The western region of the southern Pantanal is characterised by soils with high phosphorus (P) contents, derived from materials from the surrounding lithostratigraphic units, accumulated by fluvial transport. However, studies on forms and availability of P in these soils are scarce. The objective of this study was to evaluate the different forms of inorganic P and their relationship with some attributes of carbonatic soils in the Pantanal of Mato Grosso do Sul, Brazil. Hedley’s sequential fractionation scheme was used to evaluate the forms of P in soil profiles: Kastanozems (profiles P1 and P3) and Gleysol (profile P2). Total P contents were similar in the three profiles, 3782–5637 mg kg^–1, with mean values of 22% for organic P and 46% for inorganic P (P.i). The P.i results indicated that in the profiles there was a predominance of inorganic forms of P in the following order: P-NaOH 0.5 mol L^–1 > P-NaHCO₃ > P-NaOH 0.1 mol L^–1 > P-HCl, that is, adsorbed to microaggregates, labile, adsorbed to oxides and precipitated with calcium (Ca), respectively. The highest values of total organic P were verified in the surface horizons, with high correlation with total P contents. Residual P contents were high in all profiles, representing 29.0–33.3% of the total P, being correlated with CaCO₃ contents. The studied profiles had high contents of labile P, with the highest values in the fraction P.i-NaHCO₃, possibly associated with the processes of reduction of iron during the periods of floods, making the adsorbed P available. The contents of P.i-NaOH 0.1 mol L^–1, a moderately labile fraction adsorbed to oxides, showed few differences compared to the non-labile fractions associated with Ca (P.i-HCl). Possibly, organic matter was bound to Ca, inhibiting the formation of precipitates of Ca with P and making P available for the more labile fractions.

潘塔纳尔湿地南部西部地区的土壤具有高磷 (P) 含量，源自周围岩石地层单位的材料，通过河流运输积累。然而，关于这些土壤中磷的形态和有效性的研究很少。本研究的目的是评估不同形式的无机磷及其与巴西南马托格罗索州潘塔纳尔湿地碳酸盐土壤某些属性的关系。Hedley 的顺序分馏方案用于评估土壤剖面中磷的形式：Kastanozems（剖面 P1 和 P3）和 Gleysol（剖面 P2）。三个剖面中的总 P 含量相似，3782–5637 mg kg ^–1，有机磷的平均值为 22%，无机磷 (Pi) 的平均值为 46%。Pi 结果表明，在分布图中，无机形式的 P 按以下顺序占优势：P-NaOH 0.5 mol L ^–1 > P-NaHCO ₃ > P-NaOH 0.1 mol L ^–1 > P-HCl，即分别吸附到微团聚体、不稳定、吸附到氧化物和与钙 (Ca) 沉淀。总有机磷的最高值在地表层中得到验证，与总磷含量高度相关。所有剖面中的残留 P 含量都很高，占总 P 的 29.0-33.3%，与 CaCO ₃含量相关。所研究的剖面具有高含量的不稳定 P，其中 Pi-NaHCO ₃分数最高，可能与洪水期间铁的还原过程有关，从而使吸附的 P 可用。Pi-NaOH 0.1 mol L ^{–1 的}含量是吸附在氧化物上的中等不稳定部分，与与 Ca 相关的非不稳定部分（Pi-HCl）相比几乎没有差异。可能是有机物与 Ca 结合，抑制了 Ca 与 P 沉淀的形成，并使 P 可用于更不稳定的部分。