The Influence of Low Temperature and Various Concentrations of Ammonium Nitrate on Nitrification in Acid Soils

Abstract Several cultivated, acid soils were limed to pH 6.0 to 6.4, treated with 100 ppm. NH 4 ‐N as NH 4 NO 3 , and incubated for 12 weeks at low and at near‐optimum temperatures for nitrification. In sandy soils, nitrate accumulation at 42°F. was either completely suppressed or delayed for several weeks. In a clay loam incubated at 37°F. nitrates accumulated at a very slow rate throughout the 12‐weeks but at 47°F., after a 6‐week delay period, the accumulation proceeded at a rapid rate. The great influence of differing soil characteristics on nitrification is shown by the fact that nitrate accumulation in the clay loam at 37°F, was about two‐thirds of that occuring in a loamy sand at 90°F. When the amount of added NH 4 NO 3 was increased to 200 or 400 ppm. NH 4 ‐N, nitrate accumulation, with one exception, failed to occur at 42°F. in sandy soils and was delayed in the clay loam. Even at 90°F., nitrate accumulation in the sandy soils, but not in the clay loam, was delayed and the rate reduced.