Table of contents

1. Introduction
   
2. Parent material and environment
   
3. Regional Distribution
   
4. Definition
   
5. Genesis
   
6. Characteristics of Fluvisols
   a. Physical characteristics
   b. Chemical characteristics
   
7. Management and Use of Fluvisols
   

Fig.1 Fluvisols, Thailand

( Source: FAO, 2001.)

• The name Fluvisols refers to the Latin word fluvius = river.
  
• Fluvisols belong to the Reference Soil Groups set #4 of the of the WRB reference system. This set includes mineral soils whose formation was markedly influenced by their topographic/physiographic setting. Fluvisols accommodate genetically young, azonal soils in alluvial deposits, which show stratification or other evidence of recent sedimentation. Sediments can be fluvial, lacustrine or marine (World Soil Resources Report 94, 2001). Worldwide areas of sedimentation and sedimentation deposits are here:

  Fig.2 Worldwide areas of sedimentation

  
  
  • The highest yields are from:
    
    1. SE-Asia which receives high precipitation related to the summer monsoon climate
       
    2. and major high-relief mountain belts, including the Himalaya, the Alp, the Andes
       
    3. The coastal ranges of Alaska and British Colombia
       
  Further reading on the topographye/physiography of the terrain, click ( here)
  
• They are internationally known as:
  
  1. Fluvents = Soil Taxonomy, USDA
     
  2. Alluvial Soils = Russia, Australia
     
  3. Auenböden = Germany
     

Parent material:

• Recent (mainly Holocene sediments) fluvial, lacustrine or marine alluvial deposits.
  
• The texture of the parent material differs between terraces and river banks or lagoons and basins.
  

Environment:

• Periodically flooded areas of alluvial plains, river fans, valleys and tidal marshes.
  
• On all continents and in all climate zones.
  

Fig.3 Fluvisols worldwide

( Source: FAO, 2001.)

• Worldwide about 350 Mio. ha (~ 3 %) consist of Fluvisols. The areas represent important agricultural regions; ~ 50 % of the world population lives along rivers and coasts.
  

1. Along rivers and lakes:
   
   • Amazonas, lowland of Lake Chad or marshland in Bolivia and N-Argentina
     
2. Delta-areas:
   
   • Ganges/Brahmaputra, Indus, Mekong, Mississippi, Nile, Niger, Orinoco, Rio de la Plata, Zambesi
     
3. Young marine deposits:
   
   • Sumatra, Kalimantan, Irian Jaya
     

1. Soils having a thickness of 25 cm or more.
   
2. Fluvic soil material starting within 50 cm from the soil surface and continuing to a depth of at least 50 cm from the soil surface -> see  http://www.fao.org/DOCREP/003/Y1899E/Y1899E00.HTM
   a. Soil material which shows stratification in at least 25 % of the soil volume.

   Fig.4 Variation of texture and pebble content of fluvial deposits

   ( Source: FAO, 2001.)

   Fig.5 Aridic Fluvisol in Tunisia

   ( Source: Zech und Hintermaier-Erhard, 2002.)

   
   b. Stratification is surmised if the organic carbon content decreases irregularly with depth but remains greater than 0.2 % to a depth of 100 cm.
   c. Fluvic soil material must be associated with structural water bodies (seas, lakes and rivers).
   

• They are regularly flooded with depositions of fresh material (unless the land was empoldered) and show stratification and/or an irregular organic matter profile.

  Fig.6 Clear stratification of coarse textured fluvial materials in a riverbank

  ( Source: FAO, 2001.)

  
  
• They are young soils that developed a surface soil horizon and have no further characteristics of soil formation.
  

1. Fluvisols in upstream parts of the river system are confined to narrow strips of land (adjacent to the actual riverbed)
   
2. In the middle and lower stretches of the river,
   a. coarsely textured Fluvisols are found on the levees
   b. and more finely textured Fluvisols in basins
   
3. In areas with marine sediments:
   a. Coarse-textured Fluvisols occur on barrieres, cheniers, sand flats and crevasse splays
   b. Finely textured Fluvisols are found on clayey tidal flats and in chenier plains
   

See further: ( Fluvisols topography)

6a. Physical characteristics:

• Wet in all or parts of the profile due to stagnating groundwater and/or flood water from rivers or tides.
  
• Terraces and river levees are much better drained than soils in low landscape positions.
  
• Texture can vary from coarse sand in levee soils to heavy clays in basin areas.
  
• Most Fluvisols show mottling indicative of alternating reducing and oxidizing conditions.
  

b. Chemical characteristics:

• By and large, Fluvisols are fertile (depending on the deposited material).
  
• Neutral pH, good to high base saturation.
  

• Good natural fertility (young soils), many civilizations along river landscapes.

  Fig.7 Fluvisols, China

  ( Source: FAO, 2001.)

  
  
• Paddy rice cultivation is widespread.

  Fig.8 Sawah landscape in Indonesia

  ( Source: FAO, 2001.)

  Fig.9 Paddy rice field should be dry for a few weeks to prevent drop of redox potential (H2S problem) but also to stimulate microbial activity and promote mineralization of SOM

  ( Source: FAO, 2001.)

  
  
• Tidal lands are often used for shrimp farming.

  Fig.10 Shrimp farming in the coastal lowlands of Vietnam

  ( Source: FAO, 2001.)