Phosphorus speciation and distribution in a variable‐charge Oxisol under no‐till amended with lime and/or phosphogypsum for 18 years

Abstract

Long-term management with lime and/or phosphogypsum (PG) can change phosphorus (P) forms across the soil profile. In this study, we used synchrotronbased spectroscopy and sequential chemical fractionation to investigate P chemical species after long-term (18 years) application of amendments in a subtropical Oxisol. The availability of nutrients increased with the combined use of lime and PG and a stratification of attributes was identified due to long-term broadcast applications. X-ray absorption near edge structure (XANES) spectra profiles revealed the predominance of P bounded to haematite (Hm) (48% on average) and also P bound to kaolinite (32% on average) species. Low proportions (16%) of calcium-phosphates in the uppermost soil layer (0-5 cm) were found in the treatment that received high calcium (Ca) inputs by lime and PG broadcast.Few correlations were identified between the proportions of P species obtained by XANES and P fractions operationally defined by sequential chemical fractionation (SF). Our results suggest that P-species bound to kaolinite can store stable P forms, which correlated (p < 0.05) with the residual P fractions obtained by SF, highlighting the importance of kaolinite as a legacy P store in Oxisols. Highlights• Lime and phosphogypsum broadcast under no-till improve soil fertility and P availability.• Labile and moderately labile P fractions were the only ones influenced by lime and/or phosphogypsum.• Proportions among P bounded to Fe-and Al-(hydr)oxides with different structural may be affected by long-term Al-suppressors.• P-species bounded to kaolinite may store stable P forms in Oxisols.

Effect of Incorporation of Pectin on the Adsorption of Phosphate by Al (oxy)hydroxides

“…Variable-charge soils are acidic, with soluble Al and exchangeable Al being the most active components of Al pools therein [17]. Hydrolysis of active Al in soil occurs when acidic soils are ameliorated with alkaline materials; pure Al hydrolysis products rarely exist in natural environments [18].…”