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| Titel |
Influence of soil water repellency on runoff and solute loss from New Zealand pasture |
| VerfasserIn |
P. Jeyakumar, K. Müller, M. Deurer, C. van den Dijssel, K. Mason, S. Green, B. E. Clothier |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250059403
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| Zusammenfassung |
| Soil water repellency (SWR) has been reported in New Zealand, but knowledge on its
importance for the country’s economy and environment is limited. Our recent survey on the
occurrence of SWR under pasture across the North Island of New Zealand showed that most
soils exhibited SWR when dry independent of climate but influenced by the soil order. SWR
is discussed as an important soil surface condition enhancing run-off and the transfer of
fertilizers and pesticides from agricultural land into waterways. So far, the impact of
SWR on run-off has rarely been measured. We developed a laboratory-scale run-off
measurement apparatus (ROMA) to quantify directly the impact of SWR on run-off from
undisturbed soil slabs. We compared the run-off resulting from the run-on of water with
that resulting from an ethanol (30% v/v) solution, which is a fully-wetting liquid
even in severely hydrophobic soils. Thus, the experiments with the ethanol solution
can be understood as a proxy measure of the wetting-up behaviour of hydrophilic
soils.
We conducted ROMA run-off experiments with air-dried soil slabs (460 mm long x 190
mm wide x 50 mm deep) collected from pastoral sites, representing three major soil orders in
the North Island: Recent Soil (Fluvisol), Gley Soil (Gleysol), and Organic Soil (Histosol),
with water followed by the ethanol solution at a run-on rate of 60 mm/h. Bromide was
applied at 80 kg KBr/ha prior to the water experiments to assess potential solute losses via
run-off. The air-dried soils had a high degree and persistence of SWR (contact angles, 97, 98
and 104Ë , and potential water drop penetration times, 42, 54 and 231 min for the
Fluvisol, Gleysol and Histosol, respectively). Under identical soil and experimental
conditions, water generated run-off from all soils, but in the experiments with the ethanol
solution, the entire ethanol solution infiltrated into the soils. The ranking of the
run-off coefficients of the soils directly reflected their ranking in persistence and
degree of SWR. The runoff coefficients were 96 (±2), 28 (±4), and 16 (±2.5) %
for the Histosol, Gleysol and Fluvisol, respectively. However, even the extremely
hydrophobic Histosol, which had a runoff coefficient of 96%, only lost 13% of the applied
bromide via run-off demonstrating that run-off occurred in channels. In addition, SWR
reduced the water storage by 33, 14, and 41% for the Fluvisol, Gleysol and Histosol,
respectively.
We identified difficulties around the accuracy and meaningfulness of the persistence of
SWR determined with the water drop penetration time (WDPT) test, which measures the
persistence of SWR at a single point. In contrast, our ROMA experiments integrate the spatial
variability of SWR of an undisturbed soil slab. In addition, the method is faster for extremely
hydrophobic soils once the ROMA is set up. We are currently analyzing if our soil
slab experiments are representative of larger scale run-off behaviour on the field. |
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