> For the complete documentation index, see [llms.txt](https://swatplus.gitbook.io/io-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://swatplus.gitbook.io/io-docs/theoretical-documentation/section-5-land-cover-plant/actual-growth/growth-constraints/nitrogen-stress.md).

# 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).