Land development is rapidly occurring on sand--dominant soils that cover
substantial areas of the Lower Mekong Basin. Sands are at risk of
degradation on sloping uplands where agriculture is expanding and on
lowland landscapes where intensification of cropping is occurring.
Sandstone and granitic geology explain the prevalence of sand-dominant
texture in profiles. The sand terrains in uplands of Cambodia and
southern Laos mostly have not been comprehensively mapped and their
diversity and edaphic properties are poorly understood. On high
permeability sands, lowland rainfed rice crops are drought-prone, while
nutrient losses from leaching are also a risk. Furthermore,
waterlogging, inundation and subsoil hardpans are significant
water-related hazards that influence the choice of field crops and
forages for lowland soils. Land use change in the lowlands to
alternative field crops and forages on sands is contingent on their
profitability relative to rice, the amounts and reliability of early wet
season rainfall and amounts of stored water available after harvesting
rice. Soil acidity, low nutrient status, hard-setting and shallow
rooting depth are significant constraints for crops and forages on sands
in the lowlands. Low soil fertility and soil acidity are limitations to
the productivity of farming systems on the sand profiles in uplands,
while erosion, low soil organic matter levels and water balance are
concerns for their sustainable use. There is a need for widespread land
suitability assessment and the development of sustainable farming
systems before uncontrolled expansion of agriculture causes degradation
of sandy terrain of the Lower Mekong Basin.