Abstract: A randomized triple-replicate turfgrass trial was established in 2002 to evaluate the effects of amending subsoil with varying types and amounts of organic matter. Four treatments were tested including peat moss and three commercial composts (one biosolid-based, one cattle and swine manure-based and one vegetation and horse manure-based). The soil amendments were spread at varying depths of one or two inches on 48 sample plots (each 1.67m x 1.08m) and tilled to mix with the subsoil base. Six control plots were also established. A high P and K fertilizer (6.5-26-26) was applied to the surface of all 54 plots and, using a rototiller, was incorporated into half of them. Moisture measurements were taken regularly and bulk density values were calculated. The relative growth of the plots was measured with three clipping harvests and growth measurements. The clipping harvests provided samples for foliage NPK testing that revealed a strong correlation between foliage colour and nitrogen content. In the first of the three clipping harvests, the average clipping mass in the peat moss and biosolid-based amendments were significantly different for plots with incorporated P and K and plots with non-incorporated P and K. The plots with non-incorporated P and K correlated to higher average clipping mass yields for both amendments. The biosolid plots showed average yields of 1918 and 2576 g/100m² for incorporated and non-incorporated P and K, respectively while the peat moss plots showed average yields of 2288 and 2900g/100m² for incorporated and non-incorporated P and K, respectively. Combined clipping mass averages for all three harvests showed that plots with one-inch amendments had significantly lower average clipping masses for incorporated P and K (5198 g/100m²) compared to non-incorporated P and K (5738 g/100m²). Conversely, plots with two-inch amendments had significantly higher average clipping masses for incorporated P and K (6672 g/100m²) compared to non-incorporated P and K (6025 g/100m²). No other significant differences in clipping growth were observed. It is expected that variation will become more apparent in the 2003 growing season when supplemental moisture and fertilizer is restricted.