Basics of Nutrient Sources for Blueberry Fertilization in Florida

There are 17 nutrient elements essential for blueberry production. These essential nutrient elements include nine macronutrients: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) and eight micronutrients: iron (Fe), boron (B), copper (Cu), manganese (Mn), molybdenum (Mo), zinc (Zn), chlorine (Cl), and nickel (Ni), which was added to the list of essential elements in 2004 (https://edis.ifas.ufl.edu/publication/HS1191). 

Blueberry plants acquire carbon, hydrogen, and oxygen from air and water and all other nutrients from fertilizers and soil. Given the rather unique preferences of blueberry plants to fertilizers, the following fertilizers are suitable for blueberry production.

Nitrogen

Nitrogen has many important roles in plant nutrition and nitrogen fertilizer is needed annually to support vegetative and reproductive growth. Blueberry crops prefer nitrogen fertilizers with ammoniacal nitrogen (Table 1). Thus, the following nitrogen fertilizers are preferably used. Growers need to carefully minimize using fertilizers containing nitrate such as calcium nitrate, potassium nitrate, or sodium nitrate. Ammonium nitrate can be used in blended fertilizers where the nitrate is only a small portion of the nitrogen and the soil pH is below 5.3. Acid-forming ammonium sulfate is an excellent N source and is often used to help maintain soil pH in the proper range.  

 Table 1. Composition of Some Water-soluble Fertilizer Nitrogen Sources

For organic blueberry production, blood meal and fish meal (Table 2) can provide nitrogen.

Table 2. Composition of Some Organic Fertilizer Nitrogen Sources

Phosphorus

Phosphorus (P) is essential for cellular energy transfer through formation of high-energy bonds and is also important for root growth and development. Virgin, acidic, sandy soils may be initially low in P. However, P can accumulate in many soils over time. Soil tests can be used to determine preplant P fertilizer needs for new plantings and periodic soil and leaf tissue testing can be used to assess the need for additional P fertilization. Excessively high soil P levels can inhibit iron and zinc uptake and may result in iron and zinc deficiency.  

Table 3. Composition of Common Phosphorus Fertilizer Sources

Blueberry plants thrive under acidic growth conditions, phosphoric acid can provide a great opportunity for growers to control or acidify soil pH as well as supply P nutrient (Table 3).

For organic blueberry production, the following fertilizer P sources (Table 4) can be used.

Table 4. Composition of Some Organic Phosphorus Fertilizer Sources

Potassium 

Potassium is involved in many important plant processes such as photosynthesis, osmoregulation, water relations, and activation of key enzymes to name just a few. Potassium is usually applied annually to blueberry plantings. Potassium deficiency may present as marginal leaf burn, leaf cupping and/or interveinal chlorosis. Leaf tissue analyses can be used to monitor plant potassium levels. Muriate of potash (MOP, KCl) is inexpensive but is not recommended because blueberry plants are sensitive to soils with high chloride content.  

Table 5. Composition of Some Potash Fertilizer Sources

Table 5 lists all suitable potash fertilizers for conventional blueberry production. For organic blueberry production, the following fertilizer K sources (Table 6) can be used.

Table 6. Composition of Some Organic Potash Fertilizer Sources

Calcium and Magnesium

In Florida, 90% of the irrigation water source is from the Floridan Aquifer. This water source is high in calcium. Usually, calcium is not deficient in Florida blueberries. Magnesium deficiency, however, is fairly common where high-Ca irrigation water is used. Calcium (Ca) and magnesium (Mg) compete for plant uptake and high Ca in irrigation water may lead to Mg deficiency in blueberry fields. Magnesium deficiency may appear as yellowing or reddening of leaf tissue between major lateral veins with the middle of the leaf around the midvein and major lateral veins remaining green. Plant Ca and Mg status can be monitored with leaf tissue testing. Table 7 has suitable calcium and magnesium fertilizer sources.

Table 7. Composition of Common Calcium and Magnesium Fertilizer Sources

Micronutrients

Micronutrients are required in smaller amounts than macronutrients but are just as essential. Iron and other micronutrients are subject to being oxidized and then become not bioavailable to blueberry plants. Thus, chelate iron and other chelate micronutrients should be used. For chelate iron or other chelate micronutrients, this EDIS article has more at https://edis.ifas.ufl.edu/publication/HS1208. Table 8 listed the right iron and other micronutrient sources.

Table 8. Composition of Micronutrient Fertilizer Sources

Soil pH may change in response to fertilizer applications and these changes are related to the type of fertilizer applied. Basically, the application of cation nutrients such as ammonium nitrogen (NH+4), potassium (K+), calcium (Ca2+), etc. will decrease soil pH while anion nutrients such as nitrate nitrogen (NO-3) increase soil pH. Blueberry crops prefer acidic soil growth conditions. When fertilizing blueberry crops, growers select the right fertilizers with cation nutrients which can help blueberry plants keep soil in the right acidic condition. This intentional selection of fertilizers to properly manage soil pH is important for blueberry production. For more information on blueberry nutrition and fertilization, see “Nutrition and Fertilization Practices for Southern Highbush Blueberry in Florida” UF-EDIS publication #HS1356 (https://edis.ifas.ufl.edu/publication/HS1356).  

credits

GUODONG LIU & JEFF WILLIAMSON 

Horticultural Sciences Dept., IFAS, University of Florida