Effects of Nitrogen Timing and Split Application on Blast Disease in Upland Rice. E. Kürschner, Collaborative Scientist, WZ Tropeninstitut, Justus-Liebig Universitaet, Schottstr. 2, D-6300 Giessen, Germany. J. M. Bonman, D. P. Garrity, M. M. Tamisin, D. Pabale, and B. A. Estrada. Plant Pathologist, Agronomist, Senior Research Assistant, Research Aide, and Assistant Scientist, International Rice Research Institute, P.O. Box 933, Manila, Philippines. Plant Dis. 76:384-389. Accepted for publication 4 September 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0384.

Nitrogen is essential for increased upland rice productivity, but the severity of blast disease increases with N application. The potential to suppress blast disease through timing and splitting of N application was tested during the 1987 and 1988 wet seasons in the Philippines on a strongly acidic soil. We studied the effects of 90 kg of N per hectare applied as two early-split applications, two late splits, three equal splits, and five equal splits on disease progress, crop growth, and yield. A no-N check was included. Leaf blast was suppressed when N was applied late (30 and 60 days after seeding) compared with early- and equal-split applications. Panicle blast was less in the no-N check but was not consistently reduced by any of the other treatments. Leaf and panicle blast correlated with total dry matter (r = 0.60-0.70), Si/N ratio (r = –0.50 to –0.80), and with the concentrations of Si (r = –0.40 to –0.70) and N (r = 0.50-0.80). Increased leaf blast was attributable to both increased tissue susceptibility and increased canopy density. In inoculated plots, total dry matter (5.6 t/ha) and grain yields (1.1 t/ha) were reduced compared with fungicide-treated plots (6.3 and 1.8 t/ha), and the yield loss was correlated with the incidence of severe panicle infection (r = 0.86). Nitrogen treatments had no significant effect on grain yields. None of the treatments controlled both leaf and panicle blast and increased yields.

Keyword(s): Oryza sativa, Pyricularia grisea, P. oryzae.