The relative importance of texture, structure, organic matter and clay mineralogy to the nature of the soil moisture characteristic is examined for an extensive group of Australian soils using numerical classification and diagnostic methods.The presence of pedality, particle size composition and grade of structure were the soil properties most consistently associated with differences between the groups of soils with similar moisture characteristics. By association, field texture was shown to be a useful property. Although the presence of pedality and grade of structure were important, the shape and size of ped had only weak associations with differences in the soil moisture retention.Montmorillonite, iron oxide, vermiculite and quartz were the minerals in the clay size fraction which appeared to be important if they were present. In contrast, the presence of illite did not show any strong associations with a particular position or form of the moisture characteristic.The soil moisture characteristic was successfully modelled as a power function. It appears that being able to group and classify the soil moisture characteristic and then to provide a description of these groups both in terms of soil properties and model parameters is a valuable means of developing simple predictive models for field soils. The error of our predictions for 44 horizons based on this simple approach appears to be only marginally larger than that encountered in conventional laboratory methods, and in view of soil heterogeneity it is argued that following further development these predictions may be adequate in many hydrological and agricultural applications.

The water extraction of deep-rooted perennial trees and shrub belts integrated with annual cropping/grazing systems was studied at 3 sites in the 300–450 mm rainfall zone of the Murray–Darling Basin of south-eastern Australia. Within 4 years of planting alley farming systems on cropland, the soil directly below and near the belts had dried the deep profile. Between 82 and 261 mm of extra soil water storage capacity was created in the 2.5 to 5.5–6 m profile. At Palamana (the only site monitored to greater depth), living roots were found 16 m below the surface. The cumulative water content of the soil to 12 m under the belts was 600 mm less than of soil cores extracted from nearby cropland. This water storage difference created under the belts is greater than the largest episodic event likely in this region and it is therefore unlikely that leakage will occur directly under or within a few metres of the belts. The early growth of the belts was rapid and the leaf area of the belts far exceeded that of remnant mallee eucalypt vegetation. The belts used water that had accumulated deep in the profile below the annual cropping systems they replaced. However, the belts only used water from below or within a few metres from the edge with the adjacent cropland. As suggested by RJ Harper et al. (2000), a much greater amount of potential recharge could be controlled if deep-rooted perennials were planted more closely across the landscape (compared with widely spaced belts). However, although the belts may be beneficial for the catchment water balance, they would be commercially unacceptable to farmers. In practice, farmers put the belts usually no less than 50–70 m apart so that less cropland is displaced and there is less belt/crop competition. In such cases alley farming only controls a small percentage of the total leakage, similar to the amount of crop yield lost by displacement and competition. It would be better to use a full coverage of perennials on soils where annual systems are the leakiest, rather than belts across all of the landscape, some of which may not be very leaky and could be highly profitable for annual cropping. Leakage could be controlled under cropland in a few years by growing easy to establish perennial species to retrieve moisture deep in the profile. At Pallamana the belts utilised 600 mm of accumulated leakage from deep in the profile in less than 4 years. Based on the average annual recharge rates under annual cropping (11–35 mm) the land could be cropped again for between 17 and 55 years before that leakage accumulated again.

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Field calibrations of a neutron moisture meter and a gamma density meter were made on the individual layers of a duplex soil consisting of a metre depth of sand overlying a deep cracking clay. Two sources of bias were encountered in the case of the clay layer: (1) differences in bulk density and composition between sites caused a bias of 20% in the calibration coefficient resulting in an underestimate of change in water content, and (2) non-representivity of the access tubes, due to failure to sample cracks, caused an additional negative bias of up to 30%. The first of these inaccuracies can be avoided by using a better design for the calibration experiment and by correcting neutron count rate for soil density. The second bias due to poor crack sampling can be corrected for on the assumption that only three-dimensional swelling occurs on a field-wide basis.

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