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| Titel |
Characterization of tillage effects on soil permeability using different measures of macroporosity derived from tension infiltrometry |
| VerfasserIn |
G. Bodner, A. Schwen, P. Scholl, G. Kammerer, G. Buchan, H.-P. Kaul, W. Loiskandl |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250045111
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| Zusammenfassung |
| Soil macroporosity is a highly dynamic property influenced by environmental factors, such as
raindrop impact, wetting-drying and freezing-thawing cycles, soil biota and plant roots, as
well as agricultural management measures. Macroporosity represents an important indicator
of soil physical quality, particularly in relation to the site specific water transmission
properties, and can be used as a sensitive measure to assess soil structural degradation. Its
quantification is also required for the parameterization of dual porosity models that are
frequently used in environmental impact studies on erosion and solute (pesticide, nitrate)
leaching. The importance of soil macroporosity for the water transport properties of the soil
and its complexity due to high spatio-temporal heterogeneity make its quantitative assessment
still a challenging task.
Tension infiltrometers have been shown to be adequate measurement devices to obtain
data in the near-saturated range of water flow where structural (macro)pores are
dominating the transport process. Different methods have been used to derive water
transmission characteristics from tension infiltrometer measurements. Moret and
Arrúe (2007) differentiated between using a minimum equivalent capillary pore
radius and a flow weighted mean pore radius to obtain representative macropore
flow properties from tension infiltrometer data. Beside direct approaches based on
Wooding’s equation, also inverse methods have been applied to obtain soil hydraulic
properties (Šimůnek et al. 1998). Using a dual porosity model in the inverse procedure
allows estimating parameters in the dynamic near-saturated range by numerical
optimization to the infiltration measurements, while fixing parameters in the more stable
textural range of small pores using e.g. pressure plate data or even pedotransfer
functions.
The present work presents a comparison of quantitative measures of soil macroporosity
derived from tension infiltrometer data by different approaches (direct vs. inverse evaluation,
capillary vs. flow weighted pore radius). We will show the influence of the distinct evaluation
procedures on the resulting effective macroporosity, as well as on the relationships between
macropore radius and hydraulic conductivity (Moret and Arrúe, 2007) and pore fraction
respectively (Carey et al., 2007).
The infiltration measurements used in this study were obtained in a long-term tillage trial
located in the semi-arid region of Eastern Austria. Measurements were taken five times over
the vegetation period, starting immediately after tillage until harvest of the winter wheat crop.
Three tillage systems were evaluated, being conventional tillage with plough, minimum
tillage with chisel and no-tillage. Additional to infiltration measurements, also soil water
content was monitored continuously by a capacitance probe in all three replicates of each
tillage treatment in 10, 20 and 40 cm soil depth. Water content time series are used to derive
flow velocity in the wet range by cross-correlation analysis (Wu et al., 1997). This effective
parameter of water transmission will then be compared to the flow behaviour expected from
the characterization of soil macroporosity.
We will show that mainly in no-tillage systems large macropores contribute essentially to
flow and therefore the decision on pore measure and evaluation procedure to be used leads to
substantial differences. For a detailed comparison of tillage effects on soil hydraulic
properties it is therefore essential to analyse the contribution of different tension infiltrometry
based evaluation methods to explain effective water transmission through the complex porous
network of the soil.
References
Carey, S.K., Quinton, W.L., Goeller, N.T. 2007. Field and laboratory estimates of pore
size properties and hydraulic characteristics for subarctic organic soils. Hydrol. Process. 21,
2560-2571.
Moret, D., Arrúe, J.L. 2007. Characterizing soil water conducting macro- and
mesoporosity as influences by tillage using tension infiltrmetry. Soil Sci. Soc. Am. J. 71,
500-506.
Šimůnek, J., Wang Dong, Shouse, P. J., van Genuchten, M. T. 1998. Analysis of
field tension disc infiltrometer data by parameter estimation. Int. Agrophys. 12.
167-180.
Wu, L., Jury, W.A., Chang, A.C. 1997. Time series analysis of field-measured watr
content of a sandy soil. Soil Sci. Soc. Am. J. 61. 742-745. |
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