Author : Mongkorn Somsud

Summary : The studies were conducted to find out the native Fixed-NH (superscript+) (subscript4), the extent and magnitude of ammonium fixation of some Philippine and Thai soils, ammonium volatilization, availability of native fixed-NH (superscript +) (subscript 4) and recovery of applied ammonium in the presence of a growing lowland rice. The values of native fixed-NH (superscript+) (subscript 4) varied from 5 to 200 ppm pf nitrogen. There appeared to have no definite trend in the distribution of fixed-NH (superscript +) (subscript 4) with soil depths. The amounts of native fixed-NH (superscript +) (subscript 4) were related to the Orders of soil. The amounts of fixation of applied ammonium ranged from 3 to 108 ppm of nitrogen. Ovendrying tended to fix more applied ammonium than air-drying treatment. The average ammonia votalization ranged from 1.79 percent to 11.06 percent and 0.13 percent to 1.97 percent of applied ammonium without and with rice plant, respectively. The votalization was related to the amounts of exchangeable Ca, initial soil pH, and a standing rice crop caused to decrease the votalization. Votalization rate was rapid at first, then slowed down during the second week. Fixation of applied ammonium at different periods of submerge varied from 0.42 percent to 85.83 percent and 10 percent to 17 percent of applied ammonium without and with a crop, respectively. The fixation decreased with time of submerge. The availability of native fixed-NH (superscript +) (subscript 4) ranged from 2 percent to 8 percent and from 5 percent to 26 percent without and with rice crop, respectively. Recovery of applied ammonium by the rice plant ranged from 0.7 percent to 4.2 percent. The percentages were quite low owing to the immaturity of the plants.