Table of contents

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

• Parent material: most extensive on acid rock weathering, notably in strongly weathered clays which are undergoing further degradation.
  
• Environment: Acrisols are found on acid rocks (strongly quartzitic, e.g. granite, gneiss) mostly of Pleistocene age or older, on old land surfaces with hilly or undulating topography, in regions with a wet tropical/monsoonal, subtropical or warm temperate climate. Light forest is the natural vegetation type.
  

  Fig.2 Acrisols in Madagascar

  ( Source: FAO, 2001.)

Fig.3 Acrisols worldwide

( Source: FAO, 2001.)

• Worldwide are about 1000 Mio. ha of Acrisols. They are most extensive in SE Asia, S-Amazon, SE USA, E and W-Africa.
  

• Must have an argic B horizon within 100 cm or within 200 cm (when loamy sand is above). Further information in the chapter ( clay eluviation) .
  
• ( CEC) < 24 cmol_c/kg (1 M NH₄OAc solution buffered to pH 7)
  
•  BS < 50 % between 25 and 100 cm (1 M NH₄OAc solution buffered to pH 7)
  

Fig.4 Acrisols have low fertility

( Source: FAO, 2001.)

• Acrisols are characterized by their argic B-horizon, dominance of stable low activity clays and low base saturation. The formation of Acrisols involves the following processes:
  
  1. Clay dispersion (see chapter ( clay eluviation) )
     
  2. Clay transport
     
  3. Clay accumulation
     
  4. Ferralitization (see chapter ( ferralitization) )
     
  5. Translocation of Fe-compounds by  cheluviation. This process is accountable for color differentiation directly under the A-horizon where an eluviation horizon with yellowish colors overlies a more reddish colored Bst-horizon (see name Red-Yellow Podzolics, SE Asia).
     
• Acrisols are less strongly weathered than Ferralsols.
  

a. Morphological characteristics

• The profile development mostly is AEBtC. Most Acrisols have a thin, brown, ochric surface horizon, particularly in regions with pronounced dry seasons. The underlying albic is normally whitish to yellow and overlies a stronger colored yellow to red argic subsurface horizon.
  
• Please look under World Soil Resources Report 94, 2001 for description of diagnostic horizons and/or materials:  http://www.fao.org/DOCREP/003/Y1899E/Y1899E00.HTM
  

b. Physical characteristics

• Low structural stability. Most Acrisols have weak microstructure and massive macrostructure, especially in the surface and shallow subsurface soil that have become depleted of sesquioxides. Bonding between sesquioxides and negatively charged low activity clays is less strong than in Ferralsols.
  

  Fig.5 AEBtC

  ( Source: soils.usda.gov/.../orders/ alfisols.html)

c. Chemical characteristics

• Acrisols have poor chemical properties:
  
  • Low  base saturation
    
  • Low nutrient availability
    
  • P-sorption and ( Al-toxicity)
    

• Due to low inherent chemical and physical properties the preservation of the surface soil and SOM !!!! is a preconditioning for farming on Acrisols.
  
• The widely used slash-and-burn agriculture is a well adapted from of land use. Adapted cropping systems with complete fertilization and careful management are required if sedentary farming is to be practiced.
  
• Undemanding acid tolerant plants such as rubber, oil palm, pineapple can be grown with some success. Increasing areas of Acrisols are planted to oil palm (e.g. in Malaysia and on Sumatra).
  
• In the Llanos of Colombia, alternation of agriculture and pasture management including a legume (Arachis pintoi) seems quite successful. Here Al-tolerant rice is cropped for 2-3 years followed by cropping of N-fixing fodder plant for 5 years.

  Fig.6 Acrisol landscape

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

  
  
• Please click on ( here) to look at management and use of Acrisols.