Soil acidity - resilience and thresholds.

The maintenance of soil acidity (pH) at a value appropriate for optimizing crop production is an important first step in soil management because soil pH affects soil properties, nutrient availability and plant nutrition. Soil pH is easily determined and, in regions where calcitic or magnesian limestones are readily available, pH is easily adjusted and maintained at the required value. This value is usually a compromise because all those factors affected by soil acidity are not optimum at the same pH. In temperate regions, the target pH is broadly similar for all mineral soils with average soil organic matter (OM) levels when growing arable crops and is slightly lower for grassland. The exceptions are organic mineral soils, and peat soils when the recommended pH is often less. The amount of liming material required to maintain the recommended soil pH varies with soil type. This chapter discusses the effect of soil acidity on soil properties and nutrient availability. It focuses on the need to maintain soil pH, because long-term acidification adversely affects the sustainability of agricultural systems, and how maintaining soil pH varies with soil type.