Revision

Correct! On average, British soils will contain more soil organic matter than Australian soils. The cooler, wetter climate means that SOM decomposition is slower (low temperature slows respiration, as does waterlogging which is more likely to occur in wet climates). Also, in Britain plant biomass production is higher than in the relatively dry Australian climate, leading to greater inputs of residues to the soil.

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Correct! Fertiliser increases plant production, which increases residue production, which in turn increases humus production. In some improved pastures the rising SOM levels are actually a problem. Humus is acidic and increasing humus contents are a contributing factor to soil acidification.

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Correct! Leaching of most (but not all) of the Sit+ released as feldspars weather leads to formation of 1:1 clay minerals like kaolinite. Na* is not part of the clay crystal lattice and its leaching does not directly affect clay mineral formation. A13+ is not leached as it forms insoluble compounds.

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Correct! Initially leaching removes soluble salts from the profile, which reduces the electrical conductivity of an aqueous extract. Next leaching replaces the exchangeable bases with H⁺ from carbonic acid, which lowers the base saturation and makes the soil acidic. The H⁺ ions react with the clay to liberate exchangeable A1³⁺

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Correct! Illuviation is the movement of suspended material into a horizon. Eluviation is the equivalent movement out of a horizon. Leaching refers to the movement of dissolved material. What does pedoturbation mean? 

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Correct! Intermittent waterlogging mobilises and reprecipitates Fe which leads to mottling and accumulation of laterite or ironstone concretions. Gravel layers may be produced by deposition of eroded material, but the occurrence of such a layer between the A and B horizons would only happen under exceptional circumstances.

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