Measurements of intrinsic sorptivity (S*) by using both ethanol and water were used to indicate the extent of water-repellency in soil. Experiments with initially dry, acid-purified sand verified that in a non-repellent, nonswelling porous medium S' was indeed intrinsic to the medium, and independent of the sorbing liquid. For initially water-moist, non-repellent sand, the measured S* was different when ethanol and water were the invading fluids. But a bound can be put on this difference. It was concluded that in structurally stable soils, the ratio of S* from ethanol to that for water may be used as an index of water-repellency. In the laboratory, disturbance of repellent soil by sieving or shaking effectively removed the repellency. Subsequent incubation restored it. Field measurements of sorptivity, at a scaled negative surface potential, into an initially moist, fine, sandy loam were made. While the soil appeared to absorb water normally, the sorptivity for water was an order of magnitude lower than expected from the ethanol data. This was due, we suggest, to repellency. Some possible implications of this unexpected result are discussed.

No abstract

Undisturbed cores were removed from the surface of 14 New Zealand soils with a wide range of textures. The sorptivity to ethanol and water was measured with a 'sorptivity tube' to determine the repellency index (Rl) of each soil. Texture and gravimetric water content were measured, and the water drop penetration time (WDPT) and molarity of ethanol droplet (MED) tests for water repellency were conducted on the soils. The RI measured all soils water repellent (RI> 1.95) at field moisture conditions, and was more sensitive than the WDPT or MED tests. The RI was used to demonstrate that water repellency reduced short-time water infiltration of all soils by approximately an order of magnitude. Actual and 'potential' infiltration was then compared with rainfall and irrigation intensities. This illustrated the hydrological significance of the phenomenon, even in soils which appeared to wet normally (low WDPT). In all soils the curves of cumulative infiltration versus the square root of time for both water and ethanol stayed linear long enough for sorptivity evaluation. However, at longer times the slope of the curve tended to increase for water sorption in the more repellent soils, but decreased consistently for ethanol.

A series of sands on the west coast of the lower North Island, New Zealand, were studied to investigate the effects of time, topography and vegetation cover upon the development of soil water repellency. Severe repellency was measured with the molarity of ethanol droplet (MED) index in the Waitarere and Motuiti dune phase sands, of age

The behaviour of the ground in the cold regions of the world is characterized by freezing and thawing. The porous and particulate nature of soils presents conditions for phase change which lead to their unique properties and behaviour in cold climates. Accordingly, the periodic and unstable nature of atmospheric climate and of surface microclimate produces characteristic disturbances in the near-surface layers of the ground in the cold regions. These include the consequences of melting such as subsidence (thermokarst topography) and instability of slopes (landslides, mud- flows), as well as the thermodynamic and mechanical effects of freezing, especially frost heave. Frozen soils show temperature-dependent creep (some forms of solifluction and deformation of foundations) and continuing heave (expansion of ground over long periods of time). These effects have important geotechnical implications for the design of highways, airports, buildings and, notably, pipelines. The complexity of the design problems for major structures, especially pipelines, has not been widely understood. If there is global warming due to anthropogenic emissions of gases this will influence the direction and intensity of the ground disturbances, the nature of which has been recognized over the last three or four decades. However the effects of such warming due to atmospheric climate change will only become apparent over many decades. In the short term they will be masked by other ground temperature changes due to microclimatic effects and to inter-annual variability of climate and weather. Over a period of a century or more, if warming trends continue, there will be important modifications of terrain and physiography.

VVaterrepellency ofHimatangisandwas assessedby in situ waterinfiltrationmeasurements andinthelaboratory usingtheMolarityofanEthanol Droplet(11ED) technique. Infiltrationrates onwaterrepellent areas were an order of magnitude lower than rates on adjacent, less repellent areas. The surface(30mm)soilofcoresremoved from repellent areaswasseverelyrepellent(11ED >2.2),andsoilto a depthof 150 mm was moderately repellent.Mlilr was strongly correlatedwithsoil carboncontent(R2 = 0.79). Attempts weremadetoovercomerepellency by wetting the soil and by abrasion. The water repellency of Himatangi sand increased when the gravimetric soil water content, w, was increased from 0.03 to 0.05, and then declined rapidly with further increases in soil water content. Air-dry sampleswereagitatedin an end-over-end shakerfor a range of 1-48 h. Soil water repellency was significantly (P < 0.01) reducedby agitation for up to 8 h. Warerrepellencyof sampleswhichhadbeen shakenfor 2, 4,8, and 12 h significantly (P < 0.01) increasedafter standinguntil 72 h had elapsed.

A range of soil wetting agents was evaluated in glasshouse experiments using the Himatangi sand. Comparisons of application rates required to overcome water repellency and enable ryegrass seedling emergence revealed significant differences (P < 0.05) in product performance. The dilution rate for wetting agent application was also found to be a significant (P < 0.05) factor for some products. In a field trial, pasture establishment was significantly improved on plots (4.8 X 10 m) which were band-sprayed with wetting agents (Wettasoil 12 litre/ha, Aquagro 8 litre/ha). Application rates were selected from the glasshouse experiments. However, soil water content had a high spatial variability and did not differ significantly (P> 0.05) between plots. A blanket spray (20 litre/ha) of Wettasoil on a cultivated area (45 m 2) ofHimatangi sand increased the surface soil water contentrelative to untreated soil; however, this effect was not maintained over the following months. Glasshouse experiments were conducted to study the relationship between some aspects of irrigation scheduling and the performance of wetting agents. Delays of up to 14 days in initial wetting following wetting agent