Summary:

## Competition between Plant Uptake and Soil Immobilization Fluxes

- The competition between plant nitrogen demand and microbial nitrogen demand is resolved based on the available mineral nitrogen in the soil pool.
- The theoretical maximum plant nitrogen demand is distributed across soil layers in proportion to the available mineral nitrogen in each layer.
- Plants first compete for ammonia (NH4), and the total NH4 demand is calculated as the sum of the immobilization and nitrification demands.
- If the total NH4 demand is less than the available mineral nitrogen, immobilization proceeds at the maximum rate.
- If the total NH4 demand exceeds the available mineral nitrogen, immobilization is reduced proportionally to the discrepancy.
- The nitrogen available for plant uptake is calculated as the total mineralized pool minus the actual immobilized flux.
- This process of competition for nitrogen as a limiting resource is referred to as a demand-based competition, where the fraction of the available resource that flows to a particular process depends on the demand from that process relative to the total demand.