Nitrogen distribution within a sympodial branch of cotton

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Abstract
Although nitrogen (N) partitioning within the cotton (Gossypium hirsutum L.) plant has been documented, little is known about the distribution within a sympodial branch in relation to the development of individual bolls. Field studies were conducted on a Captina silt loam (Typic Fragiudults) to investigate the N distribution within a representative sympodial branch at main‐stem node 10. The dry matter, percentage N and total N were determined at 7‐day intervals during branch development for individual leaves, petioles, bolls, and the branch. The dry weight of the main‐stem leaf, and the first three sympodial leaves along the branch peaked at 21, 28, 35, and 42 days, respectively, which coincided with the time of maximum total‐N content. Peak N content for the main‐stem leaf was 63 mg, and declined progressively with 60% of the total N exported within 42 days. However, individual sympodial leaves exhibited only a slight decrease in total‐N content despite the increasing N requirement of the subtended bolls. The majority of the N accumulated in the bolls, while at the same time the N content of the leaves decreased, and the N content of the petioles and branches remained somewhat constant. The N concentration on a dry matter basis differed among various plant organs and tended to decline in both vegetative and reproductive organs as the season progressed. The leaves were the primary N sinks prior to anthesis, and thereafter the N sink was gradually shifted to the developing bolls. The N requirement of a developing boll may not be supplied solely via the subtending leaf and imports from additional sources may be required.