Strength of soil aggregates and of aggregate beds in Impact of water and external forces on soil structure. Selected papers of the 1st Workshop on soilphysics and soilmechanics, Hannover 1986.
The crushing test on soil aggregates of irregular shape is calibrated against the Brazilian test for cylinders. Factors affecting the strength of soil aggregates are reviewed. These include water content, wetting and drying cycles, and age hardening
. The stresses on individual aggregates in random beds of uniform aggregates are analysed. Changes in the structure of beds of aggregates with compaction and with rainfall are compared.
Influence of soil properties on the aggregation of some Mediterranean soils and the use of aggregate size and stability as land degradation indicators
Soil aggregation in arid and semi-arid environments
Aggregate ; Alicante ; Clay mineral ; Grain size distribution ; Indicator ; Mediterranean area ; Organic materials ; Soil ; Soil degradation ; Soil erosion ; Soil properties ; Soil water ; Spain
Soil aggregation in relation to other soil properties was studied along a climatological transect in the Southeast of Spain. Three sites were selected along this transect ranging from semiarid to subhumid climatological conditions. The aggregate
size distribution, the macro and microaggregate stability of the superficial soil horizon and their relations with other soil properties were analysed. A general conceptual scheme of associations between aggregate size distribution, water-stable
Measuring neighbourhood spatial accessibility to urban amenities : does aggregation error matter ?
Accessibility ; Aggregation ; Error ; Residential environment ; Statistics ; Urban area ; Urban district ; Urban infrastructure
Aggregation error arises when a single point is used to represent a neighbourhood. The spatial accessibility to three types of recreational amenities in Edmonton, is used to assess whether aggregation error affects the measures. Exploratory spatial
data analysis techniques are used to examine aggregation-error effects on spatial accessibility.
La résolution d'un problème de localisation à l'aide d'unités agrégées illustrant la demande introduit quelques biais statistiques qui sont sources d'erreur. Les AA. suggèrent une stratégie de contrôle de l'erreur globale.
Effect of freezing and thawing processes on soil aggregate stability
This study aims to determine the effects of freezing and thawing processes on the wet aggregate stability of Turkish soils formed from different parent materials, for different aggregate size groups, soil moisture contents at the time of freezing
Soil aggregation, aggregate stability, organic carbon and nitrogen in different soil aggregate fractions under forest and shrub vegetation on the Loess Plateau, China
Aggregate ; Carbon ; China ; Geophysics ; Land use ; Loess ; Microstructure ; Nitrogen ; Plateau ; Soil properties ; Vegetation
The AA. presumed that the aggregate stability and the distribution of organic carbon and nitrogen in different aggregate fractions were different and would be affected by different plant communities in comparison to cropland and bare fallow land
. Therefore, the aims of this study were to elucidate the effects of different plant communities on soil aggregate stability and the distribution of organic carbon and nitrogen in different aggregate fractions by using ultrasonic method, both in old forest
areas and in new afforestation areas, in order to prove that the different plant covers enhance soil aggregate stability. Soil samples were collected from the hilly-gully area on the Loess Plateau : results and discussion.
Multiscale statistical models for hierarchical spatial aggregation
Data analysis ; Model ; Scale ; Space time ; Spatial aggregation ; Spatial analysis ; Statistics
defined partitions, corresponding to successive aggregations of an initial data space. The effects of scale associated with such aggregation are captured through a fundamental decomposition of the data likelihood.
Soil aggregation in arid and semi-arid environments
Aggregate ; Agropedology ; Land use ; Methodology ; Soil ; Soil properties ; United States of America
The most common method for measuring aggregate stability in water is wet sieving. The objective of this paper is to present a low cost modified version of this method that does not require the use of a mechanized wet-sieving machine and can
Aggregation and ecological effects in geographically based data
Aggregation ; Demographic structure ; Model ; Spatial analysis ; Statistical bias ; Statistics ; United Kingdom
in the analysis of individual-level data can be magnified when the analysis based on aggregated data is carried out. The models provide an approach to the problem of adjusting an area-level analysis to correct for aggregation effects. The data come from the 1991
Problème de la stabilité des solutions d'un modèle de localisation obtenues à l'aide de données agrégées. Présentation de perspectives différentes de celles des recherches antérieures. Les configurations de localisation identifiées pour des données
agrégées sont évaluées à l'aide des données désagrégées d'origine. Dans ce cas, la stabilité des solutions présente un niveau supérieur.
The dynamics of rainsplash erosion and the role of soil aggregate stability
The work of a number of authors is integrated to reveal a sequence of events occurring during rainsplash erosion. The implication of this sequence is that aggregate stability plays a central regulatory role. Using 20 iron rich soils from Mozambique
it is shown that their temporal dynamics as regards splash loss is consistent with this proposed sequence, and that in addition aggregate stability does directly relate to total splash loss over a 50 minute period of rain. By now considering the soil
properties a statistical model is formulated. A model which seems to imply that the central regulatory role of aggregate breakdown is only a partial answer to erodibility, as important are the characteristics of the breakdown bi-products.
Drop testing aggregate stability of some soils near Merida, Spain
The drop test for aggregate stability results in a distribution of destroyed aggregates with increasing drop number. The influence of prewetting time on drop test results is considered. Secondly new indices to describe the drop test results
and modifications of the drop test are suggested to avoid undue influence of small numbers of very stable aggregates, and to shorten the test procedure.
In 10 soils from central Greece devoted to cereal cropping, seasonal wet aggregate stability (WAS) fluctuations were investigated over a period of two successive years. The wet-sieving technique of air-dried aggregates was used
the relevance between aggregate stability and actual erosion is not always consistent, depending on extreme events, storm aggressiveness, slope and other factors.
Size fractions resulting from an aggregate stability test, interrill detachment and transport
Aggregate ; Agropedology ; Cultivated land ; Erodibility ; France ; Grain size distribution ; Loam ; Midi-Pyrénées ; Normandie ; Precipitation ; Rainfall simulation ; Rill wash ; Sediment transport ; Soil erosion ; Splash ; Tarn
The aggregate size distribution is a recognized factor influencing crust characteristics and transport during interrill erosion events. This parameter was used in this work in order to improve the understanding of the relationship between aggregate
and aggregate stability tests which were performed using 2 different soils : a clay loam slightly sensitive to erosion, and a more susceptible silt loam.
Relationships between aggregation and iron oxides in Terra Rossa soils from southern Italy
This paper reports the relationships between the mineralogy of the Fe oxides and aggregation in Terra Rossa soils of Southern Italy. Consideration is given to the possible interaction between Fe oxides and other constituents.