Comparative studies on soil nitrification inhibition by pyridine compounds

Nitrification inhibition is a well-established fertilizer management that improves fertilizer use efficiency (FUE) in crop production aimed at enhanced profitability, crop quality and healthy environment. As a nitrification inhibitor, pyridine compound has been used for stabilization of fertilizer nitrogen (N) for more than 20 years now. However, pyridine compound represents a broad class of heterocyclic N compounds whose activity as nitrification inhibitors appears to be impacted by Cl and/or trichloromethl sub-stitution on C atoms immediately adjacent to the N ring. In addition, the solubility of pyridine compounds in water is very low; which decreases nitrification inhibitory activity. To prove nitrification inhibitory effects, 2-chloro-6(3-chloromethylthiazole)-sulfate, 2-chloro-6(3-chloromethylthiazole)-chloride, pyridine compounds mixture and pyridine X compounds were investigated for inhibi-tory effects on nitrification of fluvo-aquic soil, red soil and paddy soil using laboratory microcosm experiments. The results showed that nitrate contents in soils treated with pyridine compounds were significantly lower than those of the control. Nitrification inhibi-tion rate range was 2.91%~91.92%. Inhibitory effect of pyridine compounds on soil nitrification increased before 21 d, after which it decreased, with peak effect on 21^st d. Differences were noted among inhibitory effects of different pyridine compounds. The effects of 2-chloro-6(3-chloromethylthiazole)-chloride were much stronger than those of other pyridine compounds. Differences were also noted in inhibitory effects of pyridine compounds on nitrification in fluo-aquic soil, red soil and paddy soil. Inhibitory effects of pyri-dine compounds in the different soils were in the order of: fluvo-aquic soil > paddy soil > red soil. Based on soil type, pyridine com-pound inhibition effect on nitrification increased with increasing application rate the compounds.