A comparison of methods assessing soil compaction on black vertosols. South-Eastern Queensland, Australia MSc thesis by Luuk de Vetten September 2014 Soil Physics and Land Management Group 1 A comparison of methods assessing soil compaction on black vertosols. South-Eastern Queensland, Australia Master thesis Soil Physics and Land Management Group submitted in partial fulfillment of the degree of Master of Science in International Land and Water Management at Wageningen University, the Netherlands Study program: MSc International Land and Water Management Student registration number: 900424887050 SLM 80336 Supervisors: WU Supervisor: Dr. Jantiene Baartman NCEA supervisor: Dr. John McLean Bennett Examiner: Dr. Jantiene Baartman 24/09/2014 Soil Physics and Land Management Group, Wageningen University i Abstract 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. Key words: compaction, cotton, vertosol, methods, penetrometer, EM38. ii Table of contents 1: Introduction ................................................................................................................................................... 1 2: Problem statement and objectives ............................................................................................................... 3 3: Research questions ........................................................................................................................................ 4 3.1 Main research question ........................................................................................................................... 4 3.2 Sub questions .......................................................................................................................................... 4 4: Theories and concepts ................................................................................................................................... 5 4.1 Soil compaction ....................................................................................................................................... 5 4.2 Porosity, bulk density and soil strength .................................................................................................. 6 4.3 Causes and effects ................................................................................................................................... 8 4.4 Black Vertosols ...................................................................................................................................... 10 5. Research Methodology ................................................................................................................................ 13 5.1 Study area .............................................................................................................................................. 13 5.2 Indicators ............................................................................................................................................... 14 5.3 Assessment ............................................................................................................................................ 16 6. Methods tested in the field ......................................................................................................................... 17 6.1 Ring sampling and soil coring ................................................................................................................ 17 6.2 Penetrometer ........................................................................................................................................ 23 6.3 EM38 Ground Conductivity Meter ........................................................................................................ 28 7. Reviewed methods ...................................................................................................................................... 36 7.1 Ground Penetrating Radar (GPR) .......................................................................................................... 36 7.2 Electric Resistivity Tomography (ERT) ................................................................................................... 39 7.3 Thermal methods .................................................................................................................................. 42 7.4 Alternative methods .............................................................................................................................. 45 8. Summary and conclusions ........................................................................................................................... 49 References ....................................................................................................................................................... 52 Appendix A: Penetrometer data...................................................................................................................... 56 Appendix B: EM38 maps .................................................................................................................................. 57 B1: H0.5 position ................................................................................................................................... 57 B2: H1.0 position ................................................................................................................................... 58 B3: V0.5 position .................................................................................................................................... 59 B4: V1.0 position .................................................................................................................................... 60 iii 1: Introduction According to the Food and Agriculture Organization (FAO, 2009) the global population will continue to grow to 9 billion people in 2050. The large increase in population and changing consumption patterns mean that there will be a higher demand for agricultural products. To be able to feed the world’s population in 2050 food production has to increase with 70% (FAO, 2009). In addition to the population pressure, the changing consumption patterns have a large impact on how the agricultural sector will look like in 2050. Over the past decades trends are an increasing demand for animal products, energy, water and luxury products. This produces extra pressure on the existing natural resources and available arable land (Godfray et al., 2010). While the area used as arable land is still increasing globally, the area of arable land in Western countries is decreasing (FAO, 2009). As arable land is finite and already limited in Western countries, there is a need to intensify the agricultural production. In the past century the mechanization of agriculture in Western countries has contributed to the increase of agricultural production by enhancing for example the harvest efficiency and soil bed preparation. In addition, mechanization has increased the time and labour efficiency which in turn decreased the need for human labour. This is an important driver for mechanization in wealthy countries, as labour costs are relatively high. However, in some cases mechanization has led to unsustainable and undesirable side effects such as erosion, pollution and particularly soil compaction (FAO, 2013). Soil compaction is a problem which can be observed worldwide: 68 million hectares of land are estimated to be compacted due to vehicular traffic alone (Hamza and Anderson, 2005). Due to heavy machinery the soil gets compacted