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Abstract
The present work aimed to compare the effectiveness of nitrapyrin (NP), thiourea (TU), and dicyandiamide (DCD) as nitrification inhibitors (NIs) when were applied to a sandy soil treated with ammonium sulphate and incubated in the laboratory at 28 °C for 40 days. Two greenhouse column experiments were also carried out to evaluate the efficacy of the three inhibitors in increasing the efficiency of ammoniacal fertilizers in a sandy soil cultivated with wheat and maize. The obtained results can be summarized as follows :
In the laboratory experiment, the effectiveness of the three NIs, as indicated by the percent inhibition of nitrification (PIN), was increased with increasing their application rates. The highest PIN values were recorded in the soil treated with 100 mg ammonium sulphate (AS)-N + 2 mg NP kg-1 soil where they were 92.8 and 18.5% after 7 and 40 days of incubation, respectively. At the end of incubation period (40 days), the effectiveness of the three NIs could be arranged on the basis of the average PIN values as follows : NP > DCD > TU. Concerning soil microorganisms, the use of NIs decreased the highest average counts of total bacteria and fungi as compared to the control. The highest counts of ammonia oxidizing bacteria and nitrite oxidizing bacteria were recorded in the soil treated with AS alone and were found to be decreased with increasing the inhibitor rate at the end