Effect of Nitrapyrin on Nitrification of Broadcast-applied Urea, Plant Nutrient Concentrations, and Corn Yield

The use of nitrification inhibitors offers a method for decreasing initial nitrification rates and subsequently decreasing nitrate losses from soil. Thus, the use of inhibitors should increase N uptake and corn (Zea mays L.) yield in years when soil moisture conditions favor N losses. This study was conducted to evaluate the effects of nitrapyrin applied with broadcast applications of urea on nitrification, plant nutrient concentrations, and corn yield. Urea (0 to 268 kg/ha N) and nitrapyrin (0 and 2.24 kg/ha) were applied to a somewhat poorly drained soil (Flanagan silt loam - Typic Hapludoll) in the spring and fall of 1975 and spring of 1976. Soils were sampled to a depth of 45 cm and plant tissue samples were taken at first silk and at physiological maturity. Nitrapyrin was effective in decreasing nitrification rate of both fall- and springapplied N. Fall-applied N without nitrapyrin was nitrified by mid-March, but when nitrapyrin was added an average of 12% of the added N was recovered as ammonium from the top 15 an of the soil in early June. More ammonium-N was recovered from the soil in early June when N was applied in the fall with nitrapyrin than in the spring without nitrapyrin. While nitrate accumulations were found at a depth of 45 cm when urea without nitrapyrin was applied in the fall, nitrate did not accumulate below the 15-cm depth when urea was applied in the fall with nitrapyrin or in the spring with or without nitrapyrin. Nitrapyrin did not affect the concentration of P, K, Ca, Mg, Cu, B, and Mn in the ear leaf, grain, or stover, but increased the concentration of Fe in the ear leaf by 10%. Nitrapyrin added with 67 kg/ha fall-applied N increased concentration of N in the ear leaf by 15%. When applied with spring-N, nitrapyrin increased the spring-N concentration in the stover and grain by 13 and 17%, respectively. Nitrapyrin applied with 134 kg/ha spring N increased the N concentration in the ear leaf by 14'% but decreased the concentration in the grain by 11%. Nitrapyrin increased grain yield by 27% when applied with 67 kg/ha fall-N, but decreased yield by 70/, when applied with 134 kg/ha spring-N.