Effects of climate, soil and water source on the distribution of bioavailable iron in low-land paddy soils of Sri Lanka

Iron (Fe) is an essential mineral element of plants. However, the current status of bioavailable Fe in lowland paddy fields in Sri Lanka is not known. This study was conducted to examine the (i) spatial distribution of bioavailable Fe concentration, and (ii) interactive effects of agro-climatic zone (ACZ), soil order, and water source in determining the bioavailable Fe concentration in lowland paddy fields in Sri Lanka. A total of 6003 soil samples representing six ACZs, six soil orders, and three water sources were collected using a stratified random sampling approach. Bioavailable Fe was extracted using 0.01 M CaCl2 and measured using Inductively Coupled Plasma Mass Spectrophotometry. Bioavailable Fe concentration ranged between 0.0003 and 339 mg kg(- 1) with a mean of 49.4 mg kg(- 1). Samples collected from the Wet zone, particularly the Wet zone Low country, had higher Fe concentrations than those reported in other ACZs (p < 0.05). Among the soil orders, Histosols, Inceptisols and Ultisols had higher Fe concentrations while Entisols, Alfisols and Vertisols reported lower values (p < 0.05). Paddy fields receiving water from major irrigation systems in Wet zone Low country had more Fe. Moreover, Fe concentration was not correlated with rice crop productivity (p > 0.05). The spatial maps of bioavailable Fe generated in this study could be useful for making area-specific agronomic and administrative decisions based on ACZs, soil orders and water sources used in paddy cultivation in Sri Lanka.