A comparison of methods assessing soil compaction on black vertosols. South-Eastern Queensland, Australia

A comparison of methods assessing soil compaction on black vertosols. South-Eastern Queensland, Australia

Mechanical soil compaction is a major problem for cotton production on vertosols in Queensland, Australia. To understand the state and impacts of soil compaction reliable measurements are essential. However an overall comparison of measurement methods does not exist for compaction in black vertosols. This research investigates which traditional and innovative methods are the most adequate to measure soil compaction on cotton grown black vertosols. Three methods were tested in the field and lab: ring sampling, the penetrometer and the EM-38. For varying reasons several other methods could not be tested and were evaluated by means of literature research. The methods were assessed on their costs, time efficiency, user-friendliness, and most importantly their reliability and physical limits. Results indicate that there was not one particular method superior to the other methods. As hypothesized, the traditional ring sampling method provided inconsistent data on soil compaction. In contrast, the penetrometer was found to be significantly correlated to the volumetric water content of the soil and proved to be an adequate device to measure soil compaction in dry conditions. Complementing the penetrometer, the shear vane method was found to be a good alternative method for use in wetter conditions. Major advantages of modern techniques over traditional methods, such as the EM38 and Electric Resistivity Tomography (ERT), were that they are non-destructive to the soil and able to detect soil compaction in a wide range of soil moisture contents. However, ERT should be further investigated for specific use on black vertosols. Compared to traditional methods, the use of the EM38 and ERT as a routine operation for farmers is still unlikely due to the higher costs, specialized equipment and need for advanced analysis. Each method has its clear advantages and disadvantages, making not one clearly superior to the others. Thus, the context and purpose in which each method is used should be carefully considered.