Table of contents

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

• Parent material: unconsolidated, strongly weathered and strongly leached, finely textured materials.
  
• Environment: regions with a tropical, subtropical or warm temperate climate with a pronounced dry season, notably on old erosional or depositional surfaces of Pleistocene age or older. Many Lixisiols are presumed polygenetic soils with characteristics formed under a more humid climate in the past.

  Fig.2 Lixisols in the upper slope region

  ( Source: FAO, 2001.)

  Fig.3 Baobab, a typical tree of the dry Savannah regions

  ( Source: FAO, 2001.)

  
  

Fig.4 Lixisols worldwide

( Source: FAO, 2001.)

• Worldwide, Lixisols cover about 435 Mio. hectares, of which 50 % are present in sub-Sahelian Africa und E-Africa, about 25 % in South and Central America and 25 % in India, SE Asia.
  
• As Lixisols are a recent introduction in soil classification, their total extent is not accurately known (World Soil Resources Reports, 2001).
  

1. Must have an argic B horizon within 100 cm or within 200 cm (when loamy sand is above) ( see chapter clay eluviation)
   

• Cation Exchange Capacity (CEC) < 24 cmol_c/kg (1 M NH₄OAc solution buffered to pH 7)
  
• Base saturation ( BS) > 50 %
  

• It is assumed that the development of many Lixisols started in the past under a more humid climate than at present.
  

1. Strong weathering in the initial phase of soil formation resulted in:
   
   1. Clay eluviation (argic Bt); however, this process was only moderate and not as strongly pronounced as with other soils conditioned by wet tropical climate (set 6, WRB, 2001).
      
   2. Fossil plinthite and/or coarse reddish Fe-mottles indicate towards more humid conditions in the past

      Fig.5 Plinthic Lixisol

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

      
      
   3. The reddish or yellow colors of many Lixisols (notably in argic horizons) are the result of  ‘rubefaction’ by dehydration of ferrihydrite to hematite in long dry seasons.

      Fig.6 Rhodic Lixisol, Brazil

      ( Source: ISRIC, NL.)

      Fig.7 Lixisiol (Ghana)

      ( Source: FAO, 2001.)

      
      
2. The strong weathering during the early stages of soil formation could have been followed by chemical enrichment in more recent times, i.e. after the climate had changed towards an annual evaporation surplus. There are indications that base-rich aeolian deposits enriched some Lixisols whereas others could have been improved by biological activity or by lateral seepage of water (World Soil Resource Report, 2001).
   

a. Morphological characteristics

• Profile development is mostly AEBtC or ABtC
  
• Many Lixisols have ochric surface horizon (see  Annex2: Diagnostic horizons, properties and materials) over a brown or reddish brown argic Bt-horizon that often lacks clear evidence of clay illuviation other than a sharp increase in clay content over a short vertical distance. The overlying eluvial E-horizon, when still present, is commonly massive and very hard when dry (= hard setting). ( Stoneline) are not uncommon in the subsoil.

  Fig.8 Haplic Lixisol

  ( Source: ISRIC, NL.)

  Fig.9 Pale colour and iron segregation

  ( Source: FAO, 2001.)

  Fig.10 Poor surface soil structure of Lixisols

  ( Source: FAO, 2001.)

  Fig.11 Lixisols located on lower slope positions

  ( Source: FAO, 2001.)

  
  

b. Physical characteristics

• Low aggregate stability (no pseudo-sand structures like Ferralsols because of higher pH). Of importance is therefore erosion control.
  

c. Chemical characteristics

• Lixisols are strongly weathered soils with low levels of available nutrients and low nutrient reserves. However, the chemical properties of Lixisols are generally better than of Ferralsols and Acrisols because of their higher soil pH (BS > 50 %) and the absence of serious Al-toxicity (good root permeability).
  

• Due to low structural stability and moderate chemical fertility the conservation of surface soil and SOM is of primary concern.
  
• The low absolute level of plant nutrients and the low cation retention by Lixisols make recurrent inputs of fertilizers and/or lime a precondition for continuous cultivation.
  
• Perennial crops are to be preferred over annual crops, particularly on sloping land. Cultivation of tuber crops or groundnut increases the danger of soil deterioration and erosion (World Soil Resources Reports 94, 2001).
  

Fig.12 Surface sealing

( Source: FAO, 2001.)

Fig.13 Sorghum straw cover

( Source: IFAO, 2001.)

Fig.14 Farmers' fields lie close to the homestads

( Source: FAO, 2001.)

Fig.15 Land preparation

( Source: FAO, 2001.)

Fig.16 Farmers shape the surface layers into ridges

( Source: FAO, 2001.)

Fig.17 Small mounds are formed and planted to e.g. maize or cassava

( Source: FAO, 2001.)

Fig.18 Special mounds

( Source: FAO, 2001.)

Fig.19 Yam plants on mounds

( Source: FAO, 2001.)

Fig.20 Yam cropping I

( Source: IITA, Nigeria.)

Fig.20 Yam cropping II

( Source: IITA, Nigeria.)

Fig.21 Planting of cotton on Lixisols

( Source: FAO, 2001.)

Fig.22 Cattle herds feed on crop residues

( Source: FAO, 2001.)

Fig.23 Animal droppings are collected and dried in the sun to serve as fuel

( Source: FAO, 2001.)