Interaction Effects of Phosphorus and Zinc Application on Their Availability and Growth of Rice (Oryza sativa) in an Alfisol of Sri Lanka

This study investigated the interactive effects of phosphorus (P) and zinc (Zn) application on P and Zn availability, and growth of rice (Oryza sativa) in an Alfisol. In a laboratory incubation experiment, soil samples were supersaturated with treatment solutions with all possible combinations of four P levels (0, 6, 12, and 24 mg kg^-1 equivalent to 0, 10, 20, and 40 kg ha^-1, respectively) and three Zn levels (0, 1.2, and 2.4 mg kg^-1 equivalent to 0, 2, and 4 kg ha^-1, respectively), and then allowed to air-dry. Available P and Zn contents in soil increased as the application rates were increased but P×Zn rate interaction effect was not significant. In a pot experiment, rice (var Bg 358) was grown for 10 weeks with all possible combinations of three P levels (0, 5.5, and 16.5 mg kg^-1) and three Zn levels (0, 1, and 2 mg kg^-1). Initial soil P was higher than the critical level (12 mg kg^-1), but available Zn was below the critical level (1.5 mg kg^-1). The main effect of P rate did not significantly affect the number of tillers and shoot dry matter content while Zn application decreased them. Root dry matter, and root and shoot P concentrations were significantly (P<0.05) influenced by P×Zn rate interaction effect. While, plant P uptake was significantly decreased due to P and Zn application, plant Zn uptake was not affected. Therefore, for a better growth of rice plant, the soils with high available P and low Zn contents should be carefully fertilized with P and Zn fertilizers.