Phosphorus (P) sorption‐desorption isotherms were studied in several acid upland soils developed from different parent materials in Indonesia. The soils varied in their chemical and physical properties. P sorption characteristics were satisfactorily described by the Langmuir equation, which was used to determine P sorption maxima and bonding energies. The soils varied widely in their capacity to sorb P. P sorption maxima ranged from 0.294 to 1.43 × 103 mg P kg−1 (mean 0.620 × 103 mg P kg−1) and bonding energies ranged from 0.64 to 9.00 L mg−1 (mean 3.42 L mg−1). The standard P requirements (P sorbed at 0.2 mg P L−1) ranged from 35 to 909 mg P kg−1 (mean 231 mg P kg−1). Parent materials affected the P sorption maxima and bonding energies. Soils developed from andesite and volcanic ash exhibited significantly higher P sorption maxima and bonding energies with a larger variability than the soils developed from sedimentary rock and volcanic sediments. Principal component analysis demonstrated that three principal components in Indonesian acid upland soils influenced P sorption, namely oxide‐related factor (aluminum (Al) plus 1/2 iron (Fe) (by ammonium oxalate), crystalline Al and Fe oxides, cation exchange capacity, and clay content), acidity plus 1.4 nm mineral‐related factor (exchangeable Al and 1.4 nm minerals) and organic carbon (C)‐related factor (organic C and organically bound Fe). Stepwise regression demonstrated that the oxide‐related factor was the main component actively contributing to P sorption maxima and bonding energies in these acid soils. It was demonstrated that the acidity plus 1.4 nm mineral‐related factor led to the decrease of P sorption maxima. The organic C‐related factor did not influence the P sorption maxima but decreased the P bonding energies. The results suggested that not only Al and Fe oxides but also soil acidity which is associated with exchangeable Al and 1.4 nm minerals of which smectite and vermiculite are common, should be included in models to estimate P sorption maxima in Indonesian acid upland soils. Furthermore, organic C content and organically bound Fe should be included in the models to estimate P bonding energies. Extraction with 0.01 mol L−1 CaCl2 led to a low soil desorbability of sorbed P (< 5%) and the desorbability was highly significantly correlated with the bonding energies during sorption.

No abstract

No abstract

The transformation of added phosphorus (P) to soil and the effect of soil properties on P transformations were investigated for 15 acid upland soils with different physicochemical properties from Indonesia. Based on oxide‐related factor scores (aluminum (Al) plus 1/2 iron (Fe) (by ammonium oxalate), crystalline Al and Fe oxides, cation exchange capacity, and clay content) obtained from previous principal component analyses, soils were divided into two groups, namely Group 1 for soils with positive factor scores and Group 2 for those with negative factor scores. The amounts of soil P in different fractions were determined by: (i) resin strip in bicarbonate form in 30 mL distilled water followed by extraction with 0.5 mol L−1 HCl (resin‐P inorganic (Pi) that is readily available to plant), (ii) 0.5 mol L−1 NaHCO3 extracting Pi and P organic (Po) (P which is strongly related to P uptake by plants and microbes and bound to mineral surface or precipitated Ca‐P and Mg forms), (iii) 0.1 mol L−1 NaOH extracting Pi and Po (P which is more strongly held by chemisorption to Fe and Al components of soil surface) and (iv) 1 mol L−1 HCl extracting Pi (Ca‐P of low solubility). The transformation of added P (300 mg P kg−1) into other fractions was studied by the recovery of P fractions after 1, 7, 30, and 90 d incubation. After 90 d incubation, most of the added P was transformed into NaOH‐Pi fraction for soils of Group 1, while for soils of Group 2, it was transformed into resin‐Pi, NaHCO3‐Pi and NaOH‐Pi fractions in comparable amounts. The equilibrium of added P transformation was reached in 30 d incubation for soils of Group 1, while for soils of Group 2 it needed a longer time. Oxide‐related factor scores were positively correlated with the rate constant (k) of P transformation and the recovery of NaOH‐Pi. Additionally, not only the amount of but also the type (kaolinitic) of clay were positively correlated with the k value and P accumulation into NaOH‐Pi. Soils developed from andesite and volcanic ash exhibited significantly higher NaOH‐Pi than soils developed from granite, volcanic sediments and sedimentary rocks. Soil properties summarized as oxides‐related factor, parent material, and clay mineralogy were concluded very important in assessing P transformation and P accumulation in acid upland soils in Indonesia.

No abstract