Phosphorus (P) use in the turfgrass industry has recently become heavily scrutinized due to its suspected contribution to eutrophication of lakes and streams. Inorganic P is a highly immobile nutrient in the soil, binding tightly to organic matter, soil particles, and minerals immediately following fertilizer application. Though many studies have shown that P run-off from turf is not a major source of water pollution, and in many ways helps prevent it in urban and other settings, restrictions are being placed on fertilization of turf with products that contain P. The portion of P in the soil that is available for plant use, inorganic P, is only a small fraction of the total P that exists at any time in the soil. Phosphorus transformations between the unavailable organic P form and inorganic P in soil is not completely understood given that the process depends on a combination of many factors such as soil moisture; pH; temperature or seasonality; spacial variability; presence or absence of other nutrients such as nitrogen (N), iron (Fe), aluminum (Al), carbon (C) and calcium (Ca); soil type; microbial activity; climate; vegetation; etc.
A field study was conducted in 2006-2007 at the Ohio Turfgrass Research and Educational Facility, Columbus, Ohio to observe the effects of two of these factors, temperature or seasonality and the presence of nitrogen, on soil P availability. While applications of nitrogen alone in the past have been shown to maintain or increase available P levels in the soil, little evidence was seen here. Regardless of fertilizer treatment or timing, plant available P levels in all plots continuously decreased throughout the study indicating no treatment by time interaction. Some fertilizer treatment effects were observed that indicate that nitrogen fertilizer source can produce changes in plant available phosphorus.