Abstract
Chemicals may be used to reduce plant size in cotton (Gossypium barbadense L.), which can increase cotton yield by allowing an increased number of plants per unit area. Foliar sprays of growth retardants Cycocel and Alar were applied at concentrations of 250, 500, and 750 ppm 105 days after planting (square and boll setting stage) to Egyptian cotton cultivar Giza 75 planted at three plant densities (166,000, 222,000, and 333,000 plant ha
−1
). The objectives of this two-year study were to determine if growth retardants may be substituted for plant density, and vice versa, and to investigate their effects on yield and fiber properties. Number of opened bolls plant
−1
, seed-cotton yield plant
−1
, and earliness increased as plant density decreased in both years, as did seed-cotton and lint yield ha
−1
in the second season. In the first year, the intermediate plant density gave the highest yields. Plant density had no significant effect on lint percentage or fiber properties. Both Cycocel and Alar increased the number of opened bolls plant
−1
, boll weight, seed and lint indices, seed-cotton yield plant
−1
, and both seed-cotton and lint yield ha
−1
, but effects were not always significant and response varied for different traits. Neither Cycocel nor Alar affected lint percentage, yield earliness, or fiber properties at any plant density. The interaction of plant density × growth retardant was significant for the number of opened bolls m
−2
and plant
−1
, seed-cotton yield plant
−1
and ha
−1
, and for lint yield ha
−1
. The lowest plant densities, combined with application of Cycocel or Alar, gave the highest number of opened bolls m
−2
and plant
−1
, seed-cotton yield plant
−1
and ha
−1
, and lint yield ha
−1
. This implied that the effect of growth retardants on cotton yield depended essentially on the number of plants per unit area or space available to each plant and that applying growth retardants could enhance the effect of low plant density.