Nutrient dynamics, dehydrogenase activity, and response of the rice plant to fertilization sources in an acid lateritic soil

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Rice variety IR 36, grown under flooding, was studied in 1998 to determine the effects of fly ash, organic, and inorganic fertilizers on changes in pH and organic carbon, release of nutrients (NH4 +-N, Bray's P, and NH4OAc K), and dehydrogenase activity in an acid lateritic soil at 15-day intervals. Application of fly ash at 10 t ha−1 alone did not improve the availability of NH4 +-N, or P, as well as the rice grain yield. Availability of NH4 +-N (35.3–36.9 mg kg−1), and P (12.3–14.6 mg kg−1) at 15 days after transplanting, and rice grain yields (48.0–51.7 g per pot) were similar under the various fertilization sources such as inorganic fertilizer alone, inorganic fertilizer + fly ash or inorganic fertilizer + green manure + fly ash. Mean dehydrogenase activity was the highest (8.47 µg triphenyl formazon g−1 24 h−1) under the mixed fertilization treatments with green manure. At the end of the cropping season (75 days after transplanting), pH, organic carbon, and dehydrogenase activity were higher under the mixed fertilization treatments involving green manure by 3, 15 and 154%, respectively, compared with the inorganic fertilizer alone.