Near-surface distributions of soil water and water repellency under three effluent irrigation schemes in a blue gum (Eucalyptus globulus) plantation

Thwaites, L. A., de Rooij, G. H., Salzman, Scott, Allinson, G., Stagnitti, Frank, Carr, Rodney, Versace, Vince, Struck, S. and March, T. 2006, Near-surface distributions of soil water and water repellency under three effluent irrigation schemes in a blue gum (Eucalyptus globulus) plantation, Agricultural water management, vol. 86, no. 1-2, pp. 212-219.

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Title Near-surface distributions of soil water and water repellency under three effluent irrigation schemes in a blue gum (Eucalyptus globulus) plantation
Author(s) Thwaites, L. A.
de Rooij, G. H.
Salzman, Scott
Allinson, G.
Stagnitti, Frank
Carr, Rodney
Versace, Vince
Struck, S.
March, T.
Journal name Agricultural water management
Volume number 86
Issue number 1-2
Start page 212
End page 219
Publisher Elsevier BV
Place of publication The Netherlands
Publication date 2006-11-16
ISSN 0378-3774
Keyword(s) water repellency
irrigation
waste-water
unsaturated soil
soil physics
Summary Water repellent soils are difficult to irrigate and susceptible to preferential flow, which enhances the potential for accelerated leaching to groundwater of hazardous substances. Over 5 Mha of Australian soil is water repellent, while treated municipal sewage is increasingly used for irrigation. Only if a critical water content is exceeded will repellent soils become wettable. To avoid excessive loss of water from the root zone via preferential flow paths, irrigation schemes should therefore aim to keep the soil wet enough to maintain soil wettability. Our objective was to monitor the near-surface water content and water repellency in a blue gum (Eucalyptus globulus) plantation irrigated with treated sewage. The plantation's sandy soil surface was strongly water repellent when dry. For 4 months, three rows of 15 blue gum trees each received no irrigation, three other rows received 50% of the estimated potential water use minus rainfall, and three more rows received 100%. During this period, 162 soil samples were obtained in three sampling rounds, and their water content (% dry mass) and degree of water repellency determined. Both high and low irrigation effectively wetted up the soil and eliminated water repellency after 2 (high) or 4 (low) months. A single-peaked distribution of water contents was observed in the soil samples, but the water repellency distribution was dichotomous, with 44% extremely water-repellent and 36% wettable. This is consistent with a threshold water content at which a soil sample changes from water repellent to wettable, with spatial variability of this threshold creating a much wider transition zone at the field scale. We characterized this transition zone by expressing the fraction of wettable samples as a function of water content, and demonstrated a way to estimate from this the wettable portion of a field from a number of water content measurements. To keep the plantation soil wettable, the water content must be maintained at a level at which a significant downward flux is likely, with the associated enhanced leaching. At water contents with negligible downward flux, the field is water repellent, and leaching through preferential flow paths is likely. Careful management is needed to resolve these conflicting requirements.
Language eng
Field of Research 050305 Soil Physics
HERDC Research category C1 Refereed article in a scholarly journal
Copyright notice ©2006 Elsevier B.V.
Persistent URL http://hdl.handle.net/10536/DRO/DU:30003877

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