Humus Mineralization

Nitrogen is allowed to move between the active and stable organic pools in the humus fraction. The amount of nitrogen transferred from one pool to the other is calculated:

$N_{trns,ly}=\beta_{trns}*orgN_{act,ly}*(\frac{1}{fr_{actN}}-1)-orgN_{sta,ly}$ 3:1.2.3

$N_{trns,ly}$ is the amount of nitrogen transferred between the active and stable organic pools (kg N/ha), $\beta_{trns}$ is the rate constant (1×10$^{-5}$), $orgN_{act,ly}$ is the amount of nitrogen in the active organic pool (kg N/ha), $fr_{actN}$ is the fraction of humic nitrogen in the active pool (0.02), and $orgN_{sta,ly}$ is the amount of nitrogen in the stable organic pool (kg N/ha). When $N_{trns,ly}$ is positive, nitrogen is moving from the active organic pool to the stable organic pool. When $N_{trns,ly}$ is negative, nitrogen is moving from the stable organic pool to the active organic pool.

Mineralization from the humus active organic $N$ pool is calculated:

$N_{mina,ly}=\beta_{min}*(\gamma_{tmp,ly}*\gamma_{sw,ly})^{1/2}*orgN_{act,ly}$ 3:1.2.4

where $N_{mina,ly}$ is the nitrogen mineralized from the humus active organic $N$ pool (kg N/ha), $\beta_{min}$ is the rate coefficient for mineralization of the humus active organic nutrients, $\gamma_{tmp,ly}$ is the nutrient cycling temperature factor for layer $ly$, $\gamma_{sw,ly}$ is the nutrient cycling water factor for layer $ly , orgN_{act,ly}$ is the amount of nitrogen in the active organic pool (kg N/ha).

Nitrogen mineralized from the humus active organic pool is added to the nitrate pool in the layer.