The invention relates to a potassium sulphate powder wherein about 80 wt % or more of the powder has a particle size of about 0.2 mm or lower, preferably about 0.13 mm or less. The particle size preferably is such, that about 80 wt % or more is about 0.02 mm or higher, more preferably about 0.04 mm or higher. This potassium sulphate powder dissolves easily in water, more in particular, 50 gram of said potassium sulphate powder dissolves in 1 liter of water without stirring within 1 minute, preferably within 30 sec. This potassium sulphate powder is very suitable as foliar fertilizer, in particular for broad acre crops. Further, the invention relates to the use of foliar potassium fertilizer, to enhance the uptake of potassium from the soil.