Deficiency due to inadequate or ineffective N fertilization. Generally, application of 14-20 pounds N per acre each month during the February-October time period will maintain N within the sufficiency range. If N is less than 1.80%, increase the application rate to 20-28 pounds N per acre. If N is greater than 2.10%, N fertilization can be discontinued for two months and retested. N levels of approximately 2.50% 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 0.12% and the soil test level is low and no root damage is evident, apply 12-18 pounds P₂O₅ per acre (depending on row spacing) each month during the February-October time period. If leaf P is between 0.12 - 0.40% and the soil test P level is medium or higher, apply 6-9 pounds P₂O₅ per acre (depending on row spacing) each month during the February-October time period. If the leaf P is above 0.40%, do not apply phosphorous fertilizer for two months. Then retest to determine if P fertilization should be restarted.

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 16-24 pounds K₂O per acre (depending on row spacing) each month during the February-October time period. If the K level is between 0.35% and 0.65%, continue with present fertilization program or apply 12 to 20 pounds K₂O per acre (depending on row spacing) each month during the February-October time period. If the K level is 0.66% or higher, application of K₂O can be discontinued for two months. At the end of this time, crop leaves should be tested again for nutrient content to determine if K fertilization should be restarted. Care should be taken to make sure that plants have adequate potassium at harvest, which is important for fruit quality. However, excessive potassium can induce magnesium deficiency and reduce yields.

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 0.12%, 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 50 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 60 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.

Low levels may occur on very sandy and low organic matter (<1%) soils. If the B level is less than 30 ppm, soil apply 1/2 pound of actual B per acre at the next fertilizer application.

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 8 ppm, soil apply 10 to 15 pounds zinc sulfate per acre in next year's fertilization program.