[Agronomic behavior of Baja California phosphate rock in an andosol, a planosol, and an aridisol of Mexico]

anglais. Two field experiments with rainfed corn (in Andosol and Planosol) and two greenhouse trials with Lolium perenne (in Andosol and Aridisol) were carried out to assess the relative agronomic efficiency (EAR) of Baja California phosphate rock (RFBC) with different mesh size, applied alone or mixed with elemental sulphur. Additional treatments with North Carolina phosphate rock (RFCN) and RFBC plus natural zeolite from Sonora, were tested in the greenhouse trials. The field trials revealed that the EAR of RFBC on maize grain yield was almost doubled when the particle size was reduced from commercial value (-35 +100 mesh, U.S. Standard) to a value of -100 mesh. Contrarily, no favorable effect of sulphur was observed when applied to finely ground RFBC. In the greenhouse trial with Andosol, addition of sulphur had a positive effect on coarse RFBC, but not on finely ground RFBC. The opposite was found with zeolite, since it increased in 48% the EAR of fine RFBC, but it had no effect on coarse RFBC. RFBC under commercial particle size had a EAR similar to that of fine RFBC. In the greenhouse trial with Aridisol, the EAR of both phosphate rocks was of only 19 to 36% compared with triple superphosphate, without showing improvement with additions of sulphur or zeolite. These results are attributed to the high pH of this soil

espagnol; castillan. Se desarrollaron 2 experimentos de campo con maiz de temporal (en Andosol y Planosol) y 2 ensayos de invernadero con Lolium perenne (en Andosol y Aridisol), para evaluar la eficiencia agronomica relativa de roca fosforica de Baja California (RFBC) con diferente granulometria, aplicada sola o mezclada con azufre elemental. En los ensayos de invernadero se incluyeron ademas tratamientos con roca fosforica de Carolina del Norte (RFCN) y RFBC adicionada de zeolita natural de Sonora. En los experimentos de campo se observo que la eficiencia agronomica relativa (EAR) de la RFBC en produccion de grano de maiz, casi se duplico al reducir el tamano de sus particulas de granulometria comercial (-35 +100 mallas U.S. Standard) a una fineza de -100 mallas. Por el contrario, no se observo efecto favorable con la adicion de azufre elemental a la RFBC finamente molida. En el ensayo de invernadero con suelo Andosol, la adicion de azufre tuvo un efecto positivo sobre la RFBC gruesa, no asi sobre la fina. Lo contrario ocurrio con la zeolita, la cual incremento en 48% la EAR de la RFBC fina, mas no tuvo efecto sobre la RFBC gruesa. La RFCN, con granulometria comercial, tuvo una EAR semejante a la RFBC fina. En el ensayo de invernadero con suelo Aridisol, la EAR de las rocas fosforicas fue de solo 19 a 36% en comparacion con superfosfato triple, sin mostrar mejoria con adicion de azufre o zeolita, lo cual se atribuye al elevado pH de este suelo.