Exercise 6 - New York: Tomato, Rye Cover Crop, and Plastic Mulch

Skill Building: In this exercise we will start with a template rotation. We will then add rye for winter cover and then plastic mulch to the basic run. This will give you a sense of value for these conservation practices. The picture below (Figure 1.66) is an example of plastic mulch with a rye cover crop (inter-furrow) and onions. Many times there will not be a cover between the rows. The current version of WEPS can not directly model temporary barriers (between the rows) or two crops growing at the same time like the one shown below in Figure 1.66, but can simulate these situations none-the-less.

We will model systems with cover crops planted either in the fall or spring and plastic mulch added to the field near or at planting time for the crop (in this case tomatoes). The mulch is accounted for in WEPS as special residue. Therefore we can grow any other crop with plastic mulch in place. We can count the green cover crop as residue when we plant the tomatoes if we place a 'kill crop' operation before planting the tomatoes. This means that even though the rye is still growing, WEPS will not show rye growth. WEPS will however show the amount of rye biomass as dead residue when the tomatoes are planted thus providing the intended protection.

Scenario: The field we are working on is in Suffolk Co., New York. The soil is Riverhead Sandy Loam (Riverhead_RdA_80_LS.ifc). The CLIGEN station is Riverhead Research and Westhampton Beach is the correct WINGEN station. The simulation region is 600 ft for the X-Length and 1000 feet for the Y-Length to give a field size of 13.8 acres. The field is oriented -15.0 degrees from true North (i.e., 345 degrees). The filed will produce tomatoes. The yield is 300 cwt/ac for the tomatoes. The field is tilled parallel to the long side of the field. The producer indicates that in some years there is wind and soil abrasion damage to the young tomato transplants if he does not place plastic mulch on the beds.

Step 1: Be sure you are in the Student project. From the main interface enter the information listed in the inventory. Click the Soil Project Folder button and select the soil (Riverhead_RdA_80_LS.ifc). Click the Management Template Folder button to select the Tomato, conv, no plastic Z65.man file. This is the management without the rye cover crop or the plastic mulch applied.

This management file has been calibrated to give near correct yields of the crops. You can check by clicking the Yield Calibrate button in the management window and scroll left to the Biomass Adjustment Factor column. If the number in the column is other than 1.0, this indicates that the crop and the management file have already been calibrated. In case it is missing, it should be changed for tomato to 0.64.

Step 2: Check the management window to see if the tillage is parallel to the orientation of the field.

What is the current row/ridge direction value of all the tillage? Answer: 0 degrees from true North.

What is the value we are looking for? Answer: -15 degrees.

Why? Answer: Because the field is oriented -15 degrees from true North (i.e., 345o).

Highlight all the rows in the management file by clicking the header of the 'Row/Ridge Dir. (Deg.)' column. Then right click the column and click 'Decrement 15 deg'. This will set all the tillage to be the same as the field orientation mentioned in inventory (i.e., -15). Leave the editor and save the changes to the current file (see Figure 1.67).

Step 3: Make the run and save it as Tomato, conv, no plastic, Z65.

Is the yield close? Answer: Yes, at 304 cwt/ac, see Figure 1.68.

What is the erosion rate? Answer: 4.4 ton/ac. This is above the tolerance for tomatoes (see Table 1.? in the Exercises Introduction) so we sill see the effect of a rye cover crop.

Add in the Rye Cover Crop after Tomato

Step 1: Right click the killing frost operation row and change the operation to Drill or airseeder, double disk. Select Rye, winter cover for the crop to be planted. Change the date to Aug. 1, 01 for this planting. Now insert a light disk 5 days after harvest (Disk, tandem light finishing, Jul 20, 01). Save the file with a new name. Save the file with a new name by clicking 'File', 'Save as...', and enter Tomato, cover-Soybean-Corn, cover, Conv CMZ67.man. Click the blue Return button .

Step 2: Make the run and call it, Tomato, cover, conv Z65.

What is the soil loss now? Answer: It is 1.2 ton/ac (Figure 1.69).

What period of the year has the erosion problem? Answer, May 1-14, 01 (Figure 1.70).

Add Plastic Mulch

Is there an apparent need for plastic mulch indicated by the Run Summary?

Answer: Yes. The NRCS National Agronomy Manual, Crop Tolerance to Blowing Soil table lists tomatoes in the 'Very Low Tolerance' category (See Table 1.? in the Exercises Introduction) . Also, the producer stated that there is a problem some years with blowing soil damage to the young tomato plants. The 1.3 ton/ac value is an average over many years of the simulation. Some years may have higher and some may have lower erosion, with the higher erosion years causing more damage to the tomatoes. As resource planners we must also listen to the producer to determine whether a practice is needed or not.

Step 1: Close any reports you have open and click the 'Man' button to open MCREW. You should see the Tomato, cover, conv Z65.man management file. First save the file as Tomato, cover, plastic mulch Z65. Right click in the operation column on the 'May 01, 01', Planter, transplanter, vegetable operation. Select 'Insert operation'. Select Plastic mulch applic. 48 inch beds 80 percent cover; make the date 'May 01, 01'. The mulch application requires a Crop or Residue - select 'Plastic mulch'. Be sure to set the angle of tillage to -15 degrees. Now move to and right click 'Jul 20, 01' Disk, tandem light finishing. In the operation column, right click and 'Insert an operation' Plastic mulch, remove, and make the date 'Jul 18, 01'. Last, change the harvest operation for the tomatoes to Harvest, vine crops, on plastic. The completed management file should appear as in Figure 1.71.

Note: Before you leave the editor that a default Flat Residue Amount of 2000 lbs/ac has been applied to the land the day that the plastic is applied. In version 1.0 we are applying plastic as a high biomass amount of residue for WEPS to simulate no erosion while the plastic is in place. If the inter-furrow area does not have a cover there could be additional erosion occurring that is not a counted for.

Step 2: Click the blue Return button to return to the main interface. Make the run and call it Tomato, plastic mulch, cover Z65.

The Run Summary shows a significant decrease in soil loss (Figure 1.72). With the plastic mulch in place only a trace of wind erosion shows up on the run summary report. Notice though by using the plastic and the cover crop our yield has grown to 324 cwt/ac, this is 20 cwt/ac more than the first calibrated run. If you recalibrated the run it would not raise the erosion above a trace. The obvious benefit of the mulch is that the tomatoes are not damaged using the plastic, the yield is higher, and the crop does not have to be replanted.