EPIC and NPP

[Yuhang Gao]

Dear all,

I want to ask if there is any output of the first net primary productivity (NPP) in the EPIC model.

Best regards,

Gao

[Luca Doro]

Dear Gao,

Depending on the version you are using, NPP should be available in one of the output files. Please, let me know which version you are using and share with me the .OUT output file generated with the executable you are using.

Best,

Luca

[Yuhang Gao]

Dear Luca,

Thank you for your reply. The version I use is EPIC1102. The. OUT file is in the attachment

Best,

Gao

[Luca Doro]

Dear Gao,

NPP and NEE should be available in the daily crop stress file (*.DCS). You might have to edit the PRNT1102.DAT file to print DCS output file. You should be able to find some information on the EPIC user manual. Let mek now if you need information on it.

Luca

[Yuhang Gao]

Dear Luca，

Whether annual NPP can be output in EPIC model

Best,

Gao

[Luca Doro]

No, NPP is available only in the DCS and DGN output files (both of them are daily outputs).

Best,

Luca

[Yuhang Gao]

I would like to ask what is the NPP unit in the DGN file, but I can't find this part in the user manual.
I would appreciate it if you could reply to me

Best,

Gao

[Luca Doro]

Unit of NPP is kg C/ha. Let me know if the values you see make sense.

Luca

[Yuhang Gao]

Dear Luca,

Thank you for your reply. Currently, I am researching soil conservation. When simulating soil water erosion conservation, in addition to calculating the actual water erosion, I also need to calculate potential water erosion. Potential soil erosion refers to the amount of water erosion caused by exposed surface. May I ask how to simulate the scenario of this exposed surface.

 

Gao

[Yuhang Gao]

Dear Luca,

By observing the user manual, parm 60 refers to the exponential coefficient in EPIC soil erosion C factor equation relates C factor to soil cover by
flat and standing residue and growing biomass. Does this parameter refer to this equation? If so, which parameter does it specifically refer to.

Best,

Gao

[Luca Doro]

Dear Gao,

I am not familiar with the concept of potential soil erosion, and I don't know how it can be simulated in EPIC. To help you, I should study this, but I do not have the time to do so.

The PARM(60) doesn't seems to be related to the equation you have reported. Here is how PARM(69) is used in the model:

  X1=MIN(10.,PRMT(60)*CV)
  CVF=(.8*EXP(-X1)+CFMN)*(.9*(1.-CVP)+.1)

In the first equation, CV is the soil cover provided by crop above ground biomass and crop residue.

Luca

[Yuhang Gao]

Dear Luca,

Thank you for your reply.

Through reviewing the research of other personnel, I found that using EPIC to achieve potential soil erosion requires setting CE (crop management factor) to 1. How can I achieve CE=1

Best,

Gao

[Luca Doro]

What is the crop management factor?

[Yuhang Gao]

The crop management factor refers to the CE in this equation

Best,

Gao

[Luca Doro]

From what I can understand, the first equation estimates sediment yield (Y) and CE is what is the crop management factor (CVF) as in the following equation that comes from the APEX theoretical documentation:

     Y=X*EK*CVF*PE*SL*ROKF

You can download the theoretical documentation from the following webpage: Manuals and Publications | EPIC & APEX Models (tamu.edu)

A CVF equal to one should give the maximum sediment yield. From the theoretical documentation, you will see that several factors are considered to estimate CVF. I think that you have to simulate a bare soil to have a CVF close to one.

This can be achieved by planting the crop "fallow" included in the crop table.

Best,

Luca

[Yuhang Gao]

In the EPICCONT.DAT file, the meaning of ICF in columns 17-20 of the second line is how to set the C factor, can I achieve the CVF=1 you mentioned above by setting ICF=1

Best,

Gao

[Luca Doro]

Dear Gao,

From the EPIC user manual:

ICF = 0 uses RUSLE C factor for all erosion equations
ICF > 0 uses EPIC C factor for all erosion equations except RUSLE

So, it is used only to select the method used to estimate the C factor.

Luca

[Yuhang Gao]

Dear Luca,

Thank you for your reply, it solved my problem. Also, I am planning to simulate corn for the 1st year to the 5th year and then pasture for the 6th to the 20th year after that, how does this work in EPIC? My OPC file is set up as follows, but the results are not as expected.

Gao

[Luca Doro]

It is not possible to skip years (the management file you sent me goes from year 1 to year 5). At least one operation must be present in each year included in the rotation.

I am including a sort of template of the management file for 5 years corn and 15 years pasture. If you are simulating the pasture with perennial, if you do not have real operations that occurs each year, you can include a dummy operation (something like the ATV operation that should be present in the operation file).

[Yuhang Gao]

Dear Luca,

Thank you for your reply. As you said, I simulated perennial pastures, and the actual operation did not occur every year. May I ask how to set up a dummy operation.

Best,

Gao

[Luca Doro]

A "dummy" operation can be created by adding an operation that is not going to have any impact on the soil or the crop. The file with the list of operations available in the model, should have some operations like ATV, motorcycle, truck. These are used for economic purposes only and do not have any impact on the system.

Just add one of these operation in each year of the perennial pasture.

Just a note for completeness of information, the model should work skipping years in the management file when a perennial is simulated. In this case, not knowing the full setup of your simulation, I think it is safer to set up the management file treating the perennial like an annual plant.

Luca

[Yuhang Gao]

I have another question. 

I plan to simulate pasture for the 1st year to the 5th year, using herbicides to kill the grassland in the 6th year, and then simulate corn for the 6th to the 20th year.  if my OPC file is correct.

Best,

Gao

[Luca Doro]

No, your file has errors in it.

You cannot leave the fourth column as zero, a tillage ID is needed.

I recommend not leaving the crop ID as zero.

A kill operation is needed for pasture (the application of herbicide is not going to kill the plant).

Luca

[Yuhang Gao]

Dear Luca,

I found that there is an issue with wind erosion, which has been consistently 0. At the same time, I observed in the OUT file that the soil erodibility factor (WK1) is equal to 0 and the ridge roughness factor (RGRF) is equal to 0. What is the reason for this. In addition, due to the lack of wind direction, by referring to other studies, I attempted to set the length (WL) of the field along the prevailing wind direction to 100m. How can this be achieved

Gao

[Luca Doro]

Have you checked the wind erosion adjustment factor (ACW) in the control table? What's its value?

Luca

[Yuhang Gao]

Dear Luca,

Thank you for your reply. I will let you know more information.
In addition, I set up conventional tillage scenarios (CT) and no tillage scenarios (NT) to explore the impact on evaporation (ET):
1. CT: TLD=150, EMX=99%, RR=40, 25% straw returning to field, LUN=3
2. NT: TLD=50, EMX=2%, RR=10, 75% straw returning to the field, LUN=7
In theory, the ET in the NT scenario is lower than that in the CT scenario. But in fact, in my results, ET in the NT scenario is sometimes higher than ET in the CT scenario, and sometimes lower. What is the reason for this. Also, sometimes evaporation is higher than precipitation, which is due to soil moisture.

The files in the attachment are the running results of two scenarios.

Best,

Gao