Department of Soils, Punjab Agricultural University, Ludhiana, 141004.
* USDA-ARS, 119 Keim Hall, University of Nebraska, East Campus, Lincoln, Nebraska, 68583-0915, USA.
Nitrification of ammonium based fertilizers, a key process governing fertilizer use efficiency as well as N losses from soils via different mechanisms, was studied as a function of soil pH by incubation. Under upland conditions (60% water filled pore space, WFPS), nitrification rate of added NH4+-N was the highest in the Tolewal soil with pH 7.4 (7 mg N kg−1 d−1), modest in the Sodhi Nagar alkali soil with pH 9.4 (3 mg N kg−1 d−1) and lowest in the Andrettaacidic soil with pH 4.8 (1 mg N kg−1 d−1). Applied NH4+-N (100 mg N kg−1 soil) was completely nitrified in 10 d in the near neutral soil whereas it took 30 d for alkali (pH 9.4) soil and only 33 per cent was nitrified in the acidic soil at 30 d. Under flooded conditions (120% WFPS), rate of nitrification was relatively low, but followed the same trend. The Tolewal soil exhibited the highest first order rate constant (k) under both upland and flooded conditions.
nitrification, soil pH, flooding, kinetics, ammonium
