Acidic soils have a pH below 7.0 and alkaline soils have a pH above 7.0. Most plants grow best at a soil pH between 6.0 and 7.0. A small number of plants such as azalea, rhododendron, and blueberries prefer a soil pH between 4.5 and 5.5. Nitrate and Ammonium Nitrogen tests indicate nitrogen immediately available to plants, but do not necessarily indicate how much nitrogen may later be liberated from the soil. Thus proper interpretation of these results is essential.
Nitrogen favors leaf growth and imparts a deep green color to plant foliage.
Excessive ammonium nitrogen can damage plants and is often an indication of overfertilization. Very high nitrate nitrogen levels may increase the risk of nitrate contamination of surface and groundwater. Phosphorus binds strongly in soil and is often unavailable to plants. Annual applications of phosphorus fertilizer are usually necessary. Deficiencies in phosphorus are often indicated by poor root, fruit or vegetable growth and a purpling of the older leaves.