Acidic soil is any soil with a pH balance below 7. Soils that are below 7 are acidic while those with a pH balance above 7 are considered to be alkaline. Knowing the pH balance of the soil is important because certain plants and crops grow best in a certain type of soil. The pH balance may also give clues to certain properties of the soil, such as the amount of nutrients found in it. Typically, crops prefer either neutral or slightly acidic soils, though there are always exceptions to this rule.
Gardeners and farmers will benefit from understanding the properties of acidic versus alkaline soils and what each plant or crop likes best. There are other factors affected by the soil type. Not only will certain plants thrive in it, but different diseases can survive in the soil depending on the pH balance.
Decomposing items in nature are typically the cause of acidic soil. Dead leaves from plants and trees will fall to the ground and break down over time, raising the acidity of the soil in the area. The soil can be changed over time from acidic to alkaline through the breaking down of other natural elements, such as limestone. The soil changes based on the activity of the area and what the soil itself formed from. Soil formed from basic rock types will usually be alkaline, while soil formed from acidic parent rocks will normally form acidic soil.
Other factors in nature effect whether the soil is acidic or not. Areas with higher rainfall have more acidic soil than those that don't. As the rain soaks into the ground, it dissolves nutritious elements in the soil and acidic elements move in to take their place.
If a gardener or farmer is trying to increase the pH balance in the soil, it is usually because the soil doesn't have enough nutrients in it and not necessarily because the pH balance itself is a problem. While the plants may not be affected by the acidity of the soil, the soil itself may be lacking in key nutrients the plants need to live. Limestone is a common choice when trying to lower the acidity of the soil. Acidic soil can be neutralized by adding agricultural lime, quicklime, or calcium sulfate.