05-12-01 N uptake model

Changed the Nitrogen uptake demand model by accounting for the net carbon production of leaf, roots and stem. In previous version of model the Nitrogen demand was governed by the gross carbon production of respectively plant components. No Switch was connected to the change so users have to change the respectively CN values in the Table: “ Minimum CN Ratios of plants” to reproduce old model results. The new model means that the minimum values are related to the values after respiration losses and not prior respiration losses.

A new option in the N Mineral was introduced named Flexible Uptake. This switch allows the use to have either a plant specific compensatory uptake or a common uptake. The parameter for the plant specific flexible uptake is found in a table with the same name.        PEJ