Protassium+®, also known as 0-0-50 or sulfate of potash (SOP), is a dual-nutrient fertilizer containing 50 percent potash and 18 percent sulfate. There are two main potassium sources in the fertilizer industry: SOP and potassium chloride. At Midwestern BioAg, we always recommend SOP over potassium chloride because over-application of chloride can cause damage to crops, risking lost income due to lowered yields and quality. Excessive chloride can also leach calcium from the soil, causing crops to require greater amounts of fertilizer. SOP, unlike other potassium sources, contains virtually no chloride and also supplies sulfur to support plant yield and quality.