Direct-seed (DS) systems are characterized by the development of stratified soil acidity at the depth of fertilizer placement. The primary objective of this study was to characterize the stratification of soil acidity and Al chemistry in the surface 30 cm of a DS system. Detailed sampling of a 60-cm wide by 30-cm deep grid with 5-cm spacing was used to assess spatial variability of soil acidity, and Al speciation was modeled with the Visual MINTEQ chemical equilibrium program. Treatments included subsurface-banded nitrogen (N) fertilizer and subsurface-banded N fertilizer with subsurface-banded lime, broadcast lime, or broadcast sulfur. The zone of greatest acidification (5 to 10 cm) was associated with the zone of fertilizer placement. Broadcast lime effectively increased pH at depths below 10 cm and banded lime at the depth it was placed (~5 cm). Acidification of the upper 20 cm of soil indicates that soil acidity is moving vertically with repeated fertilizer application. In general, higher pH resulted in lower Al³⁺ activity. At the surface, Al activity was lowest for the broadcast lime treatment compared to the banded N fertilizer and subsurface-banded lime treatments. The aqueous chemical equilibrium model indicated that organic complexes should dominate Al speciation though AlHPO₄^-, AlSO₄⁺, Al(OH) ₂⁺, Al(OH) ₄^- are also important . An investigation of solid phase equilibria controlling equilibrium Al³⁺ activity suggest that above pH 5, Al hydroxide controlled Al³⁺ activity and below pH 5 activity is probably controlled by organic matter. Organic matter accumulated under DS conditions may buffer the system by lowering Al³⁺ activities and forming less phytotoxic aqueous Al species. Preliminary data for Al tolerance screening of pre-1950 and currently grown cultivars of wheat will be presented to determine if Al tolerant cultivars may have been selected inadvertently by breeding programs in the Inland Pacific Northwest.