Exercise 5 - Washington: Alfalfa Hay, Editing, and More Irrigation

Skill Building: In this exercise we will learn to simulate a forage crop cut for hay. We will add a year of alfalfa to the three year rotation. This will show the power of the editor. There are many ways to edit data using the copy-paste and increment and decrement groups of operations to move seeding dates. You will be able to understand the basic format to build other forage crop files based on this example. Irrigation can be added in preset amounts, added in a custom amounts, or applied as needed as the plant uses it. In this example we will model full irrigation and apply water as the crop uses it. Many circles on a quarter section of land (160 acres) have 120 acres "under the iron". For this example there is an end gun that turns on and off as needed when the circle turns. The producer can irrigate 10 more acres for a total of 130 acres.

Scenario: The producer is near Moses Lake, Washington in Grant County. The soil is a Quincy Fine Sand (Quincy_97_100_FS.ifc). The field has full pivot or circle irrigation. Potatoes are a high dollar cash rental crop and must be rotated with other crops for disease and nematode control. The rotation is Alfalfa 3 yrs-Potato-Winter Wheat. If the alfalfa stand is good and the price for hay is strong they will leave the hay for 4 years. The irrigated circle is 130 acres. The annual yield for the alfalfa crop is about 6-7 ton/ac cut 4 times with a 5th cut in some years. Alfalfa is cut on 30 day cycles. The potato yield is 30 ton/ac or (600 cwt/ac). The winter wheat yield is 100 bu/ac. The erosive wind comes in the spring from the west and tillage/planting direction is north and south.

WEPS can simulate crops that are cut multiple times in a growing season. However, forages can not calibrate biomass in the same way as grain crops. We will not calibrate the forage crop with WEPS. Calibration is very important for almost all other crops. Saving a calibrated crop to the local crop folder for use in future run can save run time on any subsequent runs. Each forage cutting yield that under-perform usually does not affect the erosion rate since there is more than adequate cover to shut down the erosion during a subsequent growing of a forage crop. So, if the hay yield is low, do not reject the run unless there is substantial erosion occurring in that 2 week management period.

Getting Started

Step 1: Make sure you are in the Student project. Set the "Shape" to Circle and the "Area" to 130 ac. Notice that the radius is 1343 feet, slightly bigger than the 1320 ft border to border of a 160 acre quarter section. In the location box set the state to Washington and the county to Grant. The field is near Moses Lake so we want to change the WINDGEN Station to Moses Lake/Grant Co. Leave the CLIGEN station set to Ephrata CAA AP.

Load a pre-made file by clicking the Man Template Folder button . Find the run called Alfalfa, fall seed, 3yr-Potato-WWheat, circle irr CMZ49.man, and load it into the management editor. Load the soil called Quincy_97_100_FS.ifc from the Soil Project Folder button .

Step 2: Make the run by clicking the management button on the main interface. Click the Yield Calibrate button button and check the yields for all the crops and make sure that all match the inventory (100 bu/ac, WWheat, 600 cwt/ac Potato, and 6.5 ton/ac Alfalfa). Also make sure you do not put a check mark in the "Calib. Yield?" column for the Alfalfa crop (Figure 1.60). The other crops will be calibrated if checked and the Alfalfa left unchecked will not be calibrated. Click the Return button to save and return.

Notice the way the alfalfa crop irrigation and harvests are modeled. Each hay harvest has an Irrigation, Start Monitor (Pivot, Linear, Wheelline); Irrigation, Stop Monitor; and Harvest, hay, legume operation associated with the harvest. The irrigation is stopped 7 days before harvest to allow the soil surface to dry out enough to help cure the hay.

Now, click 'Run' then 'Make a Calibration WEPS Run'. Name the run Alfalfa 3yr-Potato-
WWheat, circle irr CMZ 49. This file is a long 5yr rotation. It will take the computer several minutes to calibrate the 75 year run. If you were going to use these crops in future runs that were similar to this run, you should use the 'Save as...' button to store the 1.225 Biomass Adjustment Factor for wheat to a local record in the crops file. For now let's click 'Use in Current Project'. Look at the yields in the Run Summary (Figure 1.61).

WEPS can not calibrate each cutting of hay in a year but the average yield for all years can be adjusted by using the Biomass Adjustment Factor. In this example, adding up the yield in each of the three years gives 7.4 ton/ac in year 01, 8.6 ton/ac in year 02, and 8.7 ton/ac in year 03, for an annual average of 8.2 ton/ac yield of hay per year. Remember the reported yield was 6.5 ton/ac. WEPS can adjust the yield by dividing the expected yield by the observed (6.5 /8.2 = 0.793). Thus the new Biomass Adjustment Factor of 0.793 should provide an average yield close to the 6.5 ton/ac needed.

Make a second run using the new Biomass Adjustment Factor, but do not calibrate the run since we did that the on the first run and told it to use the factors in this project. Name the run the same with Adj added to indicate the yields were adjusted. By using the 0.793 factor for alfalfa we have an average alfalfa yield of 6.16 ton/ac, that is close enough to 6.5 (Figure 1.62).

The potatoes made 595 cwt/ac (about 30 ton/ac). The winter wheat made 104 bu/ac. This management file has been calibrated for this location and there is a Biomass Adjustment Factor for the potatoes, wheat, and alfalfa.

Potatoes have a high soil loss in Rotation year 5 of 30.3 ton/ac. Why is that?

Answer: Potatoes do not produce much residue and the harvest process leaves very little residue on the surface. The winter wheat grown behind the potatoes is seeded very late in the year and does not produce growth as is needed to control erosion. The average soil loss is 6.3 ton/ac.

Let's get back to the high loss on the Potato year.

What is the highest period of loss in the Potato year? Answer: 'Oct 15-31, 05'.

What is the soil loss? Answer: 11.2 ton/ac (Figure 1.63).

Why is it high? Answer: After potatoes, there is only a small amount of residue as flat mass (157 lbs/ac) and the growing winter wheat is small (77 lbs/ac Leaf and Stem Mass).

Why did the residue go up as the field was tilled and planted to wheat (75 lbs/ac to 183 lbs/ac)? Answer: 108 lbs/ac of the 4218 lbs/ac buried residue (779 lbs/ac buried potato residue + 3439 lbs/ac buried root mass) was resurfaced when planting the winter wheat.

Add in another year of alfalfa

The producer reports that sometimes he adds another year of alfalfa to the rotation if the hay market is promising and the stand of alfalfa is OK. In this part of the exercise we will use some of the editing power of MCREW.

Step 1: Close any of the report screens you have open. From the main interface open the management editor. Scroll down the operation list until you get to the 'Mar 15, 04', Irrigation, Start Monitor (Pivot, Linear, Wheelline). From there drag the mouse to highlight down to (not including) the Disk on 'Apr 10, 05'. The section should be blue now. Right click in the Operation column and select "Copy Row(s)". Now right click the Disk on 'Apr 10, 05' and paste the rows, by selecting "Paste Row(s)". You have now made a complete set of operations for year 4 of alfalfa. Note that the dates still have year 4 instead of year 5. Now with the group of cells still highlighted, right click the date column and select "Increment Year". Finally, highlight the Disk on 'Apr 10, 05' though the end of the file. Right click the date column and increment the year. The year should now be 06 for the potato crop year. We have added a year to the rotation so we must change the "Years in Rotation" box at the top of the editor screen from 5 to 6 (Figure 1.64).

Once you are sure all the dates are sequential and are correct click 'File', Save as...', and name the file Alfalfa, fall seed, 4yr-Potato-WWheat, circle irr CMZ49.

Step 2: We can now make the run without calibration since we have saved the previous run and added back to the management file the Biomass Adjustment Factors for alfalfa (0.793), potatoes (1.225), and the winter wheat (1.225). Name this run Alfalfa 4yr-Potato-WWheat, circle irr CMZ 49.

The results are shown in Figure 1.65. The erosion rate is now 5.0 tons/ac/yr, just at the Tolerable rate of 5 ton/acre/yr.