Exchangeable Manganese in Diverse Rice-Cultivated Top Soils (0–15 cm) of Sri Lanka

Abstract Manganese (Mn) is an essential mineral element required for the growth of plants. However, the current status of Mn in Sri Lankan rice-cultivated lowlands is not known. Hence, this study was conducted to determine the (i) spatial differentiation of exchangeable Mn in top soils, and (ii) examine the interactive effects of the agro-climatic zone (ACZ), soil order and water source in determining the exchangeable Mn concentration in lowland paddy fields in Sri Lanka. A total of 9137 soil samples representing six ACZs, six soil orders, and three water sources were collected. Soil Mn was extracted using 0.01 M CaCl2 and measured using an Inductively Coupled Plasma Mass Spectrophotometry. Exchangeable Mn concentration ranged between 0.72–288.8 mg kg−1 with a mean of 23.02 mg kg−1. Samples collected from Wet zone Low country had lower Mn concentration than other ACZs. Among the soil orders, Alfisols and Entisols had higher Mn concentrations while Histosols reported the lowest. Rainfed paddy fields retained more Mn than supplementary irrigated fields in the Dry zone Low country. Moreover, Mn concentration was negatively correlated with soil pH, annual rainfall and grain yield. Therefore, ACZ, soil, and water source-dependеnt Mn management strategies are needed when improving Mn nutrition of rice in Sri Lanka.