When S is finely ground and mixed with soil it is oxidized to SO4-2 by soil microorganisms. Oxidation is more rapid in warm, moist soils with high organic matter contents. Oxidation reactions of elemental S are also faster in alkaline soils than in acidic soils. Oxidation is a surface-based process which is accelerated when Sulfur particle size is reduced; therefore, particle size is one of the most important attributes affecting oxidation. In the field, sulfur deficiency and nitrogen deficiency are often confused. Symptoms of both deficiencies may appear as stunted plants, with general yellowing of leaves. With a Sulfur deficiency, yellowing symptoms often first appear in younger leaves, whereas with nitrogen deficiency, it apprears on the older leaves first. In less severe situations, visual symptoms may not be noticeable.