Deficiency due to inadequate or ineffective N fertilization. Generally, application of 30 pounds N per acre in early spring and 30 pounds N per acre after harvest will maintain N within the sufficiency range. If N is less than 1.20%, increase the post-harvest application rate to 40-50 pounds N per acre. If N post-harvest is between 1.70% and 2.00%, apply 20 pounds N per acre post-harvest and the same amount in early spring. If the mid-summer N level is over 2.00%, no post-harvest N is needed. N levels over 2.00% can result in reduced yields.

Deficiency may be due to low soil P, inadequate P fertilization, or poor root development. If P is less than 0.08% and the soil test level is low and no root damage is evident, apply 25-50 pounds P₂O₅ per acre in next year's fertilization program. If the higher rate is used, split the application, applying one half at post-harvest and one half in early spring. If leaf P is between 0.08 - 0.20% and the soil test P level is medium or higher, application of P₂O₅ can be omitted the following year. If the soil test P level is low, apply 25 pounds P₂O₅ per acre as a maintenance application.

Deficiency due to low soil K, inadequate K fertilization, and/or heavy crop load. If the leaf K level is less than 0.35%, apply 25-50 pounds K₂O per acre in next year's fertilization program. If the higher rate is used, split the application, applying one half in early spring and the other half at post-harvest. If the K level is between 0.35% and 0.60%, continue with present fertilization practices. If the K level is 0.6l% or higher, application of K₂O can be omitted in next year's fertilization program.

Deficiency is rarely detected since the soil test Ca level must be extremely low for a deficiency to occur.

Deficiencies may occur at very low soil test Mg levels. If leaf Mg is less than 0.14%, apply 15-25 pounds Mg per acre as magnesium sulfate or other forms of soluble Mg.

Sulfur levels are generally within the sufficiency range. If S is low, use sulfur containing materials such as ammonium sulfate, ordinary superphosphate, potassium-magnesium sulfate, or magnesium sulfate in the fertilization program.

Low Mn levels are not likely to occur except on very sandy low organic matter soils. If leaf Mn levels are less than 25 ppm, low Mn can be corrected by soil application of 25 pounds manganese sulfate per acre.

Iron deficiency in blueberries is a common occurrence and is very difficult to correct in established bushes. Foliar applications may be partially effective if applied in early season. If the leaf level is less than 25 ppm, next spring apply a foliar application using a chelated iron source such as NaFeEDTA plus a surfactant. Apply at a rate of 1 to 2 quarts per acre in sufficient water to completely wet the foliage. Soil application of 10 pounds of chelated iron per acre has also been partially effective in correcting iron deficiency symptoms.

Cu levels of 2 to 4 ppm are of common occurrence in blueberries. If the Cu level is less than 4 ppm, apply copper sulfate to the soil (contains 25% Cu) at a rate of 4 pounds per acre (one pound Cu per acre) each year until tissue levels improve. Higher rates of up to 25 pounds copper sulfate per acre per year can be applied if the deficiency is severe. Copper chelates may be substituted for foliar application. Follow manufacturer's directions.

Low zinc levels may occur on very sandy low organic matter soils. If the Zn level is less than 10 ppm, soil apply 10 to 15 pounds zinc sulfate per acre in next year's fertilization program.