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Stalk Rot Incidence and Yield of Corn as Affected by Inhibiting Nitrification of Fall-applied Ammonium¹

Large overwinter losses of fall-applied fertilizer N from midwestern U.S. soils occur through leaching and denitrification. These losses result in decreased efficiency in the utilization of applied N and often in lower crop yields. Of the various management techniques available to reduce N losses, previous studies with spring-applied N suggested that inhibiting nitrification of applied ammonium with specific chemicals appears to be most compatible with current fertilization and crop production practices. We tested the effectiveness of a specific nitrification inhibitor, 2-chloro-6-(trichloromethyl)pyridine (nitrapyrin), in reducing losses of fall-applied N by comparing the growth, disease incidence, and yield of corn growing in field plots receiving anhydrous ammonia with those treated with anhydrous ammonia containing the inhibitor.

Three field experiments on two soil types (Typic Argivdoll coarse-loamy, mixed mesic and Vertic Halpla-quoll fine, montmorillonitic, mesic) demonstrated that inhibition of nitrification of fall-applied ammonium markedly increased grain yields and grain protein and decreased the incidence of stalk rot in corn. Corn yields were increased as much as 207% (average increase was 68%) as a result of applying 0.55 kg of nitrapyrin/ha with fall-applied anhydrous ammonia when compared to yields obtained with anhydrous ammonia without the nitrification inhibitor. In all experiments, stalk rot incidence in corn was reduced as a result of inhibition of nitrification — the reductions varied from 60 to 96%. In two experiments, grain protein content was increased by 7 to 38% as a result of application of nitrapyrin with fall-applied N.

The results of this study indicate that severe losses of N may occur as a result of fall application of N fertilizers and that these losses may be markedly reduced by using a nitrification inhibitor to minimize the formation of nitrate. The increased yield and grain protein obtained from nitrapyrin addition likely resulted from greater availability of N in nitrapyrin-treated plots. The reduction in stalk rot may have resulted from altered N metabolism in plants growing in nitrapyrin-treated plots because of the uptake of substantial amounts of ammonium. This was indicated since stalk rot was reduced by nitrapyrin in plots which were not under N stress. Another explanation for reduced stalk rot may reside in the fact that nitrapyrin-treated plots had more vigorous plants than plots not receiving the nitrification inhibitor. The data also suggest that N application rates used for corn production may be decreased with no loss in yield if a nitrification inhibitor is used to minimize losses of applied N.

Key Words: Diplodia maydis • Gibberella roseum f. sp. cerealis • Gibberella zeae • Leaching • Denitrification • N fertilization • Nitrapyrin

² Plant pathologist, ARS-USDA; associate professor of botany and plant pathology, associate professor of agronomy, and research cooperator, respectively. Mention of a trademark or product does not constitute a guarantee or warranty of the USDA, nor does it imply its approval to the exclusion of other suitable products.

Received for publication January 8, 1975.