After conducting all the experiments at Narrabri and analysing the results we obtained, a summary is required to obviously sum all the results up. The results are different within each experiment and across all the experiments, in that some indicate a difference between the pasture and cultivated soils. However, physical appearance plays a large role in the physical properties of a soil and just from the appearance difference between the pasture and cultivated sites (see above picture) it should be obvious that there is a significant difference between the two sites. The pasture site has pasture grasses growing on it, that were sown there many years before so they are well established plants and the cultivated site has been barren for the past 5 years after being tilled by the Cotton CRC previously.

Therefore the pasture and cultivated site are different in appearance but since physical properties are inherent of the plant growth, the question is: Are the sites different in their soil physics? There’s a two-part answer to that question and it is that ultimately yes the two sites are different in the soil physical properties. Mainly their infiltration rates and hence their saturated hydraulic conductivities are different. For example their difference in infiltration rates is shown by the Falling-head Double Ring experiment where the infiltration rate against time are shown in Figure 1 for a pasture site and a cultivated site; the initial infiltration rate is significantly faster in the pasture however the steady-state infiltration rate is reached faster for the cultivated soil. Their difference in saturated hydraulic conductivity is evident from the Falling-head Single Ring where the saturated hydraulic conductivity for the pasture is significantly larger than that of the cultivated soil (Figure 2). Another way that the difference between the pasture and cultivated sites is evident is from the shear strength of the soils; where the shear strength of the pasture site was significantly higher than that of the cultivated site (Figure 3). Ultimately these are all due to the presence or non-presence of plants, since plants enhance cracking which increases infiltration and plants cause the soil to become stablised therefore becoming stronger.

Figure 1. Infiltration rates against time for pasture site 1 and cultivated site 1, respectively.

Figure 2. The distribution of saturated hydraulic conductivities as a function of land use.

Figure 3. The distribution of shear vane as a function of land use.

However the other part of the answer is that they are not statistically different from one another. This was the fact from the Amoozemeter experiment where the actual results would indicate a difference; nevertheless after a one-way analysis of variance was performed it was found that statistically the two sites were not significantly different (Figure 4). I suspect this is because the Amoozemeter is a reading of the subsurface infiltration and the likelihood of them being similar is high since the two land uses are close to one another and thus are similar in their subsurface physics, therefore they can have similar subsurface infiltration rates. As well as this, it could be that a small dataset was collected from the field, maybe if more sites were analysed and a larger dataset was formed the two different land uses would statistically show as different.

Figure 4. The results of the statistical analysis of the Amoozemeter, comparing infiltration rates.

The expected saturated hydraulic conductivities were slow for the cultivated sites and rapid for the pasture sites. From the experiments conducted the results showed that the saturated hydraulic conductivity for the cultivated sites were slow to very slow and the pasture sites were rapid to very rapid. Therefore the numbers for the cultivated sites were small and the numbers for the pasture sites were large.

All these experiments are extremely useful for agricultural and environmental management since they allow you to be able to calculate the infiltration rate for a soil. This can be useful to help calculate such things as evaporation or deep drainage for the water balance equation. This is also very useful for the management of water use. This helps to decrease the amount of irrigation thus decreasing the amount of water leaving the rivers and streams, and therefore the farmer win financially and the environment wins with more water. In conclusion, soil physics is an incredibly useful piece of science to understand and therefore to improve your water balancing techniques.