Comparison of Inhibitory Effects of Potassium Chloride, Ammonium Chloride and 3, 4-Dimethylpyrazole Phosphate on Nitrification

Nitrification is the microbial oxidation of ammonium to nitrate in the soil which results nitrate loss and water resource contamination. Nitrification inhibitors basically evolved to improve nitrogen use efficiency of crops particularly in vegetable production systems. They also aimed to reduce nitrate accumulation and oxalate problems in fresh leafy vegetables, as well as less ground water nitrate content. The effectiveness of two types of chloride salts were compared to 3, 4-dimethylpyrazole phosphate (DMPP), as a standard synthetic nitrification inhibitor, in pot experiment under controlled conditions. Results showed that DMPP strongly inhibited nitrification during the whole period of experiment (7 weeks). On the other hand, chloride in forms of ammonium chloride and potassium chloride, significantly inhibited nitrification compared to control at all sampling dates. Inhibitory effects of chloride were positively correlated to chloride concentrations, in which higher concentration (500 mg/kg soil) showed more effective inhibition compared to less concentration (250 or 100 mg/kg soil). The results also indicated that apart from commercial nitrification inhibitors, chloride also can retard nitrification in soil. Therefore, where chloride is not a soil problem, chloride forms of nitrogen fertilizers could significantly increase nitrogen use efficiency.