http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
study of two toposequences of the dry valley systems of western Niger (West Africa)
Relationship between landscape position and soil characteristics such as moisture regime, phosphorus fixing capacity, and acidity were investigated on two toposequences of western Niger (West Africa). The toposequences studied overly the Continental Terminal geologic deposits and have different mean annual rainfall (Hamdallaye, 550 mm; Malgorou, 750 mm). A survey of local farmers on land management and land degradation was also conducted at both sites. At the Hamdallaye toposequence, soils are formed on deep eolian mantle, are sandy and were classified as Ustipsamments and Kandiustalfs. At the Malgorou toposequence, soils are generally formed on Continental Terminal residuum; they are loamy in texture, shallow, and gravelly at depth. Soils at Malgorou were classified as Kandiustalfs and Kanhaplustalfs. Characteristics common to soils of both toposequences are low organic matter, low ECEC and a pH moderately to strongly acid. The standard P requirement (SPR) of soils was very low at Hamdallaye and low at Malgorou. No trend in P sorption was observed along the toposequence at Hamdallaye; at Malgorou an increase in P sorption was observed down the slope in a segment of the toposequence. The P sorption increased about 2.5 fold from surface to the upper sub-horizons at both toposequences. SPR values appear to be highly correlated with soil characteristics at the two sites. There was no simple relationship between soil moisture availability and topographic position at either toposequences; main factors controlling moisture availability were surface texture, crusting and evapotranspiration. Soil Taxonomy placements of soil moisture regime are ustic at Hamdallaye and marginally ustic to aridic at Malgorou. The survey of local farmers at Hamdallaye indicated that landscape position is not the major factor for land use at Hamdallaye; at Malgorou, farmers plant different crops depending on landscape position and type of soil. The survey also indicated that important degradation of the agro-ecological system has occurred at both sites in the last fifty years.