Exercise 7 - New Mexico: Irrigated Corn Silage, Add Manure and a Winter Forage Crop

Skill Building: In this exercise we will start with a blank management and add the operations from scratch. Corn silage is a low residue crop from the wind erosion standpoint because most of the biomass is harvested. We will add manure from a dairy and add winter wheat, cut for silage in the spring.

Inventory: The location of the dairy is in Curry Co., New Mexico, just south of Clovis. The correct CLIGEN station is CLOVIS 13N, and the correct WINDGEN station is CANNON AFB/CLOVIS. This field is an irrigated half circle on the west half of a quarter section of land. It is 62.7 acres (see soils maps in Figures 1.79, 1.80, 1.81). The soil is an Amarillo loamy fine sand: Amarillo_AnB_85_LFS. The producer has a Compressive Nutrient Management Plan that requires him to apply 15 ton/ac of very dry manure, 25% moisture by weight (15 tons/ac x 2000 lbs/ton = 30,000 lbs/ac wet wt. or 30,000 lbs/ac x 0.75 = 22,500 lbs/ac on a dry weight basis). The option of fall application exists since there is no surface or ground water near the dairy and little rainfall runoff over the winter. Spring application fits the work schedule. A Low Elevation Spray Application (LESA) nozzle package on the pivot can meet the Consumptive Use of both crops, corn and winter forage.

The field wet weight yield for the corn silage is 23 ton/ac at 65% moisture. The wet weight for the winter wheat silage is 7 ton/ac at about 70% moisture.

Table 1.2	System operations for corn silage alone.

Date	Operation	Crop	Flat Residue Amt Added (lbs/ac)
May 1	Manure spreader, solid and semi-solid manure, semi-solid	22,500
May 15	Disk, offset, heavy
May 18	Cultivator, field 6-12 in sweeps
May 20	Planter, double disk opener	Corn, silage
May 21	Irrigation, Start Monitor (Pivot, Linear, Wheelline)
Sep 1	Irrigation, Stop Monitor
Sep 20	Harvest, silage
Sep 25	Disk, tandem heavy primary operation

The amount of residue added (22,500 lbs/ac) contains some fairly fine, quickly decomposable organic material. This organic material will have a long-term impact on soil quality.

Table 1.3	Additional operations for the winter wheat silage.

Date	Operation	Crop	Flat Residue Amt Added (lbs/ac)
Mar 1	Irrigation, Start Monitor (Pivot, Linear, Wheelline)
Apr 12	Irrigation, Stop Monitor
Apr 12	Harvest, silage
Oct 3	Drill or airseeder, double disk	Wheat, winter silage

Let's get started by making a run where no manure is applied.

Step 1: Enter all the information listed above on the main interface. In the Simulation Region Information box under the Shape pull down, select the 'Half Circle VW' to indicate the vertical west half of a circle. Enter the 62.7 acres from the digitized soils map (Figures 1.79, 1.80, 1.81). In the soil section, click the 'Project Folder' button and select the Amarillo_AnB_85_LFS.ifc soil.

Step 2: Open up the management editor and enter all the operations listed above (Table 1.2) one at a time (Figure 1.73). This will give you a feel for why it is a good idea to create a template for most of the management systems that are commonly used in your area. Click 'File', 'Save as...', and call it, Corn, silage, conv, no manure, pivot CMZ19.man. Click the Return button to leave the editor.

Step 3: Click the Run button and call the run Corn, silage, conv, no manure, pivot CMZ19.

What is the yield of silage? Answer: 20.2 ton/ac (Figure 1.74). This is close enough to the 23 ton/ac mentioned in the inventory.

How much soil loss was calculated? Answer: >100 ton/ac (Figure 1.74).

Add Manure in the Spring

Step 1: Open the management editor and right click the operation cell on the first line, click 'Insert Operation' and select Manure spreader, solid and semi-solid. Set the date to 'Apr 1, 01'. Now in the Crop or Residue column, select manure, semi-solid. Move to the Total Manure Applied column, and type in the 22,500 lbs/ac manure applied in the spring (Figure 1.75). Now, click 'File', 'Save As...', and save the file as Corn, silage, conv, spring manure, pivot CMZ19.man. Finally, click the 'Return' button to return the main interface.

Step 2: Click the Run button on the main toolbar to make the run. Call it: Corn, silage, conv, spring manure, pivot CMZ19.

What is the soil loss with the manure applied in the spring and tilled in? Answer: 85 ton/ac (Figure 1.76).

When and where are the high erosion trouble spots? Answer: March is the big month with 40 ton/ac occurring in March, just before the manure is applied. March also has a large value for the Wind Energy at 6,069 KJ/m2/day and the lowest Flat Mass at 226 lbs/ac (Figure 1.77).

Add the Winter Wheat Forage Crop

Step 1: Close all reports and reopen the management editor. Add to the existing system, the additional operations for the winter wheat silage listed in Table 1.3. Hint: These can be added to the end of the run and sorted or inserted. When you have them entered and sorted, then click 'File', 'Save as...', and enter the management name as: Corn, silage-WWheat, silage, conv, spring manure, pivot CMZ19.man. Close the editor and return to the main interface.

Step 2: Make the run and call it, Corn, silage-WWheat, silage, conv, spring manure, pivot CMZ19.

How does the soil loss look now? Answer: 5.7 ton/ac. By harvesting less silage for each crop, the soil loss may be reduced below "T".

The yield has dropped off for the corn, silage to 18.6 ton/ac. This may be a little low, but remember forage crops, including winter wheat cut for silage, can not be calibrated. If you have trouble with this, contact your NRCS State Wind Erosion Specialist or the ARS Wind Erosion Research Unit in Manhattan, Kansas.

At the end of the run, some warnings are generated (Figure 1.78). These warnings tell you that the winter wheat did not reach maturity. This is because, as silage, we harvested it before it finished its growth cycle.