Exercise 2 - Texas: Add a Crop to a Rotation

Skill Building: This exercise will begin with a pre-built management file, make the run, then add another crop to the rotation in the management editor and then make the second run. We will also consider a strip tillage system to meet "T" and reduced tillage to address the erosion problem.

Scenario: The farm is located in Lubbock County, Texas. The CLIGEN station is Lubbock WB AP and the WINDGEN Station is Lubbock APT. The soil in the field is Amarillo Loamy Fine Sand, in the Student Project it is: Amarillo_4_100_LFS. The crop rotation is continuous Cotton, stripper. We think it is possible to add Milo or Sorghum, grain to the rotation. There is also some new technology from Texas A&M, using in-row subsoil planters for strip tillage that we would like to model for an alternative. The field is a half section of land (320 acres) and is oriented east and west. Normal yield for the Cotton is ¾ bale or 375 lbs lint/ac. Sorghum will yield an average 25 bu/ac. The Cotton management file we will use is: Cotton,Stripper;CT,FC,CMZ19.man. The mulch-till file we will add is: Sorghum,Grain;MT,CMZ19.man.

Getting Started

Step 1: Start up the WEPS interface and add the information listed above, except for the management. Be sure to show the field as a rectangle (simulation area as 5280 by 2640 feet) with the short side (Y-length = 2640 ft) on the east and west. See Figure 1. 30.

Step 2: Click the Template Folder button to display the managements in the project folder. Load the pre-built file called Cotton,Stripper;CT,FC,CMZ19.man by clicking selecting the File, then clicking "Select". Make the standard run as shown in Exercise 1 by clicking the Run button. Type in the Run name of Cotton, CT,FC,CMZ19 TX. Upon completion, the Run Summary will appear (Figure 1. 31).

The continuous Cotton run gave a 30.7 ton/ac/yr soil loss. How much cotton lint is listed? Answer: 631 lbs/ac/yr. The inventory states that we should have 375 lbs/ac lint. This is almost twice too much. Go back and calibrate the yield as you were shown in Exercise 1.

Step 3: Check the Yield in the MCREW (Management Editor) by clicking the 'Man' button in the lower left corner of the main interface. Second, click the Yield Calibrate button to change the editor view adding the yield columns. You may have to drag the window open a bit to see the yield column. Be sure to change the 500 lbs/ac default to 375 lbs/ac (Figure 1.32).

Notice that the Rotation name box is now blue with the word "(Modified)" appended to the end of the name. This means that you have changed the data in the original file and not saved it yet. When you click the 'Close' button , WEPS will save the file (same name) and move you back to the main interface. If you want to save it with a new name you must click "File", then "Save as..." and give it a new name. In this case we want to save it to a new name, called Cotton,Stripper;CT,FC,CMZ19 adj yield. The Rotation name returns to black text with the new name. Now return to the main interface by clicking the 'Close' button .

Step 4 - Make the run by clicking the Calibrate Run button , and append the word "Cal" to the end of the name: Cotton, CT,FC,CMZ19 TX Cal.

Notice we now have a new Biomass Adj. Factor of 0.766 (Figure 1.33). Click "Use in Current Project" then "OK". You should now have about 34.4 ton/ac/yr as your calibrated soil loss. Check to see if the yield is around the 375 lbs/ac needed.

What do you do when the soil loss is too high? Let's consider some options to lower the soil loss.

What is the total residue (flat mass) at planting time? Hint: Open the Detailed Report and check the total flat mass of residue at that time.

Answer: About 56 lbs/ac and 2% surface cover (Figure 1.34) are present at planting.

What management period has the highest erosion loss?

Answer: After planting the cotton (Jun 1-14, 01), 13.4 tons/ac (Figure 1.34).

How much total residue do we have to work with the first period after harvest?

Answer: The residue after harvest is 980 lbs/ac (20 lbs/ac flat mass + 960 lbs/ac effective standing mass) (Figure 1.34). We need more residue to effectively control the erosion. Cotton does not produce enough residue by itself. We will try adding sorghum to the rotation to see what effect this will have on the residue and erosion rate.

Add a Crop to a Rotation:

Close any of the report windows you have open until you only have the main interface window open. Click on the 'Man' button to open the MCREW management editor.

Step 1: Right click the last row in the second column (Operation Name) of the cotton file. Select 'Import Management File', then repeatedly click the up-directory button on the top toolbar until the 'projects' directory appears. Click 'projects' then 'Student.wpj' and select Sorghum,Grain;MT,CMZ19.man. Click Select.

Notice that the sorghum crop comes into the rotation in the second year and the dates are correct because both single management files have all their tillage in one year, (not 0 and 1 as with a RUSLE file) with fall tillage. The dates look right and seem reasonable. Be sure to click the and enter 25 bu/ac yield as expected for the new sorghum crop. Check that you still have 375 lbs/ac yield for the cotton also and that both "Calib. Yield?" boxes are checked.

Step 2: Notice the rotation name in the Rotation box is blue. We need to save the file with a new name.

Click 'File' then 'Save as...'. Notice MCREW has detected we only have "1" in the year box (Figure 1.35). We must either change the value in the box to something different than 2 or accept 2. Click 'OK' to accept the change to a 2 year rotation.

You are then asked for a new name for the two year rotation. Enter Cotton,Stripper;CT,FC-
Sorghum, MT CMZ19, and click 'Save'. Note that it saved the new two year rotation to the Student Project directory.

Step 3: Make the new run. This time let's see if WEPS will give us an appropriate yield for the sorghum in this rotation. Return to the main interface by clicking the Close button . Click the Run button and call the run Cotton,stripper, CT,FC-Sorghum, MT CMZ19 TX.

What is the soil loss?

Answer: You should see approximately 24 ton/ac/yr on the Run Summary (Figure 1.36) although your version of WEPS may display a different value. Average annuls soil loss is still too high!

What is the sorghum yield?

Answer: You should see approximately 14 bu/ac on the Run Summary (Figure 1.36).

Do we need to calibrate the sorghum?

Answer: Yes, 14 bu/ac/yr is not close enough to the 25 bu/ac/yr we were wanting.

Close the run summary and make another calibrated run by clicking the Calibrate Run button . Name this run Cotton, CT,FC-Sorghum, MT CMZ19 TX cal.

Notice we have a slightly different Biomass Adj. Factor for Cotton as well as a 1.300 for the Sorghum crop (Figure 1.37). Click, 'Use In Current Project' then 'OK'.

How much flat mass do we have now after planting Cotton on the detailed report?

Answer: Remember to click the Detailed Report . We have about 157 lbs/ac flat mass and the erosion rate is 6.6 tons/ac at cotton planting (Figure 1.38).

What is the date of the first erosion period after harvest of the sorghum?

Answer: After the Bedder, hipper, disk hiller, 'Mar 15-31, 01' at 2.5 tons/ac/yr (Figure 1.38).

The Average annual wind erosion of 24 tons/ac is still to high. Let's look a reduce tillage.

Reduce Tillage:

Let's try one last set of adjustments to our set of runs. We know cotton is glyphosate ready for weed control, and strip-till works for cotton. We also know that standing residue is twice as good at controlling erosion than flat residue. We will start with the last run and reduce some of the tillage. Close any of the report windows you have open, until you only have the main interface window open.

Step 1: Click the 'Man' button on the main interface. Check to see that you have the Cotton,Stripper;CT,FC-Sorghum, MT CMZ19.man file loaded. We are going to remove the 'Feb 15, 01' Chisel, sweep shovel, the Bedder, hipper, disk hiller, 'Jun 20, 01' and 'Jul 12, 01' two Cultivator, row 3 in ridge, and the 'Dec 1, 01' Shredder, flail or rotary operations. Right click on the operation name and select the next to the last selection on the menu "Delete row(s)". Do this for all the operation mentioned above.

Step 2: Now, change the standard planter for the sorghum from Planter, ridge till to Planter, in-row subsoiler. Do this by right clicking on Planter, ridge till and select 'Change Operation'. Double click 'NRCS' then select the Planter, in-row subsoiler operation from the list then click 'Select' (Figure 1.39).

Step 3: Add a spray operation on 'Jun 20, 01' for the glyphosate to control weeds in the cotton. Right click the "Harvest, cotton" operation and select "Insert Operation". Find and select "Sprayer, post emergence, in crop" so that it is now in the Operation Name cell. This operation adds 50 lbs/ac standing mass to the residue pool so you will need to click in the cell and enter 50 in the Flat Residue Amount column.

Lastly change the date of the sprayer operation from the 'May 20, 01' default to 'Jun 20, 01' by right clicking the date on the sprayer row. Select "Increment Month" and the date should now be 'Jun 20, 01' (Figure 1.40).

Save the new file as Cotton, stripper, ridgetill-Sorghum, mulchtill CMZ19, and close MCREW to return to the interface.

Note: In the future you may decide that a new management file is worthy of addition to what is known as the Local Management subdirectory. To do this, follow these steps: 1) Start with the edited and tested management file loaded in MCREW. It must have any Biomass Adjustment Factors to make the run for that locality where it will be used. 2) The location to save a Template Management Local file is C:\Program Files\USDA\WEPS\WEPS 1.0 (beta 20b)\db\man\NRCS\local. 3) Save the file by clicking 'File', 'Save as Template', and navigate to the above directory. Use the name you have given it or one consistent with any naming conventions you have chosen to use. 4) Then click 'Save'.

Note: NRCS field offices will have a file structure on the F:\WEPS Runs drive to store the Local Records. The user will have to create a subdirectory to store runs for an individual farm or customer. This will allow the local work group to have access to any locally made records.

Step 4: Make the run and call it Cotton, stripper, striptill-Sorghum, mulchtill CMZ19 TX. It is not necessary to calibrate the sorghum since it produced a 29 bu/ac yield in the last run, which is close enough to the desired 25 bu/acre yield.

This run shows that it is possible to meet the soil loss tolerance of 5 tons/acre/year using a cotton-sorghum rotation (Figure 1.41). Leaving the cotton stalks standing is very effective at controlling wind erosion. Looking at the Detailed Report shows there is over 650 lbs/ac flat mass and 20% flat cover of sorghum residue after planting cotton, and over 630 lbs/ac flat mass, 19% surface cover of cotton residue after planting sorghum.