@incollection{PAR00007514,
  title = {{P}hysical properties of tropical sandy soils : a large range of behaviours},
  author = {{B}ruand, {A}. and {H}artmann, {C}hristian and {L}esturgez, {G}.},
  editor = {},
  language = {{ENG}},
  abstract = {{S}andy soils are often considered as soils with physical properties that are easily defined, however they are far from being simple. {T}his is particularly the case for sandy soils in the tropics where they are subjected to a cycle of wetting and drying associated with seasonality. {I}n this respect small changes in composition lead to significant differences of physical properties. {O}ne of the major soil characteristics to be taken into account is the size distribution of the sand grains. {I}f fine sand induces greater porosity, water retention and resistance to penetration than coarse sand, they exhibit lower permeability. {P}orosity decreases when the heterogeneity of the sand grain distribution increases leading to an increase in resistance to penetration and decreases in permeability. {T}he presence of silt particles leads to similar consequences. {T}hus, silty sands are more compact than sandy soils, most silt particles occupying the voids between sand grains thereby reducing porosity and consequently permeability. {S}ize distribution and mineralogy of silt and clay sized particles that are associated with sand grains are also responsible for variations in physical properties of tropical sandy soils. {U}nder tropical environments, sandy soils undergo significant weathering to depth thus resulting in a mineralogy where quartz the dominant mineral in the sand and silt fraction and forms a significant proportion of the clay sized fraction. {O}n the other hand, sandy soils can be present in the lower part of the landscape where clays or salts form during the dry season. {A}s a consequence, sandy soils with similar particle size distribution but due to differences in mineralogy of the clay sized fraction that represents not more than a few percent of the soil mass, show very different physical properties. {F}inally, in sandy soils unlike other soils, the elementary fabric is easily affected by tillage practices. {I}f greater porosity can be produced through tillage operations, the stability of these systems is very weak and compaction by wheels or other actions can in return produce a dense structure. {T}hus, compaction results from a variation of the structure at all scales, i.e. from the macroscopic to microscopic scales.},
  keywords = {sandy soil ; bulk density ; structure ; porosity ; particle size distribution ; clay ; hydraulic properties ; compaction ; {THAILANDE}},
  booktitle = {{M}anagement of tropical sandy soils for sustainable agriculture : a holistic approach for sustainable development of problem soils in the tropics : proceedings},
  numero = {},
  pages = {148--158},
  address = {{B}angkok},
  publisher = {{FAO}},
  series = {},
  year = {2005},
  ISBN = {9789747946963},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00007514},
}