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The experiment reported examined the effect of sheep trampling and grazing during wet conditions on soil physical properties and pasture growth over three winter seasons. The soil type studied was a structurally unstable sandy clay loam (a calcic red-brown earth) located in a dryland agricultural area (307 mm average annual rainfall) of Western Australia. Deferred grazing was investigated as a management option to reduce structural deterioration at the soil surface. Changes in soil physical properties as a result of trampling were related to soil water storage and pasture productivity. Infiltration rates were reduced as a result of sheep trampling, but there were no measurable changes in soil bulk density. Differences in pasture production between continuously grazed and ungrazed treatments were related to the amount of stored soil water, which in turn was related to infiltration rates. Pasture root growth during the season was also reduced as a result of trampling. Deferred grazing yielded the same quantity of biomass for feed over the reduced period available for grazing and proved to be a beneficial management practice since reasonably high infiltration rates were maintained. Results from the study also indicated that pasture must be adequately grazed to reduce leaf area later in the season when evaporative demand increases. A high leaf area over this time period may result in early pasture senescence.

A number of field experiments have separately evaluated plant responses to water stress, root distribution and soil water extraction patterns, consumptive water use, grain yield, and water use efficiency (WUE); few studies have investigated water movement through the soil‐plant‐atmosphere continuum as a whole. A field study was therefore conducted on spring wheat (Triticum aestivumL. cv. SST33), sown on a Rhodic Paleustalf soil in the Republic of South Africa, to relate the response of the plant and its root system to different water application frequencies. Special emphasis was on a soil dryingout period. Treatments consisted of high‐ and low‐frequency irrigation, with one treatment from each being maintained as a wellwatered control (HFc, and LFc, respectively), and one treatment from each being subjected to a period of water stress after anthesis (HFsand LFsrespectively). Soil water content, root length and distribution, and leaf water potential (ΨL) were monitored before and after irrigations and during the soil drying‐out period. Plants in the HFsand LFstreatments developed shallower rooting systems than plants in both the LFcand LFstreatments. Soil water extraction patterns were correlated to rooting distributions. Deeper roots became increasingly efficient at extracting water as the soil became progressively drier from the surface downwards, but the total water uptake was insufficient to enable the plants to transpire at their potential rate. The departure of the evapotranspiration/potential evapotranspiration (ET/PET) ratio from its well‐wateredvalue occurred at 14% (HFs) and 17% (LFs) depletions from field capacity, and this, coupled with the concomitant decrease in ΨL, suggests that plants can maintain a constant ET/PET ratio only when water is freely available in the upper soil layers. Frequent light applications of water resulted in reduced fluctuations in ΨLthus, higher yields and an improved WUE were obtained.

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Settling velocity characteristics of sediment eroded by overland flow only, or from a combination of rainfall (100 mm h-l) and runon were measured under controlled conditions in a simulated rainfall tilting-flume facility. Two contrasting soil types were studied: a cracking clay (black earth or vertisol), and a slightly dispersive sandy clay loam (solonchak or aridisol). For a constant volumetric flux (1.0x10-1 m3 m-1 s-1) at exit from the 5.8m long flume and a slope of 0.5%, sheet erosion prevailed, whilst for the same flux at a steeper slope of 5%, rill erosion prevailed. Settling velocity characteristics of eroded sediment were found to be dependent on erosion process, flow hydraulics, soil type, and time in the erosion event. For both soil types, there was a progressive change in settling velocity characteristics with time, this change being less pronounced for sediment eroded dominantly by rill flow as opposed to sheet flow. Temporal changes in settling velocity characteristics were attributed to the development of a deposited layer of coarser, faster settling sediment on the soil surface. The net outcome of rill erosion was less size-selectivity compared with sheet erosion, as determined by the measured settling velocity characteristics of eroded sediment. This outcome was associated with the greater erosive power of rill flow compared with sheet flow. Rainfall was found to influence the settling velocity characteristics of eroded sediment substantially when sheet flow predominated. This was thought to be due to lower flow velocities under rainfall (and therefore smaller contribution to soil loss by entrainment). The findings reported in this study have important implications when assessing nutrient losses from eroded sediment, and in predicting the spatial redistribution of eroded sediment.