Accumulation of soil organic phosphorus by soil tillage and cropping systems under subtropical conditions
2003
Santos Rheinheimer, D. dos | Anghinoni, I.
Changes in the concentration of organic phosphorus (P) fractions as affected by different soil tillage and cropping systems were analyzed in four long-term experiments established on two Oxisols (very clayey and clayey Rhodic Hapludox) and one Ultisol (sandy clay loam Rhodic Paleudult) of different clay contents, in southern Brazil. No tilled and conventional tilled soil under several crop sequences were collected in 1997 at three depths (0-2.5, 2.5-7.5, 7.5-17.5 cm) and analyzed for total, inorganic and organic soluble P by using different extractants (0.5 M sodium bicarbonate (NaHCO3) and 0.1 and 0.5 M sodium hydroxide (NaOH)). Microbial P was also determined. The sum of the organic P extracted by the three extractants and microbial P were considered the biological P pool, whereas the sum of inorganic and organic P in the residue was considered the geochemical P pool. Effects of soil tillage and cropping systems were mostly observed in the low activity clay soil (sandy clay loam Paleudult), with higher values under no-tillage and for soil cropped to oat + vetch/corn + cowpea rotation. Organic P accumulated mainly as the moderately labile P pool (P-NaOH). The geochemical P pool was higher than the biological P pool, and the biological reactions showed increasing importance in the low-active surface topsoil layer of no-tilled soils.
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