algebraic equation

• entry of inorganic nitrogen into soil
• evaporation of the covered soil
• gaseous nitrogen losses
• leaching of inorganic nitrogen
• potential evaporation of crop
• potential soil surface evaporation
• water demand of arable land

dynamic equation

• amount of melted snow
• decomposition and mineralization of organic matter
• inorganic nitroge content of the soil
• movement of soil water

partial differential equation

• dynamic of the soil temperature