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| Titel |
A Novel Method to Quantify Soil Aggregate Stability by Measuring Aggregate Bond Energies |
| VerfasserIn |
Rachel Efrat, Barry G. Rawlins, John N. Quinton, Chris W. Watts, Andy P. Whitmore |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250121697
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| Publikation (Nr.) |
 EGU/EGU2016-513.pdf |
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| Zusammenfassung |
| Soil aggregate stability is a key indicator of soil quality because it controls physical,
biological and chemical functions important in cultivated soils. Micro-aggregates are
responsible for the long term sequestration of carbon in soil, therefore determine soils role in
the carbon cycle. It is thus vital that techniques to measure aggregate stability are accurate,
consistent and reliable, in order to appropriately manage and monitor soil quality, and to
develop our understanding and estimates of soil as a carbon store to appropriately incorporate
in carbon cycle models.
Practices used to assess the stability of aggregates vary in sample preparation, operational
technique and unit of results. They use proxies and lack quantification. Conflicting
results are therefore drawn between projects that do not provide methodological
or resultant comparability. Typical modern stability tests suspend aggregates in
water and monitor fragmentation upon exposure to an un-quantified amount of
ultrasonic energy, utilising a laser granulometer to measure the change in mean weight
diameter.
In this project a novel approach has been developed based on that of Zhu et al.,
(2009), to accurately quantify the stability of aggregates by specifically measuring
their bond energies. The bond energies are measured operating a combination of
calorimetry and a high powered ultrasonic probe, with computable output function.
Temperature change during sonication is monitored by an array of probes which enables
calculation of the energy spent heating the system (Ph). Our novel technique suspends
aggregates in heavy liquid lithium heteropolytungstate, as opposed to water, to
avoid exposing aggregates to an immeasurable disruptive energy source, due to
cavitation, collisions and clay swelling. Mean weight diameter is measured by a laser
granulometer to monitor aggregate breakdown after successive periods of calculated
ultrasonic energy input (Pi), until complete dispersion is achieved and bond energy
(Pb; input energy used in aggregate breakdown) can be calculated by the following
equation:
ΣPi – Ph = Pb
The novel technique was tested by comparing the bond energies measured from a series of
soil aggregates sampled from different land management histories, to the samples
corresponding stability measurement obtained from standard modern stability tests. The
effectiveness of the heavy liquid as a suspension (as opposed to water) was evaluated by
comparing the bond energies of samples measured in both suspensions. Our results determine
i) how disruptive water is in aggregate stability tests, ii) how accurate and representative
standard aggregate stability tests are, and iii) how bond strength varies depending on land
use.
Keywords: Aggregate; Bond; Fragmentation; Soil; Sonication; Stability
References:
Zhu, Z. L., Minasny, B. & Field D. J. 2009. Measurement of aggregate bond energy using
ultrasonic dispersion. European Journal of Soil Science, 60, 695-705 |
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