Soil pH determines the availability of nutrients, and is generally a function of clay type and surfaces, and organic matter content. Certain pHs are diagnostic of certain problems. Phosphorus and micronutrient problems could exist on these soils. Water infiltration could be a problem. Plants are stunted and root growth is limited.
Legumes generally prefer neutral to slightly alkaline soils.
Many quick field tests exist for evaluation of soil pH. With our increase in cropping intensity and no-till, and more frequent N fertilization, some of our surface soils are beginning to acidify, and may require addition of limestone to avoid a decrease in production. The SOM content, and its direction of change over time, can be diagnostic of the health of the soil. Generally, high SOM content is associated with good soil physical properties and good productivity. Quick field tests exist for relative comparisons among different cultural practices or rotations. The level of soil SOM, however, is sometimes used as a surrogate for sulfur needs and nitrate contribution, and its exact quantification once every three to five years is recommended.