A field experiment with large plots was established on a low P (Bray-1 P: 4.8 – 23.1, mean =11.4 mg P/kg) Alfisol in Fulton County, western Illinois to evaluate the lability of biosolids P relative to triple superphosphate (TSP). Lagoon-aged biosolids and TSP were incorporated into surface soil in fall 2005 at rates of 0, 163, 325, 488, 650 kg P/ha to be used by corn in three consecutive years. The 650 kg P/ha rate represented typical P loads under N-based biosolids application. Corn grain yield increased from 5.8 Mg/ha in control (0 P) to 6.8 Mg/ha in 488 kg TSP-P/ha and 7.0 Mg/ha in 325 kg biosolids-P/ha, but such response was not statistically (P = 0.05) significant for any type of P. Mehlich-3 P (M3-P) increased linearly with added P for both P sources with addition of 4.9 kg biosolids-P/ha and 5.0 kg TSP-P/ha raising M3-P by 1 mg P/kg. However, the increase in Bray-1 P with P rate was much slower in biosolids than TSP treatments. Within 0 to 488 kg P/ha, water soluble P increased linearly with P rate for both biosolids (slope = 0.01) and TSP (slope = 0.035). The preliminary data indicate that although biosolids P may behave the same as TSP agronomically, the potential of biosolids P to impair surface water through surface runoff is much lower, and that biosolids P could be applied at a rate of 3.5 times greater than recommended for P fertilizer. The findings will be confirmed in simulated runoff studies.