Phosphorus and aluminium solubility relationships in acidic lowbush blueberry barren soils in Maine

Lowbush blueberry (Vaccinium angustifolium) is a native plant that is not cultivated, but managed in areas of sufficient plant density to provide commercial yields. A cropping systems study was initiated to compare how organic and three levels of conventional (low, medium and high input) management practices affected soil properties at 12 grower fields in the lowbush blueberry barrens of Maine. The fields under organic and low-conventional treatments did not receive any fertilizer inputs. The high and medium conventional treatment fields received optimal and reduced diammonium phosphate inputs, respectively. Three measurements of soil P (modified-Morgan soil test, oxalate extractable and total P) showed no significant effect of management treatment on the phosphorus status of the soils. This suggests that soil P may be leaching below the 0-10cm rooting zone which was investigated in this study. Equilibrium chemical speciation of soil/water extracts showed that gibbsite was controlling the solubility of Al in these barren soils and that P was undersaturated with respect to amorphous Al(OH)(2)PO4. A laboratory one-point P sorption study showed that dissolved organic matter derived from the organic pad sampled from the study sites did not inhibit the adsorption of the added P. This suggests that addition of carbon-rich soil amendments such as compost may not increase P bioavailability of these acidic soils with high Al (oxy)hydroxide (gibbsite) mineral content.