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Abstract

Nitrification inhibition of soil-N and applied fertilizer N is desirable as the accumulation of nitrates in soils in excess of plant needs, leads to enhanced N losses and reduced fertilizer N-use efficiency. The effect of twenty-two different organic carboxylic acids, representing aliphatic (C1 to C18), di-, chloroacetic, hippuric, benzoic and heterocyclic (furoic, nicotinic and isonicotinic), on nitrification in a semi-arid subtropical sandy loam (Typic Ustrochrepts) soil in a laboratory incubation experiment is reported. The compounds were screened at 10% of applied-N dose and incubated for a period of 21 days at 300C, maintaining 50% of the water holding capacity of the soil. Most of the test acids were found to be mild inhibitors of nitrification. Nitrification inhibition was the maximum (31.4%) in nicotinic acid treated soil followed by isonicotinic, furoic, palmitic, and stearic acid treated soils (26.6-27.8%). Based on four indicators of inhibitor effectiveness, namely, concentration of ammonium-N and nitrate-N, and total mineral N, nicotinic acid showed the highest relative efficiency among all the test acids. A quantitative structure activity relationship (QSAR) model based on nitrification inhibitory activity [Arc sine (% NI)] and various physico-chemical substituent parameters for hydrophobic and steric properties has been developed using multiple linear regression (MLR) analysis technique.