Q: Why does the University of Georgia Extension service recommend adding phosphorus at the time of planting regardless of soil test results?
A: Because the phosphorus that plants require is so often chemically unavailable to plant root hairs and because it naturally moves so slowly through the soil.
The main reason phosphorus is unavailable is that soils in Georgia tend to be acidic by nature. Fertilizer, rainfall and decomposition of organic matter make our soils become more acidic with time. The chemical reaction that allows a plant root to absorb phosphorus is hindered by the low pH of most soils. This explains why regular liming, based on soil test results, is so important.
Phosphorus is strongly attracted to soil particles. It clings tightly to them, resisting being moved through the soil by water. If you apply phosphorus only to the soil surface, it may be years before it moves down to the plant roots below.
The University of Georgia Soils Lab reports that forty four percent of the soil samples processed are low in phosphorus. Since phosphorus is vital for strong root development, adding some 0-46-0 while planting is good insurance.