group and place fields within that group any time during the season. However, you may find it easiest to create an ET group for your fields at the beginning of the season. The following steps will guide you through the ET Group creation process.
1.) Start KanSched and select Start a New Field from the menu on the start screen (Figure 1.)
2.) Select the Create a New Group from the Field ET Info box on the right side of the main input screen.
3.) The Create a New ET Group window will now
be displayed on your screen (Figure 12). Enter a name for your ET Group
in the box labeled New Group Name. Give the group any name you want; however,
it’s handy to name the group according to the region it represents
(i.e. fields from the eastern part of your production area could be placed
in a group called Eastern Group, or the name may be associated with a
specific weather station). Once you have entered a name, click the Create
this new group button.
Figure 12 – The Create a New ET Group window
|Your new group will
appear in the Field ET Info box on the main screen. When you create a new
field, or open another field already created, you can simply click on the
ET Group from the list to assign the field to that group.
*If you have already entered reference ET data into a field and try to
assign that field to a new ET Group, the following window will appear
Figure 13. Change ET Group Screen
|Since the field has never been in an ET Group, it was assigned the Individual Field status, this window (Figure 13) appears. To place the field into the new ET Group (in this example, Demo Group), click the Yes button. If the field already contains some reference ET values, the window in Figure 14 will appear. To have the new ET Group copy the existing reference ET values from the field, simply click the Yes button. This feature is convenient if you create the ET Group halfway through the season and do not want to reenter every value, you can simply have the group copy the values from an existing field. If the No button is pushed, the new ET Group will not have any reference ET values associated with it and any existing reference ET values in the field that is being placed into the group will be erased.|
Figure 14. Copy ET Values Screen
ET Field Groups TOP OF PAGE
As mentioned earlier, you can view, rename, and delete ET Field groups from the View ET Field Groups button on the start screen, or from the ET Field Groups menu at the top of the main screen. It is important to note that when you delete an ET Field Group, the fields within the ET Field Group are NOT deleted! They are simply reassigned as Individual Fields, using their own reference ET data instead of the group’s data.
To enter daily reference ET values, review the section entitled Quick ET .
Extra Features in KanSched TOP OF PAGE
KanSched has several built in utilities to increase the functionality
of the program. The following section will describe each of these utilities.
Archiving a Field TOP OF PAGE
When you have completed one season and you are ready to start entering data for the next season, you can begin a new season for the same field without having to create a new field or delete the old data. Archiving a field is easy. At the end of the crop season, or before you start entering data for the next season, select Start a New Season and Archive Current Season from the Options menu at the top of the main screen. Archiving safely stores all of your field’s information and can easily be recalled for viewing by selecting View an Archived Field from the Options menu. Once your field is archived, KanSched automatically prepares your field for a new season by advancing all of the dates by one year. Obviously, those dates are likely to change, as well some of the other inputs. You will need to double check all of the field input information to ensure it still reflects your crop and season information.
Export Season Data to Text File TOP OF PAGE
If you are familiar with using spreadsheets to analyze data, you will find KanSched’s Export Season Data to Text File very useful. This feature is found in the File menu at the top of the main screen, under the item Export Season Data to Text File. When you select this option, you will be given the option of where to save the text file. After designating where you want to save it, and the name of the text file, KanSched will automatically generate a fixed width text file with all of the daily season values (Date, Reference ET, Crop ET, Rain, Gross Irrigation, Measured Soil Water Content, Calculate Soil Water Content, Root Zone Water Deficit, and Effective Rain). This text file can then be imported into any spreadsheet program you desire to use.
Still Have Questions? TOP OF PAGE
If you have a problem operating KanSched, or another KanSched related
question, you can check with your local county extension agent. Many agents
are familiar with KanSched and can refer any questions on to the MIL Team
members for you.