Two field experiments were carried out during the two successive seasons of 2001/2002 and 2002/2003 at the Experimental Station of National Research Centre at Shalkan, Kalubia Governorate to study the response of growth and yield of onion to potassium sulphate fertilizer at rates of 0, 150 and 300 kg/fed, as well as potassium humate at rate of 0, 3, 6 and 12 L/fed.
The important obtained results were as follows:-

Increasing the potassium addition level up to 150 kg/fed had a significant effect on the growth characters, i.e. plant height, number of leaves / plant, fresh and dry weight of whole plant as well as total yield and its components (bulb weight as g / bulb and bulb dimension. Also, gave the highest percentage of TSS, N, P, K, Fe, Mn, Zn and Cu. Increasing the potassium addition from 150 up to 300 kg/fed caused a reduction in growth characters, yield and chemical characters, (TSS, N, P, K and Fe, but increased Mn, Zn and Cu).
Foliar application of potassium humate at different levels, i.e. 0, 3, 6 and 12 L/fed. had a significant effect on growth characters and total yield and its components as well as chemical characters all of them resulted its highest values only with that onion plants, which sprayed with humic acid at 6 L/fed, but that onion plants, which sprayed with humic acid at levels of 12 L/fed resulted less plant growth as well as yield and its components, in addition caused an increment  in TSS, N, P, K, Fe, Mn and Zn in bulb tissues.