# Nitrogen Stress

              Nitrogen stress is calculated only for non-legumes. SWAT+ never allows legumes to experience nitrogen stress.

              Nitrogen stress is quantified by comparing actual and optimal plant nitrogen levels. Nitrogen stress varies non-linearly between 0.0 at optimal nitrogen content and 1.0 when the nitrogen content of the plant is 50% or less of the optimal value. Nitrogen stress is computed with the equation:

                 $$nstrs=1-\frac{\phi \_n}{\phi\_n +exp\[3.535-0.02597\*\phi \_n]}$$                                                  5:3.1.6

where $$nstrs$$ is the nitrogen stress for a given day, and $$\phi\_n$$ is a scaling factor for nitrogen stress. The scaling factor is calculated:

                 $$\phi\_n=200\*(\frac{bio\_N}{bio\_{N,opt}}-0.5)$$                                                                  5:3.1.7

where $$bio\_{N,opt}$$ is the optimal mass of nitrogen stored in plant material for the current growth stage (kg N/ha) and $$bio\_N$$ is the actual mass of nitrogen stored in plant material (kg N/ha).


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://swatplus.gitbook.io/io-docs/theoretical-documentation/section-5-land-cover-plant/actual-growth/growth-constraints/nitrogen-stress.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.