Understanding the Structure of Krasnozem Soils

What is Soil Structure?

The way soil particles - sand, silt, clay and organic matter - are arranged and the size and shape or gaps and channels (pores) between them. It is also how resilient these pores are to the pressures of modern day farming practices and how quickly they recover if damaged.

Krasnozems are classified as Ferrosols in the Australian soil classification due to their high free iron oxide content.

Krasnozems in good physical condition have:
  • loose and friable tilth
  • high permeability of both air and water
  • reasonable plant-available water content
  • low soil strength when moist
which makes them easy to cultivate and ideal for plant growth by allowing plant roots to explore all of the soil for water and nutrients stored there. Good soil structure is essential for achieving high crop yields.

Stability

Krasnozem topsoil structure is kept stable by different mechanisms depending on the size of aggregates.

Micro-structure

  • Important for plant water storage. Aggregates up to 0.5 mm diameter stabilised by iron and aluminium oxides.
  • Creates loamy field textures in high clay content soils.
  • Very resilient to impacts of tillage.

Meso-structure

  • Important for tilth, drainage and plant water storage.
  • Aggregates 0.5 - 5mm diameter stabilised by structural bonds from decomposed organic matter.
  • Susceptible to breakdown due to poor management

Macro-structure

  • Important for ensuring rapid permeability and drainage.
  • Aggregates greater than 5mm diameter stabilised by plant roots, bacteria and mycorrhiza binding smaller aggregates together.
  • Very susceptible to damage as soon as living plant roots and organisms die or are removed.
Krasnozems have the most stable structure of any Australian soil, but how long does it take change soil stucture?

Soil Structure Breakdown
Time Taken
Soil Structure Improvement
1 second
tyres, harvesters, stock hooves on wet soil
1 hour
raindrops or irrigation seal bare soil
1 week
1 month
excessive tillage
1 year
fine roots of plants and fungi binding soil
green manure crop
organic matter declinestubble retention
10 years
earthworms burrowing
well managed pasture phase
100 years


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