Nitrogen Rate Effect on Partitioning of Nitrogen and Dry Matter by Cotton

Increased understanding of the fate of N in cotton ( Gossypium hirsutum L.) fields will improve N efficiency, optimize crop development and yield, and may help to avoid excessive N fertilization. This study quantified the effects of N fertilization rate (0, 84, and 168 kg ha −1 ) on seasonal uptake and partitioning of N and dry matter in field‐grown cotton during 1989 and 1990. The N rates studied were part of a larger experiment initiated in 1987 where plots received annual preplant applications of 0, 28, 56, 84, 112, 140, or 168 kg N ha −1 Experiments were conducted on Commerce silt loam (fine‐silty, mixed, thermic, nonacid, aeric Fluvaquent) on the Louisiana State University Agricultural Center Northeast Research Station near St. Joseph, LA. Plants were collected at five dates in each year at about 20‐d intervals. Shed plant debris was also collected. The N content and aerial biomass of plant components were determined. Maximum N uptake occurred between 49 and 71 d after planting and was 2.9 and 4.3 kg ha −1 d −1 for cotton receiving 84 and 168 kg N ha −1 , respectively. At maturity, plants receiving 84 kg N ha −1 contained 160 kg N ha −1 in aerial biomass and an additional 50 kg N ha −1 in abscised plant debris. The total amount of N assimilated by plants receiving 84 kg fertilizer N ha −1 averaged 111 kg N ha −1 more than plants receiving no fertilizer N for an apparent fertilizer efficiency greater than 100%. By the end of effective bloom, plants receiving 168 kg N ha −1 assimilated 15 to 40% more N, primarily in leaves and lower bolls, than plants receiving 84 kg N ha −1 This excess assimilated N was recovered in surface litter and in N‐enriched plant components. Of the plant components studied, leaf‐blades most consistently reflected the amounts of fertilizer N applied.