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| Titel |
Effects of grassland on bulk density of soil and mechanical resistance |
| VerfasserIn |
Véronique Chaplain, Pauline Défossez, Ghislaine Delarue, Guy Richard, Daniel Tessier, Jean Roger-Estrade |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250048191
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| Zusammenfassung |
| Bulk density and mechanical resistance measured at core scale are good indicators of soil
structure quality. Mechanical resistance is described by the compression characteristics that
show the relationship between stress applied on a soil sample and a volumetric parameter
such as void ratio e0. Compression curves define: (i) the pre-compression stress Pc (ii) the
slope of the virgin compression line VCL, namely compression index Cc. Those two
parameters depend on soil properties, which are influenced by practices such as tilled or
no-tilled systems. However, the effect of grasslands in mechanical resistance remains to be
clarified.
In this study, we evaluated the effect of the duration of grasslands on bulk density and
mechanical properties of soils. Soils originated from a long-term experimental site: Yvetot
(France), where till, permanent and temporal grasslands are compared. We selected there four
systems: tilled and permanent grassland as reference systems and two temporal grasslands,
which began in 1994 and 2000 respectively. For each system two large undisturbed monoliths
were sampled in the 0-20 cm horizon in March 2003, so that the duration Ï of temporal
grasslands are 9 and 3 years respectively. Five small cylindrical cores, 5 cm diameter
and 2 cm height, of undisturbed soil were made from each larger monolith. The
water content was adjusted, just before mechanical test, to a matric potential pF
of 2.5. Uniaxial compression curves were measured using a hydraulic oedometer
apparatus in drained conditions by applying successive total vertical stresses (from 1 to
1500 kPa). Mechanical parameters were calculated with the Gompertz’s model fit
applied to S-shaped curves. Cc parameter was the tangent, in absolute terms, to the
compression curve at inflexion point. In bi-linear model, the VCL was established by
linear regression of compression curves, in logarithmic scale, above an external
stress of 100 k Pa. In both cases, the Pc value was the intercept of VCL with a
horizontal line taken at e0. The bulk density was the most affected variable in the set of
grasslands. In the tilled reference system, the mean value of e0 was low (0.9 ± 0.15)
and continuously increased with the duration Ï up to 1.6 ± 0.27 for permanent
grassland. In the tilled system, the global shape of the compression curves obeyed to an
S-shape model, except for the lowest values of e0 (below 0.75), where bi-linear curves
yielded a better fit. The global shape of compression curves is affected by grassland,
where bi-linear curves are obtained in an unexpected way for such high values of
e0. This fact reveals the strong change in internal soil structure and in water soil
interaction. However neither the Pc values nor their variability were affected by a
grassland effect (Pc = 41 kPa ± 9). A temporary decrease was only registered at Ï=3
years (Pc = 33 kPa ±10). The value of the compression index linearly increased
with e0 in every case. The low value of the slope revealed the anisotropy of soil
samples probably due to the set of roots. To conclude, those results highlighted the
positive impact of grassland on soil structure and their crucial role on soil mechanical
properties.
Acknowledgements: This work was carried out with the financial support of
the «Â ANR- Agence Nationale de la Recherche - The French National Research
Agency » under the «Â Programme Agriculture et Développement Durable », project
«Â ANR-05-Padd-0.13Â ». The authors would like to thank the French Programmes
GESSOL2 from the Ministry in charge of Environment and ADD from the National. |
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