Effect of anhydrous ammonia with and without nitrapyrin applied fall and spring on corn yield

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Abstract
Fall application of N for corn [Zea mays (L)] on clay pan soils in northeastern Missouri has not become an accepted practice as wet soils conductive to denitrification often delays corn plantings. Since nitrification inhibitors have the potential to reduce denitrification loss of fall applied N, a 4‐year study (1979–82) was conducted on a Mollic Albaqualf soil, subject to excessive spring wetness and representative of the corn growing region in northeastern Missouri to study the effect of the nitrification inhibitor, nitrapyrin, on fall and spring applied anhydrous ammonia. A randomized block design with 4 replications was employed using 0, 56, 112, 168 and 224 kg N/ha as anhydrous ammonia applied fall and spring with and without 0.56 kg/ha of nitrapyrin. Measurements included grain yield, leaf N and grain protein. The second year, 1980, high day and night temperatures and July rainfall 118 mm below normal eliminated any response due to N and nitrapyrin treatments. Grain yield, leaf N and grain protein followed typical response to applied N. Lack of response to fertilizer N in 1979 was attributed to residual soil N after four previous croppings of soybeans, and lack of response to N in 1981 is attributed to residual fertilizer N because of drought induced low yields of 1980. Percent grain protein was a function of N rate and was not consistently related to leaf N, and therefore, not influenced by nitrapyrin. From 15% to 18% less fertilizer N would be required for yield maximization by including nitrapyrin in the fall application, with 3.2 to 4.7% less fertilizer N required with the spring application. Fertilizer N required for yield maximization with N fall applied with nitrapyrin was calculated to be the same as N spring applied with nitrapyrin and less than the N spring applied without nitrapyrin. Results from this study indicate fall application of N as anhydrous ammonia with nitrapyrin would permit higher plant N use efficiency on this claypan soil.