EFFECTS OF SOIL ACIDITY AND LIMING ON MINERALIZATION OF SOIL NITROGEN

Abstract

Forty acid surface soils of pH 4.0–5.6 were incubated with and without lime, and the amounts of N that were mineralized or nitrified were statistically compared with several soil acidity characteristics. In addition, three field experiments were used to find the effect of liming on N mineralization. There was no relation between the amounts of mineral N released per unit of organic N in 120 days of incubation and soil pH, base saturation or soluble Fe, Al or Mn. Despite this, liming the soils to about pH 6.7 approximately doubled the amounts of N mineralized during incubation. In the field experiments, lime increased uptake of soil N by 15–42 kg/ha in the 1st yr but only 7–10 kg/ha in the 3rd yr. Thus these laboratory and field experiments indicate that soil acidity does not restrict mineralization of organic N and although liming increases mineralization of N, it is generally a temporary effect. Nitrification in the 40 incubated soils occurred much more rapidly in cultivated soils than in virgin soils. For both the virgin and cultivated soils, nitrification decreased with decreasing soil pH. However, nitrification was not statistically related to base saturation or soluble Fe, Al or Mn. Liming established good nitrification in most of the soils and this effect did not diminish with time.