Influence of nitrogen fertilization and foliar application of plant growth retardants and zinc on quantitative and qualitative properties of Egyptian cotton (Gossypium barbadense L var. Giza 75)

Field experiments, in two successive seasons, at the Agricultural Research Center, Giza, Egypt, determined the effect of N fertilization (addition at rates of 107 or 161 kg of N/ha) and foliar application of plant growth retardants (Pix, Cycocel, or Alar, each applied once at 300 ppm, 75 days after planting) and zinc (applied at 0.0 or 50 ppm, two times: 80 and 95 days after planting) on growth, mineral uptake, yield components, yield, and fiber properties of Egyptian cotton cultivar Giza 75. Dry matter yield, N and Zn uptake per plant, number of opened bolls per plant, boll weight, seed index, lint index, seed cotton yield per plant, and seed cotton and lint yield per hectare increased with increasing N rate and by foliar application of plant growth retardants (with best results when Pix was applied) and zinc. The earliness of harvest increased by the application of Zn in season I and Pix in season II only. Treatments generally had no effect on lint percentage and fiber properties, except in season II when Pix and Cycocel were applied, the 2.5% span length tended to increase over the control.