Boll Weight and Within‐Plant Yield Distribution in Field‐Grown Cotton Given Different Levels of Nitrogen

Abstract Increased understanding of N effects on fruiting and yield of cotton (Gossypium hirsutum L.) could lead to more efficient use of N fertilizer and increased yields. We determined the influence of N rate on boll size and yield distribution of cotton plants by measuring individual boll weights (IBW) and average seedcotton yield at each potential fruiting site (FS). Field experiments were conducted from 1987 through 1990 on Commerce silt loam (fine‐silty, mixed, nonacid, thermic Aeric Fluvaquent) to assess the response of cotton to preplant N rates of 0, 28, 56, 84, 112, 140, and 168 kg ha−1 and to a split application of 56 + 56 kg N ha−1. Increasing N rate from 0 to 84 kg ha−1 increased average whole‐plant IBW by 0.16 g and average yield per fruiting site by 0.29 g. Response of IBW and FS yield to N rate was dependent on the location of FS on the plant. Individual boll weight was maximized in Horizon 1 (mainstem nodes 5 through 10) with 28 kg N h−1, in Horizon 2 (mainstem nodes 11 through 16) with 56 kg N h−1, and in Horizon 3 (mainstem nodes 17 through 24) with 140 kg N h−1. Yield at fruiting site 1 (FS1) in Horizon 1 decreased from 2.3 to 1.7 g as N rate increased from 0 to 168 kg ha−1. Nitrogen fertilization of 84 kg ha−1 increased FS1 yield in Horizon 2 from 2.3 to 3.1 g, and increased FS1 yield in Horizon 3 from 0.27 to 1.1 g. Increasing N rate redistributed plant yield by decreasing the yield contribution of Horizon 1 from 43 to 28%, increasing the yield contribution of Horizon 2 from 44 to 48% and increasing the yield contribution of Horizon 3 from 7 to 22% of the total plant yield. The contribution of monopodial branches was <6% of total yield for all treatments and was decreased by application of >56 kg N ha−1. The application of optimal N rates benefited cotton yield by producing larger bolls at a greater number of fruiting sites. Increase in yield by increase in IBW and FS weight was limited, because gains in Horizon 3 were offset by negative responses in Horizon 1 when the N rate exceeded 84 kg ha−1