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This article in AJ

  1. Vol. 59 No. 1, p. 63-66
    Received: June 10, 1966

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Timing of N Fertilization of Rice. I. Effect of Applications Near Midseason on Varietal Performance1

  1. J. L. Sims,
  2. V. L. Hall and
  3. T. H. Johnston2



Field studies were conducted on Crowley silt loam soil in 1963, 1964, and 1965 to determine the optimum time near the middle of the growing season to apply N fertilizer to rice (Oryza sativa L.) and also to study interactions of time, N rates, and years. Forty pounds per acre of N was applied to all plots about 15 days after seedling emergence and just before flooding. The optimum time for the second application of N was that which resulted in near-minimum plant height and lodging, with near-maximum grain yield. Topdress N was applied at 3 levels to drained soil at each of 5 times near midseason, and plots were immediately reflooded. The source was ammonium sulfate.

Varieties (cultivars) used were 'Vegold,' 'Nato,' and 'Bluebonnet 50,' which are classed, respectively, as very short-season, short-season, and midseason in maturity.

Yields of grain were inversely related to plant height and lodging, and generally increased with time of N application up to 50, 67, and 79 days from emergence for Vegold, Nato, and Bluebonnet 50, respectively. N applied earlier than 45, 55, and 65 days to Vegold, Nato, and Bluebonnet 50, respectively, stimulated vegetative growth and resulted in taller plants, greater lodging, and lowered grain yields. Grain yield differences as great as 1,000 pounds, as an average of all N rates, could be attributed to time of N application.

Significant rate × time and year × time interactions occurred. Rates of N generally had little or no effect on grain yield and plant height at treatment dates which gave maximum grain yield. However, high rates at early dates of application tended to depress grain yields and increase plant height and lodging. Maximum grain yield and significant reductions in plant height and lodging resulted from earlier treatments in 1964 (a year in which plants grew faster) than in 1963 or 1965.

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