Effect of nitrogen and zinc fertilization and plant growth retardants on cottonseed, protein, oil yields, and oil properties

The increase in the population in Egypt makes it imperative to explore promising approaches to increase food supply, including protein and oil, to meet the needs of the Egyptian people. Cotton is the principal crop of Egyptian agriculture. It is grown mainly for its fiber, but cottonseed products are also of economic importance. Cottonseed is presently the main source of edible oil and meal for livestock in Egypt. Field experiments were conducted in two successive seasons at the Agricultural Research Center (Giza, Egypt) on cotton (Gossypium barbadense L. cv. Giza 75) to determine the effect of nitrogen (N) fertilizer rate (107 and 161 kg of N/ha applied as ammonium nitrate containing 33.5% N in two equal doses at 6 and 8 wk after sawing), together with foliar applications of plant growth retardants (mepiquat chloride "Pix," chloromequat chloride "Cycocel," and daminozide "Alar," each applied once at 288 g active ingredient/ha, after 75 d from sowing) and zinc (Zn) (applied in chelated form after 80 and 95 d from sowing at 48 g of Zn/ha) on seed, protein and oil yields and oil properties of cotton. The higher N-rate, as well as the application of all growth retardants and Zn, resulted in an increase in cottonseed yield, seed protein content, oil and protein yields/ha, seed oil refractive index, unsaponifiable matter, and total unsaturated fatty acids (oleic and linoleic). These treatments tended to decrease oil acid value, saponification value, and total saturated fatty acids. The seed oil content tended to decrease as N-rate increased and increased with the application of all growth retardants and Zn. There were some differences between Pix, Cycocel, and Alar regarding their effects on the studied characters. The highest increase in seed, oil, and protein yields/ha was found with Pix, followed by Cycocel. The Cycocel treatment gave the lowest total saturated fatty acids oil content, followed by Alar.