The amount and distribution of carbon, nitrogen, and sulfur in whole soil and in particle-size fractions were analyzed in two clayey Dark Red Latosols (LE1 and LE2). LE1 (forest as natural vegetation), from Cordeirópolis, São Paulo, cultivated with citrus since 1982 receiving two lime treatments, control and 18 t ha-1 applied twice in 1983 and 1994. Since 1976, LE2 (cerrado as natural vegetation) from Planaltina, Federal District (cerrado region), was cultivated with different crops (wheat, soybean, rice and sorghum) sown for 14 years with pasture grass (Andropogon gayanus L.), with and without the addition of 1.660 kg ha-1 of P2O5 as triple superphosphate. For reference purposes, additional samples were collected from uncropped soils in both LE1 and LE2 sites. Carbon, nitrogen and sulfur contents were determined in whole soils and in their particle-size fractions. The drastic reduction of carbon, nitrogen and sulfur contents in the cultivated areas of LE1 was followed by an intensive depletion in CEC at limed and control plots, stressing the importance of management and conservation of organic matter in this soil. In the LE2 soil, the reduction of C, N and S contents with cultivation was less intense and associated with a higher decomposition of organic compounds linked to the intermediate fraction. Liming resulted in a higher preservation of soil organic matter, although phosphorus addition did not affect carbon and nitrogen contents in the LE2 cultivated areas. Fine fraction plays a crucial role in the stabilization of soil organic matter, since the largest reservoirs of carbon, nitrogen and sulfur were associated to this particle-size. The distribution of carbon, nitrogen and sulfur between particle-size fractions is characterized by a depletion of organic materials associated to coarse, intermediate and fine fractions and a shift towards fine fraction associated materials.
Organic matter; liming; phosphorus; soil physical dispersion