Water stress in ACY different from SAD file

[Carlos E. Quezada Lambertín]

Dear all,

I´m using the APEX 1505 (Rel. 20190715) version to simulate irrigation scenarios at a plot level. I´m using the automatic irrigation component to test volumes from 90 mm to 300 mm in potato production. The problem I found is that as the irrigation increases, the sum of the daily Water Stress values of the SAD file for the study period increases (instead of reducing). On the other hand, the annual value shown in the ACY file does decrease in correspondence with the irrigation volume increase.

When I compare the annual values of WS in the ACY file vs the yearly sum in the SAD file, I get different results.

What can be causing this problem? Thanks in advance for your help,

Carlos

[Luca Doro]

Dear Carlos,

There is no error in what you see in the output files. It is just water stress (or any other stress) is reported in the SAD and ACY file.

The WS reported in the SAD file is the regulator factor that affects the biomass accumulation for the day. Since it is a multiplier, a high value indicates low stress (1 = no stress, all the potential biomass become actual biomass) and a low value indicates high stress (0 = severe stress, no biomass accumulation on that day). On each day, only the most severe stress affects the biomass accumulation. The column RES has the value of the regulator used to constrain the biomass accumulation.

In the ACY file, the model reports the number of days each stress was the most severe of all the stresses simulated. In this case, a low number indicates a low stress (in your case, low number of days with water stress). To get the WS value reported in the ACY file, from the SAD file, you have to consider only the days when WS was the most severe stress (WS=REG) and sum them as 1-WS.

Let me know if you need more information.

Luca