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This paper describes a rainfall simulator developed for field and laboratory studies that gives great flexibility in plot size covered, that is highly portable and able to be used on steep slopes, and that is economical in its water use. The simulator uses Veejet 80100 nozzles mounted on a manifold, with the nozzles controlled to sweep to and from across a plot width of 1.5 m. Effective rainfall intensity is controlled by the frequency with which the nozzles sweep. Spatial uniformity of rainfall on the plots is high, with coefficients of variation (CV) on the body of the plot being 8–10%. Use of the simulator for erosion and infiltration measurements is discussed.

The dielectric behaviour of 3 soils, a sandy loam (Red Chromosol), a highly structured non-swelling clay (Red Ferrosol), and a self-mulching swelling clay (Black Vertosol), was investigated using a waveguide and network analyser technique in the frequency range 3.0 GHz to 4.5 GHz. Curves relating the real part of the relative permittivity to water content are presented and compared with the general Topp curve. The Chromosol generally followed the Topp curve, but the Ferrosol and Vertosol both had curves below the Topp curve. The Ferrosol showed a maximum horizontal offset of 0.05 m3/m3 from the Topp curve in the mid soil-water content range of 0.2–0.3 m3/m3 offset from the Topp curve of 0.10 m3/m3, with a maximum of 0.12 m3/m3 occurring at a soil water content of 0.4 m3/m3. Similar dielectric curves were obtained for the Chromosol and Vertosol using time domain reflectometry (TDR). With this method, the Chromosol showed very close agreement with the Topp curve, but the Vertosol again gave a curve below the Topp curve, similar to the one obtained using the waveguide and network analyser, but with a smaller maximum horizontal offset of 0.08 m3/m3. The difference between the waveguide and TDR Vertosol curves was mainly attributed to low bulk densities in the waveguide where packing was difficult. Some was also attributed to the wider spectrum of frequencies used by TDR. Use of the Topp curve for TDR measurements in the Vertosol would underestimate its water content by at least 0.06 m3/m3. These results are in good agreement with others obtained from similar soils. Deviations from the Topp curve are attributed to bound water associated with the clay particles and this depends on clay mineralogy and clay content. The presented calibration curves improve the accuracy of TDR measurements in these types of clay soils. A field comparison between water contents measured by TDR and gravimetric sampling in a similar Black Vertosol is presented. This calibration showed that soil water contents can be severely overestimated by using TDR with long probes and cables. This unexpected and opposite result is discussed in terms of attenuated high frequencies in the 15-m-long connecting cable used, errors in depth of probe placement, and changes in bulk density and DC conductivity.

The physical properties of krasnozems and euchrozems in Australia have received little attention due to the widespread perception that they are 'good' soils. We present data from three locations which are representative of these soil types in the South Burnett region of southern Queensland. At each location, paired sites were chosen where continuously cropped and uncropped land existed side by side. The effect of continuous cropping on physical fertility, relative to that of soil in virgin condition, is assessed and related to published data from other locations where available. Continuous cropping has reduced infiltration rates from 80 mm h-1 or more to values as low as 25 mm h-1. Originally low bulk densities ranging from 0.6 Mg m-3 at the surface to 1.3 Mg m-3 at 70 cm depth have been increased to corresponding values of 1.0 and 1.4 Mg m-3. Local maxima of 1.3 Mg m-3 occur between 15 and 30 cm depth. Penetration resistance has been increased markedly at low water contents as a result of increased cohesion, with an uncropped soil having values <2.5 MPa over the available water content range comapred with values of >6 MPa in the continuously cropped soil. Organic carbon in the surface soil has been reduced from 4-5% to 1% and aggregate stability under rain has been reduced, the % aggregates <0.125 mm diameter increasing from 10% to 20% or more. Soil water storage has been reduced together with crop water extraction, with these effects attributed to a loss of water storage pores in the top 30-50 cm of the profile and restricted root development. The problems of rehabilitating these soils are briefly discussed. Continuous cropping under dryland conditions has greatly reduced the physical fertility of krasnozem and euchrozem soils and made them more susceptible to variation in seasonal conditions. Available data suggest degradation is also occurring on krasnozems used for intensive vegetable production. Methods of rehabilitating physical fertility of degraded krasnozems are required, as are farming systems which are more sustainable in the long term.