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Soil Phosphorus Transformations Following Forest Clearing for Pasture in the Brazilian Amazon

^a The Ecosystems Center, Marine Biological Lab., Woods Hole, MA 02543 USA
^b Centro de Energia nuclear na Agricultura, Avenida Centenário 303, CEP 13416000, Piracicaba, Sao Paolo, Brazil

View larger version (46K): [in a new window]   Fig. 1 Phosphorus contained in different inorganic and organic fractions in the top 0 to 10 cm of soil in two chronosequences at Nova Vida, Rondônia. Black solid bars represent P fractions in Chronosequence 1 and dashed bars represents P fractions in Chronosequence 2. Each bar represents the average of five soil samples and standard error. The P value indicates the significance of years since deforestation on P content for each chronosequence determined by two-way analysis of variance

View larger version (27K): [in a new window]   Fig. 2 Changes in P fractions as a proportion of total P in the top 0 to 10 cm of soil in two chronosequences of forest and pastures at Nova Vida, Rondônia. Phosphorus fractions were grouped as follows: nonoccluded Pi = resin-extractable P + (NaHCO3-extractable Pi) + (NaOH-extractable Pi), Ca-bound P = dilute HCl-extractable Pi, organic P = (NaHCO3-extractable Po) + (NaOH-extractable Po) + (concentrated HCL-extractable Po), and occluded P = (concentrated HCL-extractable Pi) + residual P

View larger version (45K): [in a new window]   Fig. 3 Changes in the proportion of total P as nonoccluded, Ca-bound, organic, and occluded forms between the forest and the older pastures of Chronosequences 1 and 2

View larger version (34K): [in a new window]   Fig. 4 Phosphorus stocks and P contained in the nonoccluded, Ca-bound, organic, and occluded fractions in 1 m soil profiles from the forests, 5- and 20-yr-old pastures of Chronosequences 1 and 2 at Nova Vida

View larger version (74K): [in a new window]   Fig. 5 Proportional redistribution of ecosystem P during the conversion of moist tropical forest in the Amazon. This conceptual model assumes that: (i) forest vegetation contained 40% of the total P contained in the to 0 to 10 cm of soil, (ii) 10% of this aboveground biomass is lost from the ecosystem after clearing and burning the forest, (iii) P that incorporated in the soil is a proportion of the P in the aboveground biomass, and (iv) P content in grasses biomass is 10% of the P in the to 0 to 10 cm of soil. Shaded areas represent soil and the white areas represent the forest or pasture biomass