Winter cropping often does not realise its full potential in south-western Victoria, where waterlogging is a major problem on the poorly drained soils of conventional cultivation (CC) systems. Consequently, cropping has been undertaken on raised beds (RB) to reduce the risk of waterlogging. Initial reports on the yields of RB were encouraging. It was hypothesized that an improvement in soil properties of RB may account for their better performance compared to CC systems. / The aim of the thesis was to evaluate selected soil physical properties of RB and to make comparisons with other treatments (CC and pasture). The specific objectives were to: 1) evaluate plant growth and crop yield; 2) quantify soil water dynamics; 3) assess changes in the soil water retention characteristic (SWRC), soil strength and soil hydraulic properties; 4) describe pore pathways from solute transport; and 5) quantify soil macropore structure. / Measurements of volumetric water content (θv) were taken at 20, 40, 60 and 80 cm and at the soil surface. These data allowed the determination of the profile soil water deficit (SWD), which was found to be greater under the RB than the CC, although at times the pasture had the largest SWD. The RB mostly remained drier than the CC, but the response to rainfall in the surface θv was similar between treatments. Below average rainfall was received during the whole study period which resulted in drier than normal conditions. / There was no consistent difference in plant growth between crops on the RB and CC; e.g. in 2004 periods of waterlogging resulted in greater dry matter production on the RB; while drier conditions in 2003 saw better crop growth on the CC. Grain yield varied annually according to rainfall, and overall the treatment yields were similar. Analysis of regional yield data showed that there was no yield difference in years with average or below average rainfall, but years with higher rainfall favoured RB. / Little difference was found in the laboratory-derived SWRC, but in the field the RB were consistently drier at all depths and at 60 cm depth the CC had a saturated zone. The RB were found to have a lower soil strength characteristic within the surface 24 cm compared to the CC. The air-filled porosity (AFP) was higher in the RB while for long periods the CC were <10 per cent AFP. There was no significant difference between the treatments in unsaturated hydraulic conductivity (Kus) in the soil surface. Saturated hydraulic conductivity (Ks) in the subsoil was very small, although the RB had significantly greater Ks than the CC. / A solute transport experiment investigated the movement of a solute in large soil cores of the RB and CC treatments. Derived parameters from a transfer function model were used to assess the solute transport characteristics. This showed that under nearly saturated conditions the CC had significantly greater solute spreading than the RB. Furthermore, the transport volume (θst) to θv ratio was smaller in the RB which indicated a greater proportion of preferential flow. These and other data suggested that the RB had a better connected and more stable pore network. / Soil macropore structure was quantified using image analysis of resin-impregnated soil. Samples were taken twice; the first samples showed that the RB had improved pore connectivity, slightly greater porosity and a pore network with smaller sized pore components than the CC. In comparison, at the second sampling time the structural parameters of the two treatments were similar. / Uncertainty exists in the scenario of higher rainfall or of the longer-term changes of soil properties under RB cropping. Nevertheless after three years of measurements, this thesis concludes that most soil physical properties of RB are distinctly better for cropping than under CC systems.
| Identifer | oai:union.ndltd.org:ADTP/245625 |
| Creators | Holland, Jonathan Eddison |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
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