Two field experiments were conducted during 2015/2016 and 2016/2017 seasons at the Agricultural
Experimental Farm of Suez Canal University at Ismailia to study the effect of four phosphorus fertilization treatments
namely 15, 22.5, 30 and 15 Kg P2O5/fad plus biofertilizer phosphorein as well as four potassium fertilization treatments
namely 24, 48, 72 and 24 Kg K2O/fad plus spraying with 1% potassium sulphate on sunflower Sakha 53 variety in
sandy soils at Ismailia. There were consistent and significant increases in head diameter, 100-seed weight, number of
seeds/head, seed weight per head, seed oil percentage as well as seed, biological and oil yields per fad by increasing
phosphorus fertilization level from 15 to 22.5 and 30 Kg P2O5/fad in the two seasons. Sunflower plants received 15 Kg
P2O5/fad plus biofertilizer (Phosphorein) significantly exceeded those fertilized with 15 Kg P2O5/fad alone in all
aforementioned characters in the two seasons. Increasing potassium fertilization level up to 72 Kg K2O/fad significantly
increased all aforementioned characters except number of seeds/head where the response up to 48 Kg K2O/fad.
Sunflower plants sprayed with 1% potassium sulphate plus 24 Kg K2O/fad exceeded significantly those fertilized with
24 Kg K2O/fad alone in all aforementioned characters in the two seasons. The highest values of all aforementioned
characters were achieved by applying 30 Kg P2O5/fad and 72 Kg K2O/fad. While the lowest values were gained by
adding 15 Kg P2O5/fad and 24 Kg K2O/fad in the two seasons.