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Acidifying the Soil

The management of soil pH is important throughout the life of a blueberry planting. Blueberry

plants are more vigorous, have more uniform color, and are more productive when growing in

acid soil conditions - below pH 5.0. Since pH is frequently between 7 and 8, or even higher in

many potential California blueberry growing areas, careful attention to soil pH management is

important. In those instances where soil pH is above 8.4, excess sodium may also be a problem,

and these soils require additional special management.

Poor drainage also limits soil

acidification, and the installation of special drainage measures will be needed before soil

acidification should be attempted.

To lower the soil pH, acid usually sulfuric acid may be applied directly to the soil. Sulfuric acid

application is a rapid and effective way to lower the pH but requires specialized equipment and

applicators specially trained to handle the potentially hazardous acid. Other acids, such as nitric,

phosphoric, etc., can also be used, but they should be used sparingly and paying close attention

to the potential for over-application of nitrogen and phosphorus that could result. Acidification

of alkaline irrigation water, is also important for pH management with blueberry plantings.

More often, elemental sulfur is applied and incorporated in the soil. When elemental sulfur is

mixed with moist soil, soil bacteria convert the sulfur to sulfuric acid.

Sulfur is oxidized by bacteria to form sulfuric acid

S + O

+ H

(elemental S + oxygen + water + thiobacillus + time

sulfuric acid)

Soil pH in fields can be quite variable initially following application of sulfur to lower pH. The

desired lower pH may not be completely uniform in the bed for several months. It is difficult to

get the sulfur uniformly distributed in newly sulfured fields, and the reaction of the sulfur

granules can be slow, depending upon the type of sulfur applied and the field conditions.

Acidified soils will require continuing ph management for optimum blueberry growth and

production throughout the life of the planting.

Apply the sulfur to the soil as early as possible prior to planting and use only finely ground sulfur

as opposed to traditional “popcorn” sulfur. The sulfur products that have shown good results in

California are Tiger Sulfur 90 and Dispersul, both of which are finely ground sulfurs formed into

pellets with bentonite clay for ease of application. The clay expands as it absorbs moisture and

breaks apart to disperse the fine sulfur particles.

The amount of sulfur to apply can be determined in a soil laboratory by an analysis for the soil in

question or can also be determined by using the current pH and the soil texture chart in Table 1.

Normally 2 million pounds representing an acre slice to a depth of 6 inches is used as the basis

for calculation of these rates. If beds are raised to 8-12 inches and additional soil volume is

moved to establish the beds, this figure may actually be 50-100% higher than the values

indicated. If the soil has high levels of bicarbonates and/or free limestone (calcareous) also

common in California - then the S-requirement may also be higher than that indicated by the

chart. Try to correct the figures with an accurate estimate of the total soil volume moved. The

Acidifying The Soil