Kevin Jackson, Cale Bigelow, Gabriel Macke and William Tracy Tudor Jr., Purdue University, West Lafayette, IN
Lawns fertilized with excess nitrogen (N) and phosphorus (P) may be an important possible contributor to declining water quality throughout the USA. This concern has led some states to ban P-fertilizer applications to turf. The long-term effects of eliminating P from lawn fertilizer programs on turf health and soil test P levels is unclear. A five-year field study evaluated the effects of six granular fertilizers consisting of synthetic and natural organic products with varying N:P ratios and an unfertilized control. Fertilizer was applied at 196 kg N ha-1 yr-1 to a turf-type tall fescue (TTTF) grown a calcareous silt-loam (initial Bray-1 soil test P, STP, = 33 ppm). Clipping management strategy (returned or removed) was also studied. Soil and leaf tissue were sampled to monitor P levels and visual appearance, green color and shoot density were also assessed. Turf receiving N-fertilizer, regardless of the N:P ratio, was superior to the unfertilized controls, which had poor vigor and a decreased shoot density. By year 3, mean STP levels ranged 36-79 ppm and fertilizers with N:P ratios of 1:1 or 3:1 caused substantial STP increases, > 60 ppm, regardless of clipping management strategy. This study indicates that where initial STP levels are sufficient, a healthy TTTF can be produced using N only fertilizers at this annual N-rate. Continued application of lawn fertilizers with N:P ratios of < 3:1 could eventually result in excess P loading and environmental loss.