Abstract: Aims Supplying optimal quantities of mineral nutrients to growing crop plants is one way to improve crop yields. Nutrients need to be used rationally in order to avoid a negative ecological impact and undesirable effects on the sustainability of agricultural production systems. Excessive application of nutrients also affects the farmer's economy. In order to calculate the amount of fertilizer to be applied to crops, it is necessary to develop recommendation programmers that adjust nutrient rates to crop requirements.
Methods Experiments in two successive seasons were conducted to investigate the effect of K fertilization and foliar application of Zn and P on yield and fiber properties of cotton cv. Giza 86. Potassium (0.0 and 47.4 kg of K ha^-1) was soil applied, while chelated zinc (0.0 and 57.6 g of Zn ha^-1, applied twice at 70 and 85 days after sowing 'DAS') and phosphorus (0.0, 576, 1?152 and 1?728 g of P ha^-1, applied twice at 80 and 95 DAS) were applied to the foliage.
Important findings Dry matter yield, total chlorophyll concentration, K, Zn and P uptake per plant, number of opened bolls per plant, boll weight, seed index, lint index, seed cotton yield per plant, seed cotton and lint yield ha^-1 and earliness of harvest increased with the application of K, Zn and P. Treatments generally had no significant effect on lint percentage and fiber properties, with exceptions, for micronaire reading and flat bundle strength, and uniformity ratio, where the mean values of these characters were significantly increased over the untreated control by applying K, and for the micronaire reading in the first season, when applying P at 1?728 g ha^-1, and uniformity ratio in the second season, when applying P at 1?152 and 1?728 g ha^-1, where the mean values of these characters were significantly increased over the untreated control by applying P. Under the conditions of this study, applying K fertilization at 47.4 kg ha^-1 combined with spraying cotton plants with zinc at 57.6 g ha^-1 and also with P at 1?728 g ha^-1 improved growth and yield of Egyptian cotton.

Key words: cotton, fiber properties, phosphorus, potassium, yield and yield components, zinc