EFFECTS OF NITRAPYRIN ON CORN YIELDS AND RECOVERY OF AMMONIUM-N AT 18 SITE-YEARS IN IOWA

Nitrapyrin [2-chloro-6-(trichloromethyl) pyridine] is a nitrification inhibitor frequently used to prevent losses of N fertilizer during corn (Zea Mays L.) production. Although many studies have shown that nitrapyrin inhibits nitrification in soils, it has not been established that use of nitrapyrin is cost effective for corn producers in the western portion of the Corn Belt. Field experiments were conducted at 18 site-years from 1985 through 1987 to determine the effects of nitrapyrin on corn yields and recovery of spring-applied fertilizer. Ammonium sulfate was broadcast at four rates (0, 50, 100, and 150 lb N/acre), with and without nitrapyrin, and replicated three times. N-15-labeled (NH4)2SO4 was substituted for unlabeled (NH4)2SO4 on subplots within yield plots at eight of the site-years. Statistically significant (P < 0.05) grain yield responses to fertilizer N were observed at 17 of the 18 site-years. Nitrapyrin significantly increased yields only at two of the 72 rate-site-years. Nitrapyrin did not influence recovery of labeled N in grain at 22 of the 24 rate-site-years having labeled fertilizer. It decreased recovery at the two other rate-site-years. Nitrapyrin had no significant effect on recovery of labeled N in the soils 8 wk and 14 mo after application. The results suggest that use of nitrapyrin was not cost effective at any of the sites studied.