Chemical properties and phosphorus fractions in profiles of acid sulfate soils of major rice growing areas in Brunei Darussalam

• Soil constraints are acidity, low CEC and P, toxicity of Al and micronutrients.
• Among P fractions, the distribution of Pis Fe–P > Al–P > Red soluble-P > Saloid P > Ca–P.
• Reductant soluble-P, Al–P and Fe–P are positively correlated with available P.
• We aimed to reduce the impact of Fe and Al, which help to improve P availability.

ABSTRACTBrunei Darussalam contains a wide range of potential acid sulfate soils, and its rice yield is only about 1.7 t/ha, which is significantly lower than that of other rice producing countries. A few studies have used the sequential phosphorus (P) fraction to investigate P dynamics and interactions in rice soils, which is necessary for the management of P. However, there is currently no information available regarding the fractions of P in Brunei Darussalam. Therefore, this study was conducted to assess the chemical properties and different inorganic forms of P in potential acid sulfate rice soils of Brunei Darussalam to enable better crop management. A total of 40 samples were collected at depths ranging from 0 to 100 cm and analyzed for soil chemical properties and inorganic P fractions. The major soil constraints for rice cultivation are extreme acidity, low cation exchange capacity, toxicity of Al and micronutrients and low P. Al, Fe and Mn toxicities are common in acid sulfate soils. Among the P fractions, the distribution of inorganic P forms in the soils was in the order of Fe–P > Al–P > Reductant soluble-P > loosely bound P (Saloid-P) > Ca–P. These findings indicate that soil reclamation with liming and a good fertilizer management program is essential to boosting rice production in potential acid sulfate soils.