Smut Disease Incidence and Mineral Composition of Corn as Affected by N Fertilizer Sources and K Application Rates

Abstract

AbstractA 2 year field experiment was initiated to compare the effect of ammonium nitrate (AN) and urea (U) fertilizer sources at 0, 45, 90 and 135 kg N acre−1 in combination with 0 and 48 kg K2O acre−1 on dry matter yield (DM), smut index (SI) and ear leaf nutrient composition. The plants at 8‐leaf growth stage were exposed to artificial infection and the severity was rated on a 1–9 scale. Elemental leaf (N, K, Ca and Mg) and DM were determined at silking and harvest time, respectively. N:(K+Ca+Mg) ratio in plant tissue was calculated. The plants supplied with AN fertilizer appeared to have had greater advantage in DM yield, accompanied by a marked increase in smut severity at higher N rates than U‐treated plants. On average, the relative increases in DM and SI for AN were 8.2 and 9.1%, respectively. Potassium application suppressed smut incidence by 19.6%. The leaf analysis data showed that the plants treated with AN were associated with greater cation uptake than LJ‐fed plants. Increasing N rates enhancedsmut severity and resulted in remarkable increases in DM and ear leaf nutrient composition. Leaf Ca and Mg contents were decreased hy increasing K3O rates. The correlation coefficients (r) between ear leaf nutrient contents and SI showed variable significant effects among N sources. Because the plant nutrient levels are determined by many variables, attention was drawn to N:(K+Ca+Mg) ratio in plant tissue for better smut disease interpretations.