Potential and kinetics of nitrification in soils from semiarid regions of northwestern India

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Abstract
Nitrification potential of 25 of 26 soil samples from semiarid regions of northwestern India ranged from 3.6 to 10 mg NO‐ 3‐N kg‐1 soil day‐1. Nitrification potential was not related to soil properties of pH, cation exchange capacity, organic carbon, CaCO3, sand, and clay contents. Nitrification in soils possessing relatively low or high nitrification potential could be described either by Michaelis‐Menten or zero‐order kinetics for conditions of 400 mg NH+ 4‐N kg‐1 soil at 35°C. Maximum nitrification rate was observed at 35°C and was reduced to <0.1 of the maximum at 20 or 8°C. Comparison of these data with optimum temperature for nitrification from different regions of the world indicated adaptation of soil nitrifiers to a high‐temperature optimum and tolerance. Nitrification rate followed first‐order kinetics and was maximum at field capacity, followed by 50% field capacity and waterlogged conditions. Actual rate of nitrification under waterlogged conditions was negligible. ATC (4‐amino‐1,2,4, triazole) even at low concentrations proved to be more effective at inhibiting nitrification than DCD (dicyandiamide). Soil texture and organic carbon contents influenced the effectiveness of nitrification inhibitors.