Nitrification and mineralization potentials in a limed Ultisol in the humid tropics

Summary We studied the effect of liming on the rates of mineralization and nitrification in a coarse-textured kaolinitic Ultisol. Soil samples were taken from field plots which received lime rates from 0 to 4mt/ha three years prior to the study. The pH of the soil samples varied from 4.2 to 6.1. Ammonification of soil organic N and added urea source proceeded readily and was not affected by lime rate. Nitrification occurred in both limed and unlimed soils but the rate of nitrification depended upon the rate of lime application. Soil pH, exchangeable Ca and exchangeable A1 were significantly correlated with the amount of NO₃-N accumulated at the end of the 65 days incubation period. Nitrification of NH₄-N from ammonium sulfate was absent in soils receiving lower rates of lime which gave pH values ranging from 4.2 to 4.8. Added ammonium source was nitrified readily after a 3-week delay period in the soil (pH 6.1) which received a higher rate of lime (4 mt/ha).