Variations in chemical and physical properties of Amazon forest soils in relation to their genesis

Abstract

Soil samples were collected in six South American countries in a total of 71 different 1 ha forest plots across the Amazon Basin as part of the RAINFOR project. They were analysed for total and exchangeable cations, C, N, pH with various P fractions also determined. Physical properties were also examined and an index of soil physical quality proposed. A diverse range of soils was found. For the western areas near the Andean cordillera and the southern and northern fringes, soils tend to be distributed among the lower pedogenetic levels, while the central and eastern areas of Amazonia have more intensely weathered soils. This gives rise to a large variation of soil chemical and physical properties across the Basin, with soil properties varying predictably along a gradient of pedogenic development. Nutrient pools generally increased slightly in concentration from the youngest to the intermediate aged soils after which a gradual decline was observed with the lowest values found in the most weathered soils. Soil physical properties were strongly correlated with soil fertility, with favourable physical properties occurring in highly weathered and nutrient depleted soils and with the least weathered, more fertile soils having higher incidence of limiting physical properties. Soil phosphorus concentrations varied markedly in accordance with weathering extent and appear to exert an important influence on the nitrogen cycle of Amazon forest soils

Do soil fertilization and forest canopy foliage affect the growth and photosynthesis of Amazonian saplings?

“…The nil effect of the mineral nutrient treatments was unexpected because the highly-weathered Amazonian soils are of low fertility (Sanchez, 1976;Quesada et al, 2010). However, our results agree with Cleveland et al (2011), who found only a weak correlation between P and net primary production.…”

Divergent Responses of Soil Buffering Capacity to Long-Term N Deposition in Three Typical Tropical Forests with Different Land-Use History

“…32,43 Hicks et al suggested that BS of 20% could be used as a threshold for predicting damage due to acidification. 4 Low BS in the tropics is likely tightly linked to high rates of weathering and leaching, 44,45 arising from the humid tropical climate with high rainfall and temperatures that favor rapid dissolution and leaching of weatherable minerals.…”

Soil-induced impacts on forest structure drive coarse woody debris stocks across central Amazonia

“…Ferralsols and Acrisols are found along the slopes and plateaux, which are highly weathered and have favourable physical conditions (i.e. stable aggregate structure, associated with good drainage) (Chauvel et al 1987;Quesada et al 2010). Near streams and valley bottoms, wet and sandy soils (Podzols) occur, but these were not included in this study.…”

“…Phillips et al 2009;Negrón-Juárez et al 2010) and to long-term differences in forest dynamics in response to environmental characteristics (Keller et al 2004;Malhi et al 2006;Chao et al 2009a). Soils represent an important environmental gradient in Amazonia, with a wide variety of soil types across the Basin and with diverse chemical and physical conditions (Quesada et al 2010;. Variations in soil physical properties across the Basin have been related to a large proportion of the variation in tree turnover rates and mean forest wood density, with disturbance levels and vegetation structure of Amazonian forests being related to different soil types (Quesada et al 2012).…”