GrasslandDNDC

Table of Contents

• User guide
  • Model structure
  • Parametrization
• Cutting and grazing
• Plant Development

User guide

The grassland growth model GrasslandDNDC originates from the DNDC Model ([40]). GrasslandDNDC simulates the carbon and nitrogen cycle of grass species only (no crops). Processes are described in a universal way and plants are primarily distinguished by species-specific parameters that can be accessed and calibrated externally.

Model structure

GrasslandDNDC can be either run in subdaily or daily time resolution.

Parametrization

The following lists includes species parameters that might be calibrated in order to represent a specific plant. See the description of respective sections for more details on parameter behaviour.

Nitrogen related parameters:

• nc_fruit_max (nitrogen content of the fruit)
• nc_fineroots_max (nitrogen content of fine roots)
• nc_structural_tissue_max (nitrogen content of structural tissue)

Allocation related parameters:

• root (assimilated carbon fraction allocated to roots)
• grain (assimilated carbon fraction allocated to the fruit)
• faleaf (determines fraction of carbon that is allocated to leafs)

Plant development related parameters:

• gdd_base_temperature
• gdd_maturity

Drought

• h2oref_a (determines drought resistance)

Nitrogen uptake

• tlimit (minimum temperature required for nitrogen uptake)
• k_mm_nitrogen_uptake (root affinity to soil nitrogen)

Nitrogen fixation

• ini_n_fix (fraction of total nitrogen that might be fixed)

Respiration

• maintenance_temp_ref (reference temperature for maintenance respiration)
• mc_root (maintenance respiration coefficient for roots)

Root exsudation

• doc_resp_ratio (ratio of doc exsudation in relation to root respiration)

Senescence

• senescence_drought (coefficient of senescence related to drought)
• senescence_frost (coefficient of senescence related to frost)
• senescence_age (coefficient of senescence related to age)

Fineroots turnover

• tofrtbas

water demand

• wuecmax (water use efficiency)

Structure

• exp_root_distribution (coefficient for exponential root distribution)
• height_max (maximum plant height)

Cutting and grazing

After cutting and grazing events plant development is linearly reduced with nitrogen loss.

\[ DVS(t_{i+1}) = \frac{N(t_{i+1})}{N(t_i)} \cdot DVS(t_i) \]

Plant Development

Plant development is calculated by growing degree days (GDD):

\[ GDD = \sum (T_{avg} - T_{base}) \]

Plant development is given by:

\[ DVS = \frac{GDD}{GDD\_MATURITY} \]