In acid soils you can select the crops that can growth in this conditions (pH 6.0 - 6.5 is slightly acidic, and you can find cultures that can be cropped under this conditions). If soil is acid to highly acidic , in some areas of Northern Spain the use to increase the pH by liming the soil in a gradual / gentle way. You can find different product for liming fron rocks, wastes (from marble industries; animal bones; etc