Generally older leaves are affected first. K deficiency is one reason among others for a physiological disorder that makes the grape berries wilt and dry. Reasons Potassium deficiency Very sandy soils and those that have been leveled (removing the topsoil) suffer worst from potassium deficiency. Potassium (K) deficiency develops when vines receive less K than what is required for normal growth and development, or with low soil pH levels (i.e., less than 5 for Vitis vinifera) that decrease the availability of potassium to the roots. As the deficiency worsens, leaf margins become necrotic and curl upwards and inter-vein alchlorosis develops. Potassium Deficiency Grapevines tend to show K deficiency when they are heavily cropped and maintenance applications of K have not been made in the vineyard. Foliar spray of urea (0.3 – 0.5%) 1- 4 times along the growing season , depending on the deficiency severity. Deficiency can be more likely to occur under these conditions: • Soil cut areas • Areas where the K-rich surface soil was removed during land leveling • On sandy soils that have low K Fertilization of Grapevines: Potassium deficiency is usually confined to small areas in a vineyard-seldom larger than 1 to 3 acres. Deficiencies are most apparent in mid to late summer. Bruno Bourrie, our agronomy expert, shows us how you can correct the levels of potassium to increase your yield and grow healthier grapevines in France. The interaction of calcium, potassium, and magnesium on grapevine nutrition is fascinating and needs to be investigated more thoroughly. Potassium Deficiency symptoms. Deficiency is likely to occur in cut areas, where the K rich surface soil Starts as yellowing (white varieties) or bronze-reddening (red varieties) of olderleaf margins.