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).