RELATIONSHIP BETWEEN RICE YIELD AND SOIL-PHOSPHORUS EVALUATED UNDER AEROBIC AND ANAEROBIC CONDITIONS

Yield response to P fertilizer application in field experiments conducted in various parts of Louisiana was statistically correlated with parameters of soil P determined under oxidized (aerobic) and reduced (anaerobic) treatments. Soil P parameters included 0.01 m CaCl2extractable P, P sorbed at 0.2 ppm P in solution and Bray No.2 extractable P. The first two P variables were determined under oxidized as well as reduced soil treatments. The soil samples were also characterized for clay content, total C, pH, and oxalate extractable Fe. Linear correlation coefficient ‘r’ values showed that rice yield at zero P and % yield increase with phosphate P were significantly correlated with the amount of added P required to give 0.2 ppm P in solution (p sorbed) determined under reduced conditions in Crowley silt loam soil only (r= -0.72, and 0.66, respectively). A significant positive correlation between P sorbed (reduced-oxidized) and % yield increase with 25 kg Pjha over zero P was also observed in Crowley silt loam (r=0.70**). This indicates that the soils exhibiting higher P sorption under reduced conditions had a greater likelihood of yield response to added fertilizer P under flooded soil conditions. A significant relationship between P sorbed under reduced conditions and total carbon, extractable P, soluble P, soil pH and oxalate Fe (the last three variables determined under reduced conditions) indicates these variables play a major role in P fixation in Crowley silt loam soil. © 1979 Taylor & Francis Group, LLC.