Responses of Grain Yield and P Uptake to Water Management and Phosphorus in Lowland Irrigated Rice (Oryza sativa L.)
Arisoa Rajaona1, Tovohery Rakotoson2, Hannah Wright3, Jemima Amielle Ramarolahy2, Kalimuthu Senthilkumar4, Kazuki Saito5, Elke Vandamme4
1Africa Rice Center (AfricaRice), Madagascar
Phosphorus (P) deficiency constitutes a major growth and yield-limiting factor in irrigated and rainfed rice systems in Madagascar. Many soils in Madagascar are highly weathered with a high Fe oxyhydroxide content leading to P sorption and low P availability, and farmers often do not apply mineral P fertilisers leading to a continuous decline in soil P stocks. Appropriate agronomic practices should be designed to increase P availability and improve P fertiliser use efficiency to encourage the application of P inputs. P availability and P uptake by the rice crop may be affected by water management. It is known that relatively high soil water content under frequent irrigation increases soil P mobility and availability through reductive dissolution of P bearing Fe-oxides. On one hand, cycles of alternate wetting and drying (AWD) can increase P availability and acquisition under suboptimal P supply. On the other hand, as P availability often increases drastically upon flooding, we hypothesised that flooding during the grain filling stage may lead to luxury P loading in grains without increasing grain yield and hence low P utilisation efficiency. The objective of this study was to evaluate grain yield and P uptake of rice under different P rates and water management treatments. The experiment was undertaken in Behenjy (1361 m asl), Madagascar using X265 rice variety. A split-plot design was used with 3 irrigation treatments (continuous flooding, continuous flooding until flowering and then drained, and AWD) in main plots, 3 doses of P (0, 10 and 25 kg/ha) in the sub plots, and 4 replications. Results on grain yield and P uptake of rice cultivated in lowland irrigated system, mainly under P stress will be discussed and presented.
Keywords: Alternate wetting and drying, Madagascar, P deficiency
Contact Address: Arisoa Rajaona, Africa Rice Center (AfricaRice), B.P. 230, Antisrabe, Madagascar, e-mail: a.rajaonacgiar.org