The focus of this information brief is the highbush blueberry. If you have a question concerning the species of blueberry best adapted to your area, call your county Cooperative Extension Service office. On most sites, blueberries are relatively free of disease and insect pests, but weeds are an ever present problem. Field preparation at least one year in advance of setting blueberry plants is strongly recommended, since herbicides cannot be used in organic production. However, blueberries are unique among the commonly grown fruit plants in their fertility requirements.
Blueberries require an acid soil and prefer nitrogen in the form of ammonium.
Soil conditions there are usually favorable for Vitrifying organisms, resulting in a high concentration of nitrates. Ammonium nitrogen is short-lived under such conditions. But in the acid soils that are naturally favorable for blueberries, denitrifying organisms predominate, and nitrates may be quickly converted to the ammonium form. It seems that providing a low soil pH is the best way to insure a source of ammonium nitrogen for the blueberry plants. A look at soil biochemistry can clarify this reasoning.