COMPOSITION AND ACTIVITY OF THE MICROBIAL-POPULATION IN AN ACIDIC UPLAND SOIL AND EFFECTS OF LIMING

The microbial population and microbial activity were examined in the strongly acidic organic horizon of a brown podzolic soil. The short- and long-term effects of liming the soil on these properties were also examined. Liming increased the bacterial population ca 20-fold in 32 days but this extreme effect did not persist. The increase in the bacterial population was mainly in acid intolerant species. None of the two methods of assessment used showed any significant change in the fungal population either in the short- or long-term after liming. Liming caused a rapid and substantial increase in both soil respiration and net nitrogen mineralized despite a rather high C-to-N ratio of soil organic matter. Comparison between the native and long-term limed soils in gross and net N mineralized together with the respiration response in the native soil to glucose and mineral nutrient additions suggested that the activity of the microbial population in the native soil was not limited by available N. Furthermore herbage yields and nutrient offtake suggested that herbage yields on the native soil were not restricted by available N. Nitrate was produced in the aerobically incubated native soil but probably not all by autotrophic nitrifiers. © 1990.