Some problems in ArcApex

[Wuyan Yan]

1.Whether the fertilizer utilization rate can be set？Or the fertilizer will all be used？

2.As shown in figure，FN always has A minimum，What factors affect in this  minimum  ？

[Luca]

1. In the EPIC and APEX models, there is no such thing like fertilization utilization rate. The user can define the amount of fertilizer to be applied manually (in the management file) or by using the automatic fertilization option.

2. FN in the image included in your message is the amount of fertilizer applied on each year included in the simulation. Without knowing the condition of the simulation, it is difficult to elaborate more. I don't understand what you mean with the minimum.

[Wuyan Yan]

Think so much, Mr. Luca.

On these two problems, 

1.Does the absence of fertilization utilization rate mean that all fertilizers are fully utilized?

2.No matter how I set it, FN is no less than 104.18, so I thought it was the minimum. If I want IRGA to be 0, I can set BIR to 0. But I want FN to be 0. If I set BFT to 0, I won't get the result I want. It won't go below 104.18.

[Luca]

1. Once applied, the fertilizer is subject to different processes like plant uptake and losses with several pathways. What do you mean with "fully utilized"?
2. Are you using manual or automatic fertilization? If you want FN to be zero, you have to remove any fertilizer operation in the management file and you have to turn off the automatic nitrogen fertilization (if it is on). Read the user manual on how to do it.

Luca

[Wuyan Yan]

Thanks for your reply. 

These two problems have been solved,  and now I have another problem.

I want to simulate the growth of rapeseed, but I can't find it in the database. How can I use the model to simulate rapeseed?

Best regards

[Luca]

You have to add rapeseed to the database (CROPCOM.DAT file). To do this, you have to define all the plant parameters used by the model to simulate plant growth.

Luca

[Wuyan Yan]

After re-running the APEX I found a problem. No matter how I set the automatic irrigation, once the sum of IGRA reaches 2000, IGRA will go to 0 in subsequent years. What might be the cause of this？

Thank you for your help.

Best regards

Yan

[Luca]

Dear Yan,

Are you simulating trees or perennial crops? If yes, it could be that the maximum amount of irrigation water allowed (variable VIMX in the subarea file) is used for the entire growing period of the plant. I will check the source code for it. Meanwhile, you can increase the VIMX value to a value larger than 2000.

Luca

[Wuyan Yan]

Dear Luca,

I'm simulating an annual crop, winter wheat. I increased the VIMX value to 2500, the sum of IGRA went to be 2500. 

I thought it was the maximum amount of irrigation in one year, so I did not try to modify this value.

I noticed one sentence in the description of VIMX, "If several crops are grown in one year, the first crop’s needs will be supplied as needed and any remaining water will be applied as needed to the next crop."  So this means that APEX can simulate multiple cropping (I thought APEX can‘t’ do that)

I have another problem. I'm trying to set up multiple crops, two crops a year.  I tried to set up a new type of Operation Schedules, and selected it in the Subarea file. But the model did not run successfully. Later, I found that the reason was the choice of different crops between Land use and IOPS (Operation Schedules). So now I have a new problem, I can't add a "crop"(Contains parameters for two crops) to the database, What do I need to do to set up multiple planting and run successfully?

Sorry, I'm not a native English speaker, so this may not be accurate, can you understand what I mean？If I do not express clearly, please tell me to express again

Thank you for your help.

Best regards

Yan

[Luca]

Yan,

Are you killing/terminating the crop each after the harvest operation? If not, that might be the reason for the problem with the irrigation.

Yes, APEX can simulate multiple plants growing at the same time in the same field. This is a feature that was already available in the EPIC model and was included in the APEX model since its first version.

About the third point, it seems that you created a management (Operation Schedule) where more than one plant are growing at the same time but the model is not working when you select this management. To simulate two or more plants growing at the same time, you only have to have two planting operations in the management you want to use. If needed for your simulation, you have to specify the harvest operation for each plant included in the management and, for annual plants, you have to add a kill/terminate operation for each plant included in the management. If you are using the ArcAPEX interface, you can do all of this from the interface. I don't have ArcAPEX installed on my computer right now so, I can't attache a screenshot of the window where you can do this. Most likely, you will find more information in the ArcAPEX user manual.

Let me know if I didn't answer your last question or if you need more information.

Best,

Luca

[Wuyan Yan]

Dear Luca,

My problem was solved with your help, these problems are caused by the fact that I did not killing the crop each after the harvest operation.

Thank you very much for your help

Best regards

Yan

[Wuyan Yan]

Dear Luca,

I have a new problem. 

There are not equal numbers of Outlet and Subarea,  in "APEX Subarea" I can only modify the Subarea where these Outlet are, how can I modify other subarea files?

Best regards

Yan

[Luca]

Dear Yan,

I don't understand the problem. Can you provide more us with information?

Luca

[Wuyan Yan]

Dear Luca,

I'm sorry I didn't make my problem clear. Let me restate my problem.

There are 18 Subareas, 12 Outlet.  If I change the parameters in Outlet13, my changes will only take effect for one subarea (ID 5). How do I make these parameters work for other subareas (ID 7 8 12 13 14)?

Best regards

Yan

[Luca]

Dear Yan,

I don't use ArcAPEX very often and I don't have it installed on my computer right now so, I can't do any test.

Which parameters are you modifying and where in the ArcAPEX interface are you modifying them?

Luca

[Wuyan Yan]

Dear Luca,

The parameters I need to change are mainly in Irrigation and Fertilization (The selected part of the black box in the figure). For example, if the parameter I need to modify is BIR, I will modify it in Fetilization and run the APEX.

Best regards

Yan

[Luca]

Dear Yan,

Now I understand the problem. What surprises me is that you have more than one outlet in the SITE dropdown menu. Usually, you have just one outlet that is the one selected during the delineation process. Probably you have selected more than one outlet during the process and this can be a mistake, or it can be what is needed to simulate the watershed you are studying. To understand if what you have done is correct or not, please take a look at the ArcAPEX user manual, page 17, step 6 of the exercise. You will find information on the selection of the outlet for the watershed. You can find the ArcAPEX manual here.

Let me know if this helps.

Best,

Luca

[Wuyan Yan]

Dear Luca,

Yes, I have selected more than one outlet. Because if I select only one outlet, then the APEX runs only upstream of that outlet, but I want as many parts of MASK eare as possible to be run by APEX, I selected more than one outlet.

Thank you for your help. Now I know what the problem is.

Best regards

Yan

[Luca]

Yan,

When you select one outlet, the model will simulate all the area that contribute to accumulate the water that reaches that outlet selected. Fix this problem and let me know how it goes.

Luca

[Wuyan Yan]

Dear Luca,

When I selected one outlet, there was no recurrence of previous problems.

I notice that APEX is very similar to SWAT. What are the main differences or strengths of APEX? Why is that?

Best regards

Yan

[Luca]

Dear Yan,

APEX and SWAT are similar, but there are differences between these two models. You might find some information in the paper I am including here. Also, a literature review will give you more information on the characteristics of these two models.

Let me know if you need more information.

Luca