Dn. Medhi et Sk. Dedatta, PHOSPHORUS AVAILABILITY TO IRRIGATED LOWLAND RICE AS AFFECTED BY SOURCES, APPLICATION LEVEL AND GREEN MANURE, Nutrient cycling in agroecosystems, 46(3), 1996, pp. 195-203
To evaluate alternative fertilizer phosphorus (P) sources in lowland r
ice, two field experiments were conducted under irrigated conditions i
n Quezon Province, Philippines during 1990-1991 crop year. In another
field experiment fertilizer P recycling through a green manure crop ap
plied in the succeeding rice, was studied. Addition of fertilizer P in
creased 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 s
ource and application level did not effect grain yield significantly.
Results indicated that the less water-soluble and less expensive parti
ally acidulated phosphate rock (PAPR), phosphate rock (PR) and less re
active PR were as effective as the more soluble but more expensive tri
ple superphosphate (TSP). The relative effectiveness (RE) of local gua
no was significantly lower than that of other sources of fertilizer P.
Fertilizer P applied to a pre-rice Sesbania rostrata green manure inc
reased rice grain yield by 1.5-1.9 t/ha during 1991 DS. Further, S. ro
strata fertilized with Morocco phosphate rock (MPR) gave significantly
higher rice grain yield than did rice fertilized with MPR applied alo
ne. In the P source experiments Olsen method and Pi correlated better
with growth attributes than Bray 2 P. Phoshorus uptake did not differ
significantly among P sources and levels. Results suggest that P uptak
e was improved with green manuring. Correlation analyses revealed a cl
ose correlation between P uptake and dry matter yield and P uptake and
grain yield.