Issue of low crop yield due to nitrogen stress

[Tetsuro Kikuchi]

Hello,

I'm running SWAT+ (rev. 61.0.1) with Editor (3.0.2) to simulate nitrate nitrogen outflow (no3_out) from a small agricultural watershed.

I've got a problem of nitrogen stress for crops (see Plant Growth_20250612.jpg attached) and low crop yields in my simulation even though I should have adequately set the management schedules, including the rates of fertilizer applications, based on the actual conditions. For example, the simulated yield of summer sugarcane ("sugc_smmr1" and "sugc_smmr2" in Land Use Summary 2_20250612.jpg attached; around 6 t/ha) was about one-twelfth of the average yield in the target region. 

I'd greatly appreciate it if you could provide possible causes of this issue and solutions for them.
The corresponding TxtInOut file is also attached.

Tetsuro Kikuchi

[Natalja C.]

Hello,

The summary shows the average values for ALL the plans, not only the sugarcane. To troubleshoot this issue I would to the following:

1. Read the SWATdoctR article and the guidance it gives on detecting issues with management and plant parametrisations: https://linkinghub.elsevier.com/retrieve/pii/S1364815223002645

2. Apply the nostress tests as is described in the article or use the doctR tool to do that.

3. Get familiar with the SWAT+ output format (text files and not GUI tools).

4. print out the management output to test, if the DTs are functioning correctly.

From experience, I think this will be a plant parametrization issue, particularly for the days_mat. You will find out while running the tests.

Also, please keep in mind that swat+ always simulates in dry weight: plants, fertilizers, etc. It might be that you need to adjust your moisture content in the observations.

Best,

Natalja