Nitrogen Effects on Boll Production of Field‐Grown Cotton

Abstract Nitrogen is an essential nutrient for cotton (Gossypium hirsutum L.) that affects plant growth, fruiting, and yield. This study was conducted to determine N effects on the development of harvestable bolls (HB) at fruiting sites among reproductive branches (sympodia). Field experiments were conducted from 1987 through 1990 on Commerce silt loam (fine‐silty, mixed, thermic, nonacid, aeric Fluvaquent) to evaluate responses to preplant N rates of 0, 28, 56, 84, 112, 140, and 168 kg ha−1, and to split applications of 56 + 56 kg N ha−1. Increasing N decreased HB production at Sympodia 5 through 10, and increased HB at Sympodia 12 through 25. At Sympodia 5 through 10, production of HB at Fruiting Site 1 (first position on sympodial branch) decreased from 49% of fruiting sites at the 0 N rate, to 36% of fruiting sites, with N fertilization of 168 kg ha−1. Harvestable boll production at Sympodia 11 through 16 increased from 58% at 0 N up to a maximum of 69% at 84 kg N ha−1. At Sympodia 17 through 25, fruiting sites developing HB increased from 9% up to a mximum of 28% with application of 140 kg N ha−1. Whole‐plant HB development at Fruiting Sites 1, 2, and 3 was optimized at 42, 23, and 8%, respectively, by N rates between 56 and 84 kg N ha−1. Averaged over all fruiting sites, maximum whole‐plant HB development of 24% was obtained with 84 kg N ha−1. Results demonstrate that increased N increased the total number of HB per plant. Increase in yield potential in response to N was limited, however, by decrease in HB at lower sympodia as N was increased, and by the inability of plants to more effectively develop bolls at Fruiting Site 2 and 3, and those at upper sympodia.