ABSTRACT
The application of fertilizer nitrogen (N) can delay crop maturity in the humid growing areas of the mid-South. Field studies wee conducted at the Northeast Research Station at St. Joseph, LA from 1987 to 1990 to determine the effects of N rate on the number of days required for boll development, and cumulative yield distribution over time. Deltapine 41 was planted each year on April 25 and fertilized with 0, 75 or 150 pounds of N per acre. The experimental design was a randomized complete block with four blocks. Plots were eight 40-inch rows 62 feet long. Each year 10 plants were randomly selected in each plot for individual plant analysis. Bolls on selected plants were hand-harvested at 3-day intervals beginning in mid-August and continuing until all boll were harvested. Each boll was dated and weighed. Boll harvest dates and weights were used to calculated boll maturation dates for each fruiting site and cumulative percent of yield harvested on each day during the boll opening period. Fertilizer N at rates of 75 and 150 pounds per acre had very small effects or no effect on the length of time required for boll development. Bolls at fruiting site 1 sympodia 8, for example, matured 119, 121 and 120 days after planting (DAP) at the 0, 75 and 150 pound N rates, respectively. Despite the lack of effect of N on boll maturity at specific fruiting sites, fertilizer N did delay crop maturity. In years with wet summers (1987, 1989) the 60% open boll sage (defoliation time) was reached 140, 147 and 150 DAP with the 0, 75 and 150 pound N rates, respectively. Delay in crop maturity due to n fertilization was caused by two factors: (1) redistribution of a portion of plant yield from earlier maturing fruiting sites to later maturing fruiting sites, and (2) additional plant growth that increased boll set at late-season fruiting sites. Tech delay in crop maturity resulting from N effects on plant yield was 6 to 8 days with the initial 75 pounds of N per acre. This delay in maturity was accompanied by an increase in yield per acre. The second 75 pound per acre increment of N resulted in an addition 1 to 3 day delay in maturity and a decrease in yield per acre.
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