Phosphorus availability to irrigated lowland rice as affected by sources, application level and green manure
Medhi, D.N. | De Datta, S.K.
To evaluate alternative fertilizer phosphorus (P) sources in lowland rice, two field experiments were conducted under irrigated conditions in Quezon Province, Philippines during 1990-1991 crop year. In another field experiment fertilizer P recycling through a green manure crop applied in the succeeding rice, was studied. Addition of fertilizer P increased grain yield by 1.5-2.0 t/ha (46%) in 1990 wet season (WS) and by 1.6-2.1 t/ha (56%) in 1991 dry season (DS). However, fertilizer P source and application level did not effect grain yield significantly. Results indicated that the less water-soluble and less expensive partially acidulated phosphate rock (PAPR), phosphate rock (PR) and less reactive PR were as effective as the more soluble but more expensive triple superphosphate (TSP). The relative effectiveness (RE) of local guano was significantly lower than that of other sources of fertilizer P. Fertilizer P applied to a pre-rice Sesbania rostrata green manure increased rice grain yield by 1.5-1.9 t/ha during 1991 DS. Further, S. rostrata fertilized with Morocco phosphate rock (MPR) gave significantly higher rice grain yield than did rice fertilized with MPR applied alone. In the P source experiments Olsen method and Pi correlated better with growth attributes than Bray 2 P. Phosphorus uptake did not differ significantly among P sources and levels. Results suggest that P uptake was improved with green manuring. Correlation analyses revealed a close correlation between P uptake and dry matter yield and P uptake and grain yield.
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