Table of contents

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

• Parent material: finely textured weathering products of intermediate to basic parent rocks, possibly rejuvenated by recent admixtures of volcanic ash. The clay assemblage is dominated by kaolinite. Nitisols are rich in Fe and have little water-dispersible (natural) clay.
  
• Environment: Nitisols are predominantly found in level to hilly land under tropical rain forest or savannah vegetation.

  Fig.2 Nitisols are found in gently undulating landscapes

  ( Source: FAO, 2001.)

  Fig.3 Rhodic Nitisol landscape, Nicaragua

  ( Source: ISRIC, NL.)

  Fig.4 a. undulating: on basic rock types and middle slope positions b. volcanic landscape: mid-slope positions c. uplifted and dissected landscapes on old surfaces: on slopes associated with Ferralsols

  ( Source: FAO, 2001.)

  
  

Fig.5 Nitisols worldwide

( Source: FAO, 2001.)

• Worldwide, about 200 Mio. hectares of Nitisols are found. More than 50 % are found in Africa, mainly on uplands higher 1000 m: Ethiopia, Kenya, Congo, Cameroon.
  
• In Asia, S-America, C-America Nitisols are present at lower altitudes.
  

• Must have a  nitic horizon within 100 cm.

  Fig.6 Nitic horizon

  ( Source: ISRIC/FAO/IUSS, 2001.)

  
  
• Having gradual to diffuse horizon boundaries.
  
• No ferric, plinthic, or vertic properties within 100 cm from the soil surface.  see LECTURE NOTES ON THE MAJOR SOILS OF THE WORLD
  

1. Ferralitization (early stage) see ( Process of ferralitization)
   
2. Nitidization: formation of angular shiny peds, most likely through
   
   • „micro-swelling and shrinking“
     
   • Shiny ped surfaces: combination of clay eluviation and pressure when the soil is wet; clay particles orientate in well-regulated form (ped face)
     
3. Homogenization: through ( termites) , ants, earthworms (Bioturbation)
   
4. Assumption: rejuvenation through deposition/enrichment of volcanic ashes
   

a. Morphological characteristics

• Nitisols are normally deeper than 150 cm and dusky red or dark red in color.

  Fig.7 Rhodic Nitisol, Nicaragua

  ( Source: ISRIC, NL.)

  Fig.8 Nitisol, Rwanda

  ( Source: ISRIC, NL.)

  Fig.9 Deep, red Nitisols on limestone in Central Italy

  ( Source: FAO, 2001.)

  
  
• They are well-drained soils with a clayey subsurface horizon that is deeply strechted and has nutty or polyhedric blocky structure elements with shiny ped faces.

  Fig.10 Deep argic horizon

  ( Source: FAO, 2001.)

  Fig.11 Rhodic Nitisol with polyhedric blocky structure elements, Nicaragua

  ( Source: ISRIC, NL.)

  Fig.12 Rhodic Nitisol, Nicaragua with well developed blocky soil structure

  ( Source: ISRIC, NL.)

  Fig.13 Soil structure elements

  ( Source: Brady and Weil, 2002.)

  
  
• Profile development mostly is ABtC.
  
• The clay assemblage of Nitisols is dominated by kaolinite with minor quantities of illite.
  
• They contain 4 % or more ‘free’ iron (Fe₂O₃, by dithionite-citrate extraction) in the fine earth fraction and more than 0.2 % active or mobile Fe (by acid oxalate extraction at pH 3).
  

b. Physical characteristics

• Normally, they have a good soil structure, good porosity and good water holding capacity and very good rootability.

  Fig.14 Good physical properties

  ( Source: FAO, 2001.)

  However, depending on their clay content they might be hard when dry and sticky when wet.
  

c. Chemical characteristics

• The CEC is higher compared to the other soils of the humid tropics (Ferralsols, Lixisols, Acrisols) due to
  
  • the high clay content: higher than 30 % and sometimes higher than 60 %. The BS varies between 10 to 90 %

    Fig.15 Clay contents of Nitisols, ferralsols, acrisols, lixisols and alisols

    ( Source: Bridges, 1997.)

    
    
  • Soil organic matter (SOM) makes a considerable contribution to the overall CEC, especially in mollic or umbric soil units.

    Fig.16 Humic Nitisol, South Africa

    ( Source: ISRIC, NL.)

    
    

d. Biological characteristics

• Intense faunal activity and termites are accountable for the typical gradual horizon boundaries of Nitisols. ( Termites) are particularly effective in homogenizing soil.
  

• Nitisols are among the most productive soils in the humid tropics.
  
• They are planted to plantation crops such as cocoa, coffee, rubber, pineapple and are widely used for food crop production on smallholdings.
  
• In many volcanic areas: rejuvenation through volcanic ash.
  

Fig.17 Intercropping on Nitisols

( Source: FAO, 2001.)

Fig.18 Plantation crops

( Source: FAO, 2001.)

Fig.19 Maize cropping on Nitisols

( Source: FAO, 2001.)

Fig.20 Maize-cassava intercropping on haplic Nitisol in Rwanda

( Source: ISRIC, NL.)