One greenhouse experiment and four field experiments were conducted during 1964–65 to determine (a) the effect of rate, time, and method of P fertilization on grain yield, yield components, and cooking quality estimation of rice, and (b) the existence of N × P interactions. Increasing P in 1964 increased lodging and reduced grain yields and 1,000 grain weight. In 1965 there was no influence of P rate. Preplant P produced darker green vegetation, broader leaves, and taller plants than did the midseason application. Differential responses disappeared by harvest time and no differences occurred except for cooking characteristics, which were more favorable with the preplant application. Cooking characteristics were not affected by P rate, but were less favorable as N was increased in three experiments and more favorable in the other experiment. Interactions between time of P application and N rate showed cooking characteristics were more favorable as N was increased and P applied at midseason than when P was applied preplant. Interactions between P application time and P rate showed that increasing P and applying it preplant improved cooking characteristics over those of the same rates applied a midseason. The N X P interactions were inconsistent. In the greenhouse study, soil‐incorporated P increased straw weight more than did broadcast P, but did not affect plant height, panicle number, or panicle weight. Increasing N increased panicle number, total panicle weight, straw weight and plant height. Increasing P decreased height and increased values for the other variables. The only interaction showed that increasing P and incorporating it increased panicle number and straw weight more than broadcasting it.
Field studies were conducted with ‘Vegold,’ ‘Nato,’ and ‘Bluebonnet 50’ rice (Oryza sativa L.) in 1963, 1964, and 1965 to determine the optimum time near midseason to apply nitrogen fertilizer for greatest yield. Internode elongation was used as a guide to estimate proper morphological stage of development for the optimum time to apply nitrogen. During the 3 years of study all three varieties had grain yield increases of over 1,120 kg/ha that could be attributed to applying midseason nitrogen at the proper time during panicle initiation. Topdressing nitrogen at midseason was found to be most effective when 50% of the plants had elongating internodes equal to or in excess of 12.8 mm for Vegold, 39.7 mm for Nato, and 32.1 mm for Bluebonnet 50.
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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