Smut Disease and Yield Performance in Corn (Zea mays L.) as Influenced by Nitrapyrin, Urea and Zinc Applications in Coarse‐textured Soils

The effects of nitrapyrin (NI), urea (U) and Zn rates on rhizosphere pH, smut incidence (S.I.), dry matter (D.M.), grain yield (G.Y.) and ear leaf N and Zn contents were studied in cemented plots, containing calcareous and non-calcareous soils. Treatments were comprised of 3 U applications (46, 92 and 138 kg N acre -1 ), combined with N1 rates (0 and 0.22 kg acre ') and 2 levels of Zn (0 and 8 kg acre -1 ). Corn seeds, cv 'Amoun' were planted in 1993 and 1994 and the seedlings were artificially injected with U. maydis-spores at the 6 and 10 leaf growth stages. Results have shown that corn plants grown in calcareous soil imposed greater advantage in D.M. and G.Y., accompanied by a relatively low smut infection than those grown in non-calcareous soil. Unlike the diversion effects of NI on soil pH and plant Zn content, its application was beneficial for improving yield and plant Zn content. Urea applications decreased the soil pH by 0.6 unit at the highest N rate and exerted stimulatory effects on ear leaf N and Zn contents. By increasing U rate to 138 kg N acre -1 , smut severity was increased by 6%. In contrast, by Zn fertilization, smut severity was decreased by 10.3%, accompanied by marked increases in G.Y. and leaf Zn content. Mixed results were detected on S.I. data, when NI was combined with U rates. In the presence of Zn, smut severity was dropped to 20.1% at 138kg N acre -1 . The results also showed that in the absence of Zn supply, S.I. was dominated in NI-treated plants and the reverse was true when Zn was included. Satisfactory results were achieved when 92kg N acre -1 were combined with 0.22 and 8 kg acre -1 of NI and Zn, respectively.