Fine‐resolution multiscale mapping of clay minerals in Australian soils measured with near infrared spectra

Clay minerals are the most reactive inorganic components of soils. They help to

determine soil properties and largely govern their behaviors and functions. Clay minerals

also play important roles in biogeochemical cycling and interact with the environment

to affect geomorphic processes such as weathering, erosion and deposition. This paper

provides new spatially explicit clay mineralogy information for Australia that will help to

improve our understanding of soils and their role in the functioning of landscapes and

ecosystems. I measured the abundances of kaolinite, illite and smectite in Australian soils

using near infrared (NIR) spectroscopy. Using a model‐tree algorithm, I built rule‐based

models for each mineral at two depths (0–20 cm, 60–80 cm) as a function of predictors that

represent the soil‐forming factors (climate, parent material, relief, vegetation and time),

their processes and the scales at which they vary. The results show that climate, parent

material and soil type exert the largest influence on the abundance and spatial distribution

of the clay minerals; relief and vegetation have more local effects. I digitally mapped

each mineral on a 3 arc‐second grid. The maps show the relative abundances and

distributions of kaolinite, illite and smectite in Australian soils. Kaolinite occurs in a range

of climates but dominates in deeply weathered soils, in soils of higher landscapes and in

regions with more rain. Illite is present in varied landscapes and may be representative of

colder, more arid climates, but may also be present in warmer and wetter soil

environments. Smectite is often an authigenic mineral, formed from the weathering of

basalt, but it also occurs on sediments and calcareous substrates. It occurs predominantly

in drier climates and in landscapes with low relief. These new clay mineral maps fill a

significant gap in the availability of soil mineralogical information. They provide data to

for example, assist with research into soil fertility and food production, carbon