Effects of nitrapyrin, terrazole, and simazine on soil nitrogen transformation and corn growth

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Abstract
Nitrapyrin, terrazole and simazine were evaluated as chemical inhibitors of biological nitrification and denitrification. Corn (Zea mays L. cv. Hybrid Pioneer 3343) was grown in 60‐liter pots filled with a 50/50 (V/V) sand/Cecil clay mixture. Chemical treatments consisted of weekly applications of 0.25 ppm nitrapyrin, terrazole and/or simazine concurrently with 20 ppm N as either (NH4)2SO4 or Ca(NO3)2 for 9 weeks. Thereafter, only N (20 ppm per pot) was applied to the media every three days for 4 weeks. Nitrapyrin, terrazole and simazine reduced nitrification resulting in both higher total plant N and residual soil NH4 content relative to the control plants and soil. Plant growth was reduced by the inhibitory effects of the chemicals on nitrification and subsequent NH4 accumulation in the medium. All chemicals reduced denitrification with terrazole being more effective than nitrapyrin as reflected by higher N contents of plants and residual soil NO3‐N. Nitrapyrin and/or terrazole applied with Ca(NO3)2 increased plant biomass, but simazine, by inducing higher N02 concentration in the plant tissues, sharply reduced plant growth relative to the other treatments. When simazine was part of the chemical treatment, its effects on plant growth and total N contents generally outweighed or masked those of nitrapyrin or terrazole.