The present invention provides a method for using a new liquid fertilizer comprising potassium from a potassium source selected from the group consisting of potassium acetate, potassium formate, potassium citrate, potassium succinate, potassium propionate, potassium phosphate, organic sources of potassium, animal manure, and combinations thereof, and having a slightly alkaline pH and relatively low salt index compared to other sources of potassium for liquid fertilizer products. The fertilizer composition may further comprise additives such as sulfur, zinc, boron, calcium, manganese, iron, copper, cobalt, magnesium, or a combination thereof.