Potential of Eppawala rock phosphate as a phosphorus fertilizer for rice cultivation in acid sulphate soils in Matara District of Sri Lanka

Abstract

Eppawala Rock Phosphate (ERP) is a phosphorus (P) resource in Sri Lanka containing about (28% to 42%) of P 2 O 5 and an alternative for imported Triple Super Phosphate (TSP). Low water solubility of ERP has limited its use as a P fertilizer for rice. However, ERP could be used as a P source for rice grown in acidic soils due to its increased solubility under acidic conditions. This study was carried out during Yala 2015 and Maha 2015/16 seasons to investigate the potential of ERP as a source of P for paddy grown in acid sulphate soils in the Nilwala valley in Matara District. Six treatments including a control were arranged in a Randomized Complete Block Design with three replicates. Treatments were comprised of TSP as a basal application (recommendation of the Department of Agriculture) and by ERP as basal and split applications at rates of 25 and 50 kg P 2 O 5 kg/ha respectively. Application of TSP resulted in a significantly higher plant height and dry matter production in comparison to the control. Application ERP at a rate of 25 P 2 O 5 kg/ha as a split application and 50 P 2 O 5 kg/ha (both split and single applications) showed a comparable plant height and an increase in dry matter production increment in comparison to the control. Significantly higher average panicle lengths and grain yields were observed in both TSP and ERP applied treatments in comparison to the control in Yala 2015. However, comparable increments were observed only in TSP applied treatment and ERP applications at a rate of 25 P 2 O 5 kg/ha as a split application and 50 P 2 O 5 kg/ha in Maha 2015/2016. Inconsistency of growth and yield performances of ERP treatments indicated the importance of long term experiments to determine suitable rates and methods of ERP application. This short-term study showed that ERP is a potential substitute for TSP for paddy grown in acid sulphate soils in Matara District.