Dynamics of Phosphorus and Carbon in the Soil Particulate Fraction Under Different Management Practices

Phosphorus in the soil particulate fraction (PF, >53 mu m) has been described to have a significant importance in P cycling. However, there is no information regarding the effect of management practices over P-PF and its association with soil organic carbon (SOC) dynamics. Changes in total phosphorus (Pt), inorganic phosphorus (Pi), organic phosphorus (Po), Bray-P, and SOC through time were evaluated in the whole soil, in the PF and in the associated fraction (AF, <53 mu m). Two different tillage systems: conventional tillage (CT) and no-till (NT), and two fertilization treatments: N (no P fertilization) and NP (30 kg ha(-1) yr(-1)) were evaluated. Tillage systems did not modify Pt, Pi, Po, or SOC in any fraction. A 0.32 g kg(-1) yr(-1) decrease in SOC-PF was observed, which was accompanied by a reduction of Po-PF (-0.87 mg kg(-1) yr(-1)). This decrease was associated with the incorporation of soybean [Glycine max (L.) Merr.] and the elimination of pastures from the original crop rotation. The Pi in N plots diminished in PF, AF, and the whole soil (-0.35, -2.82, and -3.15 mg kg(-1) yr(-1), respectively), but it was not affected in NP plots due to the adsorption of P, which was limited in PF (41.47 mg kg(-1)). Bray-P concentration also decreased through time in N (2.2 mg kg(-1) yr(-1)) but not in NP, indicating that even though P fertilization can replenish the available inorganic P pool in the soil, SOC, and Po-PF are still depleted by the use of intensive cropping rotations, consequently reducing soil fertility.