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. 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.