Exercise 1 - Wisconsin: A Basic Simulation

Skill Building: This example introduces basic skills needed to perform a simple wind erosion simulation. It uses the rotations saved in the NRCS CMZ (Crop Management Zone) Management Files.

Scenario: The farm is located near Stevens Point, Wisconsin, in Portage County. The CLIGEN station is Stevens Point and the WINDGEN station is Wausau/Alexander. The Soil Map Unit used in the evaluation is Mecan_MfB_100_LS. The original two-year cropping system is Peas, green, drilled and Bean, green snap mech harv. The field size is about 126 acres. The WEPS evaluation of the cropping system will be run for 15 rotation cycles (NRCS mode). The fields are fully irrigated with a circle system.

Getting Started: First, load the project called Student into the main interface. In the WEPS interface: Click "Project" then "Open". Click the project directory named Student.wpj and click "Open" (Figure 1.19) . You may be asked to save the current project, if so click "Yes". Now you should have the Student project loaded into the interface.

Fill in the following interface sections:

Step 1: Under the Simulation Run Information panel, for Client Name enter Exercise 1.

Step 2: Under the Simulation Region Information panel, for Shape select Circle by clicking the down arrow next to 'Shape' and for 'Area' enter 126 ac.

Step 3: Under the Location Information panel, for 'State', select Wisconsin; for 'County', select Portage. You should see the following weather stations listed; CLIGEN Station: STEVENS POINT; WINDGEN Station: MOSINEE/CENTRAL WI. Since the scenario calls for a WINDGEN station of Wausa/Alexander click the down arrow next to Mosinee/Central WI to display the list of nearby stations. Select WAUSAU/ALEXANDER.

Step 4: Click the "Template" button next to the "Man" button near the bottom of the WEPS screen. For these exercises, beginning management files have been placed in the Student project directory. From the list, select: Peas, green, drilled, st pt, disk, fcult,-Bean, green snap, st pt, disk, fcult, CMZ4.man. Note: the management files are displayed with a management symbol in front of them. The crop management file name will be displayed near the bottom of the WEPS interface.

Step 5: Click the "Project" button next to the "Soil" button near the bottom of the WEPS screen. Select the Mecan_MfB_100_LS soil. Note: the soil files are displayed with a soil symbol in front of them. When selected, the soil name will be displayed near the bottom of the WEPS interface. Also note: Most of the time you will use the Template button to select a soil from the SSURGO survey database. It is the file with .mdb extension. If connected to the internet, you can click the SDMDataAccess.nrcs.usda.gov.db file and load the file straight from the NRCS Soil Datamart.

Simulation Run:

All required information has now been entered (Figure 1.20 ). Make sure that you have set the directory configuration to the correct place to save your runs. On the main interface, click 'Configuration' then 'Directories'. Now type "C:/F Drive/WEPS Runs" in the Runs Location box or use the yellow folder to select the run location (Figure 1.22 ). If you change the location(s), click "Save" and then "OK" to save the configuration settings and leave the configuration screen.

To begin the simulation run, click the "Run" button . WEPS will ask you to enter a name for the run, type in Peas, green-Beans, green, irr, CMZ4 and Click "OK" (Figure 1.23).

During a simulation run, a window will appear that shows the simulation progress. Upon completion the WEPS Run Summary report window will appear (Figure 1.24). The simulation reports an Average Annual soil loss of 1.0 tons/ac/year. Since crop residue (correlated with crop yields) can affect erosion, the user should check to see if yields are as expected. Expected yields for this area are 3400 lbs/ac for peas and 8100 lbs/ac for the beans. However for this example, WEPS calculated 18612 lbs/acre for peas and 7880 lbs/acre for the beans (see Figure 1.24). Since these yields are more that 5% different for both crops, the run needs to be calibrated.

Calibration:

WEPS can recalculate the crop growth based on the actual yield history of the field we are evaluating. This is called "Calibration" of the crop and adjusts the Harvested Yield simulated to within 5% of the expected or historic yield entered. To calibrate the example run, close the Run Summary and the main interface should be displayed.

Step 1: On the main screen, click the "Man" button to open the Management Crop Rotation Editor for WEPS (MCREW). MCREW displays a date ordered list of all management operations and crops for the rotation (Figure 1.25). A more detailed explanation of MCREW use will be covered in later exercises. For now, click the Yield Calibrate button on the tool bar. This displays seven additional columns; the first three pertain to the target yield and calibration. The target yields can be edited on this screen. Remember, the target yield is 3400 lbs/ac for peas and 8100 lbs/ac for beans. Enter these yields on the MCREW screen. By clicking the Yield Calibrate button we have set WEPS to run in Calibration mode and the yields we want are the default values. Click the Return button to close MCREW and return to the main WEPS screen.

Step 2: On the main interface screen, click "Run" then "Make a Yield Calibration WEPS Run", or you can click the Yield Calibration Run button on the main toolbar.

You will be asked to enter a Run Name. The default Run Name is the last run name plus an incremented number appended to the name (in this example "_1" is appended). This time you should back space to remove the "_1" and add the word "cal" to the end of the name and click "OK" (Figure 1.26).

WEPS now displays a table showing two Calibration factors, one for peas and one for beans (Figure 1.27). For WEPS to produce the expected pea residue for this farm, yields need to be reduced from 18612 lbs/ac to 3400 lbs/ac. Therefore we would expect the factor to be less than 1.0 and the Biomass Adjustment Factor is 0.281. Likewise the beans need slightly more yield, hence the 1.0 value, increasing the yield by 15%. You can do three things with this screen. One, you can use both these factors for all peas and bean run in this Project by clicking "Use in Current Project". Or two, clicking "Project" then "Save as..." allows you the save a localized version of the crop file to the local subdirectory in the crop database for use with another local field. Or three, click "Close" to use the factors only in the current run. For this exercise we will click "Use In Current Project". WEPS will then display a message that "The current project is now using the calibrated management file."

Upon completion, the WEPS Run Summary report window will appear (Figure 1.28). The simulation reports an Average Annual Gross Soil Loss of 3.6 tons/acre. This is below the T-
value (Soil Loss Tolerance) of 5 T/ac/yr. Note that the Biomass Adjustment Factors appear in the "Notes" box near the bottom of the Run Summary report.

Is the percent ground cover and mass of flat residue after seeding adequate to protect both crops?

Hint: Click the Detailed Report button at the top of the Summary Report. Near the top of the Detailed Report is a window that allows the user to "Select Report". This should display "Erosion & Crop Veg, Res & Biomass (details)" as default. If not select it from the drop down list by clicking the drop down arrow . The Detailed Report includes a date ordered list of output parameters by periods (every 15 days or the period between management operations). This detailed report allows the user to view the amount of cover and flat residue after seeding each crop (Figure 1.29).

By examining the Detailed Report table you will note that Bean residue after planting Peas (Date: Apr 25-25, 01) was 6% (0.06 fraction) surface cover and 105 lbs/ac flat mass. These amounts provide enough protection that WEPS estimates an average total gross soil loss after planting to be 0.0 tons/acre. Therefore the probability of damage to Peas by blowing soil is very low.

However, the Pea residue after planting Beans (Date: May 16-31, 02) was 3% surface cover and 46 lbs/ac flat mass (Figure 1.29). For these residue amounts, WEPS estimates an average total gross soil loss after planting of 1.5 tons/acre. Although the soil loss is less than the T-value, there is a problem with 1.5 ton/ac soil loss the first 15 day period after planting beans. The NRCS National Agronomy Manual has a Crop Tolerance to Blowing Soil table that lists Green/snap beans in the "no more than 1 ton/ac" low tolerance column (See the table in the Exercises Introduction). This means that there still could be an issue with the system from the plant protection perspective.