Because most potatoes are grown on sandy soils in Michigan and sandy soils do not hold large amounts of K, growers must pay a great deal of attention to K fertilization. Soil testing is the key to determining the amount of K fertilizer to apply. Potassium Fertilizer Rates Potassium fertilizer recommendations based on K soil test level and yield goal are given in Table 4. MSU recommends more K than is removed at very low soil test levels, maintenance amounts at low to medium soil test levels, and less than is removed at medium to high soil test levels.
Recommendations also vary with yield goal.
Higher yields require higher rates of K fertilizer than lower yields because of greater removal. Potassium Fertilizer Placement Potassium fertilizer may be applied broadcast before planting or banded at planting time. Do not apply more than 100 lb of K20 per acre banded at planting time. Large amounts of K salts in this location can cause salt injury to young plants. Fall applications will reduce the amount of chloride available during the growing season, which should have a positive effect on tuber quality.