Senior soil scientist puts old ‘age of soils’ dog down

Professor Alex McBratney of the University of Sydney has no time for the 'too old' story about our soils:

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As a scientist to answer your question I would like to compare soils of similar texture under similar climates across the world, particularly in N. Hemisphere where land surfaces are supposedly younger than the southern Gondwana continents.

The equilibrium soil organic carbon content is a function of texture (clay soils tend to have higher carbon contents than sandy ones), climate (rainfall and temperature) and plant production. (The current soil carbon models do not consider the “age” of the soil.)


Most arable soils in Australia now have half the carbon content than when they were first brought into cultivation. This is because cropping removes much of the carbon that would otherwise be dropped on the soil surface under a natural vegetation system. This tells me immediately that these soils are capable of sequestering carbon (no matter how old they are.) We simply need to return more carbon to the soil, e.g., by putting a leguminous green manure crop in the rotation etc. (We’ve been mining the soil carbon – so it’s now time to put it back..)

Personally, I think the old soil argument is somewhat spurious.

Dr McBratney is Pro-Dean, Professor of Soil Science, Faculty of Agriculture, Food & Natural Resources, The University of Sydney. He was the first person to win the Webster Medal, which he did in 2006, for the application of mathematics and statistics to soil science.