Question on Irrigation Scheduling Behavior in SWAT+ Model

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Harprabhjot Kaur Dhaliwal

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Mar 18, 2026, 1:32:26 PM (2 days ago) Mar 18
to SWAT+ Editor

Hi everyone,

I am working on a SWAT+ model for a sandy watershed in central Minnesota with irrigated crops (including potato, corn, drybean, etc.), and I am using automatic irrigation through a decision table.

My decision table triggers irrigation when soil water falls below 50% of field capacity and when the plant is growing, with 25 mm applied using a sprinkler method. I tried 80 and 90% fc as well.

I am observing the following behavior:

  • When I grow potato continuously (1985–2022), the model irrigates every year as expected.

  • However, when I include potato in a crop rotation (e.g., drybean–potato or more complex rotations), the model shows zero irrigation in the years when potato is grown.

  • For example, if I grow drybeans in the first year and then rotate with corn or potato, the model irrigates only during the drybean years and not during the years when the other crops are grown in that HRU.

  • As I increase the number of crops in rotation, the number of years without irrigation also increases.

I am trying to understand why irrigation is not being triggered in rotation years, even though it works correctly when a single crop is grown continuously.

Has anyone encountered similar behavior? Could this be related to soil moisture dynamics between crops, or the “plant growing = y” condition in the decision table?

Are there alternative approaches in SWAT+ to better simulate irrigation for crops grown in rotation (e.g., crop-specific triggers, ET-based scheduling, or management-based irrigation)?

Any insights would be greatly appreciated.

Thank you!

Harprabhjot 

Nancy B. Sammons

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Mar 18, 2026, 2:22:44 PM (2 days ago) Mar 18
to Harprabhjot Kaur Dhaliwal, SWAT+ Editor

Harprabhjot: 

Please send your current txtinout folder and I will take a look at this.

Nancy

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