Your gateway to a wide range of natural resources information and associated maps

Victorian Resources Online

Fire and its influence on soil

Types of fire and consequent heat waves

McKenzie et al (2004) developed the following illustration of heat waves from various types of fires. It is based on data from Walker et al (1986) and Humphreys and Craig (1981). It shows that it takes quite intense fires to penetrate far into the soil surface.

Penetration of fire generated head into a soil

Fire and its effect on soil

Example ranging from

A - a grassline fire, through to
E - a windrow burn

The particular detail of each heat wave (apart from fire intensity and duration) is modified by soil moisture content and soil type (texture and porosity).

Changes to soil caused by fire

The following table (also from McKenzie et al., 2004), based on work of Walker et al., 1986 provides information on soil changes induced by fire induced soil temperatures

Dominant type of changeTemperature (C)Effect
Biological<25Usual soil temperatures
37Maximum stimulation of soil microorganisms
50Mild sterilisation due to water loss
60Proteins denatured
70High nitrate mineralisation
100Soil ammonium production starts
110Soil water lost
125Soil sterilisation
2001. Water repellence caused by distillation of volatiles
2. Loss of nitrogen commences
Chemical3001. Maximum amino acid nitrogen released
2. Loss of sulfur and phosphorus begins
3. Distillation and carbonisation of organic residues
4. Organic matter charred
400Organic matter carbonised
420Water lost from within clay minerals causing change in type (e.g. illite converts to kaolinite)
540Little residual nitrogen or carbon left
6001. Maximum loss of potassium and phosphorus
2. Fine ash produced. Organically bound cations form oxides
Physical950Clay minerals converted to different phases
>1200Loss of calcium as gas
Page top