Soil Test Note – No. H002

Dr. Keith Streigler, Extension Horticulturist – Fruits

 

 

FERTILIZER AND CULTURAL SUGGESTIONS FOR BLUEBERRIES

 

Blueberries are very responsive to soil acidity, and the optimum pH range appears to be 4.8 to 5.2.  Satisfactory growth may occur in a natural soil below pH 4.8.  do not apply special acidifying materials if the soil pH is 5.4 or below.  Apply the recommended wettable sulfur (or lime, in the few cases where the acidity is too low) to attain this optimum range.  Aluminum sulfate may be used in place of sulfur but requires seven times more material for the same effect.  (Salts may also become a problem.)  Use the proper source of nitrogen to help maintain an optimum soil reaction.

 

Should foliar chlorosis occur before the soil acidity is reduced or during critical seasons in the year, apply to the foliage and as a soil drench ferrous sulfate (copperas) 2 tablespoons per gallon (2 pound per 100 gallons) or foliar iron chelate (EDTA formulation) following the manufacturer’s label.

 

Test the soil within the blueberry root zone yearly and make adjustments in fertilizer materials used to maintain the desired soil acidity.  Although an acid soil is necessary for blueberries, high rates of most nitrogen fertilizers continue to reduce the pH.  Thus, a change in the form of nitrogen used may be necessary from time to time to adjust the rate of change of the soil pH.  Ammonium sulfate is more acidifying than ammonium nitrate which is more acidifying than urea.  For soils with a pH of 5.3 or above use ammonium sulfate.  If the soil pH is below 5.3 use urea.

 

Should persistent serious soil-related chlorosis appear where the soil pH is somewhat below 4.8, light applications of lime may be needed.  The low pH is not damaging in itself.  Excess manganese is more likely to be taken up at a low pH, especially under wet soil conditions.

 

Seasonal, temporary chlorotic symptoms may appear even though the optimum pH or acidity is maintained.  Apply foliar iron rather than attempting fine soil adjustments with soil amendments within the optimum range.  Conditions other than improper soil pH can cause chlorosis and include excess water (poor drainage), cold soils, and root damage such as mice in the mulch.

 

Fertilizing Timing and Rates

The University of Arkansas soil test recommended fertilizer rates are calculated for use with a sawdust mulch.  Where the sawdust mulch is not used, reduce the commercial and nitrogen fertilizer rates by about one-half.  Adjust the amounts of fertilizer applied yearly to achieve the amount of plant growth desired.

 

-          Nitrogen (N) should be applied annually, in split applications; three per season recommended.

-          If fertigation is used, the application amounts can be less per application and more applications per season made, probably every two weeks instead of at 6 week intervals with dry forms.

-          Forms of N to use are ammonium sulfate (21% N) or urea (46% N).  If soluble fertilizers for fertigation are used, the N form should be ammonium, rather than nitrate.

-          Generally, mulched plantings should have 90-120 lb/acre N each season.  Non-mulched plantings probably should have 60 lb/acre N.

-          The best method of determining if the correct N rate is being used is to examine vigor of plantings and take leaf samples.

 

 Rate examples

1 oz of urea/plant applied to 1089 plants (1 acre at 10’ x 4’ spacing) provides 31 lb N/acre.  Therefore,

1 oz/plant applied 3 times/season (bud break and 6 to 12 weeks later) provides 93 lbs N/acre which is within the recommended range.

 

2.5 oz of ammonium sulfate/plant applied to 1089 plants (1 acre) provides 35 lbs N/acre.  Therefore, 2.5 oz/plant applied 3 times/season provides 105 lbs N/acre.

 

Fertilizer Quantity Weights

 

                                          Urea                                         Ammonium Sulfate

 

                              1 tablespoon = 3/8 oz                             ˝ oz

                              1 cup = 6 oz                                          8 oz

                              1 pint = 12 oz                                        16 oz

                              1 quart = 24 oz                                      32 oz

 

Foliar Sampling

 

-          should be done after harvest, mid-July to early August; earlier season samples can have different nutrient levels than those used for standards for diagnosis of nutrient needs.

-          mid-shoot leaves on fruiting canes should be sampled.

-          best to separate by variety, region of field, health of bushes.

-          need at least 60 leaves/sample from numerous bushes.

-          contact county Extension agent for other information before sampling.

 

For further information, refer to the following publications available at the county Cooperative Extension Service offices:

 

FSA 6038    Growing Blueberries

FSA 7503    Home Fruit Orchard Sprays

FSA 6000    Blueberry Weed Control

FSA 6028    Small Fruits for Home Plantings

 

Acknowledgment:  Dr. John Clark, University of Arkansas, Associate Professor – Fruit Culture & Breeding, for his assistance in preparation of this Note.

 

May, 1995

 

The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, national origin, religion, gender, age, disability, marital or veteran status, or any other legally protected status, and is an Equal Opportunity Employer.

 

 

 


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