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Sensitivity Of Soil Structure To Changes In Organic Carbon Content: Predictions Using Pedotransfer Functions

B. D. Kay, A. P. da Silva, J. A. Baldock

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Pedotransfer functions (PTFs) were used to assess the sensitivity of the structural characteristics of coarse- and medium-textured calcareous illitic soils at different levels of relative compaction (RC) to changes in the organic carbon (OC) content. The analyses predicted that an increase in the OC content of 0.01 kg kg−1 would:• increase the available water content from 0.02 to 0.04 m3 m−3 with the largest increases occurring in coarser-textured soils and not being strongly influenced by RC;• decrease the air-filled porosity at field capacity from 0.01 to 0.04 m3 m−3 with the largest decreases occurring in the finer-textured soils and not being strongly influenced by RC;• decrease the soil resistance to penetration with the decreases most pronounced at lower water potentials and higher RC; at the permanent wilting point and a RC of 0.95 the decrease would range from 1.2 to 3.8 MPa;• increase the least limiting water range from 0.01 to 0.05 m3 m−3 with the increase varying with clay content.A comparison with predictions based on PTFs derived from data sets from other parts of the world indicated caution should be exercised in applying PTFs to soil and climatic conditions that are different from those from which the PTFs were derived until the impacts of these conditions are better understood. Key words: Bulk density, field capacity, permanent wilting point, available water; aeration, soil resistance, least limiting water range