Effects of phosphorus and zinc application on growth of rice (Oryza Sativa) in soils with contrasting phosphorus levels in Sri Lanka

Abstract

Phosphorus (P) application can interfere with Zinc (Zn) availability for rice plant affecting their growth and yield. A pot experiment was conducted to investigate the effect of P and Zn application on growth of the rice plants in an Alfisol (S1) and Entisol (S2), with contrasting P levels. Rice (var Bg 360) were grown for 10 weeks under flooded conditions in pots (5.5 kg of soil per pot) with all possible combinations of four levels of P (0, 11, 33, and 99 kg ha-1) and three levels of Zn (0, 2 and 4 kg ha-1 ). Plant growth parameters were measured at the end of the experimental period. Mehlich-3 extractable P concentrations were 8.53 and 22.65 mg kg-1 while Zn contents were 1.99 and 1.02 mg kg-1, in S1 and S2 soils, respectively. Interaction effects of P × Zn rates were not significant on any of the plant growth parameters. Total dry matter content was significantly higher (p<0.05) in S1 than that in S2 at all P levels, but the differences of dry matter contents among the two soils were low at high P levels. The low total dry matter content in S1 could be due in part to differences in P and Zn availabilities in these soils. Irrespective of soil type and P application, total dry matter yield increased with Zn application, by 12% at 2 kg ha-1 but only by 8% at 4 kg ha-1 compared to that in 0 Zn level. These observations suggested that the application of Zn has beneficial effects in rice cultivation irrespective of the available P content in these two soils. However, to better understand the root causes for the observed effects, changes in P and Zn availabilities in these soils upon their application needs to be investigated in future studies.