Transformation of added phosphorus to acid upland soils with different soil properties in Indonesia

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 (P_i) that is readily available to plant), (ii) 0.5 mol L⁻¹ NaHCO₃ extracting P_{i and} P organic (P_o) (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 P_i and P_o (P which is more strongly held by chemisorption to Fe and Al components of soil surface) and (iv) 1 mol L⁻¹ HCl extracting P_i (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-P_i fraction for soils of Group 1, while for soils of Group 2, it was transformed into resin-P_i, NaHCO₃-P_i and NaOH-P_i 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-P_i. 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-P_i. Soils developed from andesite and volcanic ash exhibited significantly higher NaOH-P_i 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.

Key words:

• acid upland soils
• Indonesia
• phosphorus
• soil properties
• transformation

ACKNOWLEDGMENTS

We thank the farmers in Java, Sumatra and East Kalimantan for their assistance in the collection of the soil samples. We also thank Mr Tetsuhiro Watanabe for his assistance in the field, Dr Hitoshi Shinjo for his assistance in the statistical analysis and Mr M. Turner for his assistance in the preparation of this manuscript.