Cereals or small grainsb 5.5–5.8

1Soil acidification, or a decrease in soil pH, is a natural process that is accelerated by crop production practices, primarily the use of nitrogen (N) fertilizers such as urea, ammonium sul-fate, or other fertilizers containing ammonium-N. As soil acidification occurs, soil chemical and biological properties change. One chemical change is increased solubility of aluminum (Al) and man-ganese (Mn), both of which can be toxic to plants. Plants vary in their tolerance of Al and Mn, creating crop-specific soil pH requirements. Adding lime (Figure 1) increases soil pH (reduces acidity), adds calcium (Ca) and/or magnesium (Mg), and reduces the solubility of Al and Mn in the soil. Soil pH management The first step is to determine the soil pH required for your crop. The pH at which yield is diminished varies among crops. Table 1 provides minimum soil pH recommendations for western Oregon crops. Crop-specific guidance is provided in Oregon State University (OSU) and Pacific Northwest (PNW) Extension nutrient management guides. Other pub-lications in this series (Soil Acidity in Oregon and Table 1.—Minimum soil pH values recommended for crops grown in western Oregon.