Potassium and Sulfur: Cornerstones of High-Yield, High-Quality Alfalfa
Written by Danica Kluth, Tessenderlo Kerley Agronomist
High producing alfalfa removes large amounts of nutrients from the soil every growing season. Among the most critical and often the most under applied nutrients in forage systems are potassium and sulfur. Together, these nutrients drive yield, forage quality, stand persistence and nutrient efficiency across all forage systems.
Modern forage programs that consistently deliver top-end yield, quality, and persistence prioritize both potassium and sulfur as foundational nutrients.
Why potassium matters in alfalfa production
Alfalfa is classified as a luxury consumer of potassium, meaning it will absorb potassium beyond immediate yield requirements when it is available. Removal is substantial even before luxury consumption begins, with around 50 lbs of K₂O removed per ton of hay harvested. In highyield systems, more than 300 lbs of K₂O can be removed in a single crop.
Potassium is one of the most heavily exported nutrients in a forage system and must be replenished to maintain productivity. When potassium is lacking, it can affect:
- Stand longevity and persistence
- Winter hardiness
- Water regulation and drought tolerance
- Forage quality
Why sulfur matters in alfalfa production
Sulfur should not be an afterthought in forage production. It is a core macronutrient essential for protein formation, nitrogen efficiency, and overall crop performance. In alfalfa, sulfur works closely with nitrogen to support growth and quality throughout the season.
On average, alfalfa can remove 5–6 lbs of sulfur per ton of dry matter harvested. In practical terms, a 6ton alfalfa cutting can remove 30–36 lbs of sulfur from the field. Adequate sulfur promotes the following benefits:
- Protein synthesis
- Nitrogen fixation and utilization
- Forage quality and feed value
- Yield consistency across cuttings
As sulfur is removed with each cutting, deficiency can appear as reduced protein, slower regrowth, pale green stands (see image), and inefficient nitrogen use.
KTS®: Potassium and Sulfur
KTS is a liquid fertilizer solution well suited for modern forage systems. It is a clear, nitrate and chloride free fertilizer that features the highest liquid potassium and sulfur content available on the market. KTS is a neutral to basic, clear liquid solution containing 25% potash and 17% sulfur.
Each gallon of KTS provides approximately:
- 3 pounds of potash (K₂O)
- 2.1 pounds of sulfur (S)
The sulfur in KTS is supplied as thiosulfate, which provides immediately available sulfate while also contributing to longer term sulfur availability as the thiosulfate converts in the soil.
Benefits
- A highly efficient chloride and nitrate free liquid source of potassium and sulfur
- Provides a unique form of sulfur that can improve nitrogen use efficiency
- Blends well with many common liquid fertilizers
- Improves phosphorus and micronutrient availability and uptake
- Enhances crop resistance to environmental stress
Applying potassium and sulfur in-season
KTS allows growers to effectively and efficiently apply potassium and sulfur back into the system as they are removed with each cutting. The thiosulfate form of sulfur provides immediately available sulfate while delaying release of the remaining sulfur. It can be applied inseason through the pivot or broadcast after each cutting.
Recommended applications
- Foliar application: 4 to 8 quarts per acre at crown greenup or on regrowth just after cutting.
- Flood and furrow application:
- Apply 4 to 8 gallons per acre of KTS to seedling alfalfa with irrigation water.
- Apply 5 to 12 gallons per acre with irrigation water to an established crop.