"Soil-plant system model"

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1 Abstract

Model for the simulation of soil water and nitrogen dynamics in the crop-soil system. The main modules simulate:

  • water dynamics, including snow accumulation and melting, evaporation from open water surfaces and soil, transpiration and water uptake by plants (based on the single root uptake and root density), infiltration, percolation and soil water dynamics (Richards'equation);
  • soil heat, including freezing and melting and soil temperature;
  • nitrogen dynamics, including turnover of organic matter (based on carbon pools, microbial biomass, and first order kinetics), mineralization/immobilization (a consequence of the carbon turnover), nitrification, denitrification, nitrogen uptake by plants (based on single root uptake and root density), and nitrogen transport (convection-dispersion equation) and leaching;
  • crop growth, i.e. crop development, dry matter production, crop nitrogen demand, crop nitrogen content, photosynthesis, water stress, nitrogen stress, assimilate partitioning, maintenance and growth respiration, leaf area development, root penetration and root density distribution.

The model allows for the simulation of different management strategies and crop rotations.

2 Implementation

Daisy is executed in two steps:

  • in a first step DAISY_1 solves the models for soil water dynamics, soil heat and crop production limited by radiation and soil water content only. It requires information about
    • physical soil layers (soil hydraulic and thermal properties)
    • numerical soil layers (user defined node points)
    • initial and boundary conditions (for the bottom boundary either a Neuman or a Dirichlet condition can be defined )
    • crop, tillage, management
    • weather data for precipitation, air temprature, potential evapotranspiration and (optionally) grondwater table depth on a daily basis.
  • The output (water content, ice content, matric ptential, plant-water-uptake, temperature and flux density versus time and depth) is stored in binary format on disc. This allows simulations over several years while maintaining a hourly timestep for the calculated fluxes. DAISY1 produces 2.5 Mbyte/year output.
  • in a second step, DAISY_2 uses the output of DAISY_1 as input. It calculates carbon turnover,microbial biomass-dynamics, solute-dynamics, and nitrogen limited crop production. Output is given on a daily basis, resulting in 0.5 MByte/Year. Daisy2 requires initialisation of the chemical and biological processes and several parameters describing the transformatin characteristics the soil. These include laboratory determined rate constants for nitrification and denitrification , impendance factors, longitudinal dispersivity, NH4-adsorption -isotherm, average dry and wet nitrogen depositon rates/concentrations. The total soil organic matter is divided into four fractions dependent upon history and origin. A fraction is further divided into two pools with fast and slow turnover rates. Each of the four main organic matter fractions is specified by a minimum of seven constants. Some of the required parameters may be difficult to access experimentally. The authors provide default values and examples of initialisation files worked out for agricultural crops in humid north-west european climate.

3 Siehe auch

4 Weblinks

Kategorien: Modelle

Letzte Änderung dieses Artikels: May 05, 2009, at 12:53 PM