LandscapeDNDC  1.36.0

Table of Contents

Initialisation

Initialization of the global soil state is separated into two parts:

  1. Initialization of soil state directly from site input information
  2. Initialization of remaining soil state (state variables not directly provided by site input)

Initialisation from site input

For each stratum the following procedure applies for:

  1. Take value if provided in the site input
  2. If not provided in the site input, use value according to the humus or layer-specific soil type (determined by the clay, sand and silt content in the specific layer, note layer specific soil types are only determined if clay+sand+silt summs up to 1.0. If not, e.g. for peat soils, the soil type that covers the complete soil profile is used as specified in the site input.)

Stone fraction

The stone fraction refers to the volumetric proportion of rocks, stones, and gravel within the soil. Depending on the measurement method and perspective, these coarse fragments may be included or excluded from bulk soil characterization. Smaller gravel particles are typically included in bulk soil samples (e.g., for bulk density measurements), whereas larger stones or rocks are usually excluded. In the context of LandscapeDNDC, all soil input data must represent the stone-free bulk soil (i.e., excluding rocks, stones, and gravel). The stone fraction is considered internally during simulations. For example, carbon stock is calculated using the product of bulk density, organic carbon concentration, and the stone-free soil volume.

Soil texture

Soil texture includes:

  • clay
  • sand
  • silt

For each stratum the following procedure applies for clay, sand and silt:

  1. Take values if provided in the site input
  2. If not provided in the site input, use value according to the general humus/soil type
  3. If the sum of all three fractions is greater than 1.0, all fractions are scaled down to exactly 1.0.

Bulk density

For each stratum the following procedure applies for:

  1. Take value if provided in the site input
  2. If not provided in the site input, use value according to the humus or layer-specific soil type (determined by the clay, sand and silt content in the specific layer, note layer specific soil types are only determined if clay+sand+silt summs up to 1.0. If not, e.g. for peat soils, the soil type that covers the complete soil profile is used as specified in the site input.)

Carbon and nitrogen content

For each stratum the following procedure applies for:

  1. Take value of soil organic carbon content if provided in the site input
  2. If soil organic carbon content is not provided in the site input, use humus type specific value for the litter layer. For the soil below the litter layer, if soil organic nitrogen content is provided determine ecosystem-specific C/N ratio to calculate the soil organic carbon content. If soil organic nitrogen content is also not provided, determine a exponential decay function using the soil organic carbon content in 5 and 30 cm soil depth as provided in the site input.
  3. Take value of soil organic nitrogen content if provided in the site input
  4. If soil organic carbon nitrogen is not provided in the site input, use humus type specific C/N ratio for the litter layer and determine ecosystem-specific C/N ratio for the soil below the litter layer to determine soil organic nitrogen content.

Porosity

For each stratum the following procedure applies for:

  1. Take value of porosity if provided in the site input
  2. If not explicitly provided, calculate porosity based on soil texture, soil organic carbon content and bulk density.

pH value

Depending on the model selection, pH may be dynamically calculated (e.g. after urea application). The pH value provided in the site input is interpretated as a mean value that is measured frequently over a longer time period.

Iron

Total iron content is distributed equally to ferric and ferrous iron pools.