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Field studies to assess the effects of various rates of nitrogen (N) fertilization on seasonal uptake and partitioning of N by cotton ('Delta-pine 41') were performed in 1989 and 1990 at St. Joseph, LA on a Commerce silt loam. Plots used in these experiments have been continuously cropped to cotton since 1987 and have received preplant applications of 0, 75 or 150 lbs N/ac annually. Plants were collected 25, 50, and 75 days after planting (DAP), at the end of their effective blooming period, and immediately prior to defoliation. Harvested plants were partitioned into stems, branches, petioles, leaves, squares and bolls. Bolls collected immediately prior to defoliation were separated into burrs, lint and seed. Ground litter was also collected between end of blooming and defoliation. The dry weight and N content of plant components were determined. During the past two seasons, seedcotton yields of plots receiving 75 lbs N/ac were significantly greater than those receiving no fertilizer N and somewhat greater than those receiving an excessive amount (150 lbs N/ac). Plots yielding the highest amounts of seedcotton assimilated 195-225 lbs N/ac in aboveground biomass prior to defoliation. Most of the N assimilated in excess of that required for maximum yield was recovered in ground litter shed between end of effective blooming and defoliation. A strong relationship was observed between biomass produced at defoliation and the amount of N assimilated. A 100% increase in biomass corresponded to a 140% increase in N assimilation (r2 = 0.92). Highest yields were obtained in plots producing 5.5-6.0 US tons biomass/ac. Total N concentrations in whole plants, upper leaves and lower petioles reflected the N status of plants at end of effective blooming. N concentrations of these components were similar in 1989 and 1990, suggesting that total N analysis of upper leaves or lower petioles may be useful in identifying midseason N deficiency. It is noteworthy that the amount of N removed as seedcotton was similar to or exceeded the amount of fertilizer N required for maximum yield. |
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©National Cotton Council, Memphis TN |
Document last modified Sunday, Dec 6 1998
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