Phosphorus Fertilisation
Phosphorus is a major element that is especially critical during turf/seedling establishment. In mature stands, phosphorus is a critical component important in the energy (ATP) required for growth. Deficiencies show as a slowing of growth and phosphorus deficient symptoms can eventually appear (bluish color leaf blades). A proper balance between soil phosphorus levels and that needed for growth is both environmentally sound and necessary for maintaining quality turf.
Dr. Wayne Kussow at the University of Wisconsin wrote a recent article (Phosphorus fact or fiction Landscape Management 42:56-58,60,62) where he mentions 2 general hints that might help you plan your phosphorus program. The first is major nutrient analysis of leaf clippings remains rather constant for turfgrasses. The ratio of nitrogen (N), phosphorus (P2O5) and potassium (K2O) roughly falls in a 4:1:3 ratios. By using a fertiliser with an N: P2O5 ratio of 4:1 you will roughly maintain the current soil test levels of phosphorus. If you use a ratio less than 4:1 such as 2:1 or 3:1 you will contribute to the phosphorus levels in the soil. On the other hand if you use a fertiliser ratio greater than 4:1 like 8:1 or 10:1 you will slowly deplete the phosphorus in the soil. You can either build-up, maintain, or deplete phosphorus levels over time by the fertiliser you use.
In addition, from research at the University of Wisconsin, it takes roughly 5 grams P2O5/ m2/year to maintain soil test levels when clippings are removed. If clippings are returned that amount drops in half to 2.5 grams P2O5/m2/year. Phosphorus levels in the soil are impacted by climate, growing season, and soil texture to name just a few. However, the 4:1 ratio and 1 lb rule for clippings removed is a good base to start designing a phosphorus fertility program