How to set it up so that the crop grows on a regular basis

[X Gao]

Hi，

I am trying to build a model using ArcAPEX.  I'm having some problems with my crop growing abnormally.  For some crops that are planted in the fall and harvested the following summer (such as winter wheat), and it should grow very slowly in the winter.  However, the simulation results of the model are not satisfactory, and the crops still grow as usual in winter (crop height, leaf area index, etc.).  I see that the Model Theoretical Documentation takes winter dormancy of crops into account.  How should this problem be solved in ArcAPEX?  In addition, I have also encountered situations where crop biomass behaves normally while yield is zero.

I appreciate it if you provide me with some solutions or references.

Kind regards,

Gao

[Luca]

Dear Gao,

Plant growth is, overall, controlled by the heat units accumulated on daily basis. During winter, the low temperature should reduce the heat units accumulated by the crop reducing the plant growth. If you are simulating winter wheat, I guess that the plant base temperature is set to zero degree. This might be a plant parameter you want to modify if you think this is correct.

The winter dormancy is regulated with parameter 6 (see the APEX user's manual for more information). The problem is that (as far as I recall) ArcAPEX interface doe not allow the user to change the parameters. I cannot check this because I had to format my computer last week and I am still in the process of reinstalling all the software I need. You can explore it by yourself and you can explore also the ArcAPEX database. If you decide to explore the database, please, make a backup copy of it before doing any modification.

Let me know how it goes.

Luca

[X Gao]

Dear Dr. Luca,

 I have carefully considered the suggestion you gave, while looking at the SAD output of the model, the simulation of winter wheat does take into account the effects of winter dormancy.  I have a good setup for manual rigid irrigation and automatic fertilization.  I am exploring the database.  The problem I am currently having is that the height, LAI of winter wheat is very abnormal in winter.  From what I know, in my study area, the aboveground height of winter wheat should not exceed 0.3m in December, while the simulation results reached nearly 0.7m.  At the same time, from October to January of the following year, the LAI first increased and then decreased made me wonder.  What parameters should I adjust to solve the above problem (high growth of crops in winter, abnormal LAI)?  If required, I can provide you with a portion of the data privately.

Best regards,

Gao

[Luca]

Dear Gao,

From what you described, it seems that the model is simulating a too fast plant growth in early winter. I can see two options:

1. You can increase the base temperature and this might help in reducing the plant growth when the temperature begins to go down in winter. Obviously, the base temperature you chose must be reasonable for winter wheat.
2. You can change the value of DLAP1 in the crop table. I don't know the value you have now, but you can modify it to reduce the biomass accumulation in the early stages. You can find more information on the DLAP1 and DLAP2 on the APEX user manual.

Let me know how it goes.

Best,

Luca

[X Gao (Gao)]

Dear Dr. Luca,

Thanks a lot for your advice.  I referred to your suggestion and modified some parameters of the crop table appropriately.  The crop is now growing reasonably well.  So far I have run simulations on irrigation and have some results.  I have a new question, with artificial irrigation set up, how can I see when a crop is water stressed?  I understand that there is data on daily water stress in the SAD file, but I don't understand what it means.

Regards,

Gao

[Luca]

Dear Gao,

The WS value reported in the SAD file can be considered as the amount of water stress on each day. A value of 1 is used when the water stress level is high enough to prevent any biomass accumulation for that day. A value of zero indicates that the plant was not water stressed on that day and water availability was not a constraint for biomass accumulation. Any value in between indicates a different level of water stress for that day.

Let me know if this answer your question.

Best,

Luca

[X Gao (Gao)]

Dear Dr.Luca,

I think I understand a little what the "WS" value means.  And I have more questions.I found that the ACY file also has the "WS" value in it.  What is the difference between the meaning of the "WS" value in the ACY file and the SAD file?  I looked at the SAD file and ACY file for one of my subwatersheds.  In the SAD file, there are many days in the crop growth period where the WS value is 1; in the ACY file, the WS value is only about 10.  I request that you are able to explain the concept of these two "WS" values ​​in more detail.

 I appreciate your patience in answering my questions.

Best,

Gao

[Luca]

Dear Gao,

The value of WS in the SAD file is a daily value of water stress while the value you have in the ACY is the cumulative annual water stress. If you import the SAD file in Excel, you can try to do some calculations to get the annual WS value reported in the ACY file.

Give it a try and, if you have trouble, share the files here and I will give you more information.

Luca